Sumatra-Andaman Earthquake and Tsunami 26 December 2004

Geological Survey of India Special Publication

(Pre- Print Copy)

A REPORT ON

THE SUMATRA- ANDAMAN EARTHQUAKE

AND TSUNAMI OF

26 DECEMBER 2004

A REPORT ON THE SUMATRA- ANDAMAN

EARTHQUAKE AND TSUNAMI OF

26 DECEMBER 2004

Editor

Sujit Dasgupta

GEOLOGICAL SURVEY OF INDIA SPECIAL PUBLICATION

(Pre- Print Copy)

September 2005

Foreword

The festivity of Christmas Day 2004 was turned into horrifying plight of

thousands of people at the outbreak of nature's fury on 26 December 2004. On the fateful day India witnessed unprecedented unleash of killer wave tsunami

following the great undersea earthquake that took away about 10,749 humanlives, rendered many thousands homeless and leading to colossal property

losses. It was a shock and tragedy to the nation due to a calamity of the earth's

system. Geological Survey of India, as the premier earthscience organization

of the country, made an all out effort in analyzing/ studying the event in this critical juncture of national crisis with a view to reassuring the society. Rising

to the occasion, GSI mobilized all its resources on war footing. The hazard and its aftermath have been investigated and analyzed from multi-pronged

scientific angle.

Geological Survey of India has a legacy of earthquake studies since the

days of Sir R.D. Oldham who laid the foundation of modern seismology and

surveyed the Great Assam earthquake of 1897. With that beginning, GSI has

continually been engaged in the study of every major Indian earthquake and publishing its findings. Equipped with that expertise, scientists of GSI

explored the different aspects of the event, faithfully documented the records and critically examined the 26 December 2004 calamity. The results and

outcome of this scientific investigation have been combined in this volume to

give a complete portrait of the mega-event. We hope this contribution will

help further scientific pursuit towards the study of earthquake.

We are bringing out this report not merely as a fulfillment of theonerous task but also to proffer the knowledge in securing a safer society in future and to accomplish the complete understanding of the science of

earthquake and tsunami.

(K.N. Mathur)

Kolkata, Director General26 August 2005. Geological Survey of India

Contents

Introduction Sujit Dasgupta 1Earthquake

1. A preliminary Report on investigation of

effects of the Sumatra-Andaman earthquake of 26 December 2004 in Andaman andNicobar Island

K.N. Mathur, S.K. Ray, S.

Sengupta, Prabhas Pande and Sujit Dasgupta

5

2. Macroseismic Survey in Andaman andNicobar Island in the aftermath of the great earthquake of 26th December 2004

A.K. Ghosh Roy, S. Bardhan, P. Jana and S.R. Basir

19

3. Analysis of satellite data for changes incoastal geomorphology of Andaman-Nicobar

island due to 26 December 2004 earthquake

D.P. Das, S.S. Ghosh,D. Chakraborty and

K. Pramanik

57

4. 26 December 2004 earthquake: coseismicvertical ground movements in the Andaman

Sumit K. Ray andAnshuman Acharyya

71

5. Bathymetry and magnetic observations along Andaman arc-trench gap in the postearthquake scenario of 26th December 2004

R. Sengupta and 12 others 91

6. Seismotectonics of the Andaman- Nicobar

region: constraints from aftershocks within 24 hours of the great 26 December 2004earthquake

Sujit Dasgupta, Basab

Mukhopadhyay andA. Acharyya

105

7. Aftershock investigation of the December 26, 2004 Sumatra-Andaman Islands earthquake

O.P. Mishra,G.K. Chakraborty and O.P.

Singh

115

Tsunami

8. Tsunami survey in the Andaman- Nicobar

Islands

T.Ghosh, P..Jana,

T.S. Giritharan, S. Bardhan, S.R Basir, A.K. Ghosh Roy

165

9. Tsunami survey in the Srikakulam-Pulicatsegment, Andhra Pradesh

M. Raju, B.K. Bhandaru, V. Singaraju and B.M. Shah

185

10. Tsunami survey in the Chennai-Nagapattinam segment

R. Srinivasan and K.Nagrajan

197

11. Tsunami survey in the Nagapattinam-

Kanyakumari segment

B. Kanishkan and

B. Lakshminarayanan

217

12. Tsunami survey in the Kanyakumari- Cochin segment

K. Jayabalan and U. Durairaj 239

______________________________________________________________________________________________REPORT ON SUMATRA -ANDAMAN EARTHQUAKE & TSUNAMI, 26 DEC ’04 1

INTRODUCTION

Sujit DasguptaGeological Survey of India, Kolkata

The Sumatra Andaman subduction zone has been a known potential tectoniccandidate for earthquakes. Tsunamis are rare but not totally absent. Yet there was insufficient guess on its capability for developing such an incomprehensible tsunami. The impression that tsunami is largely a Pacific Ocean phenomenon has been drastically confuted by the Indian Ocean earthquake and tsunami of 26 December 2004. This was one of the largest interplate shallow thrust earthquakes that occurred at the interface of the subducting Indian lithosphere and the overriding Burma plate. The event happened to be the second largest earthquake in the recorded history after the Chile earthquake of 1960 (Mw 9.5). The main shock of the great earthquake of 26 December measured Ms8.6 (IMD), Ms8.8 (GSI, Nagpur), Ms8.6 (GSI, Jabalpur), Mw9.0 (USGS), (revised Mw9.3) and occurred off the West Coast of northern Sumatra (Indonesia) at 00:58:53 hrs. [06:28:51.1hrs. IST (IMD)]. This under-sea earthquake triggered giant tsunamis that devastated the coastal regions of the Indian Ocean rim countries travelling as far as the coast of East Africa. In India, damage from the tremor of the earthquake itself was moderate to high in the Andaman and Nicobar Islands. Above and beyond, the high tsunami waves unleashed by the earthquake wreaked havoc in life and property in the coastal regions of Andhra Pradesh, Tamil Nadu, Kerala and Andaman & Nicobar Islands. Besides death of 10,479 people, a total of 2,39,024 dwelling units were affected, 35,605 cattle lost, 22,750 hectares of cropped area and 83,788 boats damaged in the calamity in India alone. This estimate may change with time but the frightening memory and potential threat will haunt the nationand the earthscientists in particular for years to come. GSI made a conscientious attempt to study and analyze the event for immediate planning and for posterity.

The Andaman - Nicobar Archipelago is located in a unique and complicated tectonic regime.It has components of trench, volcanic arc, fault systems, spreading ridge, sea-rises, transform faults and obducted suites of rocks. In a broader view, tectonic features bordering the Indian subcontinent in the west (Suleiman-Kirthar fold belt), north (the Himalayas) and east (Indo-Burmese arc) are thought to have resulted from the northward drift of India since Cretaceous and its collision with the Tibetan landmass by early-mid Eocene. The Indo-Burmese range and the Andaman island arc together describe tectonically continuous belt displaying various geologic elements of an arc-trenchsystem, though the northern part of the belt, i.e., the Indo-Burmese range, emerged above sea level as early as Oligocene. The Burmese-Andaman Arc System (BAAS) presents nearly 3500 km long subducting margin in northeastern part of the Indian plate where varying degrees of seismic activity, volcanism and active tectonism are evidenced. The region is of particular interest due to severalinteresting features. 1) It serves as an important tectonic link between the Eastern Himalayas(a typical collisional margin) and the Sunda Arc (which is a part of the Western Pacific arc system); 2) an initial collisional phase has already set in the northernmost segment of BAAS (in the Naga Hills) within an overall subducting regime; 3) Burma is one of the few regions in the world where a subduction zone up to about 200km depth is clearly discernible in a land environment; 4) coastalBurma and north part of the Andaman Sea are largely aseismic, suggesting that subduction of the Indian plate in this regions has stopped recently or occurs aseismically, and the hanging lithosperic slab is being dragged northward through the surrounding lithosphere; 5) The Andaman back-arcSpreading Ridge (ASR) underlying the Andaman Sea relates to the oblique convergence of the Indian plate at the Asian continental margin; actual spreading occurred through several short leaky-transforms, producing the 'pull-apart' Andaman basin in southern half of the BAAS and 6) further south is the intense seismic zone of the West Sunda Arc with its attendant volcanism.


The Indo-Burmese range and the Andaman-Mentawai arc form the outer arc ridge of the arc-trench system developed during the Tertiary in consequence of subduction of the Indian plate below the Burma-Sumatra segment. The various morphotectonic units recognized along the convergent margin of the Indian plate may be described as follows:

(i) The overriding Southeast Asian continental block including the west Kachin unit of northeast Burma, Shan-Tenasserim highland and Sumatra.

(ii) A narrow linear faulted backarc basin between the magmatic arc and the west Kachin unit involving the Indawgyi and also Bhamo-Myitkyina valley that extends southward up to the Andaman Sea through Shwebo, Sittang basins and Gulf of Martaban.

(iii) The magmatic arc extending from the Jade Mines in north Burma to Narcondam-Barren volcanic islands through Monywa, Mt. Popa and Irrawaddy delta; this intra-basinal arc continues to the continental margin arc in north Sumatra.

(iv) A well developed forearc basin that extends from the Chindwin valley in northBurma to the Mentawai trough, off Sumatra; in the Andaman sector the forearc basin is represented by the 'Nicobar deep’.

(v) The subduction-accretion complex at the leading edge of the Indian plate isrepresented by sediments of the Burmese-Andaman outer arc, where severaldismembered ophiolite bodies occur along the seaward flank of the forearc trough.

As already mentioned the Andaman-Nicobar arc-trench region is a highly seismic tectonic domain. Earthquakes occur along the plate margin with a well -defined seismic Benioff zone. Large magnitude shallow foci thrust earthquakes are known to occur in and around the outer-arc ridge including the events of 1847, 1881 and 1941. Besides, the Andaman spreading ridge yieldsearthquakes mainly with normal fault mechanism whereas earthquakes along the West AndamanFault display strike slip geometry.

Following the mainshock of 26 December 2004, thousands of aftershocks have beenrecorded. It is noteworthy that these aftershocks mainly occur north of the main shock till the 28 March 2005 event of magnitude 8.7 (USGS), located on a fault segment 160 kilometers to the southeast of the rupture zone of the 26 December 2004 earthquake. Previous events in the vicinity occurred in 1833 and 1861. Interestingly the earthquake of 28 March did not generate tsunami.

Geological Survey of India took up immediate assignments deploying scientists from various streams. Dr.K.N.Mathur, Director General, led a team of senior officers of the Survey to South Andaman and Baratang islands during 7-12 January 2005 to take stock of the situation and to implement the work plan. Macroseismic and tsunami survey in the Andaman Nicobar Islands and in the coastal tract of Andhra Pradesh, Tamil Nadu and Kerala were launched. Deployment of seismometers to record and analyze aftershocks and installation of geodetic instruments to studynature of deformation caused by the earthquake in the Andaman- Nicobar Islands was taken up. This was followed by cruise of GSI vessel in parts of Indian Ocean across the Andaman Islands for first hand assessment on changes of bathymetry and magnetics. Apart from that analyses of satellite digital data for pre- and post-earthquake scenes in Andaman Nicobar Islands, estimation of vertical ground movement and study of rupture propagation characteristics have been attempted to explain the overall seismotectonics of the region around the archipelago.

This report embodies the outcome of major work accomplished by the geo-scientists of GSI. There are twelve contributions in total including different aspects of earthquake and tsunami.Earthquake related studies are dealt in seven chapters. This begins with the preliminary report that


was submitted on 17 January 2005 after the visit of Director General, GSI in Andaman Islands. This was a first hand account of intensity assessment in South Andaman as well as mud volcano eruptions and surface rupture at Baratang Island from sympathetic faults. This is followed by the contribution by Ghosh Roy et al. on the macroseismic survey of the A&N Islands. Results indicated Nicobar Islands had higher intensity of VIII (revised MSK scale) than Andaman Island where the generalintensity was VII with few local highs of VIII in western part of the island. The Havelock Island showed a lower intensity of VI. Intensity in the main land varied from III to IV. Strong seismic seiches have been recorded from West Bengal, Andhra Pradesh and Tamil Nadu. In the third chapter Das et al. used pre- and post-earthquake digital satellite data to detect morphological change in A&N Islands. The study revealed emergence of islands of varying magnitude along east and west coast in the north Andaman, and submergence of islands in the south, in Nicobar. Ray and Acharyya estimated coseismic vertical movement distribution in the Andaman Group of Islands (North of11°N latitude) showing uplift in some parts and subsidence on others in a domain of thrust faulting. There are locales where there is no perceptible ground movement, designated as 'neutral line', west of that there is land emergence while submergence is recorded in the east. Sengupta et al. outlined the marine survey carried out by GSI marine vessel R.V. Samudra Manthan in Andaman Arc-Trenchgap. The cruise includes 4678 line km for bathymetric as well as magnetic studies along 24 transects. Bathymetric profile showed perceptible structural and morphological changes in the sea floorparticularly in the areas south of 10°N latitude. Dasgupta et al. explained the aftershock propagation characteristics within 24 hours of the earthquake and illustrates rupture segments, aftershockpropagation rate and differential seismic loading. Mishra et al. analyzed 1177 aftershocks (M ≥3.0)recorded from 6.1.2005 to 31.1.2005 from their total database of about 18,000 aftershocks up to 16 March 2005. The epicenter map indicated a N-S trending aftershock cluster in an area of about 750 x 300km

2. The aftershocks occurred mostly at the depth range 5-55 km, except a few beyond that

depth range.

There are five contributions on tsunami survey. Results of tsunami survey in AndamanNicobar Islands have been documented by Ghosh et al. A stronger impact in the Nicobar Group of Islands is evident. While the run up distance is more than 1 km in Car Nicobar, South Andaman witnessed about 150m of run up. Notwithstanding tsunami wave heights of nearly 10m in fewlocales, the run up height is generally restricted within 1. 5m and 5.5m. The impact of tsunami in coastal mainland has been extensive. A coastal stretch of about 2050 km from Srikakulam in the east coast to Cochin in the west coast has been affected. GSI has covered the entire coast in four segments to record the details. Raju et al. described the distribution of tsunami in Andhra Pradesh coast where run up varied from 200m to 1km with a maximum run up elevation of 2m. Srinivasan and Nagarajan demonstrated the characteristics of tsunami in Chennai-Nagpattinam of Tamil Nadu coast. The run up elevation in the Chennai-Nagpattinam segment varied between 1m and 3m while the run up distance ranged from 150m to 1km. Kanishkan and Lakshminarayanan recorded the outcome of tsunami studies between Nagapattinam and Kanyakumari, Tamil Nadu. The coastal stretch lying between Nagapattinam and Point Calimere showed a maximum run up elevation of 3m with run up length (inundation zone) varied between 200m and 1.25km. In terms of life, property and landscape loss, the stretch of coast in Karaikal-Nagpattinam-Velanganni had highest damage in the East Coast. Jayabalan and Durairaj documented impact of tsunami in part of Tamil Nadu and Kerala coast from Kanyakumari to Cochin. In the west coast, the run up distance varied from 200m to 500m and run up elevation ranges from 3m to 4m. In Kerala, the worst affected area was the stretch between Cheriyazheekkal (Kollam district) and Tharayilkadavu (Alappuzha district).


The collation of data on earthquake and tsunami survey of one of the largest recorded seismic event is indeed an assignment for the sake of better understanding of a lesser-knownphenomena in this part of the world. The attempt will be rewarding if new frontiers of science open up for the safety and existence of all living milieu in this fragile tectonic regime.

This ‘Introduction’ will remain incomplete without admitting the cooperation received from all the contributors of this volume. The support rendered by Shri K. Nagarajan, B. Kanishkan and O.P. Mishra is gratefully acknowledged. Shri Saudipta Chattopadhyay has been instrumental in final knitting of this volume with all odd DTP jobs. The task of editorial assistance was withShri Anshuman Acharyya who carried out the work meticulously. In spite of our efforts flaws may float that may be ignored.

______________________________________________________________________________________________REPORT ON SUMATRA -ANDAMAN EARTHQUAKE & TSUNAMI, 26 DEC ’04

5

A PRELIMINARY REPORT ON INVESTIGATION OF EFFECTS OF THE

SUMATRA - ANDAMAN EARTHQUAKE OF 26 DECEM BER 2004 IN ANDAMAN AND NICOBAR ISLAND#

K. N. Mathur *, S.K. Ray, S. Sengupta, Prabhas Pande and Sujit Dasgupta

Geological Survey of India

Kolkata

INTRODUCTION

A Great earthquake measuring Ms 8.6 (IMD), Mw 9.0 (USGS) occurred off the West Coast of northern Sumatra (Indonesia) at 00:58:53 hrs. [06:28:51.1hrs IST (IMD)] on 26.12.2004. This is one of the largest interplate shallow thrust earthquakes that occurred at the interface of the subducting Indian lithosphere and the overriding Burma plate. This mega seismic event from the Sumatra subduction zone in the Indian Ocean triggered giant tsunamis that devastated the coastal regions of Indonesia, Malaysia, Thailand, Sri Lanka, India and Maldives and affected even the coast of East Africa. The loss of human lives in the catastrophe has been put at 1.5 lakh. The impact of the tsunami was quite severe in the coasts of Andaman and Nicobar group of Islands, Tamil Nadu, Andhra Pradesh, Pondicherry and Kerala where over 10,000 people lost their lives, thousands injured and property worth several hundred of crores destroyed.

The Geological Survey of India has taken up the investigation of this earthquake andresultant tsunami in the Andaman - Nicobar region and other parts of the country. In this connection a team of senior scientists of the Department reached Port Blair on 7

th January 2005. After

discussions with the Officials of the Andaman & Nicobar Administration, the GSI team visited different parts of South Andaman and Baratang Islands to study the effects of the earthquake and tsunami. This team after initial surveys returned to Kolkata on 12.01.05. Another team of officers from Eastern Region, GSI also reached Port Blair on 07.01.05 and took up detailed investigations to document the effects of the earthquake and tsunami and install GPS in campaign mode. Another group of GSI scientists who reached Port Blair on 06.01.05 is installing an array of five digital short-period seismometers in different islands to record the aftershocks.

This report contains the observations from the studies carried out between 7th

and 12th

January 2005. A detailed report with analysis on the effects of the earthquake and tsunami and other related issues to be submitted on completion of the work.

* Director General, GSI# This report was submitted on 17.01.2005


6

Earthquake Parameters

Earthquake parameters for this great earthquake are continuously been revised and refined by USGS since the first estimate released on 26.12.2004. As on 13.01.2005 the parameters as per USGS are as follows:

Date: 26th

December 2004Origin Time: 00:58:53 (UTC) [local time at the epicenter 07:58:53]Location: 3.316°N, 95. 854°E [± 5.6 km (3.5 miles) horizontally]Region: Off west coast of North SumatraMagnitude: Mw 9.0Depth: 30 km (18.6 miles)

Harvard Best Double Couple Solution:NP1: Strike 329, Dip 08, slip 110NP2: Strike 129, Dip 83, slip 87Principal Axes: T: Val 4.01, Plg 52, Az 36; N: Val –0.12, Plg 3, Az 130, P: Val –3.98, Plg 38, Az 222

TECTONIC SETTING

The Andaman- Nicobar- Nias (off Sumatra) sedimentary arc in the northeastern Indian Ocean defines a nearly 2200 km long trench slope break and outer arc ridge between the Indian plateand the SE Asia/Burma plate. This convergent margin joins the Burmese arc to the north and the Sunda arc towards the south. The entire 3500 km long Burmese- Andaman arc constitutes animportant transitional link between the Himalaya and the Western Pacific arc system characterized by varying degree of seismic activity and volcanism. Active subduction of the Indian lithosphere below the Burma plate is documented by the presence of the Barren- Narcondam active volcanic arc that continues to the continental margin arc in Sumatra and an east dipping Benioff zone defined by earthquakes up to 250 km focal depth. The geologic and tectonic history of the region is complex due to the presence of active faults/tectonic features such as the West Andaman fault in the Andaman arc, the Semangko fault in Sumatra, the Sagaing fault in Burma and the Neogene Andaman back-arcspreading ridge.

Seismicity Pattern of the Region between 01.01.2004 and 25.12.2004

A total of 260 earthquake events occurred in the region during 2004 up to 25.12.2004 (USGS Catalogue). Out of these 241 events are of magnitude less than 5.0, 18 shocks betweenmagnitudes 5.0 and 6.0 while there is only one event of magnitude 6.2. Majority (162) of these earthquakes are of shallow foci (≈ 20km) origin. There is an apparent seismic quiescence between 28

th November and 25

th December 2004 with the last event registered on 27

th November 2004 (M=

5.3, depth 41 Km, 1.97N/97.89E).

MACROSEISMIC SURVEY

The 26 December 2004 earthquake was strongly felt in the entire Andaman group of Islands and the seismic intensity was enough to cause low order damage to many civil constructions. A cross section of people belonging to different parts of the Islands was interviewed to get first handinformation on the nature of seismic shaking. The general human perceptions are as follows: At


7

06.35 AM (local time) feeble tremors were felt that made many feel giddy. This was followed by strong to and fro shaking which lasted for almost 40 seconds. The time gap between the 1st feebleshocks and the following strong shocks was reported to be sufficient for most of the people to come out of their buildings even from 2

nd floor. No sound, however, accompanied the tremors. People ran

outdoors in great panic; most people lost balance, fell or sat down and crawled out of their buildings. Those riding bicycles or motorbikes felt strong wobbling effect and therefore immediately stopped. Parked cycles and a scooter fell down during strong shaking. A parked bus was visibly vibrating. Objects and utensils on racks were thrown. At few places even heavy objects like steel almirah and racks overturned. The total duration of shaking have been reported by many to be of the order of 3 minutes.

Different grades of damage to buildings have been recorded from different parts of South Andaman. In Port Blair area, places like, Marine Park, Aberdeen jetty, Chatam, Nayagaon, Bamboo Flat, etc. were visited. Buildings like the Secretariat, Haddo Circuit House, Blair Hotel, which are Type C structures suffered damage of grades 1 and 2. Most buildings of B/C type in and around Port Blair suffered similar damage. In a single case at Nayagaon a newly constructed 3-story building over stilt with RCC columns and beams suffered grade 5 damage. The entire soft-story ground floor caved in due to failure of load bearing base column (Photo 2 & 3). The upper two floors though tilted, were much less damaged. In the Bamboo Flat area many of the buildings showed grade 2cracks. In a newly constructed house belonging to C. Mahammad Arif, which at the time of the earthquake was not even occupied, much higher damage was seen in comparison with rest of the area. This two-story structure with RCC columns, beams and RCC roof caved in such a manner that the ground floor got completely crushed and the first floor came to the ground floor level (Photo 4).This was also a stilted structure where the base columns were not tied with shear walls. It appears that under condition of prolonged lateral loading the base columns supporting a heavy load sheared off resulting in grade 5 damage.

In the Kanyapuram locality one newly constructed house belonging to Mr. Hamid, was reduced to a heap of rubble. The two-storied RCC structure with GI roof completely caved in and a car parked in the ground floor completely crushed (Photo 5).

In the Ograbraj locality, a godown of Malabir Society was heavily damaged. This was a structure with approximate dimensions of 8 m (w) x 15 m (l) x 6 m (h). The walls were of hollow concrete blocks with RCC columns at the corners and at the central parts of N-S aligned long walls.The slanting roof with GI sheets was supported by heavy wooden beams and rafters. The three walls and the roof suffered total collapse. The quality of construction was very poor, where steel used was found to be rusted and concrete of low strength (Photo 6). The area was subsequently inundated by the tsunami back flow (Photo 7). In the Collinpur locality, almost all the buildings suffered grade 2 or 3 damages. In a single case, a single story restaurant suffered damage of grade 5 in the form of total collapse of the structure. The long wall of the shack of GI sheet roofing seems to have thrusted

in N45°E direction. In this area, the foundation comprised clayey soil with shallow groundwatertable.

In the Baratang Island, similar seismic intensity was recorded. The Forest Range office suffered grade 2 or 3 damage in the form of shear cracks in walls and gapping settlement cracks in the floor. A number of steel almirah and racks containing office records and the hanging tube lights fell down during the earthquake.


8

Water Supply Schemes for Port Blair

Dhanikhari Dam

This water retention structure on Dhanikhari River was constructed during 1970-1973 for supply of water to Port Blair town. The dam is a 132 m long and 32.23 m high straight gravity –concrete structure with a central gated spillway having a capacity of 26,000 cusec. The reservoir extends to an area of 0.49 x 10 sq miles and the storage capacity is of the order of 9000 lakh litres.On 26 December 2004, the reservoir stood at R.L. 60.60 m. Inspection of the dam revealed some minor distress to the main structure due to the earthquake. Development of fine cracks and chipping off plaster along two of the right abutment block joints was visible (Photo 8). Inspection of foundation gallery showed cracking of the RCC along the fifth block joint, through whichconsiderable amount of seepage was taking place. Some minor seepage was also coming from the right abutment slopes of the gallery. It was reported that prior to the earthquake, the water collecting in the foundation gallery used to be pumped after every six hours. After the earthquake and due to the increased seepage, it now requires hourly pumping. The reservoir water was also considerably agitated due to the passage of the shock waves as manifested by the seiche (standing water waves), which rose by as much as 3 to 4 m. After the earthquake, the main supply pipes were dislodged and therefore, in the initial days, the water supply to the town remained disrupted. It has later been restored.

Chouldari Dam

Chouldari water supply scheme is a 19 m high and 95 m long earthen dam structure with a 10 m wide and 80.58 m long left bank ungated RCC chute spillway. The earthen section has pitching of basalt blocks, both in the upstream and downstream sides. A concrete apron has been placed over the entire length of the crest. The distress to the dam on account of the earthquake is seen at the junction of the earthen section and spillway concrete. Here, the concrete apron has buckled by as much as 8 cm along the block joint (Photo 9). The profile of the earth sectionotherwise does not show any deformation or distress. It is reported that on 26

th morning the reservoir

level (reservoir area 15 ha) was quite low. But due to the tremors the waves in the reservoir rose so high that they splashed on to the crest portion that was about 5.6 m above the reservoir level.

Ground Fissures and Liquefaction

Ground fissures, slumping and subsidence were witnessed at several places in the coastal belt of Andaman Islands. At Collinpur locality, the fissures are arcuate in disposition, trends N-S and appeared to be a product of liquefaction and consequent lateral spreading (Photo 10). Here, the water table is barely a meter or less deep and the topsoil clayey silt. During the tremors, fissures were formed through which the ground water spouted. At a few places, cream-colored fine sand/silt also ejected out. As reported by the locals this zone of ground fissure continues intermittently for 6-7km between Tirur in the north and Khurma beach in the south. A few buildings, which were founded over such a spreading zone suffered conspicuous damage. In a stray case, rolling down of a boulder from a hill has been reported at Collinpur. In the Baratang area the ground fissures are sopronounced that they damaged considerable stretches of the metalled road. These fissures aredescribed below.


9

Mud Volcano Eruptions and Surface Rupture at Baratang

In the Island of Baratang, two major and some minor mud volcanoes among the chain of dormant ones erupted during the earthquake of 26 December 2004. Of the two major sites oferuption, the one in Jarwa Creek was examined in some detail. It is reported that soon after the major tremors, this volcano erupted with great violence. A series of explosions that lasted forseveral minutes accompanying the eruption could be heard from distances as far as 2-3 km from the site. A resident of Rajatgarh village narrated that he saw the mud splashing to above the forest tree height. At the eruption site on the following day he witnessed flames coming out of one vent.During the present study the site was visited after 17 days of the eruption. The mudflow of 26

th

December 2004, has spread in an area of around 10,000 sq m and had a very distinct bulged contact with the older mudflow (Photo-11). The shape of the mudflow can be described as that of a flattened bun. The main crater, located at the center of the mud depos its was no more active. Gases along with small quantity of sticky and viscous mud was still coming out in fits and rhythms throughanother newly formed vent located about 10m away from the previous one (Photo-12). Blowouts with an average frequency of 2 minutes accompanied by low blurring and hissing sound, was audible from a distance of 10 m or so. This crater is about 0.75 meter in diameter with a vent of about 20 cm at the center.

The erupted mud consisted of very fine clay particles containing small angular fragments of rocks. The wet spouted clay dried and hardened almost immediately after coming into contact with air and was getting deposited at the rim of the new crater. Gas and mud erupted are odorless,inflammable (probably methane) and were at ambient temperature. On the whole, a feeblesulphurous smell pervaded over the mud volcano. The maximum height of the recent deposits is estimated to be around 3 m. The total volume of the erupted mud is calculated as 1600 cu m.However, estimate by the Forest Authorities place this figure at 2400 cu m. It is quite certain that this entire mud was ejected out within a very short time span after the earthquake. The mudflow in the rim portion has partially flooded some of the tree plantations.

About 500-700m metalled road stretch from the mud volcano site towards BaratangDivisional forest office is highly fractured. These open fractures trend N25E, cut across the road (Photo 13) and continue on either side on ground as irregular fractures. Both right and left lateral slip of 5 to 10cm observed on the edge of the road. In this stretch at one place the black- topped road surface has buckled up to develop as an antiform with height at the axial region of 25-30cm. Almost parallel to the road a 90 cm to 1.5m wide surface fracture trending N55W continue for about 50m and join with one of the fracture that cut across the road. In this stretch a healthy long tree with its roots was found neatly split vertically into two parts and shifted horizontally (Photo 14). While the left hand portion of the tree remained almost insitu the right hand part was displaced about 1.20m diagonally towards north, thus showing left-lateral shear. The horizontal component of slip along the fault plane is about 85cm. Close to the intersection of this fault and the fractures cutting the road a newly formed small mud volcano with a distinct crater was seen. Through the pulsating vent small amount of odorless gas and wet clay with a film of black colored odorless substance were spouting at regular interval. In two nearby sites minor quantity of gas was continuously escaping from pool of water.


10

Effect of Tsunami in Andaman Islands

The tsunami or the sea waves generated by the main Sumatra Earthquake of 26th December 2004 was very profound in the low-lying coastal regions of Andaman & Nicobar group of Islands. The sea that rose as much as 2.5 m above the high tide line entered inhabited area with great velocity. The waves flattened a number of dwelling and constructions, breached the shore protection walls, certain sections of the low level roads, impaired some bridge and harbor structures andinundated vast stretches of shore land (Photos 15,16,17 & 18). Influence of the waves was greatly accentuated due to run-up and ingress of the seawater (Photo 19) into the low lying cultivated fields and human settlements through the various creeks. Many such areas are still inundated under the saline water and there is fear of the soil becoming unfit for cultivation in future. The tsunamis alsoflooded many of the dug wells thereby contaminating the fresh water sources.

A number of residents who witnessed the catastrophe were interviewed to reconstruct the scenario. The general observation was that after about 15 to 20 minutes of the main shock the first influx of sea waves approached the shores. The water level rose to above the high tide level. After some time the second influx came in which the water level increased still further and then receded.The recession in water level was so much that the seabed became visible for quite a distance. The residents never witnessed such phenomena earlier. The velocity of waves in the two influxes was slightly above normal. At around 8.30 AM the third influx came to the shore with such a velocity that everybody was caught unaware. The water level rose to the maximum, in some cases to over 2.5 m above the high tide level.

The velocity of the ingushing water was such that even those who were running away from the water front, were soon overtaken. After the 26 December, 2004, tsunami, the sea has remained at a higher level then normal and the difference between the high tide and low tide levels seems to have reduced. Now, during the high tide, some areas are still getting flooded and on an average the high tide level is about 1m higher than the pre-earthquake situation. This was never the situation before the tsunamis struck. However, it is observed that with the passage of time sea level is slowly tending to recede.

AFTERSHOCK MONITORING

An intense aftershock activity has been recorded following the Great Sumatra- Andaman earthquake (Figure 1). The IMD seismic observatories have recorded a total of 124 aftershocks in excess of M 5.0 from 26

th December 2004, to 11

th January 2005. The largest aftershock was of M

7.0 that occurred on 26.12.2004, 120 km west of Nicobar Island. 11 aftershocks are of magnitude ≥6.0 while the remaining 112 events are in the magnitude range 5.0- 6.0. USGS has recorded 223

aftershocks up to 09.01.05 of magnitude ≥ 4.4. While 52 events are of magnitude ≤ 5.0 remaining are above 5.0. Aftershock sequence from the IMD list gives a b-value of 1.08 while those from the USGS catalogue gives 1.20. Predicted Mmax is 7.1 from both the catalogue, which has alreadystruck on 26

th itself. p-value calculated from IMD list is 0.97 while that from USGS 1.27 suggesting

that aftershocks of magnitude ≥ 5.0 will possibly decay within 40 days.


11

(a) (b)

0

0.5

1

1.5

2

2.5

4 5 6 7 8

Magnitude in M

Log (Cumm. N) = -1.0809M+ 7.643

b = 1.08

IMD

0

0.5

1

1.5

2

2.5

4 5 6 7 8

Magnitude in M

Log (Cumm. N) = -1.2021M+ 8.5405

b=1.2021

USGS

Figure 1. (a) Aftershock seismicity map up to 09.01.05 as recorded by USGS. (b) Frequency-magnitude plot of aftershocks as recorded by IMD (top) and USGS (bottom)

The Geological Survey of India has dispatched 5 short period digital seismometers tomonitor the aftershocks. The first station was operational in the Naval Base Defense Colony, Vijaybagh, Port Blair from 6.1.2004. The second station was established in Car Nicobar Air Force Base on 8.1.2005. A third station was put in Little Andaman (Hut Bay) on 10.1.2005. Two morestations are planned to be deployed in Rangat and Diglipur, thus covering a length of 470 kmbetween the northern parts of Andaman and Nicobar Islands. It is proposed to run the seismic network for about a month.

GPS STUDIES

GSI has planned to install several GPS and operate in campaign mode in different islands from Diglipur in North Andaman to Car Nicobar in the south covering a distance of about 470 km. The GPS stations are proposed to be re-occupied 2-3 times annually. The 1

st station has been

installed over rock exposure near GSI drilling campsite Beadonabad on 10.01.05. Another station will be at Chidyatapu Forest Rest House. Diglipur in North Andaman and Baratang islands will be occupied soon. Installation at other sites will depend on the availability of logistics for going to places like Little Andaman and Car Nicobar.


12

CONCLUSIONS

1. The Sumatra Earthquake of 26 December 2004 is the largest recorded seismic event along the Andaman-Sunda subduction zone. The giant tsunamis generated by this offshore fault rupture have been unprecedented in the Indian Ocean and therefore call for inclusion of tsunami hazard in the disaster management plans of the country.

2. To locate earthquakes precisely from this highly seismic belt the 800 Km longAndaman- Nicobar Islands have to be covered by adequate seismograph stations.

3. The entire belt of Andaman & Nicobar group of Islands is an area of intense seismic activity and therefore has been included in the highest hazard class V of the Seismic Zoning Map of India. It is, therefore, of great importance that for any construction activity the BIS code on Earthquake Resistant Designs should be strictly followed. This applies more to any lifeline and structures of importance like schools, hospitals, water retention elevated structures and defense installations etc.

4. The recent earthquake has demonstrated in very clear terms that stilted structures without provision of any shear resistant walls behave very poorly under lateral seismic loading of even lower seismic Intensity of VII of MSK-64 scale. The results are similar to what was observed in case of Ahmedabad and Surat cities during the Kutchearthquake of 26 January 2001. It is, therefore, essential that design of RCC structures particularly G+2 and taller buildings, should be examined by competent structuralengineer so that earthquake resistant elements are properly incorporated.

5. Prima facie, quality of RCC in case of the three collapsed structures in and around Port Blair was found to be inferior. It is therefore necessary to carry out proper geotechnical tests to determine the strength and durability of the concrete made out of locallyavailable construction material.

6. Future development plans and activities in the tsunami run-up zones in coastal tracts, and in areas delineated by the high tide line and maximum possible tsunami run-upelevation needs to be regulated. Existing structures and human settlements are to be relocated accordingly (ports, jetties, harbors, research stations, data collection centers etc. excluded). Regulatory measures and practices being followed in other countries which are frequently visited by tsunami, may be consulted for this purpose and codal provisions made.

7. As earthquakes travel faster, the tsunami waves arrive later than the earthquake P-waves.The time lag depends on distance of the source area. So in islands and coastal areas of India, all felt earthquakes may be considered as natural tsunami alert signals and local residents as well as the administration should respond accordingly. As all earthquakes do not generate tsunami this response may be considered as a watch alert only and not a forecast or warning.

Acknowledgements

Support provided by the Andaman and Nicobar Administration during the investigationparticularly by Mr Rishikesh and Mr Bhadra of the Department of Science & Technology, A & N Administration is gratefully acknowledged. Officers of Geodata and Database Division andShri Anshuman Acharyya, Geologist, Monitoring Division, Kolkata are some among others without whose active support this document could not been released just in 3 days.

REPORT ON SUMATRA-ANDAMAN EARTHQUAKE & TSUNAMI, 26 DEC ’0413

Photo 1: GSI team led by the Director General at Port Blair investigating the tsunami effects

Photo 2: Shearing of load bearing base columns leading to caving in of G+2 storied RCC structure, Naya Gaon, Port Blair

Photo 3: Sheared base column and caved in stilt, Naya Gaon, Port Blair

Photo 4: Complete crushing of ground floor due to failure of base column with first floor collapsing to ground level, Bamboo Flat

___________________________________________________ ___________________________________________


Photo 5: Complete caving in of stilt and heavy damage of first floor (now at ground floor level). A car parked in the stilt got completely crushed; newly constructed building, Kanyapuram

Photo 6: Failure of walls and roof of Malabar Society godown, Ograbraj

Photo 7: Inundation of the structure in photo 6 and surrounding buildings by the tsunami

Photo 8: Fine cracks and chipping off plaster at the block joints of Dhanikhari

concrete dam

___________________________________________________ ___________________________________________


Photo 9: Buckling by 8cm of concrete apron at the interface of concrete spill way and earth section on the crest portion, Chouldari dam

Photo 11: Mud volcano that erupted after the 26 December 2004 earthquake in Jarwa Creek, Baratang. The recent mudflow has a distinct contact with an older flow Photo 12: An active crater within the recent mud volcano

Photo 10: a ground fissure cutting across the road through

Anganbari community center, Collinpur.

___________________________________________________ ___________________________________________


Photo 13: Fissure developed on the road at Baratang

Photo 15: Structure flattened by the tsunami in WandoorPhoto 16: Breach in a section of the shore protection wall at Nazar, Port Blair

Photo 14: A tree trunk with its roots separated into two halves along a wide open (90cm) crack. The right side part of the trunk shows left lateral

shear

___________________________________________________ ___________________________________________


Photo 17: Washing away of a bridge by the Tsunami at Corbyn,s Cove, Port Blair

Photo 18: Tsunami water mark (brown- green interface) about 2m above the high tide level at Chidiyatapu

Photo 19: Inundation of paddy field through the backwaters in Ograbraj


19

MACROSEISMIC SURVEY IN ANDAMAN AND NICOBAR ISLAND IN THE

AFTERMATH OF THE GREAT EARTHQUAKE OF 26TH DECEMBER 2004

A K Ghosh Roy, S Bardhan, P Jana and S R Basir

Earthquake Geology Division, GSI, Eastern Region,

DK-6, Sector-II, Salt Lake, Kolkata-700091

INTRODUCTION

At 0629 hrs (IST), December 26, 2004, a very strong shallow focus undersea earthquake occurred off the West Coast of Sumatra Island. This had rocked a vast area around its epicenter including the Andaman and Nicobar Islands and the eastern and southeastern coast of the Indian mainland. Moreover, it had generated a global tsunami, which swept away the Nicobar and Little Andaman coasts along with the southern Andhra Pradesh, Tamilnadu and Kerala coasts of India. Besides India, the other countries affected include Indonesia, Thailand, Sri Lanka, Bangladesh and Myanmar.

Macroseismic survey taken up in Andaman-Nicobar Islands for assigning intensity of the quake is documented in this work. The earthquake was also felt in different parts of Orissa, West Bengal, Andhra Pradesh and Tamil Nadu. Mild tremor lasting for about 30-45 seconds were felt around 06:30 hrs in Puri, Cuttack, Balasore, Jagatsinghpur, Ganjam, Jajpur, Talcher, Kendrapara and Bhadrak areas of coastal Orissa. No damage to property and casualty was reported. People of some localities of southern West Bengal also felt tremors inside the houses and few reports ofvibration/shifting of furniture or falling of utensils from racks were also received. At Gaighata(North 24 Parganas district) about 15 mud houses were damaged. Seiches have been reported from number of places in South Bengal, viz. in the districts of Kolkata, North/South 24 Parganas, Nadia, Howrah, Hooghly, Bardhaman and even Birbhum, Purulia and Bankura. Waves and ripples wereseen in confined water bodies, and in many cases water with fish was thrown out on land. Rise in water level up to 1.20m in ponds with displacement of weeds has been reported. The reports indicate intensity III-IV in affected areas of Orissa and West Bengal.

The earthquake was felt around 6.30 AM in parts of Visakhapatnam urban area, mostly by people residing in the top floor of multistoried buildings. Rattling of utensils and household articles and oscillation of hanging objects was reported. Sudden ground water sprouts was reported from Ranga Reddy, Nalgonda and Nizamabad districts of Andhra Pradesh along with rise in ground water level in some of the open wells. Tremor was felt in Chennai and surrounding areas with rattling of window, table, chair, utensil and other light objects. Seiches observed in number of water tanks in coastal tracks between Cuddalore and Nagapattinam. A tank opposite to temple at Veerampattinam near Pondicherry showed oscillatory rise of water up to 60cm. An intensity of III- IV on MSK scale may be assigned for the coastal mainland.


20

EARTHQUAKES IN THE ANDAMAN AND NICOBAR ISLAND

The islands of Andaman and Nicobar Group fall in zone V in seismic zoning map of India making them vulnerable to major/great earthquakes with MM intensity greater than IX. Following is a list of earthquake events of magnitude more than 6 (source: http://www.asc-india.org/) thatoccurred in and around the island arc

Sl. No.

Date & Time Location Magnitude Remarks

1. 31st December 1881 NNW of Andaman

islands, India.

- No recording stations were

present at that time. Tsunamiwas recorded at various points

on the coast of India withmaximum run-up of 1.2 m on

the Coromondal coasts.

Damage occurred to masonry

buildings at Port Blair.

2. 16th

November 1925

16:17:06.0 UTC

12.00 N, 94.00 E, SW

of Barren Island, India.

Ms 7.2 -

3. 28th

June 1925

13:41:35.0 UTC

10.20 N, 92.80 E

SE of Little Andaman

Island, India.

- -

4. 1st

August 1029

05:01:48.0 UTC

12.00 N, 95.50 E

Andaman Sea, ESE of

Barren Island, India.

Ms 6.5 -

5. 9th

December 1929

06:49:54.0 UTC

04.50 N, 94.50 E

SSE of Great NicobarIsland, India.

Ms 6.7

Mb 7.2

-

6. 19th

March 1936

09:04:05.0 UTC

10.50 N, 92.50 E

Little Andaman Island,India

Ms 6.5 -

7. 14th

September 1939

09:00:58.0 UTC

11.50 N, 95.00 E

Andaman Sea, SE of

Barren Island, India.

Ms 6.0 -

8. 26th

June 1941 West of Middle

Andaman Island, India.

Mw 7.7 Largest earthquake in this

region recorded instrumentally.

It caused damages in Andaman Islands, destroying many major

buildings at Port Blair. Thequake had spawned a tsunami in

the Bay of Bengal recorded

along the Coromondal coast.


21

9. 8th

August 1945

09:53:40.0 UTC

11.00 N, 92.50 E

North of Little

Andaman Island,

India.

Ms 6.7 -

10. 23rd

January 1949

06:31:13.0 UTC

09.50N, 94.50E

Andaman Sea, east of

Car Nicobar Island,India.

Ms 7.2 -

11. 17th May 1955

14:49:49 UTC

07:00 N, 94:00 E

Off the east coast of Great Nicobar Island,

India.

Mw 7.0

Ms 7.2

-

12. 18th

June 1957

14:48:17.0 UTC

14.00 N, 96.00 E

Andaman Sea, ENE of Narcondam Island,

India.

Ms 6.5 -

13. 14th

February 1967

01:36:04 UTC

13.70 N, 96.50 E

Andaman Sea, west of

Mergui Archipelago.

6.8 -

14. 20th

January 1982

04:25:11 UTC

06.95 N, 94.00 E

8.5 km east of

Bananga, GreatNicobar Island, India.

Mw 6.2

15. 20th

January 1982

07:09:17 UTC

07.12 N, 93.94 E

8 km SE of Laful,

Great Nicobar Island,

India.

Mw 6.1

Some injuries and

considerable damage

occurred in the Nicobar

Islands due to both these earthquakes.

16. 14th

September 2002

07:09:17 UTC

13.087 N, 93.94 E

23.6km SSE of

Diglipur, North

Andaman.

Mw 6.5 This earthquake causeddamage on North

Amdaman and was felt as

far south as Port Blair. Sea

surges were reported on a

few islands of North

Andaman’s eastern and

northern coasts.

MACROSEISMIC SURVEY

Macroseismic survey of 26th December 2004 earthquake off the coast of Sumatra was

initiated on 7th

of January 2005. In the first phase of work, during 7th January to 7

th February 2005

different islands of the Andaman Group was covered. During the second phase of work from 19th

march to 1st April 2005 the Campbell Bay Region of Great Nicobar and the Car Nicobar Island was

studied.


22

The macroseismic survey was carried out by extensive field survey by making groundobservations as well as gathering information from affected local people and officials. Besides,information was also collected from number of relief camps at Port Blair where affected people from southern islands were given shelter. The survey was carried out following the Medvedev-Sponheuer-Karnic (MSK)-64 guidelines along with necessary modifications following EMS-98 (Grunthal,1998) Accordingly, data on effects of the earthquake on humans, objects and nature and damage to buildings were collected through interview of the local people. Besides, the features developedduring the earthquake on ground were also studied.

The general effects of the earthquake on Andaman and Nicobar group of Islands include strong ground shaking, shifting of furnitures, sand with water sprouting in low lying areas,development of cracks on metalled road and varying degrees of damage in buildings. As far as, the effects on the mainland are concerned, mild ground shaking and widespread development of seiches have been reported from the coastal tracts of West Bengal, Orissa, Andhra Pradesh and Tamil Nadu. In the following paragraphs the damage pattern and human perceptions are described island wise from the north.

NORTH ANDAMAN

The earthquake intensity was severely felt in this island and the island got cut off from the Port Blair through road as the Austeen Bridge, connecting Middle Andaman and the North Andaman Islands, along the Andaman Trunk Road got badly damaged by the earthquake. Population of this island is centered around Diglipur and its adjoining areas and along ATR. Macroseismic survey in North Andaman revealed that the earthquake tremor was felt by most people, even in movingvehicles, with difficulty in standing, some felt blocking of ears and blurring of vision during thequake, ground fissures profuse with sand venting due to liquefaction of subsurface materials,standing objects shifted and splashing out of water took place in standing water bodies, manybuilding of vulnerability Type B and C suffered Grade-2 damages and Type A structures suffered Grade 3-4 damages. Area wise damage survey (Plate-1) report is given below:

Nabagram: This village is situated in a hilly region of the island southwest of Diglipur; most people felt the tremor and ran outdoor; standing was difficult; few reported abnormal sound prior to the main quake; ground shaken horizontally, mostly in E-W direction; standing vehicle like scooters fell; water splashed out from ponds; objects fell from racks; long ground fissures developed in plane areas as well as, in the hills; black colored sand with water injected through the fissures during the quake;Panchayet Bhavan (RC building) developed cracks and portion of concrete of the northern wall fell (Grade 3 damage) (Fig-1).

Kishorinagar: This locality is situated in the foothill region west of Diglipur; most people felt the tremor and ran outdoor; standing difficult; ground shaken horizontally; water splashing reported at ponds; ground fissures developed in roughly N80

oE direction traced for nearly 500m; N-S trending

culvert damaged; few wood framed earthen houses fallen; sand and water mixture sprouted through the fissures during the quake.

Diglipur: This town is situated partly over hills and partly over the plains of the adjoining valley; most people felt the tremor with accompanying abnormal sound; standing objects like scooters got shifted; moving vehicles had to be stopped during the quake to avoid accident; some experienced ear-blocking and vision got blurred; ground fissures profuse in the plain areas mainly near the streams; huge subsurface sandy materials ejected through the ground fissures (Fig -2); RC framed


23

PLATE-1


24

buildings developed cracks in shear walls; one RCC building in Diglipur bazaar, constructed over slope, developed cracks in foundation and got detached from the E-W trending APWD Road supporting wall (Fig -3) and is hanging precariously towards the nallah.

Aerial Bay: This is situated on the coast adjacent to hills around 10 km east of Diglipur; most people felt the tremor; tremor felt within moving vehicles; ground shaken horizontally in roughly E-Wdirection; ground fissures with liquefied sand sprout reported from the adjoining plain lands; inKeralapuram near Aerial Bay the east and west walls of a RC framed single storied house got collapsed (Fig -4); after the earthquake the coast line has been receded substantially (Fig -5). The PWD Guest House situated over a hillock suffered very little damage. E-W trending ground cracks observed on metal road at several places between Diglipur and Aerial Bay. The Helipad at Diglipur developed ground cracks and the boundary walls suffered Grade 1 damage.

Swarajnagar: This area is around 15 km N-E of Diglipur on a high ground; most people felt the tremor with accompanying abnormal sound; few tens of mm wide road cracks observed; large ground fissures sprouted liquefied sands; utensils fell from shelf; water splashed out from ponds; RCC buildings developed hairline cracks in shear walls and along lintel.

Jaltikri: This is the northernmost locality visited in this Island and small villages are scattered within the jungle. Katcha houses remained unaffected here; huge old mud volcano has erupted fresh mud immediately after the earthquake, as reported by the local people; mud eruptions were found to be continuing during the visit on 21

st January 2005(Fig -6); large ground fissures (more than a meter

wide) has been observed in the vicinity of mud volcano site (Fig -7).

Kalipur: This is a coastal village SE of Diglipur; most people felt the tremor; standing was difficult; people reported E-W horizontal shaking; water splashed in standing water bodies; ground cracks in low lying plains near water bodies; RC building of type C suffered Grade 1-2 damage; coast line

shifted towards sea after the earthquake.

Parangara: Most people felt the tremor; everybody ran outside; 50-60 cm wide ground fissure continued for a km from valley region to the hills; liquefaction profuse; buildings suffered Grade 1-2damage.

Paschim Sagar: This is a coastal village situated in the western coast of the island; high panic and standing was difficult; ground shaken horizontally; large ground fissures sprouting sands; several Katcha houses collapsed (no RC building was present over there, as reported); waves on soft ground reported and also large fissures on hill slope.

Krishnapuri: This village is situated on plane land in the NE of Diglipur; human experience is similar to the other areas; ground fissures common with step like ground subsidence (Fig -8); sand and water sprouted along fissures; Katcha houses collapsed due to lateral spreading.

Ramnagar: Most people felt the tremor; standing was difficult; people reported E-W horizontal shaking; seiches in standing water; ground cracks in low lying plains near water bodies withliquefied sand sprout at places; RC building developed cracks in walls.


25

Austeen Bridge (Chengappa Bridge): The 268 m long newly constructed bridge (which connects Middle and North Andaman Islands) at Austeen strait has been damaged. The superstructure has moved on the substructure by a substantial amount causing dislocation of middle three spans from the bearing (Fig -9).

Kalpong Dam: Rare horizontal cracks were developed at crest of this rock fill dam. Also, the turbines of Kalpong Hydro-electric power plant were reported to be damaged.

Based on the macroseismic survey, a general Intensity of VII has been assigned for this area with high intensity VIII at some localities in the western part (Table-1). It is, however, observed that many of the RC buildings got badly damaged due to poor design and inferior quality of the construction materials used.

Table 1

AREA INTENSITY

JAL TIKRI, KISHORINAGAR, PASHCHIM SAGAR

AND KRISHNAPURI

VIII

NABAGRAM, DIGLIPUR, AERIAL BAY,

SWARAJNAGAR, KALIPUR, PARANGARA AND RAMNAGAR

VII


26

Figure 1: Nabagram Panchayet Bhavan showing falling of concrete. North Andaman

Figure 2: Sandsprout along enechelon ground fissures in Diglipur, North Andaman

Figure 3: Detachment of building from supporting wall, APWD Road, North Andaman

Figure 4: Collapse of walls of a single storied RC house in Keralapuram, North Andaman

Figure 5: Retreat of shoreline in Aerial Bay, North Andaman


27

Figure 6: Recent mud eruption showing radial cracks at Jal Tikri, North Andaman

Figure 7: Large ground crack near mud volcano site at Jal Tikri, North Andaman

Figure 8: Step like ground subsidence in Krishnapuri, North Andaman

Figure 9: Damage in Austeen Bridge connecting North and Middle Andaman


28

MIDDLE ANDAMAN

In this island the habitation is mostly concentrated at pockets in southern, southeastern, eastern and northern part; a large portion of the island is within Jarwa territory where movements are restricted. Macroseismic survey in Middle Andaman revealed that the earthquake tremor was felt by most people, even in moving vehicles, with difficulty in standing, ground fissures profuse with sand venting due to liquefaction of subsurface materials, standing objects shifted and seiches produced in standing water, many building of vulnerability Type B and C suffered Grade-1-3 damages and Type A structures suffered Grade 3-4 damages. At a few instances buildings of Type C structure has shown Grade 5 damage mostly due to selection of unfavorable ground condition and poorconstruction. The area wise (Plate-2) earthquake damage survey report is given below:

Mayabunder: The Mayabunder locality is situated along a slender (100-150 m wide) ridge crest in the northern part of the island; most people have felt the tremor; standing was difficult; horizontal shaking; objects fallen from shelf and table; ground cracks minor (cracks trending N13

oE observed

on approached road to the jetty); pounding damage on main jetty observed (Fig -10); in the approach jetty shear failure of short piles (Fig -11) have been observed; ground cracks developed on the floor of the Helipad (Fig -12); minor cracks in foundation and shear walls of RC framed buildings observed (Fig -13).

Karmatang: This locality is spread over partly on hillocks and adjoining coastal plains; most people have felt the tremor; standing was difficult; few experienced giddiness during shaking; groundcracks not found; minor horizontal and vertical cracks developed in RC buildings.

Tugapur: This area is situated over undulating topography; most people have felt the tremor;standing was difficult; utensils fell from shelf; stationary objects like refrigerator shifted; groundcracks not found near the Primary Health Centre but at Tugapur 7 a number of sinuous ground cracks trending N45

oE was found to have developed in cultivated land with voluminous sand sprouting (Fig

-14); minor cracks in RC buildings.

Billiground: This locality is mostly over flat ground situated either over valley flats orundulating highlands near the hilly terrain; human response is similar to the above areas;

splashing of water in standing water bodies reported; utensils fell from shelf; long slendertrees swung; ground subsidence reported; building subsided due to liquefaction underneath;

shear wall of RC building collapsed.

Harinagar: Situated over flat lying topography; most people have felt the tremor; standing was difficult; utensils fell from shelf ; conjugate ground fissures developed on flat areas with one trending N70

oE and the other N20

oW (Fig -15); liquefied sand sprouted through the former fissures;

maximum width of the fissures measured around 20cm; minor cracks on the side walls of RCbuildings.

Duke Nagar: The topography of the area is flat; most people felt the shock; other than the horizontal shaking a circular motion in ground was also reported by some people; ground fissures developed with trend N20

oW; sand sprouting through the fissures; local land subsidence observed due to

liquefaction; tree trunk got split by ground crack trending N35oE (Fig 16); building damage not reported.


29

PLATE-2


30

Kamalapur: It is situated over an undulating topography with hilly areas on the eastern part; most people felt the shock; ground shaken horizontally with a few spurts of vertical movements; utensils fell from shelf; RC framed tin roofed two storied primary school building developed both horizontal and vertical cracks in shear walls.

Dharampur: This village is on a flat valley area; most people felt the shock; it was difficult to stand; stationary objects shifted during shaking; utensils fell from shelf; several ground fissures observedand sand venting through fissures common (Fig -17); pillars of wooden houses shifted.

Pokkadera: This locality is built on tidal flat surrounded by swamps; most people felt the shock; seiches reported; almirah tumbled during shaking; utensils fell from shelf (Photo-18); groundfissures noticed, affected metalled roads; two storied RCC building developed foundation cracks trending N20

oE (Fig -19), columns separated from shear walls with a tilt towards west.

Rampur: The area is near the coast surrounded by coastal swamps and is flat; most people felt the shock; standing difficult; few reported about giddiness; ground cracks developed with ejection of water through it; two storied RC building collapsed due to column failure which were not bounded with shear walls (Fig -20).

Danapur: The area is having flat to undulating topography; most people felt the shock; standing difficult; few reported giddiness; auto rickshaw standing on level ground swayed during the quake; standing scooter fell; ground cracks developed; RC buildings developed foundation cracks.

Chainpur: This locality is at higher elevation with undulating topography; similar effects like above reported by the people; animals behaved abnormally prior to and during the quake; ground fissures conspicuous near nallahs and ground subsidence observed at places; minor cracks in walls of RC two storied buildings.

Hanspuri: This is near to a swampy land with undulatory high topography to the east; most people felt the shock; standing difficult; apart from horizontal motions in ground a circular motion was also experienced by the people; both N-S and E-W trending ground fissures developed with as long as 50m in length, individually with nearly 20cm width; perennial well got dried up after the quake; both katcha and RC buildings developed minor cracks in foundation and walls.

Padmanavapuram: This is on the base of a hill slope near the coast; most people felt the shock; standing difficult; horizontal movement in roughly E-W direction; stationary objects like TV,Almirah fell; seiches reported in ponds; minor cracks in RC framed houses; cracks developed inpassenger waiting shade near Padmanavapuram primary school.

Rangat: This township is situated over both undulating topography and flat valley areas andadjoining hill slopes; most people experienced the tremor; difficult to stand; false wooden partition in APWD Guest House fell alongwith the utensils from shelf; splashing of water observed in ponds; extensive ground cracks developed on the banks of Rangat river (Fig -21), as well as, near Sitapur village with stepwise subsidence towards the river bed with evidences of liquefaction; one RCbuilding near Hotel Avis totally collapsed (due to constructional defects) (Fig -22); vertical cracks observed in the wall of APWD (RC framed two storied) Annexe building; minor shear cracks at passenger hall of the jetty and pounding damage at jetty floor (Fig -23).


31

Parnashala: The area is situated over a higher undulating topography; most people experienced the tremor; difficult to stand; ground shaken in E-W direction; objects fell from shelf; stationary truck moved during the quake; ground fissures observed; water level increased in Rangat river after the quake.

Kaushalyanagar: It is situated over an undulating topography surrounded by high hills in its north; most people felt the tremor; difficulty in standing; standing scooter fell; utensils fell from racks; ground fissures developed near water bodies and swampy land; water level in nallahs increased.

Atter Jig: This is in an intermountain valley area; most people felt the shock; standing was difficult; horizontal N-S trending ground shaking reported; tremor felt in moving vehicle; ground fissures near nallahs alongwith land subsidence affecting houses (in Atter Jig no 11 Police Chowki); almirah fellduring shaking; landslides reported in nearby hill; walls of katcha houses damaged.

Jarwa Territory area: A great part of Middle Andaman, along the western margin remains inaccessible due to restrictions imposed by Andaman Administration. The tribal welfare officer,Kadamtala informed that large ground fissures were observed at places on the hills. It has also been reported that the Jarwas got panicked and shifted towards the ATR (Andaman trunk Road); nocasualty was reported. Islands of the western territory viz. Flat island, have been reported to be uplifted due to the earthquake.

Hence, a general Intensity of VII has been assigned for this area with high intensity VIII at some localities in the western part (Table-2).

Table-2

AREA INTENSITY

DUKE NAGAR, KAUSHALYANAGAR, KADAMTALA AND HANSPURI

VIII

MAYABUNDER, KARMATANG, TUGAPUR, BILLIGROUND, HARINAGAR, KAMALAPUR, DHRAMPUR, POKKADERA, RAMPUR, DANAPUR, CHAINPUR, PADMANAVAPURAM, RANGAT, PARNASHALA AND ATTER JIG.

VII

Figure 10: Pounding damage near the contact of the main andapproach jetty in Mayabander,Middle Andaman

Figure 11: Structural failure of short piles below the approach jetty at Mayabander, Middle Andaman


32

Figure 12: Ground fissure on the floor of Mayabander helipad and sprouting of liquefied sand

Figure 14: Liquefied sand ejected through sinuous ground fissures at Tugapur 7 Middle Andaman

Figure 13: Cracks in shear wall of a RCC building in Mayabander jetty, Middle Andaman

Figure 15: Sinuous ground fissure trending N20E at Harinagar Middle Andaman

Figure 16: Ground fissure split tree trunk at Duke Nagar, Middle Andaman

Figure 17: Linear liquefied vents at Dhrampur, Middle Andaman


33

Figure 18: Utensils fell from shelf at Pokkadera Middle Andaman

Figure 19: Foundation crack trending N20E at Pokkadera Middle Andaman

Figure 20: First floor resting on ground due to failure of ground floor load bearing columns at Rampur Middle Andaman

Figure 21: Ground fissure with subsidence towards river at Rangat Middle Andaman

Figure 22: Total collapse of RCC building at Rangat Middle Andaman

Figure 23: Pounding damage of jetty floor at Rangat Middle Andaman


34

SOUTH ANDAMAN

In South Andaman island different grades of damage in different parts were observed. Most of the population is concentrated in this island though an appreciable portion in north and northeastern part falls under Jarwa Territory where movements are restricted. Locality wise damage (Plate-3) survey report is detailed below:

Chidiyatapu: This is the southernmost locality of South Andaman Island and situated overundulatory topography; most people felt the shock; standing difficult; one single story masonryrestaurant of Type B structure suffered Grade-1 damage.

Beadonabad-Burmanalla sector: These are coastal villages over a, more or less, undulatory topography; most people felt the shock and experienced a whining sound; it was difficult to stand; ground shook horizontally; hanging objects swayed heavily; utensils fell from racks; onenonperrenial spring, near GSI drilling camp, started to pour out water immediately after theearthquake; RC farmed Type C buildings developed Grade 1-2 damages.

Bhatu Basti-Garacharma sector: The topography of these areas are undulatory and elevated; most people felt the shock; mostly sidewise shaking experienced with spurts of vertical motions in the waning phase of the quake; giddiness felt by few people; articles fell from shelf; standing objects moved; water level at dug wells increased and few streams got water charged after the shaking; building damage not reported.

Sippighat : It is situated mostly over reclaimed tidal flat and along slopes of the adjoining hills; most people felt the shock; standing was difficult; seiches in standing water reported; one Type A building suffered Grade 5 damage; The eastern and western walls of the second floor verandah of one Type C RCC building (Bharat Sevashram Sangha) fell (Grade 3 damage)(Fig -24). Near Sippighat coffee Plantation/Ayappa Swamy temple area, over a ridge crest, Type B buildings show Grade 3-4damages with collapse of three side walls alongwith cracks in other walls and in foundation (Fig -25); nearby another masonary building developed cracks and one of the verandah wall collapsed (Fig -26); contact between two retaining walls of the temple area got detached from each other due to shaking (Fig -27).

Nayashahar: This locality is over undulatory high ground; most people felt the shock; sidewise movements felt; seiches reported; plasters fell from walls of a temple.

Calicut-Bimlitan area: Undulatory high ground; most people felt the shock; standing was difficult; materials fell from shelf; splashing of water observed in standing water bodies; Type A and B buildings suffered Grade1-2 damages.

Austinabad: Area undulatory by the side of hill slopes; most people felt the shock; standing was difficult; single storied RC building of Type C suffered Grade 2 damage.

Junglighat-Dollyganj-School Line sector: Area over undulatory high ground; most people felt the shock and panic was high; standing was very difficult; sidewise E-W movement; few felt giddiness; standing objects like Almirah fell; splashing of water in both standing water and in narrow nallah (near school Line area) reported; ground fissures developed along the Kamraj road (between Air Port and Secretariat); Type B-C buildings suffered Grade 2-3 damage.


35

PLATE-3


36

Aberdeen Bazaar-Marina Park-Cellular Jail: The area is mostly situated on undulatory high topography; most people felt the tremor and the panic was high; standing was difficult; minor cracks developed in the shear wall of Dhanalakshmi Hotel; gaping joints developed along the contact of the side walls and foundation of the two storied RCC building (Dhanalakshmi Hotel); miners fell inJama Masjid (Fig -28); N-S trending boundary wall of the Cellular jail in front of the office of the Chief Register of birth and death was collapsed (Fig -29); plasters had fallen from the frontal arch of the Ramkrishna Mission building in marina park (Fig -30); overall, in this area, the Type B-Cbuildings had suffered Grade 2-3 damages.

Phoenix Bay-Chattam Jetty area: Pounding damage on the jetty floors; RC column supported scooter stand in Phoenix Bay jetty collapsed (Fig -31); Port Management Board office building(Type C structure) suffered Grade 3 damages (Fig -32).

Guptapara-Manjery-New Manglutan sector: These localities are mostly over a flat to slightly undulatory unconsolidated valley filled sediments; most people felt the shock; standing difficult;animal behavior abnormal prior to the quake; objects fell from shelf; ground fissures (as wide as 20 cm) conspicuous affecting even metalled road; RC floored wooden house in Guptapara developed cracks in foundation; plasters fell from shear walls; in Manjery one masonry wall fell; overall, the Type B/C structures had suffered Grade 2-3 damages.

Collinpur-Manpur sector: These villages are built over clayey soils within intermountain valleys; human reactions are similar to the above; en echelon ground fissures trending N30

oW and N70

oW

sprouted liquefied sands in Collinpur area; liquefied sand was expelled through vent was alsoobserved (Fig -33); small landslide along road observed near Manpur (Fig -34); a nearly Km long ground fissure had split one RC building of Mr Biplab Biswas; near Manpur bazaar several ground fissures had expelled liquefied sand with ground subsidence; almost all the buildings of Type B/C structure had developed Grade 2 or 3 damages; one single storied restaurant suffered Grade 5damage in Collinpur .

Namunaghar-Shaitankhari-Kadakchang sector: These localities are mostly over undulatingtopography surrounded by hilly regions. Most people felt the shock in the form of a E-W sidewise movement; giddiness experienced by some; standing difficult; utensils fell from kitchen shelf;seiches in standing water bodies; near Namunaghar one stone crusher machine spring fitted on pillars (4 nos.) fell when the springs snapped during shaking. Ground fissures near nullah developed at places; spring water showing increased volume of discharge near Shaitankhari Rubber Board office. Namunagarh primary school, a two storied RC building with asbestos roof developed subverticalcracks; plasters came off along shear cracks on the walls at places; in the Rubber Board office (single storied RCC building) have developed vertical cracks in shear walls; contacts between foundation and shear walls have also developed cracks; in Kadakchang area house of Mr. N. Hamsa have developed cracks along the wall (both eastern and western) and floor; cracks have also come up in the side staircase along its contact with shear wall; Type B/C structures are showing Grade 2-3damages.

Bichadera-Miletilek-Jirkatang sector: This is a hilly region with colluvial cover; human responses are similar to above; trees swayed during the shaking; also sound of bombardment heard before the earthquake in Bichadera area; ground fissures along nallahs near Jirkatang Police Chowki andBichadera area; single storied Type B structures developed Grade 1-2 damages; two chimneys have fallen in Govt. Quarters at Mile Tilek (single storied RC building with RC roof) (Fig -35); withinJirkatang to Nilambur jetty ( within Jarwa territory) cracks along several stretches of Andaman


37

Trunk Road (ATR) was also observed; at places culverts on small streams were found to be damaged.

Shoal Bay-Wrightmyo area: Mostly flat area adjacent to creek; human responses are similar to the above; humming sound before and during the earthquake in Wrightmyo area; utensils fell from shelf; ground cracks trending N80

oE affecting both ground (Fig -36) and metalled road; culvert over one

stream got badly damaged due to shaking near Shoal Bay 8; silty material alongwith profuse water ejected through fissures near Shoal Bay 8; buildings of Type A/B suffered Grade 1-2 damages.

Ograjbraj: In this locality, a Godown of Malabar society with approximate dimension of 8m (w) x 15 m (l) x 6 m (h) got heavily damaged; the three walls and the roof suffered total collapse (Fig -37).

Kanyapuram: A two-storied RCC house with GI roof of Mr Hamid was totally collapsed; a car got trapped under the subsided first floor (see figure in chapter I).

Nayagaon: A newly constructed three-storied RCC building suffered Grade 5 damage; the entire building caved in due to failure of load bearing base columns (see figure in chapter I).

Bamboo Flat: A newly constructed house of Md Arif show Grade 5 damage (Fig -38); this two storied structure with RCC columns, beams and roof caved in and the ground floor got completely crushed and the first floor came to the ground.

Ferrarganj-Caddleganj-Tushnabad: The area is situated over a wide valley surrounded by hills; most people felt the shock; standing was difficult during the quake; ground shook laterally in both NE-SW and E-W direction; Almirah fell in Caddleganj area; materials fell from shelf; ground cracks developed in Caddleganj (in primary school campus) and Tushnabad area sprouting liquefied sandand water; Type C buildings suffered Grade 2-3 damages in Tushnabad and Type A structures suffered Grade 3 damages in Caddleganj area

Tirur-Herbertabad area: The area is situated over an intermountain valley surrounded by hillocks. Majority of people felt the shock; it was difficult to stand and walk steadily during the shaking; lateral ground shaking was noticed by all the persons interviewed; materials fell from shelf; standing bus swayed and moved; ground cracks (often arcuate) developed with sand sprouting; Type B and C buildings suffered Grade 3 damage (Fig -39).

Water supply schemes of Port Blair

See Chapter 1

Based on the macroseismic survey enumerated above, a general intensity of VII has been assigned for the South Andaman Island with a visibly higher intensity of VIII for the western part of the island (Table3).


38

Table-3

AREA INTENSITYGUPTAPARA, SIPIGHAT (AYAPPA SWAMY TEMPLE AREA), WANDOOR, COLLINPUR AND TIRUR-HERBERTABAD AREA.

VIII

CHIDYATAPU, BEADNABAD-BURMANALA, BHATU BASTI-GARACHARMA, PORT BLAIR, BICHDERA-MILE TILEK-JIRKATANG, SHOAL BAY, OGRAJBRAJ, BAMBOO FLAT, CALICUT-BIMLITAN,NAMUNAGARH-SHAITANKHARI-KADAKCHANG AND TUSHNABAD.

VII

Figure 24: Collapse of second floor side wall Bharat Sevashram Temple Sipighat South Andaman

Figure 25: Collapse of walls in poorly constructed RC building Ayappa Swamy Temple Sipighat South Andaman

Figure 26: Collapse of wall in masonrybuilding Ayappa Swamy Temple Sipighat South Andaman Figure 27: Detachment of walls Ayappa

Swamy Temple Sipighat


39

Figure 28: Fall of minars at Jama Masjid,Abeerdeen Bazaar, Port Blair

Figure 29: N-S trending boundary wall fell due to shaking at Cellular Jail, Port Blair

Figure 30: Damage of frontal arcade of RKM building, Marine Drive, Port Blair

Figure 31: Collapse of scooter shade at Phoenix Bay, Port Blair

Figure 32: Damage in Port ManagementBoard building at Phoenix Bay

Figure 33:Sand blow structure developed by expulsion of liquefied sand through vent at Collinpur. South Andaman


40

Figure 34: Landslide triggered by earthquakenear Manpur, South Andaman

Figure 35: Concrete chimney fell at Education Dept. Quarter, Mile Tilek, South Andaman

Figure 36: Ground fissure at Shoal Bay, South Andaman

Figure 37: Godown of Malabar Societyshowing grade 5 damage at Ograbraj, South Andaman

Figure 38: First floor came into ground floor level on collapse of stilted columns, Md.Arif’s house, Bamboo Flat, South Andaman Figure 39: Damaged Police Chowki showing

shear cracks, Tirur, South Andaman


41

BARATANG ISLAND

In Baratang island interview of the officer in charge (Mr Pujan Prasad) at Police Chowki, revealed that most people had felt the tremor; panic was high; it was difficult to stand during the severe shaking that lasted for nearly a minute; it was also reported that many felt upward movement first followed by lateral shaking; standing objects vibrated; hanging objects swayed; seiches reported in standing water bodies; metalled road cracked (Fig-40), subsided (Fig-41) and uparched (Fig -42)at places between Nayadera and Jarwa Creek over a stretch of about 800 m; tree trunk got split and separated (see figure in chapter I). Several new mud volcanoes appeared; land subsidence noticed near new mud volcano sites along gaping ground fissures in both N25

oE-S25

oW and E-W directions.

Some poorly constructed houses collapsed. A general intensity of VII has been assigned for this island.

The Forest Range office suffered Grade 2 –3 damage in the form of shear cracks in walls and gaping settlement cracks in the floor. A number of steel almirah and racks containing office records and the hanging tube light fell down during the earthquake (GSI, 2005).

Mud Volcano In the Baratang Island, two major and some minor mud volcanoes erupted during the

earthquake of 26 December 2004. In case of the one at Jarwa Creek (declared as a tourist spot by Andaman administration) reported to have erupted with great violence soon after the major tremor. It was also reported that a series of explosions that lasted for several minutes accompanying the eruption could be heard from distances as far as 2-5 km from the site. Splashing of mud upto great height and flames coming out of one vent were also reported (GSI, 2005). During the visit of the Director general, GSI and his team of senior scientists in the second week of January 05, the total volume of erupted mud at Jarwa Creek was found to be 1600 cubic m (as per the Forest authority this figure is 2400cubic m). It is quite certain that such huge volume of mud was ejected out within a sort period of time after the earthquake.

At one place (120 08’ 31.5”; 92

0 47’ 28.4”) gaping en echelon cracks having a depth of 1.5 m

and maximum width of 1.1 m have developed along N25oE trend extending either side of the road.

On the northern side of the road a small mud volcano site with 6 small craters have been found. The diameter of the craters varies from 4 cm to 21 cm. The largest crater emits grey colored liquid mud that produces a mud-cracked surface on drying. Ground cracks (E-W and N25

oE-S25

oW) and

associated land subsidence was also noted near the mud volcano site. At Jarwa creek the mudvolcano that erupted as recently as on 18

th February 2003, was reported to have renewed activity

since 26th December 2004. However, when visited on 17th January 2005 this activity have been found to have subsided. Here the erupted mud is having a flattened bun shaped outline. About 3 to 4 craters are found on the mud surface. Active craters still show ejection of grey viscous mud with or withoutsmall rock particles (Fig -43). Gaseous matter was emanating from these craters at times with hissing and blurring sound at irregular intervals. One dried up crater showed red colored dry mud (Fig -44). At Rajatgarh, a newly erupted mud volcano having similar features but with larger aerial extent and having larger rock particles associate with the dried mud found at the day of the visit apart from 2 to 3 dried up craters no signs of activity was noticed. Several trees were found to be partially submerged under the erupted mud.

During the second phase of field visit in 19th March-2

nd April 2005, it was found that the

mud eruptions were continuing with development of more subsidiary craters in Jarwa Creek site and the rate of expulsion had increased.


42

HAVELOCK ISLAND

General panic prevailed during the quake, most people felt the shock; utensils fell from the shelf; E-W shaking was reported; RCC buildings of Type B and C developed minor cracks (Grade 1damage).

A lower intensity of VI has been assigned for this island.

Figure 40: Cracks on metalroad, Baratang Island

Figure 41: Subsidence of metalled road, Baratang Island

Figure 42: Up arched metal road, Baratang Island

Figure 43: Subsidiary crater ejecting viscous mud at Jarwa Creek, Baratang Island

Figure 44: Dried up vent showing redcoloured mud ejecta at Jarwa Creek,Baratang Island


43

LITTLE ANDAMAN

This island (Plate-4) is situated about 250km south of Port Blair and has been severely affected by the surges of tsunami masking the effects of earthquake damages along the coastal tract. Theinterview of the local people and the field traverses during the first phase of survey revealed that the earthquake intensity was quite high viz. VIII in updated MSK-64 scale. The reactions of the shaking is summarized below:

PLATE-4


44

Hut Bay: This is the entry point in the Little Andaman and most of the population of this island is concentrated in this area. Most of the people reported that it was difficult to stand, one person was reported to have fallen on the ground during the tremor; unusual sound accompanied the earthquake; it was also felt within moving vehicles; metalled road was found to be cracked and up arched (Fig -45); second floor of a RCC building was collapsed due to failure of the columns of the first floor showing Grade 4 damage (Fig -46), the collapsed roof was shifted further by the giant waves of the tsunami later on); the columns of the Port Control Tower building was failed during shaking Grade4 damage (Fig -47), later on the building was tilted on ground by the tsunami); other than these the remnant foundations are also showing cracks in it.

16 km site: This information was collected at Car Nicobar by interview of a person present over here during 26

th December 2004; he reported development of extensive ground cracks with sprouting of

liquefied sand; an earthen dam developed cracks (dimension not known) which had totally drained out the stored water.

A general intensity of VIII has been assigned for the study area of this island.

Figure 45: Road crack and up arching

at Hut Bay, near 7km, Little Andaman

Figure 46: Grade 4 damage in RCC

building at Hut Bay, Little Andaman

Figure 47: Collapsed port Control Board Tower near je tty,

Hut Bay, Little Andaman


45

CAR NICOBAR

Most of the areas studied along the east coast are devastated by the tsunami that masked the effects of earthquake to a great extent. In addition to the ground survey, eyewitness accounts of local people had been given considerable importance.

It was reported by most people that during the earthquake (which lasted for about 3-4minutes), standing was difficult, general panic was high and the ground was shaken horizontally. In addition to that, stationary objects fell from rack and shelf, standing bus swayed at places, ground fissures were developed and sand and water were sprouted through the fissures at many places. Wooden buildings and RCC structures of Type B and C suffered grade 3 damage due to earthquake.In some cases, it was observed in case of RCC buildings, that the construction was of poor quality and design. Moreover, liquefaction of the subsurface granular unconsolidated sandy materials mighthave accentuated building/structure damage.

Summarized accounts of damage survey carried out at different areas (Plate-5) are detailed below:

PLATE-5


46

Malacca: Most people reported that it was difficult to stand during the earthquake, few felt giddiness, panic high, shaking horizontal in E-W direction, long slender objects like palm tree and electric poles swayed, standing bus shifted by few meters; water and sand mixture sprouted upto a height of 3-4 meters through ground fissures generated during the earthquake near jetty; metalled road bulged and cracked near Malacca jetty (Fig -48) due to liquefaction, supporting column of APWD water tank developed cracks, minor cracks in the shear wall of the Jetty office; cracks had developed along short columns in the ground floor of new annexe building of the hospital (Fig -49);contact between two separate portions of the Deputy commissioner

’s office got widened during

shaking (Fig -50).

Mus: Most people reported that it was difficult to stand, high panic, few felt giddiness, seiches in standing water, Almirah and TV fell on ground alongwith the objects from shelf and rack, ground fissures not conspicuous, old port control tower building (three storied RC building) got highlydamaged and passenger hall near jetty have developed both vertical and horizontal cracks). AHW building (single storied RC building with RC roofing) near jetty have developed cracks (both vertical and horizontal) on the shear walls (Fig –51); vertical cracks have developed in the columns also. Columns of water tank near jetty also got damaged (Fig -52).

Air Force Area: Effects on human was similar to the other areas of the island, utensils and other objects fell on ground, several E-W trending cracks observed on roads, Commanders house got damaged by lateral spreading during the earthquake (Fig -53) minor cracks observed in the houses escaped damages caused by tsunami, Air crew rest room at the Air strip (one storied plastic roofing on stilted column) collapsed due to column failure (Photo-54). Failed columns were bent (Fig -55)shear cracks also were visible on the remnant part, E-W walls of the second floor of Air Terminal building fell during shaking.

Kankana: Most people reported that it was difficult to stand, high panic, few felt giddiness,horizontal ground movement reported by the people along E-W direction, Almirah fell duringshaking, ground cracks conspicuous with sand and water sprouting, building damage due toearthquake was not reported by the local people interviewed.

Tamaloo-Kinyuka-Taupioming-Lapati sector: Most people had found it difficult to stand and walk steadily during shaking, high panic; materials fell from shelf; standing objects like T.V. andelectric poles fell; water splashed out of tanks, drums etc. mostly E-W lateral shaking was experienced by the people; some RCC building (one storied with tin roofing) collapsed; Severalsingle storied wooden houses on RC stilted columns at Kinyuka as well as at Taupioming (Fig -56& 57) were also damaged due to shaking.

Based on the Macroseismic survey general Intensity of VIII has been assigned for the study areas of the Car Nicobar Island.

KATCHAL

The information regarding earthquake damage intensity was collected through interview of localpeople at Relief camp in Port Blair. Most people felt the shock; standing was difficult; people crawled and felt giddiness during the earthquake shaking; both E-W and N-S shaking was felt by the people; waves observed on ground by some people. Utensils fell from shelf; Almirah fell on ground; water splashed out from the containers; ground fissures developed and sand sprouting wasconspicuous; in one instance it was reported that the latrine door got broken due to shaking in a single storied tin roofed RC building; in a single storied RC floor wooden framed hospital building


47

cracks developed in floor and plasters came off. Based on the Macroseismic survey Intensity of VIII has been assigned for the study areas of the Katchal Island.

Figure 49: Vertical fracture on the column, Hospital, Car Nicobar

Figure 50: Repaired shear wall fracture, DC office, Malacca, Car Nicobar

Figure 51: Vertical/ horizontal cracks inshear wall, AHW building, Mus jetty, Car Nicobar

Figure 52: Damaged pillar of water tank near Mus jetty, Car Nicobar

Figure 48: Damaged metalled road, up arched and eroded, exposing basement near Malacca jetty, Car

Nicobar


48

Figure 53: Tilted RC building due to lateral spreading, Air Force Colony, Car Nicobar

Figure 54: Air crew rest room damaged due to failure of load bearing column, Air strip, Car Nicobar

Figure 55: Closer view of damaged column in Figure 54

Figure 56: Grade 4 damage of Church,Kinyuka, Car Nicobar

Figure 57: Failure of RC load bearing base column causing collapse of wooden house, Taupioming, Car Nicobar


49

NANCOWRY ISLAND

Information regarding earthquake damage intensity was collected through interview at Car Nicobar. Most of the people reported that it was difficult to stand; general panic; all people came outdoor; giddiness felt by some; ground shook laterally in E-W direction; utensils fell from shelf; about 4m long and 20 cm wide ground fissures reported to have developed; two storied RC structure of Medical building developed cracks along shear walls.

PILLOWMILLOW ISLAND (NEAR LITTLE NICOBAR)

The information regarding earthquake damage intensity was collected through interview at Campbell Bay relief camps. Most people felt the shock with a hissing sound just before theearthquake; standing was difficult; ground shook laterally; ground waves observed; ground fissures developed and liquefied sand sprouted through these; one storied RC building with asbestos roofing developed minor cracks.

GREAT NICOBAR ISLAND

In this island (Plate-6) the macroseismic survey could only be done around Campbell Bay region during the second phase of work. Tsunami had inflicted severe damage masking the effects of earthquake in most of the areas along the coastal tracts.

Campbell Bay: Most of the people reported that it was difficult to stand; general panic; all people came outdoor; ground shook laterally in E-W direction; utensils fell from shelf; refrigeratoroverturned; water splashed out of tanks; longitudinal sinuous ground fissures trending N40

oW

observed near Port Control Tower Building, slumps in sloping ground near the cracks damaging the boundary walls (Fig -58 & 59); in APWD Guest House building, situated at a higher elevation, developed cracks in foundation extending into the plinth area (Fig -60), also in a short RC column holding the wooden pillars supporting the asbestos roofing had developed vertical cracks (Fig -61),in one instance the shear wall of Room no 1 had got horizontal cracks at shear wall and foundation contacts (Fig -62); near 2.5 km, lighthouse tilted during shaking (Fig -63); in Port Control Tower (a three storied RC building) is damaged, the intensity of damage decreased upward; in tall buildings inertial movement concentrate the force of shaking at the ground level produce destructive basalshear, this may be the cause for the greater damage to the lower floors; cracks are aligned both in horizontal and vertical directions along shear wall –column joints and shear wall-tie beam joints, shear walls were also developed huge cracks (Fig -64); side staircase got separated from shear wallduring shaking (Fig -65).

Jogindernagar: Tsunami had flattened almost all the houses with foundations intact in some cases; in few instances crack due to earthquake was observed over remaining foundations.Based on the Macroseismic survey Intensity of VIII has been assigned for the study areas of the Campbell Bay region of the Great Nicobar Island.

Based on the Macroseismic survey Intensity of VIII has been assigned for the study areas of the Great Nicobar Island.


50

PLATE-6


51

Figure 58: Slump scar along groundfissure, Campbell Bay, Great Nicobar

Figure 59: N40W trending ground fissure with slumping damaging boundary wall of PCT building, Campbell Bay, Great Nicobar

Figure 60: Foundation cracks in APWD guest house, Campbell Bay, GreatNicobar

Figure 61: Vertical cracks on short column inAPWD guest house, Campbell Bay, GreatNicobar


52

Figure 62: Basal cracks at the contact of wall and basement in APWD guest house,Campbell Bay, Great Nicobar

Figure 63: Tilting of Lighthouse, Campbell Bay, Great Nicobar

Figure 64: Damaged ground floor of PCTbuilding, Campbell Bay, Great Nicobar

Figure 65: Separation of staircase from shear wall, PCT building, Campbell Bay, Great Nicobar


53

CONCLUSION AND RECOMMENDATION

Macroseismic survey of the great earthquake of 26.12.2004 has revealed that theintensity (as per revised MSK-64) is higher in Nicobar Group of Islands (VIII) in general while in the Andaman Group of Islands (i.e. South, Middle and North Andamans) the intensity iscomparatively less (VII) with occasional higher intensities (VIII) at some areas along the western part of the islands. In case of Havelock Island, which occurs to the east of the Andaman Group of Islands, the intensity is distinctly less (VI). Since, many parts of the islands are inaccessible and a greater part of the study area of Middle and south Andamans lie within Jarwa territory and thus could not be studied in detail, isoseismal zones could not be delineated. As far as, the effect of the earthquake on mainland is concerned, the coastal tracts of West Bengal and Orissa have been mildly affected indicating intensity of III-IV. Also, the coastal areas of Tamilnadu and Andhra Pradesh indicated intensity of II to III. In the intensity zoning map by USGS an intensity of VII has been assigned for Port Blair while the same for Kolkata as II-III and the same for Vishakhapatnam and Chennai as IV.

Regions of lower damage may alternate with regions of higher damage as ground motions locally gets affected by the topography and geology prevailing in the vicinity. Castellani et al (1978), from his numerical model study of the topographic effects at mountain sites showed that the presence of valleys and mountains induce variety of reflections and refractions amplifying the intensity of ground motion. Moreover, it is well known that the softer the ground more severe are the damage effects (Scheidegger 1985). The pockets of higher intensity observed within otherwise lowerintensity zones all over the Andaman Islands must be due to the combined effects of topography and local geology.

Macroseismic survey has revealed that in general, wooden structures were less damagedcompared to modern RC structures. The building damages observed at various localities indicate that at many cases the structures without adequate shear resistance in vertical members resisting the earthquake effects, especially, the structures on stilts, behaved very poorly under lower seismic intensity of VII as per MSK scale. In some cases, the base columns were not tied with shear walls. Similar results were observed in case of Bhuj earthquake of 2001.It is therefore imperative that designs of structures including various RC buildings and harbor structures need to be examined by competent structural engineers to provide adequate seismic resistance in them. Since the entire Andaman and Nicobar Islands belong to an area of high seismic activity (zone V of the Seismic Zoning Map of India), for any construction activity, the BIS code on earthquake resistant designs need to be followed strictly.

It has also been observed that the quality of RCC in case of many collapse structures was found to be inferior. Presence of shell/coral fragments in sand used for construction has been found to be a common phenomenon. Also, quality of steel used in some buildings was found to be of inferior quality and concrete of low strength. The quality of construction materials also should be examined prior to their use. It was also observed that often the masonry work was very poor in case of damage buildings and proper supervision by the suitable engineers is therefore also necessary. It has also been observed that many buildings/structures got damaged due to lateral spreading and liquefaction related phenomenon in low-lying areas, in the vicinity of water bodies. Adequate care needs to be taken during construction of any building/ structures over such areas. It may be necessaryto carry out SPT, permeability and other geotechnical tests of sub-surface/soil samples forconstruction of heavy structures in such areas and also for other areas. In other words, site-specificgeotechnical investigations may have to be undertaken. It may be relevant to note that in case of


54

Bhuj earthquake, an eight storied type C building constructed over hard ferruginous sand stonesuffered only minor cracks whereas a four storied type C building constructed over sandy shale suffered grade 5 damage in the same area (Ameta et al., 2005). In the investigated areas, in many cases damage to type B structures was due to shallow foundation depth, ageing of mortars (resulting in formation of cavities) or due to absence of PCC (Plain cement concrete) layer at foundation level or RCC level at plinth level. Absence of PCC at foundation level caused loose contact of thestructures with ground and during disharmonic vertical ground motion and subsequent horizontal ground shaking, the buildings collapsed partially. Proper cares need to be taken at foundation level and during construction level by providing proper reinforcement. It is also felt necessary to upgrade technical knowledge of the engineering community engaged in planning, design and construction of structures in A&N group of islands. For this, suitable training programmes may be arranged for thepersonnel of department like APWD, AHW, MES etc., engaged in construction activities in A&N islands. Moreover, key projects for seismic design for construction of new structures and seismic retrofitting of existing structures need to be taken up in the islands.

ACKNOWLEDGEMENT

The authors are grateful to Dr M K Mukhopadhyay and Dr M M Mukherjee, DeputyDirector General, GSI for their constant encouragement, active guidance and for providing logistic supports, as and when required, during the course of work and suggesting necessary modifications for improvement of the report. The authors are also thankful to all scientists of GSI who has helped in different stages of investigation and preparation of this report. Cooperation received from the Chief Secretary and other officials of Andaman Administration is gratefully acknowledged.

REFERENCE

Ameta, S.S., Chandra Madhav, Rai, D.K., Gill, P.S., Wadhawan, S.K. and Khaparde, A.R. (2005): Geotechnical microzonation of Bhuj town area, Kutch district in view of 2001 Bhujearthquake. Contr. Kangra Earthquake Cent. Seminar, Spl. Pub. GSI, No. 85, PP. 267-277.

Billham, R and Wallace, K (2005): Future Mw>8 earthquake in the Himalaya: Implication from the 26 December 2004 Mw=9.0 earthquake on India’s eastern plate margin. Cotributions to Kangra Earthquake Centenary Seminar, GSI. Spl. Publ. No. 85, p.1-14.

Bolt, B. A. (1993): Earthquakes and geological discovery. Scientific American Library, 229 p.Castellani, A., Riccioni, R. and Robusti, G., (1978): surface effects on seismic waves. ISMES

(Bergamo) Repts. 106(3): 91-103.Dasgupta,S. and 14 others (2000): Seismotectonic Atlas of India and it’s environs. Geological

Survey of India Special Publication.Grunthal, G. (1998) European Macroseismic Scale 1998. Conseil de L'Europe, Cahiers du Centre

Europeen de Geodynamique et de Seismologie, v.15GSI (2005): Report entitled “ A Preliminary Report on Investigation of Effects of the Sumatra-

Andaman Earthquake of 26 December 2004 In Andaman and Nicobar Islands”, GSIunpublished Report.

Hochstetter, F.Von (1866): In contribution to the study Physical Geology of the Nicobar Islands in voyage of the Austrian Frigate Novara around the world in 1857-1859. (Geology, Part 2, vol. 2, p. 83-112 Vienna). Translated by F. Stoliczka, Rec. Geol. Soc. Ind. V. 2(3), p. 59-73,1869.

Scheidegger, A. E., (1985): Recent research on the Physical aspects of earthquakes. Earth-ScienceReview, 22, 173-229.

Sengupta, S, Sanyal, S and Mukherjee, A (2002): Macroseismic Survey Report on the Diglipur earthquake, in North Andaman Islands, 14 September 2002. GSI unpublished Report, 2002.


55

LOCATION INDEX

Area Latitude Longitude

NORTH ANDAMANShyamnagar 13

023

/25.5

//92

0 55

/34.5

//

Radhanagar 13023

/0.0

//92

055

/ 34.1

//

Swarajnagar 13020

/30

//92

056

/27.6

//

Krishnapuri 13015

/27.6

//92

057

/19.9

//

Jal Tikri 13026/37.3// 92053/47.4//

Kishorinagar 13011

/37.3

//92

052

/26.7

//

Diglipur 13014/37.3// 92058/37.6//

Parangara 13009

/55.1

//92

053

/11.2

//

Nabagram 13008/50.3// 92051/01.9//

Kalighat 13007

/21

//92

057

/00.3

//

Ramnagar 13006

/04.8

//92

059

/35.3

//

MIDDLE ANDAMANKarmatang 12

050

/39.1

//92

056/15.6

//

Harinagar 12040

/10.9

//92

053

/23.7

//

Duke Nagar 12039

/15.2

//92

052

/50.0

//

Kamalapur 12042/42.5

//92

053

/27.6

//

Parnashala 12031

/26.3

//92

054

/27.5

//

Pokkadera 12054/31.1

//92

054

/22.8

//

Mayabunder 12052/50.9

//92

052

/13.1

//

Tugapur 12049/50.3

//92

050

/09.5

//

Chainpur 12044

/02.5

//92

048

/39.2

//

Padmanavapuram 12036

/53.7

//92

057

/02.8

//

Rampur 12030

/29.6

//92

054

/44.4

//

Kaushalyanagar 12032/0.6// 92049/36.1//

Rangat Bay Jetty 12029

/13.5

//92

057

/32.3

//

Errata Jetty 12027/13.2// 92053/54.6//

Atter Jig 12021

/16.5

//92

046

/15.6

//

Kadamtala 12018

/53.3

//92

047

/29.2

//

BARATANGNilambur Jetty (Polica Chowki) 12

008

/31.5

//92

047

/28.4

//

Jarwa Creek mud Volcano Site 12007

/45.7

//92

047

/37.8

//

SOUTH ANDAMANDhanikhari Dam 11

034

/92

040

/45

//

Bedonabad 11034

/54.9

//92

044

/20.9

//

Garacharma 11036

/41

//92

042

/21.5

//

Sippighat 11035

/28.9

//92

040

/41.3

//

Guptapara Jetty 11032

/17.5// 92

039/21.4

//

New Manglutan 11033

/42.3

//92

039

/0.8

//

Calicut 11035

/33.2

//92

042

/59.8

//

Bimlitan 11035

/32.5// 92

042

/16.9

//

Ayappa Temple 11036/19.6// 92040/29.7//

Manglutan 11035

/46.4

//92

038

/34.6

//

New Wandoor 11035/40.2// 92036/40.4//


56

Dollyganj 11037/30.1

//92

042

/39.9

//

Namunagarh 11041

/01.3

//92

040

/55.7

//

Shoal Bay 8 11048

/41

//92

043

/13.2

//

Collinpur 11041/27.7

//92

036

/10.9

//

Bichadera 11045

/35.3

//92

039

/11.3

//

Manpur 11041

/40.2

//92

036

/23.1

//

Tushnabad 11040

/49.1

//92

037

/27.3

//

LITTLE ANDAMANHut Bay 10

037

/19.2

//92

032

/42.9

//

CAR NICOBARMus 9

014

/30.2

//92

046

/58.8

//

Lapati 9013/51.8// 92047/48.8//

Taopioming 9013

/10.9

//92

048

/35.5

//

Chuckchucha 9013/02.7// 92048/38.0//

Kinyuka 9012

/30

//92

048

/48.6

//

Tamaloo 9011/20.1// 92049/10.8//

Malacca 9010

/31.0

//92

049

/41.1

//

Air force colony 9008

/58.6

//92

049

/23.9

//

Kimios 9007/42.5

//92

046

/36.7

//

GREAT NICOBARCampbell Bay 7

000

/29.3

//93

055

/42.5

//

_____________________________________________________________________________________________REPORT ON SUMATRA -ANDAMAN EARTHQUAKE & TSUNAMI, 26 DEC ’04

57

ANALYSIS OF SATELLITE DATA FOR CHANGES IN COASTAL

GEOMORPHOLOGY OF ANDAMAN - NICOBAR ISLAND DUE TO

26 DECEMBER 2004 EARTHQUAKE

D.P.Das, S.S. Ghosh, D. Chakraborty and K.Pramanik

Photogeology and Remote Sensing Division, GSI, 29 Jawaharlal Nehru Road, Kolkata 700 016.

INTRODUCTION

An earthquake of magnitude 9.0, the world’s most severe one over the last 40 years, hit the sea off the west coast of northern Sumatra on the early morning of 26

th December, 2004 that

triggered the devastating tsunami in the Indian Ocean. The deadly tsunami waves caused widespread destruction in 11 countries bordering the Indian Ocean. The impact of earthquake on the Indiansubcontinent was considerable in the Andaman-Nicobar islands due to their proximity to theepicenter (3.24N/95.82E) of the great earthquake. Remote sensing study can provide an ample scope for detection and assessment of the impact areas on real time basis if the acquisition of satellite data covering that part of earth segment is readily available. One of the important applications of modern remote sensing technique is digital change detection over time to assess dynamic changes of terrain features for disaster management. Digital change detection using satellite data is the viable andquickest means for assessing the extent of morphological changes in the aftermath of earthquake and tsunami ravaged Andaman-Nicobar group of islands. The accuracy of analysis, however, depends upon the spatial resolution of data analysed, the degree of image registration and the scale of measurements. The change detection techniques using remotely sensed data have been mostlyapplied by the earth scientists for landuse change analysis, forest monitoring, urban changes, study of shoreline changes, drought and disaster monitoring and other environmental hazards. Realizing the temporal capability of digital remote sensing data, the present satellite remote sensing study was taken up to evaluate of the impact of devastating earthquake on coastal morphology, and the effects of tsunami that hit the entire Andaman-Nicobar islands, causing inundation of coastal areas, creek basins and large-scale damage to property and life.

METHODOLOGY

The basic premise for change detection using satellite data is that changes in radiance values due to landcover and morphological change between two dates must be large with respect to radiance changes caused by other factors like differences in cloud cover condition, variation of sun angle,atmospheric illumination condition, differences in soil moisture etc. A large number of changedetection techniques have already been developed but the accuracy of change detection techniques depend largely upon the degree of temporal de-correlation, resolution of sensor data, changedetection algorithm used and finally the scale of measurements. Among the techniques available in the digital image-processing domain, direct comparison between two co-registered data sets is the quickest and reliable means for assessment of the temporal changes.


58

Digital satellite data of pre- and post earthquake acquired by various sensors on board Indian Remote Sensing satellite (IRS) were procured from NRSA (Department of Space), Hyderabad after viewing the coverage, quality (state of cloud cover) and date of pass of the browsed data productsmade available in the NRSA website. IRS- P6 LISS III sensor data operating in four spectral bands (green, red, near infra-red and short wave infra-red wavelengths) with ground resolution of 23.5m as well as AWiFS four bands (very near infra-red and short wave infra-red wavelengths) data with ground resolution of 56m covering Andaman-Nicobar islands were used as study inputs. Besides, IRS- P4 OCM 8 band data having 360m ground resolution as acquired from NRSA were also used for synoptic study. A list of Satellite data products procured for assessing pre- and post earthquake

ground realities in parts of Andaman and Nicobar Islands are given in the table below. Survey of India degree sheets 86C, D, G, H, K, 87A, B, C, D, E, H, 88 E, F were consulted and used for geo-referencing of images and annotation of maps.

Sr.

No

Path/Row Date of pass

Pre-tsunami Post-tsunami

Satellite/Sensor Remarks

1 115:64 29.01.04 30.12.04 IRS P6/ LISS-III

2 115:65 29.01.04 30.12.04 IRS P6/ LISS-III

3 115:66 17.03.04 30.12.04 IRS P6/ LISS-III

4 115:67 12.11.04 30.12.04 IRS P6/ LISS-III

5 116:68 27.02.04 04.01.05 IRS P6/ LISS-III

6 116:69 22.03.04 04.01.05 IRS P6/ LISS-III

Pre-Tsunami data

relatively cloud

free, while the post tsunami data show

cloud coverage at patches.

7 115:65 22.02.04 30.12.04 IRS P6/ AWIFSFull scene withcloud coverage

more in thesouthern part

8 115:70 29.01.04 30.12.04 IRS P6/AWIFSSub scene withcloud coverage

9 11:14 17.01.04 28.12.04 IRS P6/ OCM

Full scenes with

relatively cloud

free data.

DIGITAL IMAGE ANALYSIS

Geometric rectification of digital temporal satellite data was initially made with the help of GCPs using Survey of India degree sheets to obtain distortion free and planimetrically corrected images (RMS error below pixel size) in one common projection system for ready comparisonbetween the co-registered temporal data sets and topographic base maps. To begin with very coarse resolution (360m) IRS- P6 OCM data of pre- and post tsunami period covering the entire island belt was studied for quick reconnaissance and over all assessment of coastal changes caused by the earthquake. The study of OCM images was followed by time contextual analysis involving both IRS-P6 AWIFS and LISS III four bands sensor data to detect significant morphological changes taken place along the coast of a few selected parts of the island belt. Time contextual analysis allows detection of ground changes in the geographic environment caused by natural phenomenon. In the present study, the change detection analysis has been performed by direct superimposition oftemporal co-registered images by swiping one over the other, which enabled detection of island wise coastal morphological changes caused by emergence and submergence of land including inundation of low lying areas as an effect of earthquake related tectonic disturbance. The study brought out information on inundation of agricultural land in the fringe areas of mangrove swamps, destructionof coastal vegetation where erosion occurred, change in coastline configuration, appearance and


59

disappearance of sandy beaches and shallow depth corals. The study, however, revealed that anoverall emergence of coastal land with increase in surface areas occurred especially along the northern and western margins of the islands situated in the north and western part of the main island belt. On the other hand, submergence of coastal land particularly along the northern and western margins has taken only in southern parts of the island belt till Indira Point. Central part of the island belt comprising major parts of the Middle and South Andamans including Little Andaman, however, shows no perceptible effect of coastal emergence or submergence at the scale of mapping (1:50K) with given pixel resolution.

Changes in Coastal Geomorphology

Landfall and East Island

These two small islands are located in the northernmost part of the island belt (Plate 1a) which experienced significant land emergence with increase in surface areas in the form of sandy beach mostly along the northern and western margin of the island (Fig.1). Earlier crenulatedcoastline configuration due to wave erosion has been markedly changed into more smoothened one as a result of land emergence accompanied by wave generated sand deposition. Maximumemergence of land in the western part of Landfall Island is about 1.3km, whereas for East Island it is about 600m.

Part of North Andaman

Evidence of emergence of rocky coast is quite evident on post tsunami image. A maximum of 300m increases in land area has been measured only along northern coastal margin of NorthAndaman (Fig.2). Significant land emergence with increase in surface areas in the form of newly formed sandy beach are observed only in the case of peripheral small islands namely, West Island (360m), Reef Island (350m) and Cliff Island (180m).

North Sentinel Island

An isolated small island lying to the west of South Andaman (Plate 1b) shows remarkable accretion of sandy beach material all along its coast, which suggests significant land emergence to an extent of 900m in the west and 75.5m in the east (Fig.3).

Part of South Andaman around Port Blair

The mapped area (Fig.4) does not show any perceptible change in coastline configurationbetween pre- and post tsunami dates. Post tsunami data only could delineate the extent of tsunami related inundation areas only along the western margin of Navy Bay and in the fringe zone of mangrove swamps around Bamboo flat area.

Katchall Island

Post tsunami image (Plate 2a) clearly depicts major change in coastal configuration due to transgression of sea across southwestern coastline. Comparison of pre- and post tsunami P6 LISS III data shows overall situation of island submergence with effects of local erosion and deposition particularly along its western margin (Fig.5). Major submergence of land is noted south of Lamoh where earlier situated creek basin has been totally submerged. Recession of coastline has taken place along the axis of the creek basin to an extent of 3.2km and across 2.5km.


60

Trinkat Island

The Trinkat Island (Plate 2b) shows major morphological changes all along its westernmargin and along the creek basins .The Island has been found separated into two parts due toimpoundment of water along NE-SW trending Kui Kamella creek in the north. Significantsubmergence of island along NW-SE southern creek channel near Kapilla is quite evident on the post tsunami image, and as a result of which the island has become almost breached along the creek (Fig.6).

CONCLUSION

i) Study of six selected sectors was taken up on the basis of reconnaissance through OCM and AWiFS data. Of the six selected areas, significant changes in coastal configuration and island morphology have been noticed in Katchall and Trinkat Islands due to the effect of landsubmergence.

ii) Overall observations made on the imagery for the entire island belt revealed (a) emergence of land of varying extent mostly along eastern and western coastal parts in the north of the islandbelt, (b) submergence of coastal land mostly along the western margin of the southerly situated islands, (c) no perceptible change in coastal morphology caused by land emergence orsubmergence in central part of island belt at the scale of mapping except North Sentinel Island, and (d) minor inundation around creek basins due to tsunami in central part of the island belt.

iii) Differential land emergence and submergence of coastal area at the western and eastern margin of the northern and southern parts of the island belt is conspicuously observed, which suggests vertical movement- cum-tilting of islands.

iv) Digital change detection analysis using temporal data always provide true picture of naturalphenomenon useful for impact assessment study. High-resolution LISS III data providedchange/no-change information at very high level of accuracy.

ACKNOWLEDGEMENT

The study was carried out under the guidance of Dr. Kalyan Sarkar, Director, PGRSDivision. The authors also express their deep gratitude to Dr. S.K. Ray and Shri Sujit Dasgupta, for the interest and the suggestion offered during the work.


61

Plate 1a: IRS P6 AWiFS FCC of 30th December, 2004 showing part of North Andaman, Landfall, East Island and West Island

Plate 1b: IRS P6 AWiFS FCC of 30th December 2004 showing North Sentinel Island


62

Plate 2a: IRS P6 LISS III FCC of 4th January 2005 showing Katchall Island


63

Plate 2b: IRS P6 LISS III FCC of 4th

January 2005 showing Trinkat Island

_____________________________________________________________________________________________REPORT ON SUMATRA-ANDAMAN EARTHQUAKE & TSUNAMI, 26 DEC ’04

64


65


66


67


68


69


71

26 DECEMBER 2004 EARTHQUAKE:COSEISMIC VERTICAL GROUND MOVEMENTS IN THE ANDAMAN

Sumit Kumar Ray and Anshuman Acharyya

Geological Survey of India, 27 Jawaharlal Nehru Road, Kolkata 700 016

INTRODUCTION

An attempt was made to study the nature of coseismic vertical ground movements of the great earthquake of 26 December 2004, in the Andaman Group of Islands. The study is based on field observations only. The objective was to characterise and determine different parameters of the causative fault, inde pendent of seismological and geodetic survey data and interpretations. At the planning stage of this work, it was considered that we may take advantage of the long coastline with several coastal swamps, inter-tidal mud flats, creeks, lagoons etc. and use the sea level as a reliable reference datum to estimate and map the vertical ground movement. Accordingly a methodology was worked out, which was found suitable in the course of the fieldwork that followed. Finally, acoseismic vertical movement map was prepared and interpreted, to characterise the causative fault.

In strike-slip or thrust faults, or in oblique slip faults with combinations of thrust and strike-slip components, no point in the hanging wall can move below its pre-faulting level. Differentia luplift, because of along-strike slip variation, may tilt the hanging wall block, but cannot cause subsidence. In that context, wide-spread land subsidence in the Andaman and Nicobar Islands, which are situated in the hanging wall of the rupture of the 26 Decemeber 2004 Sumatra-Andamanearthquake, at first appears baffling, because the seismologists have unanimously characterised the fault movement as thrust (USGS 2004). Is the submergence unrelated to coseismic verticalmovement? What then is the cause of land submergence in vast areas? Our studies primarily address these questions.

Scope of the present work

Modification of the coastline because of submergence of land below the waves was recorded in a visit to the South Andaman Island about a fortnight after the great Sumatra-Andaman earthquake of 26 December 2004. Submergence of large areas in the Sippighat-Chauldari and Ograbraij sectors, and rise of the level of the High Tide Line (HTL) above the pre-earthquake maximum HTL records in the Corbyn’s Cove area, Chatham Jetty and Bamboo Flat Jetty were observed. Residents of the Island reported that for about a week after the earthquake and tsunami, the tide cycle remaineddisrupted and did not follow the known tide pattern. The level difference between the HTL and the Low Tide Line (LTL) used to be very little (about 30 cm or so). They further reported that the tide cycle was gradually getting restored and the process was still on at the time of our field visit on 7 January 2005. The tide gauge data, which would have provided reliable information about temporal distribution of tides as well as tide levels, were not available. Only the predictive tide tables were available in the newspaper media. However, in view of the uncertainty about post-tsunamistabilisation of the sea level and the possibility of seiche effect in the bays and lagoons, no studies to map vertical ground movements using the sea level as the reference datum, was carried out at the time of the visit (during 7 - 12 January, 2005). Only a very general observation that the LTL around Port Blair remains at or slightly above the pre earthquake HTL was recorded at the time of the January 2005 visit.


72

Comparison of the pre- and post-earthquake satellite imageries shows emergence of land in some sectors and submergence in some others in the Andaman and Nicobar Islands. A detailedaccount of the studies on land emergence and submergence, based on satellite imageries is available in another chapter of this volume. Although land emergence and submergence can be mapped by using pre- and post-tsunami satellite imageries of high resolution (meter scale), those are not suitable for mapping the coseismic vertical movements because of the following reasons.

1. As the great earthquake had generated a great tsunami, a straightforward correlation of land emergence with tectonic uplift and submergence with tectonic subsidence is not possible.Erosion or deposition associated with the tsunami might have contributed to submergence andemergence respectively. So, on-the-spot examination is necessary to map coseismic verticalmovements.

2. It is difficult to have a realistic estimate of vertical movement form the satellite imageries.

We have mapped coseismic vertical movement distribution in the Andaman Group ofIslands (north of 11oN latitude), based on field observations from 7 to 12 January, and 9 to 17 May 2005, and have interpreted the map to build a model of coseismic vertical movement. The map and the model have been analysed to find an explanation to the enigmatic feature of uplift in some parts and subsidence on others in a domain of thrust faulting. Our observations and interpretations are independent of seismic data interpretation results and are based only on field observations. This paper shows how the map of vertical ground movements helps to independently arrive at the conclusion that the causative fault of the earthquake was a thrust fault, and the trace of the ground rupture of the thrust fault is parallel to the trench axis of the eastward subduction of the Indian plate below the Burma plate. The map also helps to build a model, which can explain coexistence of subsidence and uplift. We have also discussed the environmental impact, particularly impact on the mangrove swamp ecology, because of the vertical movements.

METHODOLOGY

High precision ground geodetic survey is the most appropriate and reliable method of determination of fault related ground vertical movement. However, one prerequisite of the method is that pre-faulting high precision levelling survey data must be available. The exact verticalcomponent of ground movement can be determined only by comparison of pre- and post-faultingsurvey data. We could not apply that method, as we do not have the required pre-faulting survey data.

In our present study we have used the sea level, which gives a reliable datum forcomparison. Pre and post -faulting sea level remained unchanged and by field observations along the coast of the islands, in the inland lagoons, mud flats and swamps, it was possible to estimate vertical ground movement at several spots. The tide status at the time of our observation was also considered for estimation of ground movement and necessary correction attended.

As explained in an earlier section, it was necessary to make a distinction between land emergence and uplift, and between submergence and subsidence, at every spot of observation. How this distinction was made at each spot, has been indicated in the next section, where the fieldobservations, their significance, and estimates of vertical ground movement have been presented.

Although the basic tenet of our methodology is that the sea level has remained unchanged and provides the reference datum for detection of earthquake-related ground level changes, we have, in the following discussions, used the expressions “rise” and “fall” of the level of High Tide Line (HTL) / Low Tide Line (LTL), or at places simply “rise” and “fall’ of water level. The terms “rise” and “fall” have been used depending on whether the level of the HTL/LTL on the ground or on man-made structures like embankments, retaining walls, piers of jetty etc. is at a higher or a lower


73

elevation respectively. A rise in the level of the HTL or LTL indicates ground subsidence, whereas a fall indicates uplift at the observation point.

In our estimates of vertical ground movement, we have relied mainly on the following three categories of evidence about pre-faulting coast line configuration/sea level.

i) Direct – where one of the authors (SKR), was familiar with the pre-faulting configuration of the high tide line and the low tide line, observed in the course of previous fieldwork in theAndaman Islands. In such spots, a direct comparison gave an estimate of vertical movement.

ii) Indirect (a): Several man-made structures like beach roads, landing jetties, even landing sites on small creeks through the swamps which the islanders used, give a clear idea about pre-faulting elevations with respect to the sea level. For example, the along-shore roads, landing sites etc. were obviously above the sea level even in the highest of the high tide, and the landing sites were navigable. We have observed inundation of some coastal roads at high tides, which are signs of post-faulting submergence. Some of the landing sites are no longer navigable indicating uplift.Considerable changes in the drainage have been noticed and have been used for estimating ground movement.

iii) Indirect (b). We have relied on the information provided by the local residents,particularly who live very close to the sea coast, about configuration of the previous tide levels, and that information have been used for estimation of ground movement.

OBSERVATIONS ON LAND EMERGENCE/SUBMERGENCE

Field traverses covering the eastern and western coasts of the North, Middle and South Andaman Islands were taken to record and analyse the nature of post -earthquake ground uplift and subsidence. The locations described in the following text are shown in Fig. 1. This record embodies on-the-spot observation, estimation and extensive crosschecking of information on pre-earthquakeground data gathered from number of sources. In most of the cases, unequivocal accounts of past spring tide (pre-earthquake highest high tide) and neap tide data could be obtained. No ambiguousdata were taken into consideration. Estimation of the difference between pre and post earthquake highest HTL (preferably spring tides) has enabled us to infer the signature of relative movements of ground.

SOUTH ANDAMAN ISLAND

Corbyn’s Cove

The area lies in the eastern fringe of the island. Photographs (Plate 1 & 2) of November 2004 and May 2005, depicts the changes that are also schematically shown in Fig.1. Before the earthquake, the clean sandy beach along a small cove (hence the name Corbyn’s Cove) used to be a favourite spot of the visitors from Port Blair and the tourists. An along-shore motorable road used to separate the beach from the restaurants/hotels and resorts that used to cater to the need of the tourists and visitors. A concrete-cum-masonry retaining wall on the seaward side of the road had three to four stair steps, which used to provide access from the road to the beach level below (Plate 1). A part of the beach used to remain exposed even during the spring tides. In contrast, in the second week of January 2005, we observed that the leading edge of the waves laps on the retaining wall, and the seawater completely submerges the beach at high tides. On spring tides, the water level rises to submerge even parts of the long-shore road. This ingress of the sea at the cove is an indication of ground subsidence. A comparison of the level of the HTL before and after the earthquake gives an estimate of about 1.25 m coseismic ground subsidence in this area.


74

On our revisit to the spot in May 2005, we observed about 1 meter of vertical sand accumulation all along the beach. The accumulated sand has buried the steps on the retaining wall, which are no longer visible (Plate 2). Sand replenishment has been accentuated due to coseismic subsidence and play of higher energy wave ingress almost up to the road level (Fig. 1). Thin sand layers are also noted as segregations on the shore road, indicating that the present ingress of sea

surge during high tide inundates the road level. It is noteworthy that rock outcrops along the

Corbyn’s Cove coast now remain submerged even during low tide (Plate 3). The sameoutcrops used to be exposed along the coast (Plate 4) during low tide and had repeatedlybeen examined earlier by geologists of GSI. Subsidence of land to the tune of 1 m isenvisaged in this part.

Figure 1: Schematic section across Corbyn’s cove beach showing progressive changes in beachmorphology

Sippighat and other areas in the south-central part around Port Blair

Large stretches of residential areas and agricultural fields with standing crops were seen submerged in the course of our visit to Chauldari-Sippighat areas in January 2005. (Plate 5). The area lies at the tip of a lagoon, which opens to the sea at the Port Blair-Bamboo Flat gap. Because of ground subsidence, the lagoon boundary has advanced further inland resulting in submergence of residential areas and agricultural fields. Similarly, coseismic ground subsidence has resulted insubmergence of large tracts of agricultural fields in the Ograbraij area, along the fringe of a lagoon, which opens to the sea at a strait further to the north. The Andaman Trunk Road connecting the South Andaman with the Middle and North Andaman passes from Port Blair, through Garacharama, and through the Sippighat-Chauldari area, to the Middle Andaman. This was a busy all-weatherasphalt-topped road. However, after the earthquake, in the course of our visit in January 2005, we


75

Plate 2: Corbyn’s cove beach, South Andaman, May 2005. Note the sand accumulation up to road level (marked by yellow bar), covering entire retaining wall. Arrow indicates HTL during spring

tides.

observed inundation of wide stretches of residential areas and agricultural lands on both the sides of the road in the area, and the high tide water flowing over the road. The submerged areas are affected by tidal play. Revisit to the area in May 2005, revealed that the areas are still submerged and affectedby tidal play (Plate 5). It may be mentioned here that about a decade ago, the areas were open low lands where construction activities started only recently. Construction activities to raise the level of the road by about 1 meter, is going on in this area since January 2005. Our estimate is about 1 meter ground subsidence in the Sippighat area and about 80 cm in the Ograbraij area.

Plate 1: Corbyn’s cove beach, South Andaman, November 2004. Note retaining wall with steps (inset for close up view) in the backshore.

Plate 3: Corbyn’s cove, opposite museum. Rock outcrops marked by red circle have become submerged.

Plate 4: Corbyn’s cove, opposite museum, prior to earthquake. Note outcrops of Andaman flysch. (Courtesy: Dr. T. Pal, GSI, ER)


76

Plate 6: Chidiyatapu beach with very narrow strip of intertidal zone

Plate 7: Vijaynagar 5 beach, Havelock island. Green arrow shows pre-earthquake HTL while red arrow indicates post earthquake HTL

Plate 8: Harmony resort area (near Radhanagar), Havelock island. Note submerged agricultural land.

Plate 9: Karmatang beach, Middle Andaman. Arrow indicates the berm.

Plate 10: Aerial bay (near Machhidera), North Andaman. Note recession of sea from mangrove colony.

9.1.05

Plate 5: Sippighat

area in Jan and May ‘05. Note

theunfinishedsubmergedbuildings.

10.5.05


77

The accounts of the local sources reveal that there is a rise of 80cm of high water line (HWL) compared to pre -earthquake HWL in the Mithakari Jetty. Present high water flows only20cm below the jetty level, creating problem for berthing of boats and hence the jetty has become non-functional. However, the jetty height at Dandaspoint was about 1.5m above the previous high water level. There is still a difference of about 0.5m between the present high water level and the jetty level, making the Dandaspoint jetty functional. The Junglighat jetty has also become non-functional due to this problem.

Chatham

At the Chatham Jetty, the difference between the level of the pre-earthquake HTL and the present level was measured as 1.2m. The road in front of the Fire Brigade at Chatham gets inundated during the new moon / full moon, which is in stark contrast to the pre-earthquake records. Before 26.12.04, the level even at high tides used to remain more than a meter below the road level. Ground subsidence of about 1.2m is estimated at Chatham.

Chidiya Tapu

The area lies at the southernmost tip of the island. The sea water line has risen in the area inundating the beach even during low tide. At present the net beach width becomes almost nil (Plate 6) with sea front touching the bank. The estimated subsidence here is about 0.75m.

Wandoor

The area falls in the western coast. The present spring tide line is about 30 cm higher than the corresponding pre-earthquake level, indicaing about 30 cm vertical subsidence in the Wandoor jetty area. In the Wandoor new beach area, in front of the restaurants and the resort about a kilometer to the west of the Wandoor jetty, the New Moon (08.05.2005) HTL level was measured as 26m above the previous (i.e. pre-earthquake) level. The forest officials and the local people reported no apparent change in the coastline of Grub Island and Tarmugli Island. The estimated subsidence of land (26-30cm) in Wandoor is much lower than what has been estimated at Sippighat or Corbyn’s Cove areas.

Havelock Island

Havelock Island lies to the east of South Andaman Island in the Andaman Sea. The Havelock, Neil and other islands form the easternmost group of Islands in the Archipelago, which is known as the Ritchies Archipelago. Within the island, the jetty (Gobindanagar area), Vijaynagar, Mithanali, Kalapathar areas fall in the eastern part whereas the Radhanagar beach falls in the western part.

The beach at the Dolphin Resort (Vijaynagar) records a 30cm higher level of the high tide line compared to the pre-earthquake level. In the Mithanali (Vijaynagar 5) area, the level difference between the line of maximum ingress of New Moon high water prior to the earthquake and the recent has been measured as 24 cm (Plate 7, man at left indicates present HTL of new moon). The Forest Range Officer, Havelock informed that agricultural fields in Kalapathar area have been badlyaffected as those get submerged during (post-earthquake) high tide. Near the Harmony Resort, the agricultural land of Shri Manidra Mridha was found submerged (Plate 8). Shri Mridha reported that post-earthquake, the agricultural land around his house gets submerged under ∼20 cm of water during new/full moon days. There is no appreciable change in water level in Havelock jetty. But


78

interestingly there is tsunami deposited sand both near the embankment of jetty as well as in the Radhanagar beach. The beach slope at Radhanagar is ∼3

0. One tidal creek inlet, at right angle to

coast, was found blocked because of tsunami sand deposition. Through this creek, tidal water enters and floods the paddy fields of Shri Mridha (mentioned earlier) on new moon/full moon high tides. Plunging type breakers were observed here, which may be due to local uplift of the beach andconsequent change in beach slope

It is inferred that there is only minor land subsidence of about 20cm in the western part of the Havelock Island. It is recommended that the tsunami depositional facies may be studied in few locales in the island.

Nilambur jetty, Baratang Island

Forest department sources report a maximum of 50cm of rise in water level in comparison to pre-earthquake conditions, which implies about 50cm ground subsidence in the area. The creeks in the mangrove swamp remains filled with tidal water even during low tide.

MIDDLE ANDAMAN

Uttara jetty

This area represents southernmost part of Middle Andaman. Inquiry and observations reveal 20-40cm rise in water level both in high tide and low tide. The small creeks in the mangrove swamp areas, which used to get completely drained during low tide time before the 26 Decemberearthquake, now always remain filled with water. Submergence due to minor subsidence (20-30cm)is inferred here.

Bakultala creek/Shyamkund

The water level during tides remains almost the same as in the pre-earthquake times. However, rise of about 5-10cm in the water level has been reported from some parts of the creek. There is negligible submergence, if any, in this sector.

Nimbutala/Rangat jetty

Precise estimation of changes in the pre and post earthquake water level in the jetty area is difficult. However, tips of several rock outcrops (near the coast), which earlier used to remainprojected above the waters, now get submerged beneath 20-30cm of water during high tide. The observations suggest land subsidence in the area.

Panchabati beach

There is no change of tidal water level or configuration of the beach in the pre and post earthquake scenario.

Aamkunj beach

No detectable change in HTL.


79

Sivapuram beach (south of Cuthbert bay)

No detectable change in HTL.

Dharmapur/Nimbudera/Billiground

All the nalas including the Betapur nala between Nimbudera and Billiground are flowing easterly to the sea without any significant post -earthquake change. There is no evidence of reversal, drying up or ponding of water flow.

Mayabandar jetty

The high tide/low tide water in the jetty flows 10-15cm lower than the previous levels, indicating very minor uplift in this part.

Rampur creek/Rampur beach

The creak indicates about 15cm lowering of high tide level. Rampur beach as suchrepresents a domain of tsunami erosion with removal of beach sand.

Karmatang beach

The beach, situated in the eastern coast of Middle Andaman, is characterized by a berm (raised beach) having landward slope of 1-20 (Plate 9). A comparison of the pre and post earthquake HTL level shows a fall of about 15cm indicating coseismic uplift in the area.

NORTH ANDAMAN

Aerial Bay/Machhidera

The mangrove colony along the coast in the Aerial Bay stands now on dry ground, even during high tides, because of land uplift and consequent recession of the sea front (Plate 10). In the

Aerial Bay jetty, the present high water line is ∼20cm below the barnacle layers mounted on the jetty piers, which indicates about 20 cm vertical uplift.

Kalipur beach

The present high water mark is about 20-40cm below the previous (pre-earthquake) mark. The noteworthy feature is the emergence of rocky sea floor as a linear island between Kalipur beach and the Craggy’s Island. Previously the rock outcrops of the linear island were not visible during high tide. But in the post-earthquake scenario the rocky outcrops are always visible (Plate 11).

North of Kalighat

There is noticeable change in the northern part of Kalighat tidal creek. After the earthquake, the high water line shows a remarkable drop of about 95cm (Plate12). The nearby mangrove colony stands now on dry exposed ground, as the area is no longer affected by tidal play. Navigation along the creek has been badly affected.


80

Kalighat jetty

The jetty was previously used for the ferry service from Kalighat to Mayabandaralong the creek and the strait leading to the open sea. Ferry service has been withdrawn asthe creek has lost the required navigability, which may be due to tsunami sand depositionalong the creek and/or ground uplift. Presently, small boats can sail only during spring tides.The difference between the post-quake spring tide HTL and the previous/pre-earthquakespring tide HTL (high water line) in the jetty was estimated (Plate 13) as 95cm. Themaximum high tide flow on many occasions in the pre-earthquake scenario, used to overtop the jetty level. Coseismic vertical uplift of about 90-95cm has been estimated in the Kalighat area.

River Bridge at Ramnagar

This is a bridge over a perennial river that used to flow towards east. The river has become completely dry after the earthquake (Plate 14). Bank erosion and fresh channel sands (Plate 15) indicate that the river channel was active till recently. The sluice below the bridge has several openings, which are clogged with water borne debris (Plate 16). Uplift and consequent tilting of the ground is postulated in this location where the base level of the river has risen above the LTL thwarting tidal action.

Taralait Bay (Ramnagar beach)

The area is located in the eastern part of North Andaman. The high water line in the beach is 40-50cm lower than that of the pre-earthquake time. There are two distinct marine terraces on the beach – the older raised one is covered by vegetation/grass and the new terrace is about 8m east of older terrace. The HWL used to touch the surface of the older (higher) terrace in pre-earthquaketime. There is a tidal inlet, which used to debouch in this coast, but now occurs as a hanging featurewithout water (Plate 17, arrow points to the mouth of the tidal inlet). This is an example of a hanging stream, formed as a result of ground uplift.

Radhanagar nala/creek

Radhanagar is situated in the western part of North Andaman. During lowest lowtide, it was observed that the creak was almost dry except for a thin layer of water flowing towards sea. The pre-earthquake level of the low water line (LWL) used to be at least 1m above the present level (Plate 18). The creek was navigable round the year and local people used it as a waterway for carrying sand and other marine products from the sea coast to the inland villages by boat. The boats with sand and other cargo could sail along the creek. It is no longer so because of ground uplift.

Shyamnagar /Shaymnagar creek

The creek at Shyamnagar has got cut off from the sea, with several boats stranded on the dried up channel (Plate 19). Presently (i.e. post-earthquake) there is no tidal inflow into the creek even during high tide. The remnants of the creek and vestiges occur as local stagnant pools of water (Plate 20). Navigation along the creek, transport of material etc. used to be regular activities prior to earthquake. Emergence of land because of coseismic vertical uplift of about 1.0m has been inferredhere.


81

Plate 11: View from Kalipur beach, North Andaman. Circle shows emerged islands in post-quake scenario.

Plate 12: North of Kalighat, North Andaman. Green arrow shows pre-earthquake HTL while red arrow indicates post earthquake HTL

Plate 13: Kalighat jetty, North Andaman. Green arrow shows pre-earthquake HTL while red arrow indicates post earthquake HTL

Plate 14: Ramnagar, North Andaman. Arrow indicates direction of river water flow before earthquake

Plate 15: Ramnagar, North Andaman. Evidence of active river bed with bank erosion and sand deposition prior the quake

Plate 16: Ramnagar river bridge, North Andaman. Arrow indicates pre-earthquakedirection of river water flow with clogged debris in the sluice of the bridge.


82

Kishorinagar/ Mangrove Forest/ Gudinala creek

This area lies in the western fringe of North Andaman. All the tidal creeks near Kishorinagar village have almost dried up, and large stretches of mangrove are under threat of extinction because of withdrawal of tidal water from this area (Plate 21, the creek shown is located east of Gudi nala). The difference of highest high tide measured in the region is 1.2m below the level before earthquake. Ground fissure, lateral spreading and landslip were noted in the nearby Kishorinagar village. The adjacent mangrove forest has totally dried up because of lack of any tidal play even during highest high tide (Plate 22). The marginal parts of the mangrove swamps near the creeks show evidence of ground movement due to lateral spread (Plate 23), which may be attribute d to seismic ground shaking associated with the 26 December 2004 earthquake. The ground surface of the mangrove forest exhibit mud cracks (Plate 24) suggesting post-earthquake aerial exposure of the mangrove soil. During our boat cruise, effects of lateral spread on the mangrove forests were observed. Large chunks of ground of about 30 to 40 m length, along with the mangrove plants standing on them, have slipped about 10-15m from the bank to the middle of the creek (Plate 25, note the dried up colony of mangrove brought by landslip to the middle of the creek from the bank). Although we were sailing in the creeks during high tides, the barnacles were seen attached to the substrate of mangrove branches at a higher level – about 1 m higher than the creek water level (Plate 26). Another unusual feature observed in the course of the cruise was the greenish brown to greenish yellow colour of the creek water. As we cruised along towards the open sea, the colour gradually started changing to the normal sea-green, and about a couple of kilometers inland from the open sea, the creek water colour was normal sea green (see discussions in a later section).

Paschim Sagar/Casuarina Bay

The beach shows retreat of sea with exposure of large span of foreshore and backshore (Plate27). Near the mouth of the tidal creek there is currently active erosion of the coast. The present high water line is 1.3m below the pre-earthquake high tide line. On the vertical section of the beach (now raised as a berm), a dark coloured 30cm layer of dried up and compressed mangrove twigs and branches partly altered to peat, and overlain by 80cm thick sand layer was noted (Plate 28). This sand layer may as well represent an earlier episode of storm surge or palaeo-tsunami with a transient subsidence. The entire section has got exposed due to recent vertical uplift of the beach by about 1.2m. Recent uplift has exposed rocky surfaces along the coast of the island towards south of the Casuarina Bay.

Our observations reveal that vertical ground uplift increases from about 30cm to about 1.2m from the eastern to the western coast of the northern part of North Andaman Island. The abrupt post-earthquake changes in the drainage system, particularly of the creeks and streams flowing to the west to the sea , indicate differential vertical uplift.

INTERPRETATION

Based on the estimated vertical movements at different observation points, we have drawn contours, of +1.0, +0.5, 0, -0.5, and -1.0 meter vertical movement (Fig. 2). The positive signs indicate uplift, and negative sign subsidence with respect to the pre-earthquake elevation. The zero contour indicates no vertical movement, and may be called the neutral line (Bilham et al., 2005, in press). The hachured and stippled characters in Fig.1 demarcate the areas of tectonic uplift and tectonic subsidence respectively. The following conclusions can be drawn from the contour map.


83

Plate 19: Shyamnagar creek, North Andaman. Note the completely dried up tidal river as a direct spin off earthquake.

Plate 17: Ramnagar beach, North Andaman. Arrow indicates tidal inlet that became hanging and hence dry.

Plate 18: Radhanagar creek, North Andaman. Note narrow relic of a once navigable

waterway.

Plate 20: Shyamnagar creek, North Andaman. Note ponding of stagnant water in lower levels

Plate 21: Kishorinagar creek, North Andaman; totally dried up after earthquake

Plate 22: Mangrove forest near Kishorinagar, North Andaman, remains dried after earthquake. Arrow indicates pre-earthquake

HTL.

______________________________________________________________________________________________

REPORT ON SUMATRA -ANDAMAN EARTHQUAKE & TSUNAMI, 26 DEC ’0484

Plate 24: West of Kishorinagar, North Andaman. Note mud cracked surface on a previously submerged mangrove forest.

Plate 25: Gudi nala. Note the dried up colony of mangrove brought by landslip to the middle of the creek from the bank; also

note the colour of water.

Plate 26: Gudi nala , North Andaman, near sea; during high tide. Arrow indicates pre-earthquake HTL (spring tide)

Plate 28: Paschim sagar, North Andaman.

Note the newly emerged expanse of beach.Plate 29: Paschim sagar, North Andaman. Arrow shows rootlets of mangrove.

Plate 23: Kishorinagar (Gudi nala) creek, North Andaman. Wide lateral spread near

the bank of the creek.

______________________________________________________________________________________________


1. All the contours are sub-parallel, with a general NNE-SSW trend. Those, in turn are parallel to the trench axis of subduction of the Indian plate below the Burmese plate (Curray et al., 2005). This parallelism of the contours with the trench axis indicates that the causative fault of the vertical movements, i.e. the surface of the earthquake-generating fault of 26 December 2004, is sub-parallel to the trench axis, and so is the trace of the fault. From observations in the Islands only, the exact trace of the fault in the Bay of Bengal sea floor to the west of the Andaman Islands, can not be inferred. However, generation of a great tsunami because of the earthquake indicates that the tip line of the fault slip intersected the ground surface, i.e. the fault was a ground-rupturing fault.

2. Sub-parallel disposition of the contours indicates that, in the scale of our observation and resolution, there was no significant lateral slip variation in the study area.

3. The ground to the west of the neutral line has been uplifted, and uplift increases from the neutral line to the west. This pattern of spatial variation of vertical uplift indicates that the causative fault has a significant thrust component (i.e. the fault is either a pure thrust fault, or a thrust fault with strike-slip component). The westerly increase of uplift indicates that the trace of the thrust fault lies further to the west of the Andaman Islands. This westerly increase in uplift is likely to continue up to the trace of the fault, where it would be maximum (Fig. 3). How far to the west the rising trend of uplift continues, i.e. location of the trench axis on the sea floor, could not be determined by this study, which was restricted to ground observations.

4. The gradient of westerly increase of uplift may be used to estimate uplift (i.e. vertical component of slip) of the causative fault. From Kalipur/ Ramnagar beach at the eastern coast, to the Paschimsagar area in the western coast, through Kishorinagar village in North Andaman Island, we have well constrained data set, which gives an off-fault gradient of tectonic uplift (in a direction orthogonal to the fault trace). By extending the gradient up to the trench axis (Fig.5), we get 6.3 m vertical uplift on the fault, if the fault trace coincides with the trench axis. This estimate will be less if the fault trace is further to the east of the trench axis. So, 6.3m is the estimate of maximumpossible vertical component of slip on the causative fault along that particular line.

5. The ground to the east of the neutral line has been affected by tectonic subsidence, which increases from the neutral line towards the east. How far to the east the subsidence continues is not clear. We have estimated maximum subsidence in our study area around Port Blair. To the east of Port Blair area in South Andaman, we have only one set of observations in the Havelock Island in the Ritchies Archipelago. In the Havelock Island, the vertical movement is almost negligible (less than 30 cm). So we may infer that east of the neutral line the subsidence increases up to a certain distance and then decreases to neutral, i.e. the regional level. However this conclusion is constrained by only one set of observations at the Havelock Island.

The contours of subsidence are also parallel to the neutral line. As already discussed, the subsidence cannot be explained by faulting.

______________________________________________________________________________________________


Figure 2. Distribution of co-seismic vertical movement of the 26 December 2004 earthquake in theNorth, Middle and South Andaman Islands. The estimates of vertical movement are shown in the contours (dashed line). Contours indicate +1.0, +0.5, 0, -0.5, -1.0 meters of vertical movement with positive and negative signs for uplift and subsidence of ground respectively. The 0 contour passes through the area of no vertical movement (the neutral line). Hachured character -area of tectonic uplift; Stippled character- area of tectonic subsidence. Tectonic elements taken fromSeismotectonic Atlas, GSI, 2000

______________________________________________________________________________________________


MODEL TO EXPLAIN LAND SUBSIDENCE

Fig.3 illustrates that in thrust faults, the vertical component of dip-slip is maximum in the hanging wall at the fault interface. As we move away from the interface, the component gradually decreases and ultimately becomes nil at the neutral line. The contour pattern of vertical movement is in agreement with this theoretical deduction of off-fault variation in vertical component of slip (i.e. vertical uplift) of thrust faults.

However, beyond the neutral line, in the dip direction of the fault, all points in the hanging wall should remain at their pre-thrusting level. In that context subsidence to the east of the neutral line, and parallelism of the subsidence contours with the neutral line appears enigmatic.

Our observations at Havelock Island indicate that subsidence increases towards east of the neutral line up to a maximum, and then as one proceeds further to the east, gradually decreases to nil. This feature of subsidence can be explained by a model (Fig.4), which envisages elastic crustalbuckling because of the horizontal compression due to convergence of the two plates of thesubduction zone. The crustal shortening during the long interseismic period, resulted in antiformal arch and resultant increase in accumulated elastic strain. Slip, generating earthquake, occurred when the accumulated strain exceeded the strength of the fault plane. The coseismic slip was associated with down buckling or elastic unfolding of the antiform, which resulted in land subsidence, asexplained in the model (Fig. 4).

Figure 3. Sketch to show that in thrust faulting, vertical uplift is maximum at the fault interface, and gradually decreases away from the fault (F-F’) to nil (off-fault decrease in verticalcomponent of slip) at the neutral line. The lines a-a", b-b", c-c" are pre-faulting horizontal markers in the hanging wall, Because of thrust faulting, the points a, b, and c, on the hanging wall at the fault interface, slips to a', b' and c' respectively. a-a', b-b' and c-c' are dip slip components at different depths.

______________________________________________________________________________________________


Figure 4. Schematic diagram to explain simultaneous uplift and subsidence in different sectorsbecause of coseismic vertical movement of the 26 December 2004 earthquake. (a) Configuration at the early inter-seismic stage. Thin lines are horizontal markers in the crust. PP' is the pin line. The earth's surface with respect to the sea level, the position of the islands and the trench axis are shown. (b) Because of horizontal compression due to subduction-related plate convergence, the crust deforms by elastic buckling. The pin line PP' moves closer to the fault surface. L-L' is the crustal shortening. Because of this uparching of the crust (red lines), the islands rise at higher elevations, and grow in area because of land emergence above the waves. This is the phase of interseismic uplift because of elastic buckling of the crust, which is a slow process (30-50 mm per year rate of convergence). (c) Release of the accumulated elastic strain by reverse faulting, and simultaneous unfolding of the anticlinal arch. Slip (i.e. earthquake) occurs when the accumulated elastic strain exceeds the strength of the fault plane. As a result of reverse faulting, areas close to the fault shows tectonic uplift which, from a maximum at the fault interface, gradually decreases towards the neutral line. On the far side of the neutral line, the ground surface subsides because of unfolding of the anticlinal arch. Subsidence increases away from the neutral line to a maximum and then decreases to nil (i.e. return to pre-faulting regional level).

______________________________________________________________________________________________


ENVIRONMENTAL IMPACT

The North Andaman Island has been affected by uplift resulting in disruption of drainage and change in ecology of the areas, which were intertidal mud flats and mangrove swamps before the earthquake. Large areas of the mangrove swamps have been uplifted above the present high tide level. As a consequence seawater cannot enter these uplifted parts of the mangrove forests and the forests on those parts will gradually perish. However, if the local administration and the Forest Authorities arrange adequate protection, these uplifted parts of the tidal flats, which earlier used to support a rich mangrove colony, will gradually change to a sweet-water-fed forest.

The drainage of the westerly flowing rivers in North Andaman has been affected because of a change in their gradients. Segments of the creeks and inland channels have dried up, leaving stagnant pools of water on the riverbed. This has adversely affected the lives of the local residents of Radhanagar, Shyamnagar, Kishorinagar and other areas in North Andaman, who earlier used these channels for transportation of men and material by boat, and access to the sea for fishing and other activities related to their livelihood. However, there is a possibility of restoration of the westerlygradient by erosion of the riverbeds by monsoon water, in the subsequent years.

In the course of boat journey through the Gudi nala and the creeks leading to Paschim Sagar area, it was observed that the colour of the creek water is deep yellow (turmeric yellow)/ brownish

Figure 5: Across the Andaman Islands, an E-W gradient of tectonic uplift is observed. Uplift increases from 0.3m at the eastern coast (Kalipur) of North Andaman Island to about 1.2m at the western coast (Paschimsagar) along a particular line. Extending the same gradient further to the west up to the trench, an estimate of 6.3 m vertical component of the earthquake slip along that line is obtained.

______________________________________________________________________________________________


yellow. The yellow colour gradually fades and changes to normal greenish blue colour as we approached the open sea. According to the local residents of Kishorinagar, this abnormal change in the colour of water in the creeks of the mangrove swamp was recorded after the rains in early May 2005. This feature indicates changes in water quality because of the earthquake and the resultant vertical uplift in the area. It has been mentioned earlier that the mud flats in the mangrove swamp in the Kishorinagar area have been raised above the present high tide level. The salt water of the sea, which supported the wide variety of biota in the mud flats including the mangrove colony, is nolonger available in the swamps and mud flats, which are gradually drying up (Plate 24, desiccationcracks) posing a threat to the biota. Change in the colour of creek water, according to ourobservations, is an impact of the ecological changes in the swamps.

RECOMMENDATIONS

Similar studies may be carried out in the islands south of 110N latitude i.e. in the Little

Andaman Island and the islands of the Nicobar group.There is a possibility of restoration of the westerly gradient of the river channels in North

Andaman, which has been disrupted because of differential uplift. Field observations to monitor the changes in the drainage may be undertaken.

Studies to monitor change in water quality and soil properties in the uplifted and submerged parts of the Andaman and Nicobar islands may be taken up.

REFERENCES

Bilham, R., Engdahl, E.R., Fedl, N., and Satyabala, S.P. (2005). Partial and complete rupture of the Indo-Andaman plate boundary 1847-2004, Seis.Res.Lett (in press)

Curray, J.R. (2005) Tectonics and history of the Andaman Sea region, Jr. Asian Earth Sc. (in press)

USGS (2004) http://equint.or.uss.gov/neic

____________________________________________________________________________________________REPORT ON SUMATRA-ANDAMAN EARTHQUAKE & TSUNAMI, 26 DEC ’04

91

BATHYMETRY AND MAGNETIC OBSERVATIONS ALONG ANDAMAN

ARC-TRENCH GAP IN THE POST EARTHQUAKE SCENARIO OF

26TH DECEMBER 2004

R. Sengupta, D.K. Deb Ray, A.K.Dasgupta, S.K.Ghosh, S.Dutta, Renjith M.L., N.G.Tom D.Chakraborty, S.C.Biswas, B.K.Nandi, K.K.Mukherjee, P.J.Joseph and A.Das

Marine Wing, Geological Survey of India, Kolkata 700 091.

ABSTRACT

Comprehensive and wide scale variation in the seabed morphology and magneticanomaly patterns have been recorded over ten different transects after the great earthquake of Sumatra, which occurred on the 26

th December 2004. These changes are indicative of

tremendous hydromechanical failures and associated low temperature oxidation and alteration of mineral phases in the oceanic basalt wherein titanomagnetite series changes due to low

temperature (< ∼300°C) oxidation reducing the magnetic intensity of the ocean floor. Evidences of such changes and the elastic rebound along these planes of the oceanic floor have beenrecorded by the present survey. This explains the cause of epidemic aftershocks in the region.

INTRODUCTION

The great earthquake in Sumatra on the 26th

December 2004 has been the fourthdevastating earthquake in the millennium, which has attracted the attention of earth scientists on a global scale. The associated Tsunami and loss of life and property have added a dimension of propanity and social evil to this event, which is probably the highest in degree in therememberable past. This has changed the morphology of this Arc-Trench system, changing bathymetry in local scale and fracturing the oceanic lithosphere over a wide zone of about 100-120 km, over a north-south distance of 1000-1200 km from its epicenter (USGS website) in the south to the northern tip of Andaman Nicobar group of island. This entire zone now represent a varitable laboratory for the study of dynamic changes in the lithosphere caused due to a sudden release of energy to the tune of 10

24 Nm by the earthquake and its potential rebound to normal

state by readjustment over a span of time in future, through creation of more and more aftershocks of lesser magnitude that are cascading even now.

Obviously such huge burst of potential energy in such a shot time span, will be converted partly into mechanical energy which will definitely produce changes in the morphology of the lithosphere; part of it will be transformed into acoustic energy to produce a rocking motion in the lithospheric columns; but a substantial part of it will be transformed into heat energy that will cause convection from the lithospheric mantle to the layers above, as much water will be released from the down going subduction slab. Such movement of channlized water and other fluids will eventually set-in hydrothermal activities along a few favoured zones, where secondarypermeability will develop due to mechanical failures. This will eventually bring forth lowtemperature oxidation and alteration of the minerals in the overlying ‘layer-2’ and ‘layer-3’ of oceanic crust.

It is well known that important ferromagnetic minerals in ocean basalts like thetitanomagnetite (xFe2TiO4. (1-x) Fe3O4) and the titanomaghemite series (x FeTiO3. (1-x) Fe2O3)are primarily responsible for oceanic magnetic anomalies. It is also known that the minerals in the titanomaghemite series are much less magnetic, being essentially antiferromagnetic with


92

small defects (Vacquier, 1972; Jones, 2004). The Curie temperature of the titanomagnetite series

decreases with increasing x in an approximately linear fashion from 578°C (x=0, magnetite) to –

153°C (x=1, ulvospinel). So the normal remnant magnetization (NRM) in rocks depends mostly on the concentration of their magnetite contents. This reduces when titanomagnetite is oxidized

at temperatures less than, 300°C. This produces cation-deficient titanomaghemite, a process in deep-sea basalts (Smith & Banerjee; 1986). The lowering is as much by at least one order of magnitude (Jones, 2004).

In northern hemisphere comparatively more and more negative anomalies are recorded with increasing normal remnant magnetization (NRM) in the present field. A loss ofmagnetization (magnetic susceptibility) will therefore appear as decrement in the amplitude of magnetic anomaly, when compared with the old one. Thus any changes in the patterns of magnetic anomalies which are bound to occur due to mechanical, acoustic and hydrothermal (heat) changes, already discussed above, will provide insights to the propagation of mechanical failures/ invasion of hydrothermal and associated oxidation/ alteration of mineral phases andfinally into the layer of decollement (horizontal stratification) and vertical faults (normal/ thrust/ strike-slip) which help in separating/ cutting of such hydrothermal/ mechanical energypropagation across the horizontal and vertical planes. Obviously such horizontal/ vertical planes delimiting energy propagation, discussed above, are the new signatures of crustal deformities inflicted into the crustal/ lithospheric mosaic due to the great earthquake. The opposite is true for reverse magnetization, which pertains to older age.

PRESENT WORK

With a view to map zones/ areas of profound crustal deformities, in the post great earthquake scenario, the Marine Wing of Geological Survey of India, mounted a special cruise SM-177, onboard its Research Vessel Samudra Manthan on 18

th January 2005 for a period of 25

days. Fig.1 shows the cruise tracks along with tectonic elements (Curray, 2005-in press) on which fresh bathymetry and magnetic (TF) observations are taken. The cruise tracks covered the area of the Andaman Arc-Trench system, down to the southern limit of the EEZ, south of which the great earthquake of Sumatra occurred. Care has been taken to repeat atleast ten earlier transects on which previous bathymetry and magnetic (TF) data exist, for comparison.

The position location for the present bathymetry as well as magnetic data in SM-177 has been controlled by GP-1650 WD System, Bathy-2000 and Cesium vapour magnetometer have been used for recording the bathymetry and the magnetic (TF) data respectively. The old data were however acquired using different instruments and positioning systems in different cruises, a description of which is given in the Appendix-I.

Magnetic data of SM-177 has been corrected applying IGRF coefficients of 2010. The old data have been processed using the DGRF coefficients of the respective epochs. In a few cases, partial coverage along a particular transect, in two different times, have been synthesized to figure out the complete transect for comparison with the new data. Over transect-8, a baselinecorrection has been applied to one segment of the profile for continuity.

Results and Discussions

Bathymetry

Ten different transects from down south to north in increasing order have been plotted in Figures 2, 3 and 4. The recent bathymetry has been plotted in solid blue over the old counterpart in solid red colour. Considering the errors in position location and bathymetry data recorded previously by SATNAV (location) and read from analog charts (bathymetry) respectively, the errors in the position is 200-300 m; while in bathymetry the maximum error (instruments plus personal) is


93


94

approximately ± 13.7m. The error in position location reduced to 50m and 10m afterintroduction of GPS and DGPS in year from 1995 and 2001 respectively (Appendix-I).Installation of Bathy-2000 permitted depth determination with the accuracy of few centimeters.

Analyses of bathymetry data show significant structural and morphological changes of the seafloor as a result of this major earthquake. The basis of the findings is a comparative view of the seafloor before (within the last 15 years) and after the earthquake. The replicatemeasurements are not error free. Different location finding techniques and different instruments for measurement of depth (discussed above) introduce artifacts and enlarge the error bounds.Proper care was however taken to filter out and minimize such noise from the signals. These are presented in the profiles (Figs. 2, 3 & 4) and discussed below.

Bathymetric profile along traverse 1 (Fig. 2), the southern most E-W profile in the area,

indicates change in topography between longitude 93o04′ and 93

o12′, on the inner slope of the

accretionary prism, compared to the bathymetric data recorded in the year 2001 (SM-148).Bathymetric profile (Fig. 2) along line-2 (6

oN lat.) shows minor change in the bathymetry along

the trench slope and the accretionary prism between 92o45′ and 92

o55′E when compared with the

profile of SM-142 cruise during which same positioning system was used and bathymetric data

were recorded on Raytheon Echo sounder. Profile along line-3 (lat. 7o40′) when compared with

SM-55 data (ship’s positioning system used – SATNAV system with Raytheon Echo sounder) shows some irregularities in the accretionary prism part between 92

° and 93

°E (Fig. 2). These

irregularities might also be due to data acquisition from different instrumental sources. Profile

along line-4 (8o40′N lat.) when compared with earlier cruise profile (SM-87) again shows

bathymetric changes along the trench axis and minor topographical mismatch with the earlier

data within the accretionary prism, but beyond 92.1°E the comparison is not reliable as the earlier

data did not follow the same latitude. The data is very much compatible between 91.3°

E and

92.1° E.

Bathymetric profile (Fig. 3) along line-5 (9°40′N lat.) when compared with earlier SM-55

data does not show much variation except for minor irregularities around 91.5oE long. This could

happen also due to positional error as during SM–55 when position fixing was carried out with

SATNAV. Around 91°E longitude a rift with graben like structure is observed. The bathymetry

along the traverse-6 (Fig. 3) brings out clearly the accretionary prism, East Margin Fault,Diligent Fault, Invisible Bank and West Andaman Fault from the west to the east. The

bathymetry data could be compared continuously up to 92.5 ° and as such no major changes

except for a change in the sea floor morphology between 91°10.4′ and 91

°19.4′E where a very

prominent u-shaped valley exists. When echograms of SM-55 and the present cruise arecompared, some reactivation of about 8 to 14m in the seabed is observed in the post earthquake

scenario. In areas north of 10°N latitude, bathymetric profiles (Figure 4; profiles 7, 8, 9 and 10)

do not show any significant change when compared to earlier bathymetric profiles except for some minor changes. Plotted on a compressed scale of 1cm equal to 1000m the change in the seafloor morphology is not very apparent to comprehend. Moreover, the position locations are also different which makes comparison ineffective. To overcome the constraints in datapresentation we have determined the bathymetry value, constraining the position location, and plotted them over two different traverses 1 and 2 (Fig.5) where GPS has been used for locating cruise tracks. It is significant to note from this exercise that while overall changes in bathymetry is well within the acceptable limits of error (25m), in a zone nearly 1.5-5 km in width, the changes in bathymetry is remarkable and is over several tens and hundreds of meter. These zones certainly represent the hydromechanical flextures and associated deformations indicating large-scale mechanical disruptions of the ocean floor that occurred following the great earthquake. The elastic rebound of the oceanic lithosphere is still continuing through these cracks, which has created an epidemic of aftershocks in the area.


95


96

Magnetics


97

Magnetic anomalies over the ten transects have been plotted along with bathymetry in the same Figures 2, 3 and 4. The recent magnetic (TF) anomalies have been plotted in dotted blue over the old counterpart in dotted red. A perusal of these clearly depicts that the magnetic (TF) anomalies are quiter compared to the normal oceanic strip magnetic anomaly in the east of the trench and over the accretionary prism. It is worthwhile to note that the degree of quietness is variable from south to north. As one proceeds northward the quietness diminishes and the old order prevails qualitatively (along a portion of profile 4 and 5; 6 to 10) signifying minimumchanges in magnetization even in the post great earthquake scenario. Thus the disappearance of sudden jumps (quietness) in the magnetic anomalies in the northern sector can be directlycorrelated with slow rate of subduction of the Indian plate under the Burmese Arc/ Asian plate –a view expressed by Vacquier (1972) and supported by Curray (2005-in press) in hisreconstruction of the tectonics of the Central Andaman Basin from 32 Ma through 4 Ma. Thus

we conclude presence of asperities, along 8°N, 10°N and north of 12°30′ latitude, in an E-Wdirection, where rate of the eastward subduction has been hindered by different transcurrent faults. This is corroborated by the study of the seismotectonic pattern in this area (Das et al, DST News Letter, 2004) whereas the rate of subduction elsewhere, towards south, is more rapid when compared to the north.

Normally the consumption of oceanic lithosphere at the trenches implies disappearance of fossil remanant magnetization (Vacquier, 1972). Thus lineated magnetic anomalies are absent in the Andaman Arc-Trench system east of Ninety East Ridge due to destruction of remanant magnetization as an effect of deformation and movement of fluids in the secondary pore spaces(Jones, 2004). This is evident in some portion of outer slope and accretionary prism and over trench zone across the Sunda subduction complex. Depending on the nature and degree of change in the magnetic anomalies, recorded during the present survey with respect to the old one along each traverse, is divided into two/ three sectors (profiles 1 to 7) viz., S1, S2 and S3.

Reduction of magnetic anomalies about 100-150 nT are observed in the sector S1 over the profiles 2 to 5 and a huge change of –500 nT is recorded over the same sector of the profile -1.In this sector the subducting Indian plate suffers intense deformation during the great earthquake of Sumatra resulting cracks/ faults increasing permeability through which hydrothermal fluidcome up to the upper label. Low temperature oxidation in this region, induced by thermal fluid, reduced magnetic susceptibility of the oceanic layers ‘3’ and ‘2’ lowering magnetic anomalies in this sector. This conclusion is supported by the fact that the sea-floor heat flow on accretionary complexes is normally lower than over sediment-covered oceanic crust of the same age situated far from the plate boundary (Watanabe et al, 1977). But the absence of linear or smoothlyvarying temperature gradients at many sites shows that fluid flow is common. Regions where anomalous temperature gradients i.e., the large variation in heat flow on the surface of the accretionary prism indicate that heat is passed to shallow levels by channelized fluid flowthrough high permeability fault zones (Langseth et al, 1990; Foucher, et al, 1990).

The previous magnetic profile over the transect-1, the southernmost transectshowever, still remains an enigma to be explained. A look at the profile immediately suggests that the bathymetry and the magnetic anomaly over this area are totally contradictory to each other. Such a situation can only happen when the magnetization of oceanic layers ‘2’ and ‘3’ cannot be modeled by horizontal tectonic elements below the outer slope, the trench zone and theaccretionary prism. But a diapiric intrusion below these will certainly explain the magneticbehaviour. In such an eventuality since the diapiric intrusion will have a lithospheric mantle root it will reflect in the free air gravity signature of the area. Das et al (DST Newsletter sent in Feb.’05) have reported a huge gravity high over this area, which corroborates out present hypothesis. Thus this huge diapiric intrusion which has been acting as a strong asperitieshindering subduction, as a result of which the Sunda trench has taken a easterly bent producing a

cusp structure near 5°N has been shattered by this devastating earthquake due to flexure deformation of the oceanic crust. Thus the observations of Laryseth and Silver (1996) suggesting


98

vigorous hydrothermal cooling of the upper oceanic crust, enhanced by faulting during flexure deformation holds the key to the loss of the magnetic response over this traverse over the part of outer slope, the trench zone and the accretionary prism. This intense deformation also propagated

towards north along the Sunda subduction complex. Considering the location (nearly 3.2°N) of this great earthquake, which is very near to this zone, this is easily acceptable. Hence the highest intensity of low temperature oxidation, recorded over profile 1, where a previous –500 nT anomaly has changed to –50 nT is ideally acceptable due to nearness (170 km) of the epicenter of this devastating earthquake. This zone (i.e., zone-1) over transects 1 to 5 is shown by hatches in the Figure 1. The +200nT anomaly can be explained through activation of pre-existing fault with

vertical slip, which restricted the movement of fluid in the west of 92.7°E

The sector S2 marked over the transect 4, 5, 6 and 7 over the accretionary prism, the newly observed magnetic anomalies retain its old patters but change in the amplitudes. This only suggests that the thrust fault associated with the overriding plate along the plane of subduction is not continuous all along its depth. On the contrary these changes their behaviour and become decollement and their near horizontal attitude below the accretionary prism (AP) creates a permeability barrier for the upcoming low temperature fluids, responsible for alteration ofminerals and associated reduction of magnetic susceptibility as discussed above. The changes in amplitudes of the anomalies are accounted for activation of the pre-existing faults changing its slip and invasion of hydrothermal fluid in the fault planes. These sectors (S2 over abovetransects) are marked by the hatches zone-2 in the Fig. 1, inferred as asperity and obstruct the subduction process. This is also true for a small section over the transect 2 and 3 where pre earthquake magnetic anomaly show a small high over the magnetically quiet zone.

Similarly, the changes in the anomaly values/ patterns over the sector S3 of the profiles 1 to 8 suggests that the great earthquake of Sumatra has mechanically damaged the ocean floor and re-activated the pre-existing faults to produce pathways for the low temperature fluids to come up, for reduction of magnetic susceptibility. The careful study of bathymetry, which is presented in compressed scale, reveals impression of deep-seated faults on the seabed. Change in the slips of these faults and invasion of hydrothermal fluid through these fault planes promotes low temperature oxidation as discussed earlier. Any one of these or both the process might have been active in the zone-3 (Fig. 1), comprising of the sector S3 over the above transects, accounted for the change in the observed magnetic anomaly. The high amplitude magnetic anomaly indicating faults in the outer slope along traverses 3, 4 and 5 might have been destroyed due to the normal process of subduction (discussed earlier) suggest zone of asperity obstructing subduction of Indian plate beneath the Burmese plate.

The changes in the magnetic anomalies observed (parallel shift and reduction in the amplitudes) over the transect 9 & 10 are due to slow rate of subduction of Indian plate. This area is not affected by intense hot fluid activity as the aftershocks due to the recent earthquake of Sumata have been hindered by different transcurrent faults (in E-W direction) discussed above.

Spectral analyses of magnetic data

Conventional analyses of power spectrum (Treitel et al., 1971) of the pre and post earthquake magnetic anomalies over all the ten transects have been performed through shifting window (overlap of 70-80%) of variable length (60-100 km) depending on the profile length. The deepest magnetic interface determined for two sets of data (pre and post earthquake data) along each profile and plotted in the Figure 6. The information about the depth of magnetic interface is not possible at the both end (30-50 km) of a profile because each window yields a single depth and it is plotted in the middle point of the window. This fact imposes a limitation on thequantitative interpretation. The root mean square error in determination of these interfaces is about 10% and it is acceptable in geophysical interpretation.


99


100


101

The disposition of the magnetic interfaces (Fig. 6) for pre and post earthquake magnetic data brought out a gap of variable width over transects along different latitudes as well as different sectors of a given profile. The gap is measured with respect to the pre earthquake magnetic interface and it is attributed to the change in magnetization of the oceanic crust and the


102

change in the depth of the faulted oceanic blocks due to the recent devastating earthquake as discussed in the earlier sections. So, a negative gap indicates shallowing of the magneticinterface with respect to old one. The negative gap is more in almost all portions of southern profiles (profile 1, 2 & 3) where magnetic interface raised by 2-4 km and supports the more rapid rate of subduction of Indian plate and the most intense tectonic activities discussed earlier.Similarly, relatively slow rate of subduction is supported by the small negative gap in the northern sector of the area (transects 5 to 10). The small positive gaps along the traverses 4, 5, 6 & 8 can be explained by faulted oceanic blocks in the outer slope, the trench zone and in the inner slope of accretionary prism of the Sunda subduction complex. The asperities suggested in earlier sections are also corroborated with this view.

CONCLUSIONS

1) Recent bathymetry and magnetic survey over the Andaman-Arc-Trench system indicate large-scale hydro-mechanical fracture of the ocean floor caused by the great earthquake of Sumatra on 26

th December 2004.

2) These fractures have induced large-scale upward movement of huge quantity of water by low temperature convection.

3) Such low temperature convection (≈300°C) has influenced oxidation/alteration of mineral grains and a reduction in magnetic intensity/susceptibility which has been recorded hasmagnetic highs in several transects over the Outer Slope and Trench.

4) Low cost bathymetric and magnetic survey has thus proved to be an important technique to comprehend the tectonic effects of the great earthquake in the region.

ACKNOWLEDGEMENTS

The authors are thankful to Mr. B. K. Saha, Dy. D. G., Marine Wing, Geological Survey of India for his inspiration to conduct the work. They wish a deep sense of gratitude to Dr. L. K. Das, the then Director (Geophysics), MW for his involvement with this work and valuable suggestions for interpretation of magnetic data. Thanks to Dr. B. P. Pal, Director (Geophysics), MW for his guidance for data processing. The cruise participants collecting the pre earthquake bathymetry and data used in this report have been acknowledged.

REFERENCES

Curray, J. R. (2005). Tectonics and history of the Andaman Sea region. Journal of Asian Earth Sciences, 73, (Article in Press), Figures 19-22.

Das, L. K., Pal, B. P., Ghatak, S. K., Nandi, B. K., Singh, R., Saha, B. K. (2004) Morphotectonic connotations of the eastern seaboard of India from free air gravity map – A study. DCS – DST News, August 2004, 18-21.

Das, L. K., Pal, B. P., Nandi, B. K., Singh, R., Ghatak, S. K., Mukherjee, K. K. (2005) Post earthquake changes in the crustal architecture of the Arc-Trench system in the Bay of Bengal and the Andaman Sea – A crustal dynamic study. DCS – DST News (in press).

Foucher, J.P., Le Pichon, X., Lallemant, S., Hobart, M., Henry, P., Benedetti, M., Westbrook, G. and Langseth, M., Hoba, M. (1990). Heat flow, tectonics and fluid circulation at the toe of the Barbados Ridge accretionary prism. Journal of GeophysicalResearch, 95, 8859-8867.

Jones, E. J. W. (2004), Marine Geophysics. John Wiley & Sons, Ltd., Chichester, pages 177-181,342-343, 441-442,

Langseth, M. G., Westbrook, G. K. and Hoba, M. (1990). Contrasting geothermal regimes of the Barbados accretionary complex. Journal of Geophysical Research, 95, 8829-8842.


103

Smith, G. M. and Banerjee, S. K. (1986). Magnetic structure of the upper kilometer of marine crust at Deep Sea Drilling Hole 504B, eastern Pacific Ocean. Journal ofGeophysical Research, 91, 10337-10354.

Trietel, S., Clement, W. O. and Kaul., R. K. (1971). Spectral determination of the depths of buried magnetic basement rocks. Geophys. Jour. Roy. Asia. Soc., 24, 415-428.

Vacquier, V. (1972) Geomagnetism in Marine Geology. Elsevier Oceanography Series, 6,Amsterdam, pages 68-69.

Watanabe, T., Langseth, M. G. and Anderson, R. N. (1977). Heat flow in back-arc basins of the western Pacific. In Island arcs, Deep Sea Trenches and Back-arc Basins (EditorsM. Talwani and W. C. Pitman III). Maurice Ewing Series 1, AmericanGeophysical Union, Washington DC, 137-161.

__________________________________________________________________________________ __________REPORT ON SUMATRA-ANDAMAN EARTHQUAKE & TSUNAMI, 26 DEC ’04

104

APPENDIX - I

The equipments deployed for collecting bathymetry, magnetic and navigation data onboard R. V. Samudra Manthan for different cruises from 1987 to 2005.

Echo sounder employed Magnetometer employed Positioning System emp loyedSl.

No.

Cruise Year

Type Accuracy/ error Type Accuracy/

error

Type Accuracy/ error

1. SM-177 2005

Bathy-2000

Frequency : 3.5 kHz ∼10 cm

Cesium

magnetometerModel : G-880

0.01 nT

2. SM-148 2001

FURUNO GPS

receiverModel : GP-

1650WD

10 m(GPS mode)

3. SM-142 2000

4. SM-128 1998

5. SM-121 1997

6. SM-120 1997

7. SM-104 1995

GPS

Model : NP-210 50 m

8. SM-095 1994

9. SM-055 1989

10. SM-36A 1987

Raytheon LSR

Frequency : 3.5 kHz

Instrument : ∼ 50 cm +

Maximum personal error: 13.2 m

(for the least sweep

rate used for

measurement of higher depth)

Proton precession

magnetometer

Model: G-811

0.1 nT

MX1107 Dual Channel Satellite

Navigator

50m (rms) +

∼370 m/knot

speed error.


SEISMOTECTONICS OF THE ANDAMAN- NICOBAR REGION: CONSTRAINTS FROM AFTERSHOCKS WITHIN 24 HOURS OF THE GREAT

26 DECEMBER 2004 EARTHQUAKE

Sujit Dasgupta, Basab Mukhopadhyay and A. AcharyyaGeological Survey of India, 27 J. l. Nehru Road, Kolkata- 700 016, India

ABSTRACT

174 aftershocks of magnitude ≥ 4.8 occurred on 26 December 2004 following the great Sumatra-Andaman shallow foci thrust earthquake that struck on the India- Southeast Asia plate interface. Out of these, 112 shocks define the fault rupture plane while another 62 events locate along the different strands of the West Andaman Fault (WAF). From spatio- temporal distribution of aftershocks the primary rupture plane show 3 distinct segmentation from south to north. Thesesegments terminate along the transverse lithospheric hinge faults. Average down-dip width of

rupture is 140km and total rupture area is around 2.0 × 105 sq km; with an average slip of 15 meter

seismic moment (Mo) calculates to the order of 1.2 × 1030

dyne.cm. Seven unilaterally propagatingshocks from south towards north occurred within 130 minutes of the mainshock that ruptured the entire fault segment with an average rate of 167m/ sec. Similar seven sequential northwardpropagating shocks also characterize the WAF. 13 best double couple HRVD solutions including the mainshock indicate primarily thrust mechanism though normal and strikeslip solutions are alsoincluded.

INTRODUCTION

The Andaman arc together with the Burmese Arakan Yoma hill ranges present nearly3500km long subducting margin in the northeastern part of the Indian plate where varying degrees of seismic activity, volcanism and active deformation are evidenced. The region serves as an important transitional link between the Eastern Himalaya collision margin and the Sunda arc (a part of the West Pacific arc system). Seismicity and tectonics of this convergent margin though studied indetails (see among others Curray, 2005; Dasgupta et al. 2003), nevertheless is insufficient to propose any medium to short-term predictive model for the occurrence of such great inter-plate earthquake like the one that struck on 26 December 2004. Notwithstanding a few soft claims in the media on the forecast of this major earthquake that created havoc via tsunami all along the Indian Ocean rimcountries, the event could not have been predicted within a reasonable space, time and size window with the present knowledge of earthquake physics, statistics and tectonics.

Basic seismological data, on which our understanding of this mega-event is derived, is largely provided by the USGS web site. From the study of NEIC earthquake catalogue both in the pre- and post- 26 December 2004 scenario we had demonstrated (see http//:www.gsi.gov.in/suma_eq.htm) spatio-temporal variation of seismicity pattern; between 1

st January

and 26th

November 2004 there are records of 260 events from the region, while in the period since 27

th November till the great earthquake of 26 December there was a clear seismic quiescence of one

month. We had further shown that all aftershocks that struck on 26 December 2004 (193 as listed on 08.02.2005) form three distinct linear clusters along the subduction mega-thrust and two more clusters along the West Andaman fault. We have revisited the NEIC catalogue (as on 09.06.2005) to find that 283 aftershocks are recorded on 26 th December itself and in this note we discuss the seismotectonic setup of the Andaman- Nicobar region based on spatio-temporal behavior of 174 aftershocks (M ≥ 4.8) that occurred on 26th December following the mainshock.

ANALYSIS

A total of 112 aftershocks (M ≥ 4.8) occur along the mega-thrust plane. Except one event (no.25; Table 1) that locates south of Nias the rest occur north of the mainshock. The northernmost

aftershock (no. 147; Table 3) recorded locates close to 14°N latitude. The fault rupture due the earthquake thus propagated 11 degrees (> 1200 km) from 3° (epicenter) to 14°N. Another 62 aftershocks occur within the overriding Andaman-Sumatra lithospheric plate, loading primarily the West Andaman Fault (WAF) system up to western part of the Andaman Spreading Ridge (ASR). Except 11 slightly deeper (max depth: 61 km) shocks all are shallow foci events (< 40km). Ten aftershocks are of magnitude (mb, Ms or Mw) greater than 6.0 including one event of Mw 7.2 (no. 53; Table 1). These 112 mega -thrust plane aftershocks are plotted in solid circles (Figure 1) on a simplified tectonic map (after Curray, 2005) superimposed with 40km contour (red line) on top of the Benioff zone and nine (f8 to f16) lithospheric hinge faults within the subducting Indian plate (both after Dasgupta, et al, 2003). The mainshock locates on the Benioff zone where it is segmented by the fault f16.

From the spatial distribution pattern of aftershocks the entire rupture plane can be divided into three segments. The southernmost segment I containing the mainshock, is about 570km long, trends N40W and extends up to the hinge fault f13 (revised from our earlier study; see Dasgupta et al. 2005). 54 aftershocks originated from this segment define the rupture plane. The strongest aftershock (no.53) locates close to the northern margin of segment I. Best double couple solutions (HRVD) for the mainshock and 6 aftershocks (no. 53, 133, 141, 150, 164 and 165; in bold font, Table 1) are schematically shown (Figure 1) and parameters listed (Table 5). While the mainshock, aftershocks 53 and 133 show thrust mechanism, no.141 is a downdip compression reverse fault with moderate right-lateral slip and no. 150 & 164 display normal faulting. The central or segment II is between the hinge faults f13 and f11. This segment trends N15-20E and is about 400km long with 31recorded aftershocks (Table 2). The northern sector of this segment (between shock 63 and fault f11) has apparently remained unbroken on 26 December. The largest aftershock (no. 100, Table 2) is of magnitude (Mw) 6.6 that gives thrust fault solution (HRVD). Fault segment III, between f11 and f8, trends N15E with a fault rupture length of 500km. 26 aftershocks (Table 3) define the rupture plane with the strongest shock (no.110) of magnitude (Mw) 6.3. While this event shows normal fault mechanism, 3 more close by shocks (no. 120, 140 and 162) give strike-slip solutions with the NW nodal plane indicating activity along fault f9 (see also Dasgupta et al 2003). Due to the presence of lithospheric hinge faults within the subducting Indian plate, the Benioff zone is segmented resulting several shallow and steeper dip segments; this is clearly brought out by the swerving nature of the 40km contour on top of the Benioff zone (see Dasgupta et al. 2003). Though aftershocks aredistributed throughout the entire mega-thrust plane they appear to be more concentrated in the steeper segments.

We further shortlist 7 events that occurred in temporal succession along the unilateraldirection of rupture propagation. These 7 aftershocks (red solid circle in Figure 1) are no.1, 2 (in rupture segment I, bold font, Table 1) and 9, 13, 14, 24 & 30 (in rupture segment III, bold font, Table 3) that define the entire fault rupture from the mainshock in the south to shock no. 30 in the north. It took 2h 9m 50.76s to break up to the northern-most point of the mega-thrust since the mainshock, traversing a total of about 1300 km fault length with an average rate of about 167meter/ sec. We are inclined to believe that these 7 sequentially propagating shocks are triggered events rather thanaftershocks (sensu stricto) that usually strike via residual stress to break small asperities left by the mainshock rupture. The unilateral propagating rates for the inter-events given by the respective length/time are: 242m/sec (from mainshock to aftershock 1); 730m/ sec (from aftershocks 1 to 2); 250m/ sec (from 2 to 9); 158m/ sec (from 9 to 14) and 147m/ sec (from 24 to 30). These unilateral

______________________________________________________________________________________________


Figure 1. Tectonic Map of Sumatra- Andaman Region (after Curray, 2005) with 112 aftershocks (• focal depth

≤ 40 km; + > 40 km) that occur on 26 December 2004 following the mainshock (star). f8- f16 are lithospheric

hinge faults and red line is the 40 km contour on top of the subducting Indian lithosphere (both after Dasgupta

et al. 2003). The fault rupture plane is shown in shades of yellow and green for the 3 segments (I-III).

• 7aftershocks that occur sequentially from south to north along the mega-thrust; for numbers refer to Tables 1-

4. Beach ball diagrams are HRVD best double couple solutions; for parameters see Table 5. Red star: volcano; N- Narcondam, B- Barren. ASR- Andaman spreading ridge; MPF- Mae Ping Fault; TPF- Three Pagodas Fault;

SSF- Shan Scrap Fault; WAF- West Andaman Fault; RF- Ranong Fault; KMF- Khlong Marui Fault.

______________________________________________________________________________________________


Table 1: Chronological listing of aftershocks on 26 December from fault rupture segment I

No YEAR MO DA Hr Mn Sec LAT LONG DEPTH MAGNITUDE

mb Ms Mw Mo

0 2004 12 26 00 58 53.45 3.30 95.98 30 8.9 8.9 9.0 3.95E+29

1 2004 12 26 01 17 10.33 4.94 94.27 30 5.5

2 2004 12 26 01 21 20.66 6.34 93.36 30 6.1

7 2004 12 26 01 40 07.13 5.84 93.15 30 5.3

8 2004 12 26 01 48 52.07 5.43 94.46 51 5.7

12 2004 12 26 02 15 23.57 6.17 93.47 30 5.6

16 2004 12 26 02 30 28.94 6.72 93.08 15 5.1

17 2004 12 26 02 34 52.15 3.99 94.14 30 5.7

23 2004 12 26 02 46 20.74 4.24 93.61 30 5.7

25 2004 12 26 02 53 13.04 0.06 97.04 30 5.4

27 2004 12 26 02 59 14.39 3.18 94.38 30 5.7

31 2004 12 26 03 09 34.08 4.05 93.53 30 5.4

34 2004 12 26 03 19 13.05 3.55 94.29 30 5.5

36 2004 12 26 03 24 54.94 4.47 94.07 26 5.8

38 2004 12 26 03 30 01.38 4.64 94.00 25 5.2

41 2004 12 26 03 46 42.04 6.72 93.33 46 5.0

42 2004 12 26 03 50 22.18 5.51 94.25 48 5.3

44 2004 12 26 03 54 44.77 6.48 92.89 30 5.1

45 2004 12 26 04 00 42.83 4.76 93.79 16 5.2

47 2004 12 26 04 02 12.52 3.04 95.89 30 5.4

50 2004 12 26 04 10 12.71 5.48 92.92 36 5.4

51 2004 12 26 04 12 35.65 6.44 93.23 3 4.8

53 2004 12 26 04 21 29.81 6.91 92.96 39 6.1 7.5 7.2 7.23E+26

55 2004 12 26 04 31 29.06 6.99 93.18 36 5.0

69 2004 12 26 05 23 50.8 3.35 94.09 18 5.2

71 2004 12 26 05 51 40.01 6.45 93.43 29 5.2

72 2004 12 26 05 55 49.4 3.17 93.94 23 5.1

74 2004 12 26 06 09 30.84 6.34 93.20 29 4.8

76 2004 12 26 06 16 14.68 5.84 93.36 26 4.9

78 2004 12 26 06 22 35.25 5.34 93.07 23 5.1

80 2004 12 26 06 38 36.05 6.65 92.96 16 5.4

90 2004 12 26 07 59 37.72 3.23 93.91 31 5.3

97 2004 12 26 09 07 38.95 3.42 94.34 25 4.9

105 2004 12 26 09 43 19.38 5.53 93.14 30 5.1

106 2004 12 26 09 44 20.36 5.73 93.10 36 5.2

111 2004 12 26 10 29 49.0 5.17 93.48 46 5.3

113 2004 12 26 10 43 29.95 6.53 92.83 36 5.4

121 2004 12 26 11 17 08.52 3.25 93.75 30 5.2

123 2004 12 26 11 50 28.09 6.39 93.25 61 5.2

126 2004 12 26 12 30 59.49 3.89 94.44 30 4.9

127 2004 12 26 12 46 06.37 5.40 93.28 25 4.9

132 2004 12 26 13 44 08.07 3.97 94.39 31 5.1

133 2004 12 26 13 56 40.17 2.78 94.47 30 5.5 5.9 5.9 8.62E+24

135 2004 12 26 14 11 28.31 3.67 94.02 30 5.2

141 2004 12 26 15 06 33.24 3.65 94.09 17 5.6 6.1 6.0 1.07E+25

Table 1 continued

______________________________________________________________________________________________



mb Ms Mw Mo

142 2004 12 26 15 12 21.55 6.73 92.98 18 5.3

143 2004 12 26 15 13 20.84 5.37 93.43 30 5.4

146 2004 12 26 15 36 54.02 4.12 93.85 39 4.9

148 2004 12 26 16 21 27.41 5.15 94.32 41 5.4

150 2004 12 26 16 55 17.27 3.86 94.50 30 5.3 5.4 1.70E+24

156 2004 12 26 181449.54 4.80 94.09 30 4.8

157 2004 12 26 181655.97 3.37 94.10 28 4.8

159 2004 12 26 183143.48 6.32 93.32 30 5.3

160 2004 12 26 183207.92 3.84 93.32 26 5.1

164 2004 12 26 19 03 49.21 4.09 94.22 30 5.5 5.5 2.36E+24

165 2004 12 26 191955.57 2.79 94.16 30 5.5 6.2 6.1 1.76E+25

Table 2: Chronological listing of aftershocks on 26 December from fault rupture segment II

No YEAR MO DA Hr Mn Sec LAT LONG Depth MAGNITUDE

mb Ms Mw Mo

10 2004 12 26 01 59 13.99 8.39 92.45 30 5.3

15 2004 12 26 02 22 01.84 8.87 92.47 15 5.7

19 2004 12 26 02 38 09.35 8.49 92.35 33 5.6

20 2004 12 26 02 40 59.85 7.48 92.43 30 5.4

22 2004 12 26 02 45 17.65 8.46 92.61 30 5.2

26 2004 12 26 02 56 40.37 8.61 92.29 30 4.9

28 2004 12 26 03 02 38.08 8.61 92.33 30 5.5

29 2004 12 26 03 06 13.05 8.19 92.46 27 5.1

33 2004 12 26 03 17 52.38 7.21 92.92 30 5.6

59 2004 12 26 04 53 09.1 8.19 92.93 30 4.9

62 2004 12 26 05 01 10.56 9.30 92.21 30 5.3

63 2004 12 26 05 01 21.37 9.46 92.18 30 5.4

64 2004 12 26 05 08 04.83 9.03 92.46 30 5.0

66 2004 12 26 05 12 34.14 8.46 92.28 36 5.1

86 2004 12 26 07 24 53.05 7.42 92.64 34 5.1

89 2004 12 26 07 55 27.13 7.48 92.36 30 5.3

98 2004 12 26 09 13 54.71 7.31 92.19 33 5.2

100 2004 12 26 09 20 01.61 8.88 92.38 16 6.0 6.6 6.6 9.77E+25

103 2004 12 26 09 36 39.27 9.35 91.86 30 4.6

104 2004 12 26 09 38 39.35 8.96 92.33 30 4.9

107 2004 12 26 10 02 07.76 7.65 92.79 31 4.8

112 2004 12 26 10 33 05.16 8.70 92.62 39 5.4

114 2004 12 26 10 51 19.82 7.63 92.31 30 5.5

137 2004 12 26 14 39 07.37 8.30 92.36 30 5.1

149 2004 12 26 16 48 24.11 7.22 93.03 49 4.9

158 2004 12 26 182931.78 8.06 92.20 30 5.0

168 2004 12 26 21 20 42.31 8.58 92.14 30 4.9

171 2004 12 26 21 44 38.22 7.03 92.56 30 4.8

172 2004 12 26 22 46 11.06 8.99 92.51 36 4.9

173 2004 12 26 23 04 26.65 9.29 91.97 30 5.1

174 2004 12 26 23 31 45.58 9.02 92.38 30 4.8

______________________________________________________________________________________________


Table 3: Chronological listing of aftershocks on 26 December from fault rupture segment III

No YEAR MO DA Hr Mn Sec LAT LONG Depth MAGNITUDE

mb Ms Mw Mo

9 2004 12 26 01 52 43.0 10.38 92.12 12 5.2

13 2004 12 26 02 15 49.5 12.26 92.28 20 5.3

14 2004 12 26 02 15 59.78 12.32 92.50 26 5.7

18 2004 12 26 02 36 10.09 12.18 92.94 38 5.8

24 2004 12 26 02 52 01.83 12.50 92.60 30 5.8

30 2004 12 26 03 08 44.21 13.74 93.01 30 5.9

40 2004 12 26 03 44 08.34 13.47 92.74 22 5.2

60 2004 12 26 04 58 04.02 11.07 92.00 29 5.3

68 2004 12 26 05 20 27.92 12.16 92.40 31 5.3

77 2004 12 26 06 22 00.42 10.68 92.32 26 5.4

81 2004 12 26 06 56 47.4 10.98 92.28 23 5.5

87 2004 12 26 07 38 27.0 13.13 93.04 30 5.7

110 2004 12 26 10 19 31.73 13.46 92.74 26 6.1 6.0 6.3 3.22E+25

118 2004 12 26 10 57 38.36 12.45 92.44 5 5.4

119 2004 12 26 11 03 53.29 11.10 93.95 30 4.8

120 2004 12 26 11 05 00.72 13.53 92.84 13 6.3 6.3 6.2 2.37E+25

124 2004 12 26 12 09 42.46 12.19 92.60 20 5.4

125 2004 12 26 12 11 57.66 11.57 92.41 25 5.4

136 2004 12 26 14 14 18.03 13.50 92.92 17 5.0

138 2004 12 26 14 40 30.41 11.47 92.18 30 5.3

140 2004 12 26 14 48 44.26 13.59 92.91 30 5.8 5.7 5.7 4.40E+24

147 2004 12 26 16 12 53.01 13.94 93.31 4 4.8

152 2004 12 26 17 50 12.59 13.60 92.85 26 5.0

153 2004 12 26 17 56 35.84 12.86 92.48 45 5.1

162 2004 12 26 18 42 43.89 13.71 92.95 26 5.3 4.7 5.4 1.69E+24

163 2004 12 26 18 55 46.1 11.98 91.97 30 4.9

afterslip or triggered slip rates are however less than the modeled rupture velocity of 2.0 to 2.5km/ sec in the mainshock rupture segment [Yagi, 2005; Chen Ji, 2005; Yamanaki, 2005]. Average down-dip width of fault rupture is 150km in fault segment I, and 130km in segments II and III. Totalrupture area is around 2.0 × 10

5 sq km. With an average slip of 15 meter [and rigidity (µ) as 4×

1011

dyne/cm2], seismic moment (Mo) calculates to the order of 1.2 × 10

30 dyne.cm, a value very

close to that given by Stein and Okal (2005).

The main earthquake of 26th December has loaded the entire fault system in the region both in the subducting and overriding plates and transferred stress particularly to the West Andaman fault.

Several large aftershocks locate along this fault system and continue up to 10.5°N latitude close to the junction of WAF transform and ASR (Figure 2). 62 Aftershocks of magnitude ≥ 4.8 (Table 3) are recorded on 26 December that display two distinct linear clusters. The southern cluster locates west

______________________________________________________________________________________________


Figure 2. Tectonic Map of Sumatra- Andaman Region (after Curray, 2005) with 62 overriding plate aftershocks (• focal depth ≤ 40 km; + > 40 km) that occur on 26 December 2004 following the

mainshock (star). • Sequential aftershocks along the West Andaman fault. Others legend same as Figure1.

______________________________________________________________________________________________


of northern Sumatra while the other occurs east of Nicobar group of Islands, both due to activity along different strands of WAF. Four shocks are of magnitude (mb or Mw) ≥ 6.0 and the largest (no. 109) gives a reverse fault solution (HRVD) but both the nodal planes trend ENE almost normal to the WSF. In this segment of WAF there are also 7 unilaterally propagating aftershocks from no. 3 in the south to no.128 close to ASR through no. 5, 21, 67, 82 and 83 (bold font in Table 3 & green solid circle in Figure 2). Northward propagation rate from shock no.3 to 5 is 335m/ sec and 255m/ sec

from 82 to 83, while it is very slow (≈ 5m/ sec) in a patch between shocks 5 and 82 through 21 and 67 involving junction of two strands of WAF.

CONCLUSION

The 26 December 2004 Sumatra-Andaman Mw 9.3 earthquake is the largest recorded event from this part of Indo- Southeast Asia convergent margin. Aftershock distribution pattern on the day the earthquake struck indicate that rupture propagated unilaterally northwards from the mainshock epicenter to break around 1300km of plate interface. Though this part of the subducting Indian plate is fragmented by a number of lithospheric hinge faults, some of them acted as barriers for smooth propagation of rupture resulting three well-defined fault segments. 7 unilaterally northwardpropagating shocks from the mainshock to the distal part of the rupture occurred within 130 minutes at a rate of 167m/ sec and these events are likely to be triggered earthquakes rather than usual aftershocks. This great shallow foci interplate thrust earthquake has also seismically loaded the overriding plate to activate two different strands of the WAF. HRVD best double couple solutions indicate that though thrust faulting is the main mode of rupture, normal and strikeslip mechanism is also operative. Detail study of aftershocks in relation to seismo-geological depth sections across and along the arc is necessary to decipher the details of seismotectonics.

REFERENCES

Curray, J.R. (2005). Tectonics and History of the Andaman Sea Region. J. Asian Earth Sc. (in press).

Dasgupta, S., Mukhopadhyay, M., Bhattacharya, A. and Jana, T.K. (2003). The geometry of the Burmese-Andaman subducting lithosphere. Jour. Seism. V. 7, pp. 155-174.

Dasgupta, S., Mukhopadhyay, B. and Acharyya, A. (2005). Aftershock propagationcharacteristics during first 3hours following the 26 December 2004 Sumatra- AndamanEarthquake. Gondwana Research (GNL section), V.8, n.4 (in press)

HRVD (2005). http://www.seismology.harvard.edu/CMTsearch.html

Ji Chen (2005) http://www.gps.caltech.edu/~jichen/Earthquake/2004/aceh/aceh.html

Mukhopadhyay, B., Acharyya, A. and Dasgupta, S. (2005) Aftershock investigation of 26th

December 2004 earthquake. http://www.gsi.gov.in/suma_eq.htm

Stein, S. and Okal, E.A. (2005). Speed and Size of the Sumatra earthquake. Nature, v. 434, pp. 581-582.

Yagi, Y. (2005) http://iisee.kenken.go.jp/staff/yagi/eq/Sumatra2004/Sumatra2004.html

Yamanaki, Y. (2005) http://www.eri.u-tokyo.ac.jp/sanchu/Seismo_Note/2004/EIC161e.html

______________________________________________________________________________________________


Table 4: Chronological listing of aftershocks on 26 December from the Andaman- Sumatra upper plate


mb Ms Mw Mo

3 2004 12 26 01 22 25.59 7.42 93.99 30 6.0

4 2004 12 26 01 25 48.76 5.50 94.21 30 6.1

5 2004 12 26 01 30 15.74 8.83 93.71 30 5.5

6 2004 12 26 01 33 22.38 7.76 93.71 25 5.5

11 2004 12 26 02 00 40.03 6.85 94.67 30 6.0

21 2004 12 26 02 43 05.26 9.22 94.00 30 4.9

32 2004 12 26 03 14 13.84 7.44 94.26 30 5.4

35 2004 12 26 03 22 57.48 5.82 95.09 20 5.4

37 2004 12 26 03 26 45.79 4.91 96.40 30 5.3

39 2004 12 26 03 40 15.64 5.53 94.33 30 5.6

43 2004 12 26 03 51 12.36 5.05 94.77 30 5.7

46 2004 12 26 04 00 58.43 6.79 94.08 29 5.5

48 2004 12 26 04 02 55.73 4.98 94.72 47 5.8

49 2004 12 26 04 09 08.4 8.16 93.82 30 4.9

52 2004 12 26 04 17 56.81 8.96 93.72 30 5.3

54 2004 12 26 04 26 03.63 7.89 93.99 30 5.2

56 2004 12 26 04 40 11.46 9.12 93.84 38 5.2

57 2004 12 26 04 46 23.44 8.53 93.88 32 5.4

58 2004 12 26 04 48 56.49 8.87 93.75 27 5.2

61 2004 12 26 04 59 15.4 8.97 93.43 25 5.2

65 2004 12 26 05 09 32.5 9.16 93.89 26 5.2

67 2004 12 26 05 16 10.98 9.32 94.04 22 5.4

70 2004 12 26 05 42 49.27 5.49 94.29 30 5.1

73 2004 12 26 06 02 28.38 8.27 94.06 23 5.7

75 2004 12 26 06 11 04.6 9.31 93.91 23 5.1

79 2004 12 26 06 28 48.4 4.96 94.79 30 5.4

82 2004 12 26 06 59 57.26 9.36 93.70 30 5.4

83 2004 12 26 07 07 10.27 10.36 93.75 19 5.6

84 2004 12 26 07 11 40.39 4.81 94.97 35 5.2

85 2004 12 26 07 23 38.81 5.44 94.41 30 4.7

88 2004 12 26 07 52 28.8 8.13 94.07 17 5.5

91 2004 12 26 08 02 34.62 5.34 94.48 34 5.1

92 2004 12 26 08 12 38.7 9.26 93.84 36 4.8

93 2004 12 26 08 14 59.09 6.79 94.54 30 4.8

94 2004 12 26 08 41 48.85 8.90 93.48 25 5.2

95 2004 12 26 08 47 46.72 4.86 95.10 50 5.3

96 2004 12 26 09 02 42.55 8.29 93.98 26 4.9

99 2004 12 26 09 17 51.19 7.06 94.39 21 5.0

101 2004 12 26 09 30 29.54 7.39 93.99 13 4.9

102 2004 12 26 09 30 55.8 7.18 93.76 30 5.4

108 2004 12 26 10 12 10.15 10.25 94.31 30 5.1

109 2004 12 26 10 18 13.79 8.86 93.74 30 5.5 6.3 3.87E+25

115 2004 12 26 105358.42 10.19 93.68 30 5.3

116 2004 12 26 10 55 07.5 4.26 95.13 30 5.2

117 2004 12 26 10 56 02.59 10.07 93.83 30 5.5

Table 4 continued

______________________________________________________________________________________________



mb Ms Mw Mo

122 2004 12 26 11 34 20.02 5.28 94.36 30 4.8

128 2004 12 26 12 52 45.76 10.43 93.91 30 5.1

129 2004 12 26 13 10 42.5 7.59 94.24 30 4.8

130 2004 12 26 13 13 27.14 6.14 95.43 30 4.9

131 2004 12 26 13 28 56.52 7.72 94.03 19 5.2

134 2004 12 26 14 02 05.02 4.80 94.78 30 4.8

139 2004 12 26 14 47 17.44 4.63 95.10 30 4.9

144 2004 12 26 15 23 05.33 7.44 94.22 17 5.0

145 2004 12 26 15 24 08.86 7.56 94.23 17 4.9

151 2004 12 26 17 44 52.77 8.93 93.97 22 5.2

154 2004 12 26 17 59 00.46 8.31 93.95 0 4.8

155 2004 12 26 18 10 43.16 8.95 94.04 25 5.0

161 2004 12 26 18 33 55.6 9.43 93.66 47 5.1

166 2004 12 26 21 06 48.8 4.47 96.34 30 5.5

167 2004 12 26 21 19 30.79 4.23 97.81 30 4.9

169 2004 12 26 21 25 33.15 4.75 94.85 30 5.0

170 2004 12 26 21 25 43.24 4.33 95.07 30 4.8

Table 5: Parameters for Best Double Couple Solution (HRVD) of Mainshock and 12 Aftershocks

No* Nodal plane 1 Nodal plane 2 T- axis P- axis B-axis

st dip slip st dip slip Pl Az Pl Az Pl Az

0 329 8 110 129 83 87 53 35 37 221 3 130

53 351 27 121 137 67 75 64 25 22 239 13 144

100 333 38 82 163 53 96 80 102 7 248 4 340

109 272 40 115 61 54 70 73 283 7 164 15 72

110 1 41 -116 215 54 -69 9 291 71 181 17 23

120 29 56 158 132 72 36 38 355 11 257 49 155

133 307 35 83 136 56 95 78 58 11 221 4 314

140 137 56 15 38 78 145 33 350 13 91 53 200

141 96 48 33 343 67 133 47 299 12 43 39 144

150 289 37 -73 88 55 -102 10 190 76 317 10 96

162 144 69 174 236 84 21 19 102 11 09 68 251

164 304 38 -91 126 52 -89 9 216 82 38 16 23

165 342 34 139 108 68 63 56 342 19 220 24 120

* Refer to Tables 1-4


115

AFTERSHOCK INVESTIGATION OF THE DECEMBER 26, 2004

SUMATRA-ANDAMAN ISLANDS EARTHQUAKE

O. P. Mishra, G. K. Chakraborty and O.P. Singh Geological Survey of India, Kolkata 700 016.

SUMMARY

The devastating megathrust earthquake, mainshock (Mw 9.3) of December 26, 2004 (00h 58m 53s UTC) in the Indian Ocean occurred on the interface of the India and Burma plates in the north Sumatra, about 1605 km NW of Jakarta, Java, Indonesia. The USGS estimated the epicenter of the mainshock at 3.32

0N and 95.85

0E and its depth at 28.6 km. The mainshock triggered by reverse

faulting generated a large rupture that propagated from the north Sumatra, Indonesia to northAndaman Islands, India as a major source of aftershocks. The mainshock caused wide -scale damages to both property and person (about 300,000 people were killed) due to strong shaking and tsunamis, the devastation extended to most coastal countries of the Southeast Asia and its adjoining regions. The Andaman-Nicobar (A & N) Islands was one of the worst effected Indian states due to this killer tsunamigenic earthquake.

Six three-component digital short period seismograph (4-Reftek and 2-Kinemetrics)stations were established in different parts of the A & N Islands, covering Car Nicobar, Hutbay, Port Blair, Rangat, Diglipur, and Narcondum. About 18,000 aftershocks (M ≥ 3.0) were recorded during the period from January 6 to March 16, 2005. Here, we present analyses of data recorded up to January 31, 2005. The aftershocks attenuation with time follows the power law t

-p, which stands

valid for the entire tectonic region of A & N Island, sudden burst of aftershocks activity was also observed. Estimate of p-value = 0.9532 is near to normal value of 1.0, which suggests a slow decay sequence of aftershock with complex and non-uniform stress change in a fault system (creep effects and history dependent stress changes). The frequency-magnitude relation of the aftershocks also followed the power law with average b-value = 0.7723 and it varies from 0.49 to 1.03, indicating the compressive stress state of the region and its heterogeneous structure.

The aftershocks are located by one-station, two-station and multi-station methods depending on the availability of the data, and 1177 events (M ≥ 3.0) are located that were recorded till January 31, 2005 using multi-station technique. The epicenter map shows a N – S trending aftershock cluster in an area of about 750 × 300 km2, which reflects an approximate rupture dimension of the mainshock beneath the study area; the ruptures propagated heterogeneously. The stress release,stabilization of the A & N Islands and decay of aftershocks may take several months or even years because of the large rupture dimension, about 1300 km from the north Sumatra to north Andaman as reported by the USGS.

Depth estimate of the aftershocks was not accurate because of poor azimuthal coverage and occurrence of aftershocks outside the seismic network in the region. One-station and two-stationmethods provide epicenter locations with poor depth constraints. Multi-station method, however, provided fair estimate of focal depth for nearby events. Aftershocks occurring outside seismicnetwork are located using differential time technique of converted depth phase, sP and direct P- and S-phases, detected on the recorded seismograms for more than one-station. The aftershocks occurred mostly at the depth range of 5 – 55 km, except a few beyond this depth range.


116

We determined fault plane solutions of aftershocks recorded by temporary seismic network, occurred at three different depth ranges (0-15; 16-30; and >31 km) in ten sub-blocks of the A & N Islands and found that rupture propagated by normal, reverse and strike-slip faulting. The aftershocks occurred off the subducted plate at a much shallower depth (< 10 km), and are caused due to local tension in the overriding plate. The area in the vicinity of Barren volcanic zone shows normal tostrike-slip faulting due to predominant tensional forces, suggesting facilitation of brittle failure in the weakened crust by the process of under-heating. The Narcondum volcanic zone exhibits thrust faulting, indicating regional compressive stress, and the effect of under-heating is possibly not prevalent in the month of January 2005 as Norcondum is dormant for few years.

INTRODUCTION

The devastating megathrust earthquake of December 26, 2004, occurred at the interface of the India and Burma plates and was caused by the release of stresses that develop as the India plate subducts beneath the overriding Burma plate (Bilham, 2005). The India plate begins its descent into the mantle at the Sunda trench, which lies to the west of the earthquake's epicenter. The trench is the surface expression of the plate interface between the Australia and India plates, situated to the southwest of the trench, and the Burma and Sunda plates, situated to the northeast (Fig. 1). This is the second largest earthquake after the 1960 great Chilean earthquake (Mw 9.5), which caused a huge devastation in most countries of Southeast Asia (Kanamori and Cippar, 1974). The region has been associated with several past damaging tsunamigenic earthquakes (Table 1) that caused enough damage to both property and person (Petroy and Wiens, 1989; Zhou et al., 2002., Ortiz and Bilham, 2003).

The 26 December 2004 tsunamis caused damage in the entire coastal countries of southeast Asia, which crossed into the Pacific Ocean and was recorded in New Zealand and along the west coast of South and North America (USGS). The earthquake was felt (VIII) at Banda Aceh, (V) at Medan, Sumatra, and (II-IV) in parts of Bangladesh, India, Malaysia, Maldives, Myanmar,Singapore, Sri Lanka and Thailand. The earthquake was severely felt in the entire Andaman-NicobarIslands including Diglipur (north Andaman) and Mayabandar (middle Andaman) that caused severe cracks in the well-built buildings and dislocations in pillars and floor of the Austin bridge which connects middle Andaman and north Andaman. Strong earthquake shaking, however, caused cracks and collapse of buildings leaving many injured, which in turn may suggest the severe shaking could have resulted in easy collapse and more damage by subsequent tsunamis. A mud volcano near Baratung, Andaman Islands began erupting on December 28, 2004 following the earthquake. The pattern of damage provided us a vital clue to recognize the zone of the mainshock rupture, where setting up of temporary 3-component digital seismographs were made.

Setting of Seismographs and Aftershocks Recording

It is observed that four large aftershocks (M > 6.0) occurred in a well- defined trend, extending from the south to north (Fig. 1). Several aftershocks (M ≥ 5.0) were reported to

occur in the Andaman-Nicobar region by National Earthquake Information Center, USGS(Fig. 2). Five digital seismographs were installed at Port Blair, Carnic, Hutbay, Rangat, and Diglipur despite poor azimuthal coverage. Fortunately, these are places which comparativelyaccessible in comparison to that of other adjoining areas of Andaman – Nicobar Islands. The station spacing ranges from 90 to 130 km. One seismograph was installed in the volcanic zone of Narcondum for better coverage in the north Andaman region (Fig. 1). Efficientinstrument parameters are set up under event- triggered mode for recording more number of

aftershocks. The seismographs were operated by rechargeable Power-safe battery of 100


117

ampere hour and the seismographs were incorporated with Global Positioning System (GPS)

for getting precise co-ordinates of station locations and for high precision time. Thelocations of the seismograph stations are given in Table 2.


118

Table 1: Past damaging tsunamigenic earthquakes in Sumatra-Andaman region

(Petroy and Wiens, 1989; Zhou et al., 2002; Ortiz and Bilham, 2003)

Year of occurrence Place of occurrence Magnitude (Mw)1797 Centralwestern Sumatra 8.41833 Southwestern Sumatra 8.71843 Southeast Nias 8.01861 Western Coast Sumatra 8.51881 Car-Nicobar 7.91941 Andaman Islands 7.72000 Pagai Island 7.82002 Simeulue Island 7.6

Table 2: Details of seismograph stations that installed in different parts of theAndaman-Nicobar Islands following the 26 December 2004 mainshock (Mw 9.3)

Place of Installation

StationCode

Latitude(in

degree)

Longitude(in

degree)

Date of Installation

Date of Removal

Type of the Seismograph

Port Balir PBR 11.6559N 92.7316E 06.01.2005 16.03.2005

3-component SP DigitalinstrumentREFTEK(U.S.A)1hz, 24 bit;130db

CarNicobar CNB 09.1545N 92.8219E 08.01.2005 13.03.2005 Do

Hutbay HTB 10.5967N 92.5364E 11.01.2005 12.03.2005 Do

Rangat RGT 12.5072N 92.9134E 13.01.2005 14.03.2005 Do

Diglipur DGP 13.2465N 92.9763E 17.01.2005 15.03.20053-component SP

Digitalinstrument

KINEMETRICS(U.S.A)

1hz, 24bit;130db

Narcondum NCD 13.500N 94.300E 08.03.2005 16.03.20053-component SP

DigitalinstrumentREFTEK(U.S.A)


119

This seismic network consisting of 6-stations was continuously monitored to recordoccurring in the Andaman & Nicobar Islands and its adjoining region. A total of about 18,000aftershocks were recorded between January 6, 2005 (16:30 IST) and March 16, 2005 (24:00 IST) (Fig. 3) with an average of 240 aftershocks in a day during the month of January, 2005 (Fig.4a-e).Seismograms recorded at 6-digital seismic stations are very much informative. Data recorded till January 31, 2005 are analyzed, and an attempt has been made to understand seismotectonics of the aftershocks in the Andaman-Nicobar forearc region.

Seismotectonic Setting

The Burma-Andaman arc marks the eastern margin of the Indian plate along which an oblique convergence is suggested by many authors (e.g. Fitch, 1970; Curray et al., 1979; Verma et al., 1978). The nature of convergence varies from continental type in the Burmese arc to oceanic type in the Andaman arc. Based on seismic activity, the region is grossly divided into three zones: The Burmese Arc (20-28

0N), the north Andaman arc (7-15

0N) and the south Andaman arc (0-7

0N), (Fig.

5). The central portion (15-200N), which is charactersied by low seismicity, marks a transition zone between the two arcs, the Burmese arc and the north Andaman arc (Chandra, 1984). West of the island arc is the Andaman-Nicobar Trench; it is linked with the Sunda Trench in the south. The trench is a buried feature off Andaman-Nicobar Islands, and is filled with Bengal-Nicobar fan sediments. The Burma sub-plate often referred to an overriding sliver plate or subduction fault zone, forms western segment of the main Sunda plate. Oblique convergence of the India plate develops arc parallel strike-slip faults all along the edges of the sliver plate that is also folded and uplifted in strips, as the sub-plate rides over the subducted India plate.


120

The major tectonic features in the region are the N-S trending Indo-Burma ranges in the north, Andaman - Nicobar Islands in the south and the Sumatra fault system to the southeast (Fig.1). The Andaman sea basin is considered to be a complex backarc spreading center. The sliver plate runs along the plate convergent boundary from northern Burma past Sumatra and possibly past Java. InBurma, the eastern border of the sliver plate, is defined by the dextral Sagaing fault zone (Curray, et al., 1979) and the western fringe is marked by the Arakan-Yoma accretionary subduction complex (Fig. 1). At the Andaman Sea, the western domain is composed of Andaman-Nicobar Trench and accretionary subduction complex ridges. The oceanic layer between the Andaman-Nicobar group of Islands and the Andaman Sea spreading center, in the east, is made up with complex north-southtrending faults, Nicobar rift valley and westward tilting little deformed cuesta of sedimentary frontal arc ridges (Invisible Bank). The West-Andaman-Fault (WAF) is most prominent all along the Andaman - Nicobar Islands, which appears to be continuous from west off of northern Sumatra towhere it is lost beneath the terrigenous fill of the Irrawaddy – Martaban shelf (Curray et al., 1979). Focal mechanism studies indicate that WAF is a north-south oriented dextral strike-slip fault (Fitch, 1972) (Fig. 1). Further east, the line of this fault is marked by the proximity of volcanic islands (Barren and Narcondum) and seamounts (Alcock and Sewell). The inner volcanic arc forms a belt with discontinuous submarine ridges of volcanic seamounts and the andesite volcanoes of Barren and Narcondam Islands (Hamilton, 1979). The Narcondam is now extinct but the Barren is still marked by an active volcano; it erupted in March 1991 after lying dormant for about two centuries (Haldar et al., 1992).

Andaman-Nicobar region has high seismic potential and it falls in the highest seismic hazard zone V, on par of the Himalayan collision zone. A detailed study of past seismicity for the period 1916-1975 in the Andaman Sea was illustrated by (Verma et al. 1978). Dasgupta and Mukhopadhyay (1993) and Dasgupta et al. (2003) studied subduction tectonics at Andaman arc and reported an east-

dipping (40 -55°) Benioff zone down to about 200 km focal depth in the forearc. Kumar et al. (1996)

studied 167 Harvard Centroid Moment Tensor (CMT) data in the Burma and Andaman arc regions for the period 1977-1992. They reported distinct tectonic patterns between the northern and southern parts of the Andaman. Orientations of the P and T axes in the southern part indicate active subduction along the slab, whereas in the northern part the focal mechanisms do not conformable with local trend of the arc. Presence of deeper (depth>90 km) thrust events is in disagreement with the observation of Le Dian et al. (1984). The shallower (depth < 10 km) off the slab events show normal and strike-slip faulting. Kayal et al. (2004) made aftershock investigation of the 13September 2002 earthquake (Mw 6.5) and reported a transverse seismogenic structure to the north of Andaman Islands. A detailed study of satellite gravity data in the region was made by Ghosh (1997) to get 2-D subduction model in the Andaman Sea basin. Regional distribution of backgroundseismicity shows distinct tectonic patterns in northern and southern parts of the Andaman-NicobarIslands.

December 26 2004 Sumatra -Andaman Mainshock (Mw 9.3)

Earthquake parameters of the mainshock of December 26, 2004, in the Indian Ocean and four large aftershocks occurred within 12 hours of the mainshock were estimated by the USGS (US Geological Survey), National Earthquake Information Centre (NEIC), which are given in Table 3. The mainshock shows 1.48 X 10

30 dyne-cm as its seismic moment which is almost equivalent to the

1960 great Chilean earthquake (Mw 9.5) that associated with a seismic moment of 2.7 X 1030

dyne-cm (Kanamori and Cippar, 1974). The moment magnitude of the 26 December 2004 earthquake has been modified from Mw 9.0 to Mw 9.3 based on the normal mode theory of vibration(Stein and Okal, 2005). The USGS determined the Centroid Moment Tensor (CMT) solution thatshows a low angle thrust faulting (Figure 1). The fault plane details are given in Table 4.


121

Table 3: Earthquake parameters of the 26 December 2004 mainshock and four bigaftershocks that occurred within 24 hours of the megathrust mainshock

Earthquake Origin time LocationLat. Long

Depth(km)

Magnitude(Mw)

Type of Faulting

Source

Themainshock

2004.12.2600hh: 58mm:

53.4ss

3.30N 95.98E 28.6 9.0 (USGS)9.3 (Steinand Okal,

2005)

Thrust IRIS,NEIC

The Ist big

aftershock2004.12.2604hh:21mm:

26ss

6.90N 92.95E 10.0 7.3 Thrust do

The 2nd

big aftershock

2004.12.2609hh:20mm:

1.6ss

8.88N 92.38E 16.1 6.6 Thrust do

The 3rd

big aftershock

2004.12.2610hh:19mm:

29.7ss

13.45N 92.79E 10.0 6.4 Thrust do

The 4th

big aftershock

2004.12.2611hh:05mm

00.5ss

13.54N 92.88E 10.0 6.3 Thrust do

Table 4: The Centroid Moment Tensor (CMT) solution of the mainshock (Mw 9.3)Best double couple solution by USGS


122

Principal AxesNodal Plane 1 Nodal Plane 2

P T N

Strike Dip Rake Strike Dip Rake Az Pl Az Pl Az Pl

N31W 8 110 S51E 83 87 222 38 36 52 130 03


123

Larger Aftershocks (M ≥≥ 5.0)

About 150 aftershocks (Mw ≥ 5.0) were recorded by different seismological institutions of India (IMD) and abroad (USGS and IRIS) within one month of the mainshock (Fig. 2).

Seismological parameters are given in Table 6. Four largest aftershocks (M ≥ 6.3) occurred within 12 hours at a shallower depth (≤ 25 km), comparable with the mainshock faulting (Fig. 1). Normally largest aftershock occurs within 24 hours with a 1.0 – 1.5 magnitude units lower than the mainshock. The first largest aftershock (Mw 7.3) occurred near Campbell in the Great Nicobar Island within 3 hours of the mainshock (Mw 9.3), and subsequently, three other aftershocks occurred at Carnicobar (Mw 6.6), Rangat (6.4), and Diglipur (6.3) along the mainshock rupture direction (Fig. 1). The USGS and Harward University reported CMT solutions for the mainshock and these aftershocks. All these four aftershocks occurred dominantly by thrust faulting as that of the mainshock.

AFTERSHOCK INVESTIGATION BY TEMPORARY NETWORK

Frohlich (1989) defined an aftershock as a secondary earthquake following a stronger primary one (the mainshock) whose location and time of occurrence are a direct result of theoccurrence of the mains hock. This definition is regarded as a fundamental definition and it is in unison with that given by Kisslinger (1996). One characteristic of aftershock sequences since the beginnings of observational seismology is that the rate at which the events occur decrease steadily with time after the mainshock. Detection and recording of aftershocks in the source zone by dense seismic network (permanent and temporary) may shed important lights on aftershock sequences,local tectonics, dimension of rupture zone and seismic imaging of the crustal heterogeneity and its bearing on the genesis of earthquakes (Kisslinger and Hasegawa, 1991).

Six temporary seismic stations were set up in the Andaman-Nicobar Islands as mentioned above to monitor the aftershocks. Due to several geographical locations, it was not possible to obtain a good azimuthal control in laying the temporary network. However, we made a best possible network and managed to monitor all installed seismographs continuously using Air, Sea and road conveyances with the help of Andaman-Nicobar district administration. Out of 18000 recorded events, about 15,000 common events were recorded by three or more stations, 2000 by two stations and as many as 960 tremors were recorded at a single station at Port Blair. Here, we present analyses of data, which were recorded up to January 31, 2005.

DATA ANALYSIS

Velocity Model

Earthquake location program requires a good velocity model given by Kayal et al. (2004) for computations. The following velocity model (after Kayal et al, 2004), which is based on the study of DSS (Deep Seismic Soundings), gravity data and knowledge of the geological information, is used for the earthquake location analysis:

Velocity (Vp) Depth

(km/s) (km)4.50 05.60 3

6.80 10 8.00 25 8.25 50


124

The moho depth at 25 km is taken from gravity study (Ghosh, 1997). The DSS results show that in the eastern shield margin the velocity (Vp) range is 5.6-6.2 km/s for the upper crust and 6.2-7.2 km/s for the lower crust (Kaila and Tewari, 1986). The computer program also requires Vp/Vs for computation of the S wave arrival times. We used an average Vp/Vs 1.74 for the computation.

Aftershock Location

Precise location of an earthquake requires high precision P- and S- phase arrival data recorded by a network with good azimuthal coverage. Further, it needs at least four seismic phase data for the multiple regressions to estimate the four parameters of an earthquake: the origin time, latitude and longitude of the epicenter and focal depth.

Although we had high precision digital data, we had many constraints for precise location of the aftershocks. The main constraint was the poor azimuthal coverage of the network. Further, as the seismic stations at all six locations were far away from the main shock epicenter; smaller magnitude (M<3) aftershocks, were not recorded by these stations. However, the mainshock rupture propagated up to north Andaman and our seismic stations were established up to the northern part of 600 km rupture segment that extends from Carnicobar to Diglipur (Figure1). So, we recorded a large volume of aftershock.

The common events recorded by multi-seismic stations were quite high, about 1200 events were till 31 January, 2005 due to the adequate distances between stations. The higher magnitude (M>5.0) aftershocks were, however, recorded by the global stations. We also attempted to locate the aftershocks using the following methods to prepare PDE files:

i) Multi-Station method,ii) Two-Station method,iii) Single-Station method.

Multi-Station Method

This is the common method of locating earthquakes. We used minimum 3P and 3S phases recorded by at least three stations. The data are analysed by using the SEISAN computer program (Havskov and Otte moller, 2000). Total 1177 events, recorded by three or more stations (up toDecember 31, 2005), are analysed by this method. Epicenter and focal depths are fairly wellestimated (Fig. 5). The seismic (P & S) phases from multi-stations were used during location (Figs 6 – 7). However, the events occurred outside the seismic network in the forearc are required to be relocated using sp-depth phase for better depth estimates (Mishra et al., 2003; Mishra and Zhao, 2004) The epicentre map is shown in Figure 5. The estimated parameters are shown in Table 7.

Two-Station Method

Although two seismic stations provide four seismic phase data (2-P and 2-S), good control on depth or on the epicentre are not obtained due to large azimuthal gap. It is, however, possible tohave a better control on the hypocentre location by incorporating back azimuth of one of the stations. The back azimuth is estimated using the three - component seismograms by the SEISAN program. Out of 2000 events recorded by at least two stations, 77- aftershocks (up to January 31, 2005) are located using the two-station method. The epicentres of the 77 aftershocks are fairly well located but not the focal depths; the epicentre map is shown in Figure 8 and some sampes of seismograms recorded by two stations are shown in Figures 9 -10. The estimated parameters are shown in Table 8.


125


126

One -Station Method

Single station three component digital seismograms may also be used for an estimate of epicentre location. Roberts et al. (1989) illustrated epicentre location of an earthquake using single station three-component seismic data. This method is now popular to have an estimate of epicentre from the three component records at an observatory immediately after an earthquake. The arrival times of P and S phases and the back azimuth (from station to source) are used for estimation of origin time and epicentre (latitude and longitude). The ratio of horizontal component amplitudes (east-west and north-south) at P arrival is used to derive back azimuth. We used the SEISAN program to estimate the back azimuth.

This technique is, however, used only to estimate origin time and epicentre; focal depth cannot be determined by this method. 165 events were recorded by single station (mostly at Port Blair). 165 events are reliably located by repeatable azimuth and positive covariance (Fig. 11). The method uses a fixed depth for epicentre location. We used 30 km as fixed depth, as most of the aftershocks located by the multi-station method occurred at a depth range 15-55 km. Samples of seismograms recorded on single station are shown in Figures 12 – 13. The estimated parameters are shown in Table9.


127


128


129


130

Epicenter Map

Thus a total of 1419 events are located by the three different methods. Details of these events are given in Tables 7 - 9. Epicenter map of all these events are shown in Figure 14. The map shows a NW-SE trending cluster of aftershocks within an area 750 x 300 km

2. Some epicenters are away

from the N-S cluster of aftershocks; these may be local events triggered by the mainshock or by reactivation of local fault system by the mainshock.

Aftershock Magnitude

In microearthquake survey, particularly with the analog records, duration magnitude ismostly estimated as amplitude of the higher magnitude (M>3) earthquakes are clipped. Duration magnitude of an event is estimated using the following relation: Md = - 0.87 + 2109 (T) + 0.0035D, where Md = duration magnitude, T = signal duration in sec and D = epicentral distance in km. The above relation is obtained by least square fit of the Richter magnitude and signal duration data of known earthquakes (Lee et al., 1972). Hence, computed Md is comparable with the Richter Magnitude (ML). The digital seismographs, however, have an advantage of recording earthquakes with its full amplitude. Thus it is possible to estimate magnitude using the recorded maximumamplitude of an earthquake. For estimation of ML equivalent amplitude of Wood AndersonSeismogram is required. The SEISAN program has the facility of computing Richter magnitude (ML)using the equivalent Wood - Anderson amplitude of the digital seismograms. The estimatedearthquake magnitudes are given in Tables 7-9.

Aftershock Attenuation

The modified Omori law describes aftershock activity on frequency-decay with time, which

follows the power law n(t) α t-p

, where p is the rate of aftershock decay with time and n(t) is the number of aftershocks in unit interval of time (Watanabe, 1989). The p-value is the slope of log-logrelation. The p - value is normally equal to 1.0, but it is observed that it varies from 0.5 to 2.5 (Guo and Ogate, 1995, Nanjo et al., 1998).

All the six seismic stations established along the rupture zone that propagated in theAndaman-Nicobar Islands. They recorded maximum number of aftershocks. We installed the first seismograph station on January 6, and it was in operation till March 16, 2005. Temporal variation of the aftershocks recorded by seismograph stations are shown in Figures 4 (a - e), and the computed p-value is shown in Figure 15. The observed p-value = 0.9532, which is near to normal value 1.0. This estimate may suggest a slow decay sequence of aftershock along with complex and non-uniformstress change in a fault system (creep effects and history dependent stress changes) (Gavrilenko, 2005).

Frequency - Magnitude Relation

The frequency-magnitude relation is also characterised by power law: Log10N = a - bM, where N is cumulative number of earthquakes of magnitude M, and a and b are constants (Gutenberg and Richter, 1954). It is a log-linear relation, the constant b is known as b-value, and is normally close to 1.0. The b-value, however, varies from 0.5 to 1.5 depending on tectonic setting, tectonic stress, magnitude ranges etc. (Scholz, 1990; Weimer and Wyss, 1997). The b-value is an indicator of structural heterogeneity in 2-D fault plane, which varies from region to region depending upon its tectonic behavior. The pattern of expansion of the aftershock zone differs from one tectonic regime to another, and the expanding limits of that zone are related to the distributions of strength and stress on the fault. This is why we divided the entire Andaman-Nicobar region into ten blocks depending on aftershocks concentration and geotectonic settings for estimating b-value in each block and then its overall average value.


131


132

The b-value is estimated using the aftershocks located in this study (Fig. 5). It is, however, observed that the threshold value of magnitude is 4.5, above which more or less all aftershocks arelocated. Thus more than 250 aftershocks (M>3.0) were available for b-value estimation in each block (Table 5). The b-value varies from 0.49 to 1.03. The usual least-square fit method was applied to estimate the b-value and it was found to be 0.7723 as overall value in the entire Andaman-Nicobarregion, which is lesser than the normal value 1.0 (Fig. 16), indicating a compressive and veryheterogeneous structure of the region.

Table 5: Showing ‘b’ values in the different blocks with corresponding ‘a’ values

Location of Blocks LogN = a – bM Parameters ‘a’ and ‘b’

BlockNumber

Latitude Longitude ‘a’ ‘b’

Block 1 9 – 10N 92 – 93E 5.77 0.89

Block 2 10 – 11N 92 – 93E 5.52 0.83

Block 3 11 – 12N 92 – 93E 5.61 0.83

Block 4 12 – 13N 92.5– 93.5E 6.34 1.03

Block 5 13 – 14N 92.5-93.5E 4.96 0.77

Block 6 11.5– 12.5N 93.5-94.5E 3.56 0.49

Block 7 11 – 13N 91 – 92E 4.07 0.58

Block 8 9 -11N 93 -95E 5.39 0.79

Block 9 11.5 -14N 94 – 96E 3.82 0.50

Block 10 7 – 9N 93.5 – 96E 4.15 0.63


133

Figure 16b. b- value estimation in different blocks


134

The b-value is also estimated by the Maximum Likelihood method, which is based ontheoretical consideration (Aki, 1965). The b-value is estimated by the following formula :

logeb = ------------

M - M min

where M is average magnitude and Mmin is minimum magnitude in the given sample data. The estimated b-value for the aftershock sequence is found to be 0.69. The value is comparable with that estimated by the least square method.

Fault-plane Solution

Fault-plane solutions of the aftershocks play an important role in understanding themain shock and aftershock generating processes. We selected the aftershocks at varyingdepths (0-15; 16-30; > 31km) in each block (Fig. 14) and plotted the reliable first motiondata on the lower hemisphere by the SEISAN program. It is evident that the solution is fairlyconstrained; all types of faulting normal, thrust, and strike-slip solutions are obtained indifferent tectonic blocks (Figs. 17-18). The descriptions of solution parameters are given inTable 10. The Bartung mud volcanic zone is associated with thrust faulting where the mudand slurry materials were ejected to the surface on December 28, 2004 just after themainshock. The zone, comparatively near to the mainshock (near Carnic), generally strike-slip to normal fault solutions. It is important to note that the region of Barren volcanic zoneshow normal to strike-slip faulting that may indicate crustal weakening due to under-heatingand contributing to dominant local tensional stress, which may facilitate the brittle failure(Tatsumi, 1989; Zhao et al., 2002), whereas the Narcondum volcanic zone shows thrustfaulting, indicating that the effect of under-heating is possibly not prevalent as Narcondumis dormant for few years, and seismogenic strength is possibly due to regional compressivestress. The zone near Narcondum may relatively be compact in comparison to that of Barren

volcanic zone. The region near Andaman Trench shows thrust faulting, the compressivestress acting normal to the trench. Some deeper events (>31 km) show normal faultingindicating the events in the subducted Indian plate and generated by bending (tension) of thesubducted plate.

Depth Section

As explained above, focal depth estimate of the aftershocks was not well constrained due to poor azimuthal coverage of the temporary network as well as the occurrence of aftershocks outside the seismic network. The one-station method used a fixed depth to estimate the epicenter and origin time. The two-station method did not provide reliable focal depth. About 1177 events were located by the multi-station method. An E-W depth-section of these 1177 events along 9

0N latitude is shown

in Figure 19. The depth section shows an east dipping seismic zone, which is similar to that obtained by Kayal et al. (2004). However, focal depths of forearc aftershocks are still poorly constrained. In order to overcome this constraint, we have to relocate focal depths of aftershocks by using converted phases between direct P- and S-arrivals. We detected sP-depth phase on recorded seismogram, which may be used to estimate accurate focal depths of aftershocks that occurred outside the seismic network in the forearc region. This technique of relocating depth of forearc and backarc aftershocks has been used (Mishra et al., 2003; Mishra and Zhao 2004) for Japan subduction zone.


135


136

Table 10a. Composite Fault-plane solutions of aftershock clusters at three different depth rangesin ten different blocks

Inferred Fault-planeBlock No. Depth Range (km)

Aftershock clusters at

three depth rangesStrike Dip Rake/

SlipType ofFaulting

0-15 129.1 33.2 -61.8 NF

16-30 283.7 74.4 -43.8 NF

1

≥ 31 183.9 79.1 -65.5 NF

0-15 298.9 83.3 -18.9 NF

16-30 309.4 59.3 -23.6 NF

2

≥ 31 250.9 41.4 -40.9 NF

0-15 344.2 35.4 61.6 TF

16-30 138.1 70.5 23.2 RF

3

≥ 31 169.0 71.3 23.9 RF

0-15 123.9 83.3 -18.9 NF

16-30 300.0 50.0 -90.0 NF

4

≥ 31 306.5 82.4 -49.6 NF

0-15 107.7 63.5 -59.5 NF5

16-30 357.6 35.3 72.5 TF

0-15 332.5 49.0 51.5 TF6

≥ 31 140.0 41.6 -46.9 NF

0-15 323.8 62.4 -16.9 NF

16-30 189.0 33.0 -90.0 NF

7

31 288.0 42.0 -90.0 NF

0-15 257.8 44.0 60.5 TF

16-30 40.2 24.7 -75.5 NF

8

31 202.7 50.5 -79.6 NF

0-15 136.0 71.3 -23.9 NF

16-30 194.7 74.4 -43.8 NF

9

31 19.2 83.7 -13.6 NF

0-15 270.4 85.0 8.7 SSF10

31 304.0 62.0 -90.0 NFNF : Normal Fault; TF : Thrust Fault; RF : Reverse Fault; SSF : Strike-slip Fault

sP-depth phase and depth location

The sP-depth phase data are used for relocating these aftershocks, which occurred outside of seismic network. The sP depth phase is a remarkable later phase, radiated as an S-wave from an earthquake under the subducted lithosphere, reflected at the ocean floor and at the same timeconverted to P-wave and subsequently recorded by land seismometer as P-wave (Fig. 20a). The sP depth phase appears clearly between the P- and S-wave arrivals predominantly on verticalcomponents of the recorded seismograms (Fig. 20b). There are several criteria to detect sP-depthphase from the recorded seismograms. The reliability of focal depth by sP-depth phase is very high and it is as accurate as Ocean Bottom Seismometer (OBS) observation (Mishra et al., 2003). Infuture, extensive exercise to detect sP-depth phase is needed to relocate aftershocks accurately for determining geometry of the subducting Indian plate and subduction 3-D images in Andaman-Nicobar Islands.


137

Table 10b. Composite Fault-plane solutions of aftershock clusters at three different depth ranges inten different blocks

Inferred Fault-planeBlock No. Depth Range (km)

Aftershock clusters at

three depth rangesStrike Dip Rake/

SlipType ofFaulting

0-15 216.1 40.8 15.5 TF

16-30 330.7 60.5 42.4 TF

1

≥ 31 176.6 73.0 17.2 TF

0-15 110.6 73.0 17.2 TF2

16-30 171.7 60.5 42.4 TF

0-15 161.0 56.0 90.0 TF

16-30 110.3 55.7 7.6 TF

3

≥ 31 169.0 71.3 23.9 TF

0-15 300.0 90.0 20.0 TF

16-30 359.0 90.0 82.0 TF

4

≥ 31 278.9 62.4 -20.7 NF

0-15 166.8 74.8 48.2 TF5

16-30 61.6 37.6 61.3 TF

0-15 197.6 61.3 46.7 TF

16-30 137.5 54.1 -37.5 NF

6

≥ 31 355.3 62.3 -34.3 NF

0-15 332.7 83.6 -39.6 NF7

31 285.0 35.0 -90.0 NF

0-15 229.4 35.5 53.9 TF

16-30 116.7 62.4 -50.9 NF

8

31 219.0 51.8 -69.5 NF

0-15 261.3 62.3 -34.3 NF9

16-30 152.7 65.6 -32.7 NF

0-15 90.0 90.0 0.0 SSF10

31 290.0 55.0 -90.0 NFNF : Normal Fault; TF : Thrust Fault; RF : Reverse Fault; SSF : Strike-slip Fault


138


139


140

DISCUSSION AND CONCLUSION

The Andaman Islands are far way from the mainland of India. Detailed seismotectonics or structural studies by close - spaced seismological network are not made in the past. The aftershock investigation of the September 13, 2002 earthquake sequence in the Andaman Islands was the first survey of its kind, which was confined to the north Andaman. Sudden occurrence of big megathrust earthquake (Mw 9.3) in north Sumatra provided us an opportunity to collect huge number of aftershocks in the Andaman-Nicobar Islands for understanding the earthquake generating processes, seismogenic structure/source area of the aftershocks in the regions of forearc and backarc ofAndaman-Nicobar Island. The outcome of this study may be useful for evolving a comprehensive earthquake hazard mitigation model in near future. This investigation provided close-spacedmicroearthquake network data, which is very useful in understanding the geodynamical processes of the region.

Although due to inaccessibility in the sea the temporary six-station network lacks a good azimuthal coverage, the epicentral locations are made with a fair degree of precision by different methods, and the observed source area is fairly consistent. Three methods were applied to make maximum use of the digital seismic data for epicentre determination. The epicentre maps produced by the three methods show a consistent N-S trending aftershock zone (Fig. 14). Epicentres of all the 1419 aftershocks located in this study are shown in Figure 14; this map shows aftershock cluster area 750 x 300 km

2, oriented to N-S direction. However, aftershocks concentration is clearly visible to its

east and west, indicating heterogeneous propagation of the mainshock rupture in the Andaman-Nicobar Islands. The USGS locations of the main shock and the larger aftershocks fall within this aftershock zone (Fig. 2). The aftershock cluster delineated in this study reflects the rupture area beneath Andaman-Nicobar Islands.

The aftershock zone is well defined by the close-spaced temporary network. It has provided a good data set showing a better picture of the aftershock zone (Fig. 5). It is interesting to note that the global data (M ≥ 5.0) (Fig. 2) shows two prominent gap zones near 100N latitude, where almost

no aftershock (M ≥ 5.0) occurred. Two maps are compared in Figure 21. Our aftershock map (Fig. 21) revealed that these gaps witnessed many aftershocks of magnitude lesser than 5.0. This close-spaced temporary network data proves the efficacy of microearthquake investigation. Thisobservation was useful to minimize the local panic that there may not be a chance of a bigearthquake in these gap zones. We found that the entire Andaman-Nicobar Islands is associated with all three classes of aftershocks (initial aftershocks, describe the mainshock rupture; represent the growth of original aftershock zone; triggered distant events by reactivation of pre-existing fault system by the mainshock) that propagated from Nicobar to Andaman towards unlocked or decoupled zone (Fig. 1).

Depth estimate of the aftershocks located by the two-station method is not well constrained, and the estimate could not be made by the single-station method. Thus we have only 1177aftershocks with a good estimate of depth, which are located by the multi-station method. The global network located almost all the aftershocks (M>5.0) with some restricted depths at 10 and 33 km (Table 6). The deeper event may be a local event, not an aftershock. Depth section of the temporary network data shows an east dipping seismogenic structure (Fig. 19).

As explained above, fault-plane solutions of the main shock (MW 9.3) and the largest aftershocks (MW 6.3 - 7.3) are compatible (Fig. 1). The northeast dipping NW-SE nodal plane is comparable with the observed aftershock trend and oblique subduction (Fig. 1). The mainshockoccurred by a low angle thrust fault. Further, it is reported that to the north of the Andaman basin, between latitude 15

0-20

0N, there is no much seismic activity. The Burma Trench activity, farther

north, latitude 200-28

0N, is explained by northward dragging of the dipping Indian lithosphere rather


141

than by an active subduction (Le Dian et al., 1984). These evidences suggest a transition in the tectonic structure, and the low seismic activity in the central portion, latitude 15

0-20

0N, may be

explained by this transition zone, or due to presence of thick pile of deep seated Irrawady sediments that may hinder the brittle failure due to its ductility behavior. However, we located someaftershocks beyond 14

0N at 15 – 30 km depth range (Figs.5 & 14).

The subducted seismic zone as evidenced by the local seismicity and the gravity observation is used to understand the seismotectonics of the 2002 main shock and the best located aftershocks (Kayal et al., 2004). A seismotectonic model is given in Fig. 19. The largest aftershock occurred within the steeply dipping subducted plate due to regional compressional stress. These are typical interplate thrust/reverse faulting earthquakes due to subduction tectonics. CMT solutions of thrust faulting within the subducted plate at shallower (depth ~ 20 km) as well as at deeper depth (depth>90 km) in the Andaman basin area were reported by Kumar et al. (1996). They further reported normal faulting and strike slip faulting for much shallower events (depth <10 km) off the subducted plate. Our best located aftershocks at shallow (<10 km) and are located off the subducted slab; thecomposite fault-plane solution of these shallower events indicates a normal faulting. Normal faulting may be explained due to local tension in the overriding plate (Figs. 18 -19).

Two important aftershock parameters, p-value and b-value, are estimated. The p-value = 0.9532 is near to normal value1.0, indicates slow attenuation of the aftershock sequence (Fig. 15) along the large rupture length generated by megathrust tsunamigenic earthquake. The completedecay of aftershocks, however, may take several months or even a year in Andaman-Nicobar Islands.Sudden burst of activity is also noted almost all seismograph stations (Fig. 4). This is Epidemic-typeof aftershock (ETAS) is a noticeable example of this deviation (Ogata, 1988). In such case, some larger aftershocks yield new sequences of aftershocks and the deviation from the Omori’s law can be directly related to the occurrence of some large aftershocks in the region under investigation. As noticed by Dieterich (1994) time-dependent nucleation process may not be required to explain the temporal decay of aftershocks if other effects such as visco-elsatic or poroelastic processes are taken into account. A recent study made by Gavrilenko (2005) demonstrated that hydromechanicalcoupling in response to earthquake could be the possible consequences for aftershocks, showing deviation from the Omori’s law.

Andaman-Nicobar has been badly devastated and possibly associated with several minor to major sea faulting, through which permeation of huge volume of sea water into the aftershock zone can’t be ruled out. This may facilitate the occurrence of more aftershocks due to poroelastic effects and hence erratic trend of aftershock decay. Thus, we can infer that more than one variable is likely to be playing a role in determining the rate of aftershock decay. Theoretical study suggests that fault -zone heterogeneity and the rheology of the fault -zone materials, and the presence or absence of water or other pore fluids are likely to be key components for much activity. The b-value was estimated for different blocks and its variability is very significant from 0.49 – 1.03. The lower b-value, however, indicates that lower magnitude aftershocks are less, and the region as a whole is under higher stress regime.

The world's largest recorded earthquakes have all been megathrust events, occurring where one tectonic plate subducts beneath another. These include: The 1960 Chile earthquake (Mw 9.5), the 1964 Prince William Sound, Alaska, earthquake (Mw 9.2), the 1957 Andreanof Islands, Alaska, earthquake (Mw 9.2), and the 1952 Kamchatka earthquake (Mw 9.0). All have generated large ruptures. As with the recent event, megathrust earthquakes often generate large tsunamis that cause damage over a much wider area than is directly affected by ground shaking near the earthquake's rupture.


142

ACKNOWLEDGEMENT

We are thankful to the Director General, GSI, for his kind support and encouragement. Guidance and support extended by Dr. M.K. Mukhopadhyay, Sri K.Chowdhury, Dr. J. R. Kayal, Dr S. Sengupta Dy. Director Generals, GSI are gratefully acknowledged. We express our sincerethanks to Sri. Shyamal De, Sri C. S. Pathak, Sri N. P. Singh and Dr. D. Ghosh, Directors GSI, for valuable suggestions during the field survey. The authors would also like to thank Shri C. S.Venkiteswaran, Shri Basab Mukhopadhyay, Shri Angshuman Acharyya and Shri P. K. Chakraborty for helping in data processing.

We are very much grateful to the local authorities, especially to His Excellency Prof. Ram Kapse, Lt. Governor, A & Nicobar Islands, Mr. B. B. Bhatt, Ex. Chief Secretary, A & N, Mr. D. S. Negi, Chief Secretary, A & N Islands, Mr. Gyanesh Bharti, Dy. Commisioner, Dy. Commissioner of Nicobar, Mr. A. K. Singh, Suptd. Police, Mr. Ajay Chagti, Addl. Commissioner, Mr. Rajesh Kumar, Addl. Commissioner, Mr. CDQ Paul James, Director, Shipping services, Andaman-Nicobar Islands, Mr. P. Nair, Tehsildar, Diglipur, Mr. S. S. Pillai, Tehsildar, Rangat, Mr. Sunil Kumar, Tehsildar,Hutbay of Andaman Administration for their kind help and support during the field investigation. We acknowledge thanks to Carnicobar Indian Airforce base especially to Mr. Ravi Dhar, Station Commander, CARNIC, Mr. A. Srivastav, SQ. Ldr., MET (now in Hyderabad) and the entire group of Airforce pilots for providing outstanding support in monitoring seismographic stations, installed in remote places of the Islands. We sincerely thank Nandip Roy Sharma, Director, Hotel Blair for arranging several accessories to conduct the field investigation.

Last but not least, meticulous scrutiny and useful suggestions by Dr. Sujit Dasgupta,Director (Monitoring), GSI, Kolkata, GSI, Kolkata have greatly improved the presentation of our results in the present form. Almost all figures in this paper are plotted using GMT (Wessel andSmith, 1995).

REFERENCES

Aki, K., 1965. Maximum-likelihood estimate of b in the formula 108N = a-bM and its confidence limits, Bull. Earthquake Res. Inst., Tokyo Univ., 43, 237-239.

Bilham, R., Engdahl, E.R., Feldl, N., and Satyabala, S.P., 2005. Partial and complete rupture of the Indo-Andaman plate boundary 1847-2004, submitted to Seismol. Res., Letts., 21p.

Bilham, R., 2005. A flying start,then a slow slip, Science, 308, 1126 – 1127.

Chandra, U., 1984. Seismicity, earthquake mechanisms and tectonics of Burma 20-28 degree N, Geophys. J.R. Astro. Soc. 40, 367-381.

Curray, J.R., Moore, D.G., Lawver, L.A., Emmel, F.J., Raitt, R.W., Henry, M. and Kieckhefer, R., 1979. Tectonics of the Andaman sea and Burma, Am. Assoc. Pet. Geol. Mem., 29, In : Geological and Geophysical Investigations of continental margins, Ed : J.S. Watkins, L. Montadert and P. Dickenson, pp. 189-198.

Curray, J.R., Emmel, F.J., Moore, D.G. and Raitt, R.W., 1982. Structure tectonics and geological history of the northeastern Indian ocean, In : The ocean Basins and Margins, Vol. VI, The Indian Ocean, ed. A.E.M. Nairn and F.G. Stehli, pp. 399-450, Planum, N.Y.

Curray, J. R., 2005. Tectonics and history of the Andaman Sea region, J. Asian Earth Sci., 187 (25), 1 - 42.

Dasgupta, S. and Mukhopadhyay, M., 1993. Seismicity and plalte deformation below the Andaman arc, northeastern Indian ocean, Tectonophysics, 225, 529-542.


143

Dasgupta, S., Mukhopadhyay, M., Bhattacharya, A., Jana, T.K., 2003. The geometry of theBurmese-Andaman subducting lithosphere, J. Seismology, 7, 155-174.

Dickinson, W.R. and Seely, D.R., 1979. Structure and stratigraphy of forearc regions, Am. Assoc. Pet. Geol., Bull., 63(1); 2-31.

Dieterich, J. 1994. A constructive law for rate of earthquake production and its application toearthquake clustering. J. Geophys. Res. 99, 2601-2618.

Fitch, T.J., 1970. Earthquake mechanisms in the Himalaya, Burmese and Andaman Regions and continental tectonics in Central Asia, J. Geophys. Res., 75 : 2699-2709

Frohlich, C. 1989. The nature of deep-focus earthquake. Annu. Rev. Earth Planet. Sci. 17, 227-254.

Gavrilenko, P., 2005. Hydromechanical coupling in response to earthquakes:on the possibleconsequences for aftershocks, Geophys. J. Int., 161, 113-129.

Ghosh, D., 1997. Crustal modeling of parts of Indian sub-continent and Bay of Bengal usingsatellite magnetic, gravity and other available geophysical data, Geol. Surv. India Unpub Report, 20P.

Ghosh, D., Mishra, O.P., 2005. Rupture nucleations of the 26 December 2004 Sumatra-Andaman(Mw 9.3) and the 28 March 2005 Simeulue – Nias (Mw 8.7) earthquake: Futurevulnerability, Submitted to Earth Planet Sci. Letts.

Guo, Z and Ogata, Y., 1995. Correlation between characteristic parameters of aftershockdistribution in time, space and magnitude, Geophys. Res. Lett., 22, 993-996.

Gutenberg, B. and Richter, C.F., 1954. Seismicity of the Earth, Princeton University Press, New Jersey, 310p.

Haldar, D., Laskar, T., Bandopadhyay, P.C., Sarkar, N.K. and Biswas, J.K., 1992. Volcanic eruption of the Barren Island Volcano, Andaman sea, J. Geol. Soc. India, 39, 407-419.

Hamilton, W., 1979. Tectonics of the Indonesian Region, U.S., Geol. Surv. Prof. Paper, Vol. 1078,1-345.

Havskov, J. and Ottemoller, L., 2000. SEISAN : The earthquake analysis software, Institute of Solid Earth Physics, Norway.

Kanamori, H., Cippar, J. J., 1974. Focal process of the great Chilean earthquake, May 22, 1960, Phys. Earth Planet Inter. 9, 128-136.

Kaila, K.L. and Tewari, H.C., 1986. Deep seismic soundings and crustal tectonics. In : K.L. Kaila and H.C. Tewari (Eds), Proc Int. Symp. on Deep Seismic sounding traverses, Assoc. Exp. Geophys. India.

Kayal, J.R., De, Reena, Sagina Ram, Srirama, B.V., Gaonkar, S.G., 2002a. Aftershocks of the 26 January, 2001 Bhuj earthquake in western India and its seismotectonic implications, J. Geol. Soc. India, 59, 395-417.

Kayal, J.R., Gaonkar, S.G., Chakraborty, G..K., Singh, O.P., 2004. Aftershocks and seismotectonic implications of the 13 September 2002 Earthquake (Mw 6.5) in the Andaman Sea Basin, Bull. Seismol. Soc. Am. 94, 326-333.

Kisslinger, C., 1996. Aftershocks and fault-zone properties, Advance Geophys. , 38, 1-36.

Kisslinger,C., Hasegawa, A., 1991. Seismotectonics of intermediate-depth earthquakes fromproperties of aftershock sequences, Tectonophysics, 197, 27-40.


144

Kumar, M.R., Rao, N.P. and Chalam, S.V., 1996. A seismotectonic study of the Burma andAndaman arc regions using centroid moment tensor data, Tectonophysics, 253 : 155-165.

Le Dian, A.Y., Tapponnier, P. and Molnar, P., 1984. Active faulting and tectonics of Burma and surrounding regions, J. Geophys. Res., 89; 453-472.

Lermo, J.F., Francisco, S. and Chavez-Garcia, J., 1993. Site effect evaluation using spectral ratios with only one station, Bull. Seism. Soc. Am., 83, 1574-1594.

Mishra, O.P., Zhao, D., Umino, N., Hasegawa, A., 2003. Tomography of northeast Japan forearc and its implications for interplate seismic coupling, Geophys. Res. Letts., 30,10.1029/2003GL017736.

Mishra, O.P., Zhao, D., 2004. Seismic evidence for dehydration embrittlement of the subductingPacific slab, Geophys. Res. Letts., 31, 10.1029/2004GL019489 L09610.

Nanjo, K., Nagahama, H. and Satmura, M., 1998. Roles of aftershock decay and the fractal structure of active fault systems, Tectonophysics, 287, 173-186.

Ogta, Y., 1988. Statistical model of aftershocks temporal behaviour, J. Am. Statist. Assoc., 83, 9-27.

Ortiz, M., Bilham, R., 2003. Source area and rupture parameters of 31 December, 1881, Mw 7.9 Car Nicobar earthquake estimated from Tsunamis recorded in the Bay of Bengal, J. Geophys. Res., 108, 2215- 2230.

Petroy, D.E., Wiens, D.A., 1989. Historical seismicity and implications for diffuse plateconvergence in the northeast Indian Ocean, J. Geophys. Res., 94, 12,301 – 12,319.

Roberts, R.G., Christoffersson, A. and Cassidy, F., 1989. Real time event detection, phaseidentification and source location estimation using single station three component seismic data, Geophys. J. Roy, Astro. Soc., 97 : 471-480.

Scholz, C.H., 1990. The mechanics of earthquakes and faulting, Cambridge Univ. Press,Cambridge.

Stein, S., Okal, E. A., 2005. Speed and size of the Sumatra earthquake, Nature, 434, 581-582.

Tatsumi, Y., 1989. Migration of fluid phases and genesis of basalt magmas in subduction zones,Geophys. J. Res., 94, 4697 - 4707.

Verma, R.K., Mukhopadhyay, M and Bhuin, N.C., 1978. Seismicity, gravity and tectonics in the Andaman sea, J. Phys. Earth, 26; Suppl : S233-S248.

Watanabe, K., 1989. On the duration time of Aftershock activity, Bull. Disaster Prevention Res. Inst., 39 : 1-22.

Weimer, S. and Wyss, M., 1997. Mapping the frequency-magnitude distribution in asperities : An improved technique to calculate recurrence times, J. Geophys. Res., 102, 15,115-15,128.

Wessel, P., Smith, W.H.F., 1995. New version of the generic mapping tools released. EOS Trans., AGU, 76, 329.

Zhao, D., Mishra, O.P., Sanda, R., 2002. Influence of fluids and magma on earthquakes:seismological evidence, Phys. Earth Planet. Inter., 132, 249 – 267.

Zhou, Y.H., Xu, L.S., Chen, Y.T., 2002. Source processes of the 4 June 2000 southernSumatra, Indonesia, Earthquake, Bull. Seismol. Soc. Am., 92, 2027-2035.


145

TABLE-6

Aftershocks ( M > 5.0 ) ( USGS, IRIS/IMD )

Origin Time Location MAG Source

YYMMDD HH MM SS LAT LONG DEPTH Mw Mb IRIS/IMD

20041226 0058 50.70 3.30 95.78 10.0 8.5 IRIS

20041226 0058 53.40 3.30 95.98 30.0 9.0 IRIS

20041226 0121 18.10 6.37 93.36 10.0 6.2 IRIS

20041226 0148 46.70 5.39 94.42 10.0 5.9 IRIS

20041226 0215 57.50 12.37 92.51 10.0 5.8 IRIS

20041226 0222 1.80 8.86 92.50 10.0 6.0 IRIS

20041226 0234 50.10 4.10 94.18 10.0 5.8 IRIS

20041226 0236 6.40 12.14 93.01 10.0 5.8 IRIS

20041226 0251 59.20 12.51 92.59 10.0 6.0 IRIS

20041226 0259 12.30 3.18 94.26 10.0 5.9 IRIS

20041226 0308 42.10 13.81 92.97 10.0 6.1 IRIS

20041226 0421 26.00 6.90 92.95 10.0 7.3 IRIS

20041226 0421 29.80 6.91 92.96 39.2 7.1 IRIS

20041226 0621 58.00 10.62 92.32 10.0 5.7 IRIS

20041226 0707 9.60 10.34 93.76 10.0 5.7 IRIS

20041226 0738 24.50 13.12 93.05 10.0 5.8 IRIS

20041226 0920 1.20 8.87 92.38 10.0 6.5 IRIS

20041226 0920 1.60 8.88 92.38 16.1 6.6 IRIS

20041226 1018 12.70 8.95 93.73 10.0 5.5 IRIS

20041226 1019 29.70 13.45 92.79 10.0 6.2 IRIS

20041226 1105 0.50 13.54 92.88 10.0 6.3 IRIS

20041226 1105 0.70 13.53 92.84 13.3 6.2 IRIS

20041226 1211 55.90 11.59 92.45 10.0 5.5 IRIS

20041226 1356 37.40 2.79 94.46 10.0 5.9 IRIS

20041226 1356 40.10 2.78 94.47 30.0 5.9 IRIS

20041226 1448 41.50 13.60 92.87 10.0 5.9 IRIS

20041226 1506 32.50 3.70 94.02 10.0 5.7 IRIS

20041226 1506 33.20 3.65 94.09 17.8 5.9 IRIS

20041226 1512 21.20 6.70 93.02 10.0 5.6 IRIS

20041226 1903 46.70 4.07 94.20 10.0 5.6 IRIS

20041226 1919 53.10 2.77 94.16 10.0 6.2 IRIS

20041226 1919 55.50 2.79 94.16 30.0 6.1 IRIS

20041226 0058 51.10 3.34 96.13 10.0 8.6 IMD

20041226 0148 42.70 5.39 94.42 10.0 5.9 IMD

20041226 0215 57.00 12.38 92.51 10.0 5.8 IMD

20041226 0222 1.00 8.84 92.53 10.0 6.0 IMD

20041226 0234 50.00 4.10 94.18 10.0 5.8 IMD

20041226 0236 6.00 12.14 93.01 10.0 5.8 IMD

20041226 0251 59.00 12.51 92.59 10.0 6.0 IMD

20041226 0259 12.00 3.18 94.26 10.0 5.9 IMD

20041226 0308 42.00 13.81 92.97 10.0 6.1 IMD

20041226 0421 27.80 6.97 92.81 10.0 7.0 IMD

20041226 0621 58.00 10.62 92.32 10.0 5.7 IMD


146

20041226 0707 9.00 10.34 93.76 10.0 5.7 IMD

20041226 0738 24.00 13.12 93.05 10.0 5.8 IMD

20041226 0919 48.50 6.10 90.95 10.0 6.2 IMD

20041226 1018 12.00 8.95 93.73 10.0 5.5 IMD

20041226 1019 29.00 12.65 94.69 10.0 6.2 IMD

20041226 1105 14.50 14.80 92.42 10.0 6.1 IMD

20041226 1209 56.50 13.80 92.25 10.0 5.8 IMD

20041226 1211 12.80 11.59 92.46 10.0 5.5 IMD

20041226 1356 37.20 2.62 94.60 10.0 5.5 IMD

20041226 1448 47.20 13.66 92.37 10.0 5.9 IMD

20041227 0032 13.10 5.50 94.46 10.0 6.0 IRIS

20041227 0049 26.70 12.98 92.45 10.0 6.1 IRIS

20041227 0049 28.50 12.98 92.40 23.7 5.8 IRIS

20041227 0747 36.40 2.68 94.48 32.3 5.6 IRIS

20041227 0821 39.80 5.54 94.60 48.1 5.4 IRIS

20041227 0837 38.60 6.49 93.26 30.0 5.7 IRIS

20041227 0939 3.30 5.38 94.71 10.0 6.3 IRIS

20041227 0939 6.80 5.35 94.65 35.0 6.0 IRIS

20041227 0957 53.00 7.74 92.69 10.0 5.6 IRIS

20041227 1005 0.10 4.78 95.12 10.0 5.9 IRIS

20041227 1446 45.10 12.36 92.50 10.0 5.8 IRIS

20041227 2010 48.20 2.86 95.59 10.0 5.8 IRIS

20041228 1117 43.20 4.71 95.18 28.2 5.9 IRIS

20041228 1117 43.80 4.73 95.21 36.0 5.7 IRIS

20041228 1711 14.70 9.91 93.76 30.0 5.5 IRIS

20041228 2147 26.80 8.93 93.74 9.5 5.5 IRIS

20041229 0139 40.30 8.20 93.10 30.0 5.8 IRIS

20041229 0139 41.20 8.38 93.16 34.0 6.0 IRIS

20041229 0150 52.50 9.11 93.76 8.0 6.0 IRIS

20041229 0150 53.10 9.08 93.86 10.0 6.1 IRIS

20041229 0556 47.50 8.79 93.20 12.0 6.2 IRIS

20041229 0556 50.90 8.78 93.22 30.0 6.2 IRIS

20041229 1850 20.70 5.54 94.35 38.6 5.6 IRIS

20041229 2112 59.00 5.20 94.71 25.8 5.7 IRIS

20041230 0104 51.10 4.23 94.20 12.7 5.6 IRIS

20041230 0427 38.40 5.57 94.27 37.7 5.3 IRIS

20041230 1734 44.40 6.74 92.89 27.9 5.5 IRIS

20041230 1758 11.40 12.23 92.52 30.0 5.7 IRIS

20041231 0224 0.50 7.12 92.53 14.0 6.0 IRIS

20041231 0224 1.00 7.13 92.56 11.9 6.3 IRIS

20041231 0957 0.20 7.62 93.97 23.3 5.4 IRIS

20041231 1058 24.90 5.03 94.80 36.4 5.5 IRIS

20041231 1204 56.60 6.22 92.91 4.6 6.1 IRIS

20041231 1204 57.50 6.20 92.91 11.0 6.0 IRIS

20041231 1341 48.30 3.18 95.23 30.3 5.6 IRIS

20041231 1438 46.40 5.11 94.83 48.2 5.6 IRIS

20041231 1748 5.70 4.73 95.14 49.0 5.8 IRIS

20050101 0155 28.20 2.87 95.60 26.0 5.7 IRIS

20050101 0403 12.60 5.46 94.45 45.5 5.8 IRIS

20050101 0625 44.80 5.10 92.30 11.7 6.6 IRIS


147

20050101 0625 44.90 5.05 92.26 10.0 6.5 IRIS

20050101 1908 6.20 7.29 94.35 37.7 5.9 IRIS

20050101 1908 7.80 7.34 94.46 55.4 6.1 IRIS

20050101 0155 43.00 4.33 94.63 10.0 5.2 IMD

20050101 0403 20.20 6.05 93.23 10.0 5.5 IMD

20050101 0625 56.20 5.60 91.70 10.0 6.3 IMD

20050101 1429 11.90 7.84 92.55 10.0 5.6 IMD

20050101 1728 31.40 8.89 91.19 10.0 5.0 IMD

20050101 1908 13.20 8.14 93.97 10.0 5.9 IMD

20050101 2223 22.10 9.03 93.98 10.0 5.0 IMD

20050101 2228 27.50 8.01 91.99 10.0 5.5 IMD

20050101 2311 32.80 6.61 92.15 10.0 5.0 IMD

20050102 0827 41.60 3.21 95.43 8.4 5.9 IRIS

20050102 0827 41.80 3.24 95.46 8.4 5.8 IRIS

20050102 1535 56.40 6.33 92.80 30.0 6.2 IRIS

20050102 1535 56.70 6.36 92.79 30.0 6.3 IRIS

20050102 0827 50.00 2.80 94.70 10.0 5.2 IMD

20050102 1212 31.00 6.14 92.94 10.0 5.2 IMD

20050102 1536 3.40 6.48 91.98 10.0 6.0 IMD

20050103 0914 6.80 10.90 91.99 10.0 5.0 IMD

20050103 1936 16.30 6.20 92.20 10.0 5.3 IMD

20050104 0913 12.20 10.67 92.36 23.2 6.1 IRIS

20050104 0913 12.40 10.67 92.40 24.7 6.0 IRIS

20050104 1826 45.70 4.98 94.79 53.1 5.6 IRIS

20050104 1914 49.40 10.60 91.74 10.0 5.8 IRIS

20050104 0205 5.00 5.50 91.80 10.0 5.3

20050104 0913 19.20 10.52 91.39 10.0 6.0

20050104 1215 34.60 9.25 93.55 10.0 5.0

20050104 1256 9.90 7.70 92.67 10.0 5.4

20050104 1518 34.00 5.91 93.79 10.0 5.3

20050104 1826 54.00 5.69 93.61 10.0 5.3 IMD

20050104 1908 15.00 6.09 93.92 10.0 5.2 IMD

20050104 1914 52.00 10.70 91.53 10.0 5.5 IMD

20050105 0532 38.90 3.57 93.62 30.0 5.5 IRIS

20050105 1434 31.30 5.54 94.75 30.0 5.5 IRIS

20050105 1454 4.20 5.52 94.38 41.1 5.6 IRIS

20050105 1454 4.80 5.49 94.39 48.8 5.9 IRIS

20050105 0532 45.40 4.40 93.30 10.0 5.3 IMD

20050105 0833 3.00 13.40 92.40 10.0 5.4 IMD

20050105 1231 47.00 8.00 93.20 10.0 5.3 IMD

20050105 1434 39.90 6.15 93.82 10.0 5.4 IMD

20050105 1454 15.30 6.51 93.57 10.0 5.8 IMD

20050106 0011 16.90 5.59 93.15 24.6 5.7 IRIS

20050106 0056 26.50 5.31 94.82 22.4 6.2 IRIS

20050106 0011 31.60 6.34 92.14 15.0 5.7 IMD

20050106 0056 43.30 5.94 93.79 40.5 5.8 IMD

20050106 0452 44.00 7.10 91.80 33.0 5.2 IMD

20050106 0754 24.00 11.06 93.68 33.0 5.6 IMD

20050106 1155 49.40 11.36 91.57 10.0 5.1 IMD

20050107 1049 15.00 8.82 93.57 30.0 5.7 IRIS


148

20050107 0759 45.00 7.33 93.49 33.0 5.7 IMD

20050107 1049 20.00 8.32 92.45 15.0 5.4 IMD

20050107 1850 35.00 6.41 92.19 15.0 5.2 IMD

20050108 0248 30.90 13.41 93.03 15.0 5.0 IMD

20050108 0530 45.30 10.72 91.84 10.0 5.2 IMD

20050108 0558 32.90 5.35 93.59 10.0 5.0 IMD

20050108 1231 36.50 11.90 92.70 10.0 5.3 IMD

20050108 1500 3.70 4.97 91.12 10.0 5.2 IMD

20050109 1716 46.50 3.25 94.23 30.0 5.5 IRIS

20050109 2212 53.20 4.97 95.13 14.3 6.2 IRIS

20050109 1716 58.20 4.23 93.48 15.0 5.4 IMD

20050109 2213 5.10 5.43 93.97 15.0 6.2 IMD

20050111 0549 34.20 8.67 93.67 33.0 5.2 IMD

20050111 2256 5.00 12.40 91.00 33.0 5.1 IMD

20050112 1358 18.60 5.54 94.64 34.0 5.7 IRIS

20050112 1358 24.30 5.64 93.61 10.0 5.4 IMD

20050113 0530 21.40 12.20 93.30 20.0 5.1 IMD

20050113 0852 58.00 6.00 93.00 33.0 5.1 IMD

20050114 1622 8.10 9.30 93.30 10.0 5.0 IMD

20050114 1748 47.60 11.80 92.70 38.0 5.0 IMD

20050115 0746 56.30 15.20 92.20 15.0 5.3 IMD

20050118 0302 53.00 23.00 94.40 33.0 5.0 IMD

20050119 1609 28.10 4.50 92.00 15.0 5.2 IMD

20050120 1517 41.10 13.60 92.50 10.0 5.0 IMD

20050120 1925 54.20 7.40 92.80 33.0 5.2 IMD

20050122 1838 12.80 14.68 92.67 30.0 5.5 IRIS

20050122 1258 44.30 6.00 94.50 33.0 5.0 IMD

20050122 1838 15.00 14.40 92.00 30.0 5.0 IMD

20050123 0431 24.30 5.50 92.50 15.0 5.1 IMD

20050124 0416 48.10 7.37 92.45 30.0 6.3 IRIS

20050124 0416 47.10 7.50 91.80 15.0 6.5 IMD

20050124 1800 1.60 9.10 94.50 15.0 5.0 IMD

20050126 1730 29.40 8.30 93.98 25.8 5.6 IRIS

20050126 2200 42.20 2.91 94.43 10.0 6.1 IRIS

20050126 1730 32.80 8.40 93.90 20.0 5.7 IMD

20050126 2200 3.70 1.10 97.10 33.0 5.4 IMD

20050127 0656 59.30 7.99 94.05 30.0 5.5 IRIS

20050127 0819 7.70 7.97 94.02 30.0 5.5 IRIS

20050127 0842 16.30 7.97 94.30 30.0 5.5 IRIS

20050127 1147 38.80 8.10 93.98 36.6 5.5 IRIS

20050127 1658 51.50 7.95 94.07 30.0 5.8 IRIS

20050127 1740 46.80 8.02 94.15 10.1 6.0 IRIS

20050127 1852 38.90 7.88 94.08 30.0 5.5 IRIS

20050127 2009 52.60 5.56 94.36 30.0 5.8 IRIS

20050127 2240 48.10 8.06 94.09 30.0 5.6 IRIS

20050127 0358 41.50 7.70 93.60 33.0 5.4 IMD

20050127 0522 25.10 8.10 93.10 33.0 5.0 IMD

20050127 0657 3.70 8.80 93.80 15.0 5.8 IMD

20050127 0726 6.40 8.80 94.00 15.0 5.6 IMD

20050127 0735 55.30 8.90 93.90 15.0 5.4 IMD


149

20050127 0819 17.30 8.80 93.80 26.3 5.5 IMD

20050127 0837 1.90 9.30 94.20 22.4 5.1 IMD

20050127 0842 22.20 8.20 93.20 15.2 5.3 IMD

20050127 0910 54.90 7.60 94.90 15.0 5.1 IMD

20050127 0925 33.40 8.60 93.90 20.0 5.2 IMD

20050127 0952 30.90 8.90 93.90 30.0 5.4 IMD

20050127 1058 13.00 8.80 94.00 20.0 5.1 IMD

20050127 1147 43.20 8.80 93.80 15.2 5.6 IMD

20050127 1524 27.00 7.60 96.60 33.0 5.1 IMD

20050127 1534 39.00 8.50 93.80 33.0 5.3 IMD

20050127 1658 59.00 8.00 93.40 33.0 5.4 IMD

20050127 1740 58.00 8.40 93.50 33.0 5.4 IMD

20050127 1852 52.00 8.30 93.30 33.0 5.1 IMD

20050127 2010 14.00 6.90 93.80 33.0 5.1 IMD

20050127 2017 45.00 7.30 92.20 33.0 5.1 IMD

20050127 2045 22.00 8.30 93.40 33.0 5.2 IMD

20050127 2100 43.00 9.60 93.80 33.0 5.2 IMD

20050127 2147 50.80 8.00 94.20 33.0 5.3 IMD

20050127 2240 54.40 8.80 93.80 33.0 5.5 IMD

20050127 2327 8.70 8.50 93.70 33.0 5.2 IMD

20050128 0610 31.00 7.94 94.04 42.2 5.5 IRIS

20050128 0613 27.70 8.11 93.96 30.0 5.5 IRIS

20050128 0331 34.00 7.20 92.00 33.0 5.3 IMD

20050128 0504 31.10 8.50 94.50 33.0 5.1 IMD

20050128 0538 30.90 9.60 95.20 15.0 5.2 IMD

20050128 0610 41.10 8.70 93.70 33.0 5.6 IMD

20050128 0749 26.50 8.30 93.30 12.2 5.3 IMD

20050128 1153 10.60 8.70 93.80 33.0 5.4 IMD

20050128 1237 22.10 8.70 93.70 16.0 5.2 IMD

20050128 1749 40.10 8.30 94.50 23.0 5.3 IMD

20050128 1919 1.70 8.90 93.80 15.0 5.4 IMD

20050128 2235 35.60 8.60 93.60 15.0 5.2 IMD

20050129 0544 12.70 13.10 93.03 20.0 5.6 IRIS

20050129 0610 43.60 3.30 93.68 27.3 5.5 IRIS

20050129 2028 25.80 7.85 94.30 52.8 5.6 IRIS

20050129 0113 43.50 8.20 93.20 15.0 5.3 IMD

20050129 0150 14.20 9.20 95.50 14.1 5.3 IMD

20050129 0338 13.30 9.20 94.10 33.0 5.4 IMD

20050129 0544 15.80 13.20 92.70 18.2 5.4 IMD

20050129 0610 54.90 4.20 93.40 48.5 5.4 IMD

20050129 1636 54.40 8.30 94.30 14.6 5.1 IMD

20050129 1821 11.50 6.60 93.80 20.0 5.3 IMD

20050129 1906 26.80 7.80 92.90 25.0 5.3 IMD

20050129 2002 5.40 8.70 93.80 25.0 5.4 IMD

20050129 2028 34.80 9.90 94.90 15.0 5.7 IMD

20050129 2203 32.20 8.50 95.40 33.0 5.2 IMD

20050130 1533 13.60 8.13 94.09 15.9 5.6 IRIS

20050130 0007 42.50 9.10 94.00 25.0 5.3 IMD

20050130 0034 17.00 9.00 94.40 33.0 5.0 IMD

20050130 0225 42.50 9.30 94.20 15.0 5.1 IMD


150

20050130 0235 23.00 8.70 93.80 15.0 5.3 IMD

20050130 0313 38.00 6.90 91.90 15.0 5.3 IMD

20050130 0626 20.40 13.80 92.60 30.0 5.0 IMD

20050130 0702 25.00 13.30 92.70 10.0 5.0 IMD

20050130 0849 45.90 8.40 93.40 15.0 5.0 IMD

20050130 1533 21.40 8.60 93.90 33.0 5.5 IMD

20050130 2139 46.30 11.50 91.70 33.0 5.1 IMD

20050131 1630 26.00 8.80 93.90 33.0 5.2 IMD

TABLE-7

Aftershock ( ≥≥ 4.5) Parameters

(December 26, 2005 Sumatra-Andaman earthquake sequence)

Multi -station method

Origin Time LAT LONG DEPTH MAG

YY MMDD HH MM SS ( Deg. ) ( Deg. ) ( km ) ( Ml )

2005 0111 0816 44.5 10.942 93.375 25.0 5.4

2005 0111 1622 1.5 10.140 93.623 158.3 5.3

2005 0111 1647 50 11.039 93.775 26.4 5.5

2005 0111 1803 60 11.398 93.804 25.7 4.7

2005 0111 1828 17 10.917 92.617 13.5 4.6

2005 0111 1857 4.4 10.337 94.026 25.0 4.9

2005 0111 2027 23.9 9.419 93.184 16.3 4.7

2005 0111 2116 12.6 10.778 93.173 25.1 4.9

2005 0111 2218 33.8 10.780 92.948 25.2 4.6

2005 0112 0041 50.3 11.055 94.145 30.0 4.9

2005 0112 0059 18.9 8.209 93.487 41.6 5.4

2005 0112 1722 54.9 9.253 92.801 11.0 4.8

2005 0112 1856 42.5 11.225 94.259 25.1 5.3

2005 0112 1954 17.1 9.193 92.954 1.9 5.6

2005 0112 2007 0.1 10.673 94.019 25.1 5.1

2005 0112 2226 21.2 10.319 92.457 7.8 5.2

2005 0121 0326 43 13.262 92.958 18.6 4.6

2005 0121 0647 28.9 10.953 92.610 30.0 4.6

2005 0121 0712 54.7 10.519 94.030 25.0 4.5

2005 0121 0716 27.2 11.657 92.730 1.7 4.7

2005 0113 0806 31.2 9.230 92.761 105.1 5.3

2005 0113 1023 19.6 11.606 92.802 10.1 4.7

2005 0113 1319 43.9 11.954 92.995 86.2 4.7

2005 0113 1402 21.5 11.751 93.143 111.8 4.9

2005 0113 1512 17 11.377 93.711 128.2 5.1

2005 0113 1527 14.7 10.367 93.563 26.3 4.7

2005 0113 1540 10.7 9.387 92.305 3.0 5.5

2005 0113 1705 4 10.888 93.877 148.8 4.5

2005 0113 1743 25.3 10.578 92.013 22.0 5.0

2005 0113 1833 34.2 10.214 92.426 15.7 5.0

2005 0113 1918 21.7 11.107 91.859 48.8 4.9

2005 0113 1925 39.9 8.849 92.801 4.9 5.1

2005 0113 1951 22.4 12.430 93.619 8.6 4.7

2005 0113 2018 48.9 9.993 92.459 30.0 4.6

2005 0113 2116 11 10.694 94.239 26.2 4.5


151

2005 0113 2158 19.1 8.654 93.220 32.6 4.7

2005 0113 2202 51.7 9.266 92.802 11.8 4.6

2005 0113 2245 7.3 12.801 94.131 30.0 5.5

2005 0113 2256 9.5 10.945 93.209 4.6 4.7

2005 0114 0150 15.4 11.734 93.204 121.3 5.2

2005 0114 0657 3.7 10.262 92.454 11.6 5.0

2005 0114 0705 11.5 14.406 93.385 30.0 5.3

2005 0114 0818 23.3 11.930 92.841 41.4 4.6

2005 0114 0836 47.9 16.643 92.828 47.7 5.7

2005 0114 0856 33.5 11.505 94.842 25.1 5.6

2005 0114 0908 23.4 11.219 95.642 50.7 5.6

2005 0114 0910 57.2 10.425 92.583 20.6 5.0

2005 0114 0916 9.4 11.925 93.720 25.0 5.4

2005 0114 0918 20.4 11.190 92.687 10.1 4.7

2005 0114 0921 1.2 12.796 93.648 30.0 5.0

2005 0114 0922 54 10.243 93.988 25.3 5.2

2005 0114 1010 47 10.695 92.659 17.2 4.7

2005 0114 1043 19.4 11.723 95.604 30.0 5.5

2005 0114 1102 0.6 9.195 92.588 4.2 5.3

2005 0114 1110 48.2 11.923 93.140 15.4 4.7

2005 0114 1137 52.2 9.545 95.009 40.4 6.1

2005 0114 1154 38.6 9.972 91.872 8.9 4.9

2005 0114 1215 9.7 9.198 93.585 57.1 5.1

2005 0114 1311 35.2 14.252 93.305 38.2 5.1

2005 0114 1436 54.9 10.375 92.437 14.9 4.7

2005 0114 1533 34.3 10.329 93.056 9.4 4.5

2005 0114 1607 34.1 10.428 92.460 29.0 4.9

2005 0114 1637 37.8 9.463 92.492 25.1 5.1

2005 0114 1813 10.3 11.084 93.671 26.6 5.8

2005 0114 1816 45.3 9.078 93.568 45.3 5.0

2005 0114 1832 34.3 13.157 93.040 21.1 5.0

2005 0114 1941 40.3 9.112 94.269 35.0 5.0

2005 0114 2129 1.3 10.583 95.037 25.4 5.0

2005 0114 2139 11.3 10.474 94.626 25.3 5.2

2005 0114 2153 16.5 9.442 93.646 30.0 4.9

2005 0114 2216 26.5 9.436 92.373 24.0 4.5

2005 0114 2308 25.5 8.898 92.840 12.0 4.6

2005 0114 2314 33.2 10.537 93.338 26.0 4.5

2005 0114 2358 26.7 11.675 94.201 25.1 4.9

2005 0115 0153 38.7 12.257 94.044 30.0 5.3

2005 0115 0204 40.1 11.657 93.521 138.9 5.1

2005 0115 0250 7.8 10.557 92.534 4.6 4.5

2005 0115 0446 1.6 10.456 92.498 3.6 4.6

2005 0115 0820 25.8 10.739 92.539 19.4 4.7

2005 0115 0938 25.4 11.143 93.327 108.2 5.0

2005 0115 1001 18.5 11.688 92.741 19.3 4.7

2005 0115 1010 53.8 8.916 92.827 30.0 5.1

2005 0115 1241 21.8 10.328 93.463 26.0 5.2

2005 0115 1312 27.2 9.547 92.415 23.5 5.3

2005 0115 1340 51.4 12.373 93.450 99.4 5.2


152

2005 0115 1406 58.7 10.888 92.633 25.1 4.5

2005 0115 1424 5.6 12.425 92.890 9.7 4.8

2005 0115 1517 4.6 12.484 92.906 5.9 4.6

2005 0115 1536 34.8 11.634 94.745 25.1 5.3

2005 0115 1551 19.7 12.411 92.864 24.3 4.5

2005 0115 1603 54.2 10.217 93.564 86.5 5.3

2005 0115 1649 40.9 10.059 92.685 25.4 4.8

2005 0115 1738 48.7 11.665 92.619 22.4 4.9

2005 0115 1852 21 9.221 92.746 10.1 4.9

2005 0115 1912 18.5 11.647 95.080 51.8 5.6

2005 0115 1924 26.4 9.160 92.824 1.0 4.8

2005 0115 1957 0.9 12.139 93.767 127.6 4.8

2005 0115 2036 8.9 12.401 93.414 10.1 4.5

2005 0115 2126 25.1 13.596 93.109 14.1 5.0

2005 0115 2214 0.7 10.822 93.097 57.4 4.6

2005 0115 2256 11.6 10.826 94.925 165.1 5.2

2005 0116 0101 26.1 10.582 93.146 46.7 5.2

2005 0116 0103 34.2 10.367 92.439 8.5 4.8

2005 0116 0119 20.7 10.368 92.460 8.6 4.9

2005 0116 0136 36.4 13.863 92.281 30.0 5.7

2005 0116 0152 44.8 10.970 93.570 139.9 5.0

2005 0116 0713 12.3 11.985 93.338 116.0 4.9

2005 0116 0830 21.2 10.595 91.789 30.0 5.4

2005 0116 0918 27.6 12.542 92.333 30.0 4.8

2005 0116 1020 28.6 10.749 92.549 19.6 4.5

2005 0116 1041 46.4 12.311 94.161 30.0 5.1

2005 0116 1157 10.1 12.679 92.950 25.1 4.7

2005 0116 1214 6.3 12.878 92.910 2.6 4.9

2005 0116 1217 13.2 11.386 93.498 139.9 5.2

2005 0116 1248 39.5 11.592 94.033 30.0 4.9

2005 0116 1346 41.4 12.510 92.912 14.3 4.7

2005 0116 1418 9.9 12.551 93.991 30.0 5.2

2005 0116 1456 50.1 10.573 91.778 30.0 5.7

2005 0116 1605 46.3 10.370 92.488 5.5 4.5

2005 0116 1632 2.9 11.204 93.788 150.5 5.1

2005 0116 1723 20.7 13.488 93.162 12.9 4.8

2005 0116 1803 45.5 12.905 92.960 13.7 4.7

2005 0116 2110 39.2 12.327 94.172 30.0 4.9

2005 0116 2151 28.6 10.748 92.567 20.6 4.7

2005 0116 2229 40.7 12.667 92.948 8.7 4.6

2005 0116 2236 56.2 12.846 93.380 30.0 4.9

2005 0116 2327 50 8.613 93.144 33.1 4.6

2005 0117 0006 15.5 12.370 93.694 30.0 4.7

2005 0117 0009 1 11.433 93.666 144.5 4.9

2005 0117 0013 9.5 10.060 92.451 30.0 4.9

2005 0117 0034 15.2 14.099 93.227 18.2 5.0

2005 0117 0036 38.5 9.662 95.571 31.5 5.3

2005 0117 0043 52.7 10.315 94.046 25.5 5.0

2005 0117 0046 41.2 10.866 92.324 19.6 4.7

2005 0117 0154 43.9 12.499 94.669 51.3 5.4


153

2005 0117 0201 33.6 11.712 93.084 105.5 5.3

2005 0117 0355 52.8 13.944 94.423 41.0 5.9

2005 0117 0511 20.2 13.388 93.199 23.6 5.2

2005 0117 0551 22.2 12.618 92.932 14.4 4.5

2005 0117 0623 53.4 11.781 94.566 157.5 5.5

2005 0117 0756 37.9 8.911 93.988 30.0 5.4

2005 0117 0938 51.7 9.133 92.296 3.3 4.9

2005 0117 1009 32.1 12.859 93.054 41.7 4.6

2005 0117 1116 3.3 13.348 92.364 11.9 4.7

2005 0117 1148 21.9 10.141 91.939 112.8 5.7

2005 0117 1203 18.5 12.718 91.182 127.1 6.1

2005 0117 1231 47.8 10.781 92.567 15.2 4.8

2005 0117 1312 49.9 12.340 90.691 93.5 4.9

2005 0117 1424 20.1 13.038 90.471 107.9 5.2

2005 0117 1525 18 13.236 93.632 30.0 4.6

2005 0117 1821 5.4 10.090 95.396 58.5 5.0

2005 0117 1834 10.1 13.170 92.963 10.0 4.8

2005 0117 1918 17.8 9.108 92.809 6.6 4.8

2005 0117 1920 12.3 13.025 93.016 24.8 5.1

2005 0117 2000 48.6 10.261 94.900 25.1 5.0

2005 0117 2006 1.9 9.103 93.518 10.1 4.6

2005 0117 2008 44.7 11.874 93.001 21.4 4.5

2005 0117 2118 18.8 13.086 94.421 37.0 4.7

2005 0117 2124 8.7 13.534 93.021 15.6 4.3

2005 0117 2126 50.9 8.716 92.990 30.4 4.9

2005 0117 2251 41.2 9.349 95.201 30.0 4.8

2005 0117 2259 36.6 8.861 93.607 48.1 5.6

2005 0117 2357 25.7 12.943 92.962 10.1 4.5

2005 0118 0029 21.4 11.924 94.665 25.6 4.9

2005 0118 0039 57.1 9.986 94.151 26.5 4.9

2005 0118 0104 53.5 10.310 96.027 51.1 5.4

2005 0118 0107 58.1 12.213 91.588 95.8 5.1

2005 0118 0111 32.1 10.685 90.640 127.3 5.1

2005 0118 0123 27.2 12.273 93.675 101.9 5.0

2005 0118 0758 4.9 9.772 93.644 25.1 4.8

2005 0118 1026 54.2 9.925 92.101 30.0 5.2

2005 0118 1724 5.2 13.183 93.023 21.7 4.6

2005 0118 1746 21.8 12.961 95.044 30.0 5.2

2005 0118 1823 40.7 12.426 93.331 76.0 4.5

2005 0118 1826 6.1 9.192 92.910 2.7 4.6

2005 0118 1828 48 13.141 93.815 30.0 5.0

2005 0118 1839 15.2 9.645 92.473 25.4 4.6

2005 0118 2100 59.5 12.469 93.179 12.0 4.9

2005 0118 2204 34.8 9.341 95.193 39.1 5.4

2005 0118 2226 13.1 12.105 94.226 25.0 4.8

2005 0119 0028 58.6 10.179 92.465 30.0 5.1

2005 0119 0120 1.7 12.407 93.108 10.1 5.1

2005 0119 0128 50.3 13.124 93.621 30.0 4.5

2005 0119 0200 14.5 10.336 91.389 0.0 5.2

2005 0119 0230 53.2 11.195 93.744 150.1 4.9


154

2005 0119 0244 11.7 12.092 94.684 129.1 5.4

2005 0119 0314 52.8 11.953 93.479 122.4 4.8

2005 0119 0515 2.1 12.617 93.369 10.1 4.9

2005 0119 0623 32.4 12.849 94.123 30.0 5.0

2005 0119 0645 59.3 10.896 92.570 23.1 4.9

2005 0119 0823 23.9 11.655 93.553 128.8 5.3

2005 0119 0917 27.2 10.474 93.232 10.0 5.1

2005 0119 1027 23 10.439 93.365 27.2 4.6

2005 0119 1042 50 13.514 93.110 16.2 5.9

2005 0119 1623 12.3 11.203 93.836 149.8 5.0

2005 0120 0104 14.5 10.373 94.065 129.9 4.7

2005 0120 0321 0 10.696 93.172 110.5 5.1

2005 0120 0851 18.9 12.778 92.894 10.0 4.8

2005 0120 1255 13.5 11.888 90.754 26.4 5.2

2005 0120 1327 26.5 11.724 89.634 62.3 5.0

2005 0120 1352 39.3 10.365 92.481 8.0 4.5

2005 0120 1359 47.9 9.767 92.363 17.0 4.8

2005 0120 1440 20.6 10.844 91.814 30.0 4.8

2005 0120 1517 34.2 13.844 93.174 11.0 6.6

2005 0120 1541 0.3 13.214 93.014 18.7 4.6

2005 0120 1553 33.3 10.884 91.563 25.2 4.5

2005 0120 1732 8.1 13.539 93.654 21.3 4.9

2005 0120 1747 46.4 10.707 92.620 30.0 4.5

2005 0120 2050 24.2 12.061 93.216 14.7 5.0

2005 0120 2309 48.7 13.164 90.036 62.8 5.5

2005 0122 0013 8.9 9.403 92.460 31.9 4.9

2005 0122 0034 20.1 12.997 90.651 50.1 4.6

2005 0122 0037 49.6 14.224 91.165 37.9 5.0

2005 0122 0125 33.8 9.831 92.604 30.0 4.6

2005 0122 0208 36.3 12.985 90.069 26.7 5.3

2005 0122 0228 28.6 13.179 93.031 27.7 5.0

2005 0122 0313 54.3 10.559 95.721 51.0 5.4

2005 0122 0316 45.6 9.689 92.338 19.2 5.1

2005 0122 0405 25.5 9.899 93.936 46.1 5.0

2005 0122 0505 8.7 14.084 93.129 20.4 5.8

2005 0122 0531 0 13.378 93.695 49.9 5.1

2005 0122 0534 48.9 10.914 92.459 30.0 5.1

2005 0122 0554 20.1 14.552 93.150 22.2 5.3

2005 0122 0605 27.3 10.685 94.184 25.0 5.3

2005 0122 0612 15.4 11.796 91.982 25.3 4.7

2005 0122 0731 38 11.295 93.282 26.4 5.2

2005 0122 0742 29.5 11.438 90.413 55.9 5.3

2005 0122 0802 33.8 10.778 95.311 30.0 5.8

2005 0122 0901 32.6 11.696 94.716 25.0 4.9

2005 0122 0936 46.4 13.642 93.041 30.0 4.7

2005 0122 0942 42.4 12.709 92.268 25.2 5.0

2005 0122 1117 35.4 10.428 95.224 54.9 5.0

2005 0122 1130 23.7 10.253 93.141 25.5 4.6

2005 0122 1141 20 11.372 91.388 81.5 4.6

2005 0122 1154 9.2 8.826 94.642 30.0 5.1


155

2005 0122 1207 0 6.107 90.398 46.1 5.9

2005 0122 1211 47.6 11.111 90.798 25.1 5.3

2005 0122 1259 29.8 5.917 92.445 26.7 6.1

2005 0122 1302 5.1 15.241 92.980 30.0 5.5

2005 0122 1314 13.4 10.539 94.150 109.6 4.6

2005 0122 1345 18.6 10.262 92.323 30.0 4.7

2005 0122 1357 12.4 9.653 89.210 17.3 5.7

2005 0122 1428 31.7 8.468 95.266 30.0 5.4

2005 0122 1439 14.3 9.991 92.472 4.7 4.5

2005 0122 1533 52.4 10.907 95.505 53.5 4.8

2005 0122 1551 15.3 10.797 92.136 48.4 5.1

2005 0122 1656 45.4 11.294 94.894 25.6 5.0

2005 0122 1952 56.5 13.895 93.060 22.8 4.5

2005 0122 2043 19.6 7.381 93.299 48.7 5.0

2005 0122 2104 50.9 8.806 89.506 29.7 5.2

2005 0122 2135 41 11.963 90.508 27.1 4.8

2005 0122 2151 15.8 10.922 89.115 16.1 5.4

2005 0122 2154 32.7 9.265 92.859 1.0 4.5

2005 0122 2208 6.4 8.021 92.794 30.0 4.7

2005 0122 2304 53.4 10.429 92.597 19.3 4.8

2005 0122 2330 49.7 7.365 92.723 18.6 5.0

2005 0122 2358 42.6 10.740 94.756 25.3 5.0

2005 0123 0049 28 9.185 94.918 39.4 5.6

2005 0123 0156 1.7 10.757 95.588 96.1 5.3

2005 0123 0331 51.8 11.972 94.385 25.0 5.0

2005 0123 0504 12.2 13.927 93.587 14.6 4.5

2005 0123 0517 38 12.890 93.315 138.7 4.8

2005 0123 0537 34 9.245 94.638 40.2 5.7

2005 0123 0552 57.5 11.443 91.285 25.2 4.6

2005 0123 0833 32.5 13.466 93.045 22.5 4.7

2005 0123 0842 5.9 11.467 94.057 124.3 4.7

2005 0123 1002 4.5 12.505 91.534 30.0 4.6

2005 0123 1008 21.9 10.610 92.530 22.3 4.7

2005 0123 1229 28 11.126 95.558 25.2 4.7

2005 0123 1237 17.2 12.591 93.396 45.2 5.2

2005 0123 1317 37.7 8.649 93.364 30.0 4.6

2005 0123 1321 30.1 8.457 94.882 35.0 4.8

2005 0123 1336 22.4 12.980 91.607 87.9 5.0

2005 0123 1340 0.5 9.156 92.807 2.0 4.6

2005 0123 1353 49.6 9.424 92.533 22.3 4.5

2005 0123 1412 43.8 9.355 93.411 36.2 4.9

2005 0123 1454 27.6 10.800 94.192 25.0 5.1

2005 0123 1506 18.8 13.352 92.590 15.1 4.6

2005 0123 1736 14.4 10.610 92.550 28.3 5.0

2005 0123 1741 23.5 10.540 93.172 10.1 4.7

2005 0123 1744 40.7 13.674 92.213 25.1 5.3

2005 0123 1949 2 10.629 94.496 25.0 4.5

2005 0123 2033 48.1 14.828 93.414 21.5 4.5

2005 0123 2043 54.4 9.207 92.824 16.4 4.4

2005 0123 2121 2 9.368 94.375 45.2 5.0


156

2005 0123 2137 31.8 13.656 93.027 30.0 4.5

2005 0123 2142 19.1 10.377 91.354 114.0 5.3

2005 0124 0124 1.6 11.668 91.225 25.1 4.7

2005 0124 0152 43.2 11.125 91.587 175.6 5.0

2005 0124 0255 26.3 14.216 93.074 13.1 4.8

2005 0124 0400 57.1 10.864 92.868 83.9 5.3

2005 0124 0511 5.3 11.047 92.644 17.7 4.6

2005 0124 0643 1.2 11.223 92.666 25.1 4.7

2005 0124 0741 16.4 11.694 94.103 25.5 4.7

2005 0124 0818 10.7 12.540 89.701 50.2 4.8

2005 0124 0841 47.9 9.221 92.642 10.8 4.9

2005 0124 0910 27.4 9.214 92.838 7.0 4.9

2005 0124 0926 15.2 9.510 94.754 42.7 5.0

2005 0124 1003 35 11.670 93.722 25.3 4.9

2005 0124 1006 22.1 12.907 93.644 42.4 4.9

2005 0124 1009 35.5 9.116 92.837 3.8 4.7

2005 0124 1324 28.1 12.757 93.906 46.2 4.8

2005 0124 1404 39.9 9.679 94.475 44.9 5.1

2005 0124 1408 2.3 10.167 94.746 25.1 4.9

2005 0124 1415 13.6 11.820 94.272 25.3 4.8

2005 0124 1421 51.2 12.418 92.371 79.2 4.5

2005 0124 1617 24.1 11.971 94.138 144.5 4.7

2005 0124 1818 39.4 9.157 93.420 41.1 4.5

2005 0124 1859 1.3 11.545 94.570 25.1 5.1

2005 0124 2102 52.9 9.379 93.500 43.5 5.4

2005 0125 0030 56.2 11.994 90.535 25.3 4.5

2005 0125 0033 57.9 9.483 93.285 50.0 4.5

2005 0125 0102 24.8 11.805 93.354 7.9 4.8

2005 0125 0134 18 10.059 91.316 1.1 5.1

2005 0125 0143 4.2 9.397 92.781 21.9 4.8

2005 0125 0203 17.3 9.571 94.658 43.8 5.6

2005 0125 0217 4.1 14.152 93.174 18.2 4.5

2005 0125 0234 41.6 14.659 92.942 45.3 4.6

2005 0125 1723 52.5 13.697 96.412 9.3 6.6

2005 0125 1757 11.5 13.029 92.982 24.7 5.7

2005 0125 2019 57.1 10.019 93.665 87.6 5.0

2005 0125 2142 23.1 9.790 93.591 25.1 4.6

2005 0125 2224 29.9 9.253 92.290 174.5 5.9

2005 0126 0023 2.9 9.590 92.020 6.1 5.3

2005 0126 0034 50.3 10.258 94.545 140.5 4.9

2005 0126 0040 53.1 8.753 92.209 15.7 5.3

2005 0126 0115 52.2 16.137 93.703 30.0 5.8

2005 0126 0135 14.8 8.844 92.227 24.4 5.2

2005 0126 0204 46.5 12.325 93.706 109.4 4.9

2005 0126 0213 31 13.808 93.195 8.2 5.1

2005 0126 0308 58.1 10.147 91.877 25.9 4.8

2005 0126 0326 35.7 9.888 92.423 5.4 5.1

2005 0126 0331 13.8 9.908 92.436 21.6 5.0

2005 0126 0428 26.4 12.577 93.663 116.9 5.1

2005 0126 0432 48.2 9.817 93.751 77.4 5.3


157

2005 0126 0441 10.2 13.718 93.250 22.1 4.7

2005 0126 0452 21.3 13.785 93.117 18.7 5.0

2005 0126 0519 46.8 13.876 93.186 6.6 5.1

2005 0126 0531 47.7 13.766 93.147 22.0 4.7

2005 0126 0541 32.6 16.605 93.801 30.0 5.2

2005 0126 0601 56 9.375 92.315 5.8 5.2

2005 0126 0609 49 9.230 95.328 30.4 5.0

2005 0126 0655 16 7.531 92.002 4.4 5.6

2005 0126 0701 36.8 13.636 93.178 20.8 4.8

2005 0126 0708 15.5 14.509 94.906 30.0 5.2

2005 0126 0730 11 11.294 94.037 157.5 5.4

2005 0126 0916 25.2 9.988 94.177 51.4 5.2

2005 0126 0918 23.6 10.198 95.332 30.0 5.1

2005 0126 1001 55.2 13.074 92.942 23.0 4.8

2005 0126 1030 45.4 13.703 93.168 30.0 4.8

2005 0126 1040 10.9 9.181 92.326 8.2 4.9

2005 0126 1050 36 9.788 95.198 30.0 5.1

2005 0126 1223 38.9 8.044 94.556 17.6 5.0

2005 0126 1230 46.8 9.501 92.420 22.5 5.0

2005 0126 1244 2.7 5.286 96.124 30.0 5.8

2005 0126 1326 24.3 12.760 94.881 34.9 5.3

2005 0126 1330 44.9 10.433 95.370 26.7 5.2

2005 0126 1406 43 7.393 93.155 21.0 5.3

2005 0126 1423 12.7 9.140 94.622 25.0 5.0

2005 0126 1425 25.4 12.568 93.544 10.0 4.6

2005 0126 1431 53.4 7.578 93.339 35.5 5.2

2005 0126 1434 55.8 9.205 92.157 14.5 5.1

2005 0126 1449 4.2 11.767 93.478 10.0 4.8

2005 0126 1509 50.5 4.489 83.250 30.0 7.0

2005 0126 1547 27.8 11.836 93.504 131.7 4.5

2005 0126 1632 46.3 14.900 92.999 4.4 6.2

2005 0126 1641 14.8 9.424 92.375 20.7 4.6

2005 0126 1651 57.6 9.449 92.487 25.5 4.7

2005 0126 1805 10.7 8.996 94.153 44.4 5.0

2005 0126 1807 26.5 11.284 94.176 160.3 4.6

2005 0126 1850 57.6 13.339 95.163 25.0 5.3

2005 0126 2012 36.2 9.102 92.378 36.0 4.8

2005 0126 2045 41.5 14.386 93.326 36.5 4.9

2005 0126 2047 51.8 13.779 95.206 11.4 5.1

2005 0126 2051 24.4 10.254 95.250 25.8 4.9

2005 0126 2053 24.5 4.532 93.008 30.0 5.6

2005 0126 2107 31.2 4.679 92.669 30.0 5.6

2005 0126 2119 39.2 11.784 95.070 86.3 4.7

2005 0126 2201 16.4 5.888 87.509 30.0 6.0

2005 0126 2309 39.4 13.663 93.169 3.1 4.8

2005 0126 2316 31.5 9.917 95.617 30.0 4.7

2005 0126 2322 27.2 9.837 94.921 124.4 4.8

2005 0126 2339 49.5 7.573 93.867 30.0 5.1

2005 0126 2351 16.4 11.536 95.945 154.7 4.9

2005 0127 0004 53.5 16.210 93.695 30.0 5.2


158

2005 0127 0019 48.4 13.737 93.118 20.4 4.5

2005 0127 0123 0.9 10.596 94.309 152.4 4.9

2005 0127 0808 11.1 8.470 92.175 30.0 5.4

2005 0127 0849 37 12.183 96.309 30.0 5.2

2005 0127 1647 38 5.505 94.137 36.6 5.7

2005 0127 1739 36.7 5.011 88.968 37.2 6.5

2005 0127 1757 27.8 9.142 93.431 10.1 4.7

2005 0127 2025 53.1 17.873 84.746 30.0 6.5

2005 0127 2050 57.3 6.936 91.022 45.3 5.8

2005 0128 0016 10.5 7.501 92.159 4.4 5.4

2005 0128 0021 21.9 14.400 93.225 15.8 5.3

2005 0128 0040 30 9.385 92.344 10.6 4.7

2005 0128 0045 21.5 12.113 94.164 187.1 4.7

2005 0128 0119 48.2 10.173 92.417 19.9 4.7

2005 0128 0134 27.3 11.685 93.466 132.3 4.8

2005 0128 0135 24.8 6.920 95.917 444.9 6.0

2005 0128 0143 2.5 7.803 89.494 8.8 5.5

2005 0128 0156 14.8 9.759 92.191 20.4 5.1

2005 0128 0220 37.3 8.466 92.062 6.3 5.4

2005 0128 0241 26 9.371 92.331 11.9 5.1

2005 0128 0247 43.5 9.965 95.638 137.6 5.0

2005 0128 0250 28.7 14.319 94.636 34.0 5.3

2005 0128 0308 47.5 6.704 91.888 30.0 5.6

2005 0128 0709 49.4 10.633 94.173 148.0 5.2

2005 0128 0716 55.5 9.980 95.458 141.0 5.6

2005 0128 0719 47.3 10.130 93.653 48.8 4.9

2005 0128 0725 10.1 16.961 93.386 30.0 6.3

2005 0128 0812 18.7 6.878 92.382 30.0 5.5

2005 0128 0844 13.7 14.605 95.570 16.6 5.8

2005 0128 1005 52.7 9.913 92.382 1.9 4.9

2005 0128 1041 37.8 13.916 94.102 44.0 5.3

2005 0128 1050 30.5 10.027 92.423 22.8 4.8

2005 0128 1125 18.9 13.234 95.053 39.4 5.1

2005 0128 1153 0.5 8.116 90.598 83.2 5.7

2005 0128 1303 3.2 12.282 93.848 50.0 5.0

2005 0128 1340 48.3 12.593 93.053 21.8 5.0

2005 0128 1344 45.7 15.541 88.395 30.0 6.1

2005 0128 1418 34.5 12.600 93.558 9.9 4.7

2005 0128 1426 50 10.425 93.757 121.8 5.3

2005 0128 1510 14.8 8.868 95.522 31.3 5.5

2005 0128 1555 37.9 9.601 94.290 25.1 5.3

2005 0128 1600 21.8 7.362 93.661 194.2 5.6

2005 0128 1623 24 8.786 92.193 18.0 5.2

2005 0128 1648 3.2 11.031 94.796 25.2 5.7

2005 0128 1723 24.9 9.317 94.566 25.8 5.4

2005 0128 1726 0.1 10.244 96.697 30.0 5.6

2005 0128 1747 28.2 4.145 86.324 30.0 6.4

2005 0128 1909 4.4 9.795 95.558 30.0 4.9

2005 0128 1911 46.6 9.325 95.750 31.7 4.8

2005 0128 1918 30.2 5.937 94.799 30.0 6.1


159

2005 0128 1934 37.3 13.110 93.992 30.0 5.1

2005 0128 2000 27.8 11.263 95.098 25.3 4.8

2005 0128 2034 8.7 7.597 92.865 1.5 4.9

2005 0128 2054 14.2 9.785 94.313 25.1 4.5

2005 0128 2104 4.1 7.100 93.733 88.8 5.3

2005 0128 2113 54.3 10.589 95.621 25.1 5.0

2005 0128 2130 17.3 8.012 95.478 25.5 5.3

2005 0128 2147 45.1 13.689 93.169 27.4 5.0

2005 0128 2212 58.2 4.369 90.240 30.0 5.7

2005 0128 2222 20.4 9.694 95.466 30.0 4.8

2005 0128 2302 43.8 11.261 93.872 152.8 5.0

2005 0128 2317 0.4 17.109 95.836 30.0 6.1

2005 0128 2323 30.6 6.172 92.631 1.2 5.6

2005 0128 2351 37 8.595 97.311 30.0 5.3

2005 0129 0037 41.2 8.486 90.722 80.0 5.1

2005 0129 0113 17.6 6.774 89.921 30.0 6.7

2005 0129 0131 49.1 11.254 94.685 164.5 4.8

2005 0129 0139 30.5 9.838 90.313 50.1 5.2

2005 0129 0212 53.3 13.775 93.149 3.5 4.9

2005 0129 0236 11.8 14.280 95.613 25.0 5.2

2005 0129 0408 10.3 13.161 92.455 67.2 5.7

2005 0129 0443 57.6 10.228 94.537 137.1 5.1

2005 0129 0625 13.9 11.709 93.606 136.9 5.1

2005 0129 0659 35.6 9.976 92.435 30.0 4.6

2005 0129 1055 24.1 10.369 95.097 151.8 5.2

2005 0129 1243 31.1 10.223 95.489 54.5 5.2

2005 0129 1247 59.4 10.675 94.546 25.4 5.0

2005 0129 1254 39.9 11.965 93.272 0.3 5.5

2005 0129 1306 49.3 7.570 95.681 43.7 5.6

2005 0129 1348 58.1 11.528 95.511 25.0 5.1

2005 0129 1413 60 10.902 94.912 25.5 5.0

2005 0129 1427 55.7 7.141 94.153 23.1 5.4

2005 0129 1613 36.2 8.645 92.451 30.0 5.1

2005 0129 1756 55.3 12.703 92.909 29.6 4.7

2005 0129 1837 45.2 13.599 93.080 16.1 4.7

2005 0129 1939 8.4 14.566 93.314 14.5 5.6

2005 0129 1948 21.3 12.166 94.374 30.0 4.6

2005 0129 2028 27.8 8.263 90.602 107.8 5.7

2005 0129 2054 11.5 7.484 93.280 293.7 5.8

2005 0129 2108 27.8 10.590 93.134 25.0 4.5

2005 0129 2126 7.5 12.432 95.105 35.4 4.8

2005 0129 2129 29.9 10.277 96.000 53.6 5.3

2005 0129 2221 40.1 12.250 96.543 25.1 5.0

2005 0129 2241 16.7 8.549 95.387 30.0 5.0

2005 0129 2258 31.4 6.822 93.996 18.1 6.8

2005 0130 0006 16.5 3.987 94.578 30.0 6.2

2005 0130 0039 37.8 10.067 94.462 25.1 4.8

2005 0130 0041 51.2 8.701 92.066 15.8 5.1

2005 0130 1254 49.6 9.584 92.346 15.5 4.8

2005 0130 1413 31.5 9.083 92.429 11.0 4.6


160

2005 0130 1444 11 12.367 94.364 25.0 5.0

2005 0130 1447 25.8 10.114 94.208 26.7 5.3

2005 0130 1450 11.6 11.325 95.941 64.7 5.5

2005 0130 1530 21.4 10.185 94.514 25.1 5.0

2005 0130 1532 43.1 9.330 96.988 30.0 6.2

2005 0130 1659 4.3 11.967 95.922 30.0 5.6

2005 0130 1748 57.1 9.122 93.500 25.0 5.9

2005 0130 1845 10.8 8.005 93.109 38.4 5.4

2005 0130 1901 29.1 8.829 94.586 25.3 5.1

2005 0130 2004 58 8.911 95.287 50.1 5.1

2005 0130 2010 26.7 12.756 93.079 34.8 5.0

2005 0130 2017 8.3 8.533 93.521 0.2 5.1

2005 0130 2149 12.2 9.329 94.343 43.9 4.7

2005 0130 2304 2.6 12.533 96.120 30.0 4.7

2005 0130 2307 25.8 11.5 38 94.886 160.0 4.7

2005 0130 2330 26.7 9.527 93.507 29.5 4.8

2005 0131 0010 29.1 10.108 95.026 26.8 5.1

2005 0131 0016 36.5 9.709 92.365 24.5 4.6

2005 0131 0114 12.2 7.866 90.813 42.5 5.7

2005 0131 0146 0.2 14.119 93.215 14.2 5.0

2005 0131 0220 37.4 11.494 94.807 25.7 5.4

2005 0131 0254 11.7 11.290 94.196 26.4 5.1

2005 0131 0343 1.9 10.030 95.247 27.1 5.8

2005 0131 0354 37.9 12.813 92.965 9.4 4.9

2005 0131 0401 14.5 8.913 94.252 34.2 5.3

2005 0131 0431 40 12.957 92.470 21.4 5.4

2005 0131 0518 29.5 12.265 93.982 73.9 5.2

2005 0131 0524 38.3 9.781 92.520 25.1 5.3

2005 0131 0543 2.1 12.760 93.624 49.6 5.3

2005 0131 1252 7 11.457 96.041 50.9 5.2

2005 0131 1314 26.2 10.799 95.507 26.2 6.1

2005 0131 1530 42 10.727 92.531 28.9 4.8

2005 0131 1533 47.9 10.450 94.742 25.1 5.1

2005 0131 1546 55.4 10.091 92.446 13.3 4.9

2005 0131 1752 30 12.849 92.569 40.8 4.9

2005 0131 1755 56.8 15.351 94.344 18.2 5.5

2005 0131 1802 52 9.990 92.418 30.0 4.6

2005 0131 1831 15.9 9.032 92.505 30.0 5.2

2005 0131 1909 22.7 13.908 93.199 27.5 5.0

2005 0131 2042 19.5 6.951 94.359 15.4 5.7

2005 0131 2052 28.3 16.513 93.844 30.0 5.9

2005 0131 2055 57.1 11.875 92.295 9.1 4.6

2005 0131 2121 5.6 13.772 93.210 30.0 5.1

2005 0131 2124 48.6 9.855 94.547 25.1 4.6

2005 0131 2131 20.5 9.657 95.224 25.9 4.8

2005 0131 2159 57.8 10.041 95.147 51.2 5.1

2005 0131 2234 11.3 8.419 96.321 23.3 5.3

2005 0131 2304 3.1 12.994 93.801 30.0 5.1

2005 0131 2308 26.8 11.045 96.493 50.5 4.9


161

TABLE-8 TABLE-8(Contd.)

Aftershock Parameters

Y M D HM SS ( Deg. ) (Deg. ) ( km ) Ml

Double-station Method 2005 1 9 855 47.1 11.190 92.295 30.0 5.3

2005 1 9 1811 55.4 10.286 92.022 30.0 4.9

Origin Time LAT LONG DEPTH MAG 2005 1 9 1822 53 11.026 91.975 30.0 4.6

Y M D HM SS ( Deg. ) (Deg. ) ( km ) Ml 2005 1 9 1844 9.5 11.555 91.206 56.9 5.5

2005 1 9 1915 14.7 10.742 92.422 25.1 4.7

2005 1 8 923 5.4 11.673 92.738 0.1 4.4 2005 1 9 1919 29.6 11.002 93.082 30.0 4.8

2005 1 8 1010 50.6 11.557 92.725 10.7 5.0 2005 1 9 2016 39.2 9.294 92.973 14.1 4.2

2005 1 8 1618 19.9 11.165 91.780 25.2 5.1 2005 1 9 2043 22.9 10.127 95.166 43.4 5.2

2005 1 8 1639 0.5 11.145 91.843 25.0 5.4 2005 1 9 2050 14.4 11.659 92.731 0.1 4.6

2005 1 8 1641 2.4 10.288 91.916 25.1 5.2 2005 1 9 2056 52.7 8.534 92.931 0.1 5.0

2005 1 8 1715 29.3 9.776 93.382 25.0 5.2 2005 1 9 2102 53.1 11.337 91.145 30.0 4.9

2005 1 8 1730 26.3 9.529 92.761 30.0 5.3 2005 1 9 2131 23.4 11.651 93.380 30.0 4.6

2005 1 8 1733 52.7 11.678 92.782 0.1 4.4 2005 1 9 2141 30 9.127 92.828 0.1 4.0

2005 1 8 1740 29.8 9.022 92.626 0.3 4.8 2005 1 9 2145 40.4 10.306 94.032 25.0 4.7

2005 1 8 1741 29.2 11.041 92.442 30.0 5.3 2005 1 9 2152 28.5 11.659 92.732 9.8 4.6

2005 1 8 1750 41 11.038 92.009 30.0 5.2 2005 1 9 2155 3.1 11.363 92.520 30.0 4.8

2005 1 8 1813 32.2 9.351 92.680 30.0 4.7 2005 1 9 2210 22.9 20.739 86.622 30.0 7.4

2005 1 8 1840 25.9 9.931 91.826 25.0 5.2 2005 1 9 2234 49.6 11.590 92.815 7.9 4.0

2005 1 8 1848 25.7 9.154 92.822 0.1 5.0 2005 1 9 2320 45.2 11.098 93.559 40.4 6.6

2005 1 8 1859 1.8 11.538 92.430 30.0 4.4 2005 1 10 26 0.4 9.039 91.051 30.0 5.5

2005 1 8 1904 1.1 9.624 93.094 30.0 4.6 2005 1 10 101 45.6 11.817 92.702 0.1 5.2

2005 1 8 1906 52.6 10.635 91.647 30.0 5.0 2005 1 10 103 55.5 9.399 92.996 138.8 6.3

2005 1 8 1919 16.3 9.313 93.420 26.2 4.9 2005 1 10 220 34.3 11.718 93.208 30.0 6.4

2005 1 8 1931 13.3 11.410 92.293 25.1 4.9 2005 1 10 950 22.2 11.658 92.728 0.1 5.8

2005 1 8 1937 15.4 8.290 92.793 28.4 5.2 2005 1 10 1716 25.8 10.430 93.230 25.1 4.8

2005 1 8 1959 11.1 8.337 91.675 0.2 5.0 2005 1 10 1750 17.5 11.460 92.756 17.5 4.5

2005 1 8 2002 17.4 11.628 92.176 30.0 6.0 2005 1 10 1923 2.8 8.997 96.725 30.4 5.8

2005 1 8 2006 52.2 11.242 92.907 30.0 4.3 2005 1 10 1927 44.6 8.973 92.877 30.0 5.0

2005 1 8 2110 21.6 9.770 93.152 30.0 5.0 2005 1 10 1942 26.4 11.100 93.451 29.4 4.8

2005 1 8 2134 35.2 9.444 93.521 30.0 5.2 2005 1 10 1958 59.2 9.907 93.716 25.0 4.7

2005 1 8 2140 36.2 11.005 92.600 26.4 4.6 2005 1 10 2128 44.2 13.474 91.695 136.2 6.0

2005 1 8 2147 34.4 9.154 92.931 30.0 4.4 2005 1 10 2139 31.3 9.147 92.817 0.1 4.1

2005 1 8 2153 50.7 9.909 93.484 25.1 5.0 2005 1 10 2224 43.6 10.653 90.724 30.0 5.1

2005 1 8 2232 7.3 11.685 92.552 30.0 4.5 2005 1 10 2240 11 8.934 92.518 30.0 4.6

2005 1 8 2325 32 8.988 90.578 34.8 5.8 2005 1 10 2308 44.5 9.147 92.840 0.1 5.1

2005 1 8 2333 9.8 10.613 91.807 25.1 4.8 2005 1 10 2344 53.7 11.073 94.650 30.0 6.1

2005 1 8 2344 47.8 9.233 92.898 30.0 5.7 2005 1 26 9 18.6 11.261 90.258 25.0 5.2

2005 1 8 2348 22.1 9.602 92.892 30.0 5.2 2005 1 26 59 51.2 12.103 93.359 30.0 4.9

2005 1 9 15 21.6 9.587 92.805 25.0 4.8 2005 1 26 112 12.6 11.851 93.127 30.0 4.4

2005 1 9 58 36.1 10.568 94.103 30.0 5.1 2005 1 26 121 45.6 11.273 92.352 24.4 4.6

2005 1 9 706 43.4 11.287 92.618 30.0 5.3 2005 1 26 159 49.1 16.228 93.726 30.0 5.8


162

TABLE-9 TABLE-9(Contd.)

2005 1 6 2049 26.5 11.535 94.680 30.0 5.4

Aftershock Parameters 2005 1 6 2053 22.9 10.515 91.780 30.0 6.1

2005 1 6 2115 47.3 12.093 92.700 30.0 5.4

2005 1 6 2118 7.3 12.427 93.880 30.0 5.2

Single-station Method 2005 1 6 2123 52.6 12.116 92.690 30.0 4.4

2005 1 6 2126 24.0 11.310 92.600 30.0 4.7

Origin Time LAT LONG DEPTH MAG 2005 1 6 2128 19.7 12.154 92.540 30.0 4.5

Y M D H M SS ( Deg. ) (Deg. ) ( km ) Ml 2005 1 6 2130 11.3 10.169 94.250 30.0 4.4

2005 1 6 2135 34.6 10.945 94.000 30.0 3.9

2005 1 6 1155 43.4 10.150 92.410 30.0 7.2 2005 1 6 2143 40.2 12.181 91.370 30.0 5.0

2005 1 6 1208 59.3 11.246 92.570 30.0 5.3 2005 1 6 2145 37.9 10.925 94.010 30.0 6.4

2005 1 6 1235 22.5 10.277 92.220 30.0 5.9 2005 1 6 2148 29.0 11.559 91.220 30.0 5.2

2005 1 6 1240 26.2 13.108 93.280 30.0 5.7 2005 1 6 2226 59.9 12.191 92.540 30.0 4.7

2005 1 6 1256 10.6 10.271 92.340 30.0 6.5 2005 1 6 2240 19.1 11.669 93.700 30.0 5.3

2005 1 6 1319 58.3 10.282 93.320 30.0 5.6 2005 1 6 2249 37.8 12.214 92.780 30.0 4.5

2005 1 6 1333 57.5 12.869 91.920 30.0 5.6 2005 1 6 2311 0.1 10.629 93.220 30.0 5.3

2005 1 6 1509 53.0 12.659 91.620 30.0 5.9 2005 1 6 2317 15.2 10.476 93.600 30.0 4.7

2005 1 6 1520 52.2 11.303 93.660 30.0 5.6 2005 1 7 1316 0.2 11.042 94.280 30.0 5.8

2005 1 6 1527 5.0 12.794 93.700 30.0 5.5 2005 1 7 1436 0.6 11.803 93.110 30.0 5.0

2005 1 6 1536 22.4 11.801 92.360 30.0 5.0 2005 1 7 1441 27.9 11.373 92.220 30.0 5.7

2005 1 6 1551 4.1 12.684 92.890 30.0 5.3 2005 1 7 1447 11.6 11.415 92.730 30.0 4.7

2005 1 6 1630 19.9 12.321 93.540 30.0 5.0 2005 1 7 1520 7.2 12.373 92.720 30.0 4.8

2005 1 6 1632 39.4 12.956 91.990 30.0 5.3 2005 1 7 1535 37.7 11.898 92.670 30.0 5.1

2005 1 6 1640 2.4 12.954 91.960 30.0 5.2 2005 1 7 1619 2.1 10.628 92.700 30.0 5.2

2005 1 6 1702 4.9 12.204 91.350 30.0 4.9 2005 1 7 1636 1.3 12.464 92.480 30.0 5.1

2005 1 6 1753 13.9 11.683 93.860 30.0 5.4 2005 1 7 1703 25.7 11.894 92.130 30.0 4.8

2005 1 6 1807 8.1 10.173 92.830 30.0 5.7 2005 1 7 1819 59.9 11.904 91.570 30.0 4.7

2005 1 6 1819 59.6 11.840 93.150 30.0 5.4 2005 1 7 1850 23.7 13.156 92.180 30.0 5.2

2005 1 6 1824 46.4 12.561 92.660 30.0 4.8 2005 1 7 1852 40.7 11.605 93.270 30.0 4.3

2005 1 6 1831 49.5 11.016 93.260 30.0 4.9 2005 1 7 1856 54.2 11.951 92.600 30.0 5.1

2005 1 6 1834 30.9 10.380 92.160 30.0 5.1 2005 1 7 1902 18.9 12.986 91.960 30.0 5.9

2005 1 6 1836 18.0 12.074 93.180 30.0 4.6 2005 1 7 1910 4.6 12.378 92.330 30.0 5.1

2005 1 6 1838 34.2 11.926 93.210 30.0 4.5 2005 1 7 1914 31.0 12.153 93.080 30.0 4.7

2005 1 6 1844 26.6 10.592 91.820 30.0 5.4 2005 1 7 1932 52.1 12.646 92.650 30.0 4.5

2005 1 6 1855 4.8 11.844 91.380 30.0 4.1 2005 1 7 1950 36.7 11.903 92.990 30.0 4.3

2005 1 6 1900 15.3 11.999 92.680 30.0 4.0 2005 1 7 1952 49.0 13.058 92.440 30.0 4.6

2005 1 6 1901 54.3 11.035 94.030 30.0 5.1 2005 1 7 2008 41.7 12.364 92.500 30.0 5.2

2005 1 6 1908 9.9 12.850 93.600 30.0 4.7 2005 1 7 2027 44.3 11.736 92.800 30.0 4.5

2005 1 6 1928 7.0 13.342 91.870 30.0 5.5 2005 1 7 2029 22.0 10.277 92.300 30.0 5.3

2005 1 6 1943 7.3 12.205 92.540 30.0 5.4 2005 1 7 2035 21.9 13.593 92.440 30.0 5.6

2005 1 6 1956 5.2 10.294 92.980 30.0 5.0 2005 1 7 2037 49.3 10.347 92.090 30.0 5.1

2005 1 6 2001 13.3 12.101 91.340 30.0 5.5 2005 1 7 2047 21.3 13.551 92.290 30.0 5.1

2005 1 6 2010 2.1 10.272 93.840 30.0 5.7 2005 1 7 2050 25.4 12.693 92.800 30.0 5.5

2005 1 6 2024 59.1 11.466 93.200 30.0 5.2 2005 1 7 2118 40.2 10.924 94.350 30.0 5.1

2005 1 6 2026 37.2 12.303 92.980 30.0 4.6 2005 1 7 2129 53.0 11.266 92.360 30.0 5.2

2005 1 6 2031 5.0 11.609 93.780 30.0 5.5 2005 1 7 2136 10.0 12.096 92.380 30.0 4.6

2005 1 6 2032 52.4 12.226 92.290 30.0 4.7 2005 1 7 2140 28.4 12.349 92.990 30.0 5.2

2005 1 6 2035 59.7 12.042 93.130 30.0 4.5 2005 1 7 2147 37.2 11.430 93.460 30.0 4.7

2005 1 6 2040 48.9 12.678 93.030 30.0 4.9 2005 1 7 2150 28.6 12.042 92.010 30.0 6.0

2005 1 6 2044 57.3 14.875 93.730 30.0 5.4 2005 1 7 2216 5.6 12.134 92.790 30.0 4.6

2005 1 6 2047 22.9 11.940 93.070 30.0 4.4 2005 1 7 2257 11.5 12.756 91.220 30.0 4.1


163

TABLE-9(Contd.) TABLE-9 (Contd.)

2005 1 7 2336 23.7 10.834 92.480 30.0 4.8 2005 1 8 808 41.5 12.371 91.970 30.0 5.0

2005 1 7 2356 15.1 11.784 93.280 30.0 5.1 2005 1 8 812 46.3 9.677 92.240 30.0 5.3

2005 1 8 5 26.7 11.845 91.450 30.0 4.9 2005 1 8 815 31.9 9.785 92.150 30.0 5.5

2005 1 8 10 2.9 12.222 93.160 30.0 5.4 2005 1 8 820 5.3 9.234 92.890 30.0 4.3

2005 1 8 15 26.6 11.825 92.730 30.0 4.9 2005 1 8 839 37.2 9.340 91.980 30.0 5.2

2005 1 8 18 20.0 12.263 92.880 30.0 4.7 2005 1 8 852 21.5 9.761 92.160 30.0 5.0

2005 1 8 33 26.5 11.885 92.320 30.0 4.8 2005 1 8 856 29.3 10.539 92.290 30.0 5.6

2005 1 8 38 49.6 12.489 91.850 30.0 5.7 2005 1 8 859 24.1 9.864 93.650 30.0 5.0

2005 1 8 49 53.1 11.372 95.660 30.0 5.5 2005 1 8 902 29.2 11.665 93.210 30.0 4.4

2005 1 8 116 9.3 11.518 93.180 30.0 4.5 2005 1 8 906 43.7 11.264 93.700 30.0 5.6

2005 1 8 120 57.6 11.159 93.230 30.0 4.9 2005 1 8 921 21.5 9.986 93.090 30.0 4.8

2005 1 8 248 8.5 14.188 92.120 30.0 6.6 2005 1 8 929 17.9 8.520 93.430 30.0 5.0

2005 1 8 254 25.6 12.867 94.230 30.0 5.7 2005 1 8 931 17.3 12.655 92.640 30.0 5.0

2005 1 8 257 27.7 11.637 93.080 30.0 4.9 2005 1 8 940 54.1 9.141 94.110 30.0 5.1

2005 1 8 310 58.5 12.043 92.710 30.0 4.7 2005 1 8 949 47.9 9.705 92.130 30.0 5.7

2005 1 8 330 59.5 12.066 92.930 30.0 4.7 2005 1 8 956 43.5 8.942 93.520 30.0 5.5

2005 1 8 352 45.6 12.758 92.240 30.0 6.1 2005 1 8 958 18.1 9.159 93.800 30.0 5.1

2005 1 8 406 50.3 12.168 92.420 30.0 4.9 2005 1 8 1005 15.4 9.927 92.390 30.0 4.8

2005 1 8 408 48.2 12.451 91.940 30.0 5.8 2005 1 8 1008 0.5 9.931 91.810 30.0 5.6

2005 1 8 421 40.5 12.117 92.270 30.0 5.0 2005 1 8 1019 24.1 11.673 93.170 30.0 4.9

2005 1 8 450 54.2 12.004 92.530 30.0 6.2 2005 1 8 1023 54.2 9.682 91.700 30.0 5.4

2005 1 8 503 25.4 12.305 92.570 30.0 5.0 2005 1 8 1026 42.5 10.294 92.620 30.0 5.5

2005 1 8 528 17.8 12.229 92.500 30.0 4.9 2005 1 8 1037 21.3 9.289 93.710 30.0 5.0

2005 1 8 541 44.3 14.400 91.110 30.0 6.1 2005 1 8 1040 51.7 11.418 92.490 30.0 6.6

2005 1 8 547 54.1 14.128 92.620 30.0 5.8 2005 1 8 1050 41.5 11.945 92.610 30.0 4.7

2005 1 8 638 24.8 11.702 93.320 30.0 5.0 2005 1 8 1054 33.4 9.507 93.540 30.0 5.4

2005 1 8 652 18.9 8.010 93.710 30.0 5.4 2005 1 8 1106 33.4 12.137 92.710 30.0 5.2

2005 1 8 704 38.9 10.145 93.060 30.0 5.1 2005 1 8 1130 16.3 12.078 92.610 30.0 5.5

2005 1 8 708 59.0 9.705 92.780 30.0 4.9 2005 1 8 1159 50.8 11.638 93.210 30.0 5.2

2005 1 8 712 16.7 10.201 94.860 30.0 6.7 2005 1 8 1224 9.6 10.426 93.990 30.0 6.0

2005 1 8 721 55.1 9.483 94.060 30.0 5.5 2005 1 8 1231 34.8 11.913 92.640 30.0 6.5

2005 1 8 727 56.0 11.390 95.160 30.0 5.9 2005 1 8 1332 16.9 12.162 92.510 30.0 4.9

2005 1 8 745 17.6 11.700 93.410 30.0 4.9 2005 1 8 1403 32.4 11.594 93.090 30.0 4.9

2005 1 8 755 46.1 8.343 93.190 30.0 5.1 2005 1 8 1405 21.1 11.173 93.050 30.0 5.1

2005 1 8 801 0.6 11.014 93.340 30.0 5.4 2005 1 8 1723 45.0 9.528 92.830 30.0 5.5

2005 1 8 805 16.7 11.005 93.230 30.0 5.0 2005 1 9 2026 11.6 10.538 93.230 30.0 5.3

Segment I: Srikakulam- Pulicat

Segment II: Chennai- Nagapattinam

Segment III: Nagapattinam- Kanyakumari

Segment IV: Kanyakumari- Cochin


165

TSUNAMI SURVEY IN ANDAMAN AND NICOBAR GROUP OF ISLANDS

T. Ghosh, P. Jana, T. S. Giritharan, S. Bardhan, S. R. Basir and A K Ghosh Roy.

Geological Survey of India, Eastern Region,DK-6, Sector II, Salt Lake, Kolkata 700091

INTRODUCTION

A tsunami is an oceanic gravity wave generated by submarine earthquakes or othergeological processes such as volcanic eruptions, landslides or meteorite impact. Generally ashallow, large, thrust earthquake (of Mw= 7.5 or above) has the potential of generating hazardoustsunami. The earthquakes that generate tsunamis are known as ‘tsunamigenic earthquakes’.

In deep open sea tsunami travels at a speed of 700-800 km/hr; the distance between crests of tsunami waves may exceed 100km and the crest height may be less than 1m. As the tsunami approaches the coast (i.e. shallower water), its speed decreases sharply while the wave height increases many times even up to 30m. As the successive trains of waves hit the coast, the sea water penetrates the coast with high speed and causes extensive inundation which is called ‘Run up’. Depending on the bathymetry and the coastline configuration the run up from the same tsunami can vary from place to place. The power of a tsunami is a function of its wave speed and wave height.

The coasts of Pacific Ocean experience higher tsunami frequencies than the coasts of Indian Ocean. The references of tsunamis in the Indian Ocean are found in several literatures(Berninghausen, 1966; Murthy, 1999 and Oritz and Bilham, 2003). The tsunami generate d by the Sumatra Earthquake is now considered to be the worst recorded history of tsunamis. According to one estimate, the loss of lives from this event in the Indian Ocean has been higher by several orders of magnitude in comparison to the most severe tsunamis occurred over the last 30 years in the Pacific Ocean. In India, the Andaman and Nicobar Group of Islands, and coastal states of Tamil Nadu, Andhra Pradesh and Kerala were severely affected.

Historical records of Tsunami in Andaman and Nicobar Islands

The details of past tsunamis in Andaman & Nicobar group of islands are given in Table-1.While details of the location of epicenter, death/damage caused etc. are not known, run up level up to 4 m in Port Blair, 0.76 m in Car Nicobar islands were reported.

Table-1: Run up levels for tsunamis in A&N group of islands during the period 1700-2004.

Sl.No.

Name of the area Year/Date Earthquakemagnitude

Source Run up level (m)

1. Port Blair, SouthAndaman

19.08.1868 Mw 7.5 Bay of Bengal 4.0

2. Car Nicobar island 31.12.1881 Ms 7.9 Bay of Bengal 0.76

3. Port Blair, SouthAndaman

31.12.1881 Ms 7.9 Bay of Bengal 1.22

4. A & N islands 26.6.1941 Mw 7.7 Bay of Bengal -Data source: National Geophysical Data Centre, USA.


166

TSUNAMI SURVEY

In the aftermath of the disastrous tsunamigenic earthquake of 26th December 2004 a post-tsunami field survey was taken up to study the effects of tsunami on different areas of Andaman & Nicobar group of Islands. The tsunami survey consists of measurement of run up lengths and run up heights along selected profiles, marking areas of inundation based on ground observation and taking information from local people. The tsunami survey was carried out in Little Andaman(mainly at Hut Bay), South Andaman (mainly in and around Port Blair), Car Nicobar (along Kankana-Mus sector), Great Nicobar (mainly at Campbell Bay and Joginder Nagar area). The surveyed localities in Andaman & Nicobar Group of Islands are shown in the key map (Plate-1).

SOUTH ANDAMAN

The eastern part of South Andaman is characterised by a coastline with high cliffs (broken occasionally by deep bays with steep sides), but flat slopes running into valleys are also not rare. The settlement areas are situated either on the low lands at the heads of bays or at higher slopes bordering the bays and coastal flat lands. The western part of the island is having a more gentle and gradually sloping topography facing the open sea.

According to the information provided by the local people the tsunami waves attacked three times, the first of which arrived around 0715 hrs. Of the three, the third one was the most devastating. The coastlines of the islands or low-lying areas inland, which are connected to open sea through creeks, were flooded. These areas were still under water at the time of investigation (March 2005). Inundation has been observed, along east coast of South Andaman Island and is

Plate 1: Locations of study area in

Andaman - Nicobar Islands


167

found to be restricted at Chidiyatapu, Burmanallah, Kodiaghat, Beadnabad, Corbyn’s cove andMarina Park/Aberdeen Jetty areas. Along west coast, the inundation has been observed around Guptapara, Manjeri, Wandoor, Collinpur and Tirur regions. Other than these localities, several low-lying areas adjacent to Flat Bay have also been inundated. The seawater from open sea has enteredFlat Bay from east and inundated some areas viz. Phoenix Bay, Chatham, Bamboo Flat, Dundus Point, Junglighat Jetty, Dollyganj, Garacharma and Chouldari (Fig.1). Vast stretches of cultivated lands around Sipighat, Chouldari and southwest of Wimberlygunj were inundated by seawater

Plate 2: Tsunami inundation map in South Andaman


168

Fig.-2: Crop damage due to inundationnear Chouldari, South Andaman.

entering through adjacent creeks causing extensive damages to the standing crops (Fig.2). Flooding of these low-lying areas (Plate 2) have become a permanent feature and coseismic land subsidenceseems to be the most likely cause. Roads between Garacharma and Sipighat sector (that was negotiable during high tides before the earthquake) are now getting submerged during high tides. Jetties at Phoneix Bay, Chatham, Aberdeen (Marina Park), Junglighat were damaged (Fig.3) affecting the sea traffic. During the course of investigation some of these jetties were found getting submerged at the time of high tides (Fig.4). At several places seawalls were breached; sandy to silty deposits with salt encrustations was found in a number of places invaded by seawater during tsunami (Fig.5). Flooding of the 20 MW diesel generated power plant at Bamboo Flat had caused extensive damages to the electrical and mechanical instruments disrupting the power supply to the city of Port Blair. Near shore establishments suffered heavy damages at places (Fig.6). At several places watermarks indicating standing water height were noted (Figs.7&8).

.It has been observed that along coastline, it is either the topography or the existing land

cover has controlled the intensity of inundation. The areas with higher topography on either side were unaffected. Similarly, the areas with dense mangrove cover have protected the immediate inland regions from the inundation due to tsunami.

Tsunami survey was carried out along selected profiles in Chiriyatapu, Corbyn’s Cove and Wandoor beaches (Plate-3). The results of the survey is given in Table-2

TABLE: 2 Summarized result of tsunami survey in South Andaman

AREA Date of Survey

Runuplength

Maximum run up level measure from land-sea water contact

MaximumTsunamiheight

LandwardFlowDirection

ChiriyatapuBeach

17.03.2005 130m. 4.24m 5.0m N15oW

Corbyn”sCove Beach

20.03.2005 150m. 5.48m 5.48m N55oW

WandoorBeach

16.03.2005 150m. 4.63m 6.64m N450E

Fig.-1: Aerial view of the inundation(marked by solid line) at Garacharmaarea, Port Blair, South Andaman.


169

Fig.4: Inundated Jetty at Junglighat,

Port Blair, South Andaman.

Fig.-5: Salt deposition over cultivatedland inundated during tsunami at NewManglutan, South Andaman.

Fig.3: Wall Collapse at Junglighat jetty, South Andaman.

Fig.-8: Watermark in a house nearSipighat during high tide (on 10.01.2005), South Andaman.

Fig. -7: Tsunami watermark on treebark (shown by arrow) at Guptapara jetty, South Andaman.

Fig.-6: Damaged boundary wall near Guest House at Chidiyatapu, SouthAndaman.


170

LITTLE ANDAMAN

In Little Andaman, tsunami damage survey was carried out in and around Hut Bay only. According to the eyewitnesses tsunami waves impinged on the eastern shore of this island 25 to 30 minutes after the earthquake. It was a four-wave cycle; out of which the fourth one was most devastating with a tsunami wave height of about 10 m. The tsunami water had converted the settlements at Hut Bay into rubbles within a range of 1 km inland from the seashore (Figs.9, 10 & 11). Everything was destroyed including the jetty and the breakwater. Run up level up to 3.3 m. have been noted (Fig.12). Several stretches of the coastal road between 0 km up to 11 km along the coastline got either damaged or washed away (Fig.13). At one place the mouth of a channel debouching into the sea got blocked by huge tsunami sand deposits consequently changing the flow direction of the channel (Fig.14).

Plate 3: Run up profiles across Corbyn’s cove, Chidiyatapu and Wandoor beach


171

Fig. -14: Deposition of tsunami sandobstructing a stream at Hut Bay, Little Andaman.

Fig.-12: Objects lifted to thebranches of a tree indicatingtsunami height at that point,Hut Bay, Little Andaman.

Fig.-9: Remains of a Hospital at Hut Bay, Little Andaman.

Fig.-10: Steeple of a church fell anddrifted by tsunami at Hut Bay, LittleAndaman.

Fig.-11: Bus overturned and drifted by tsunami waves crushing the wall of the STS busterminus at Hut Bay, Little Andaman.

Fig.-13: Damaged road at 7 Km. with fallen trees showing landward flow direction of

tsunami at Hut Bay 7 km, Little Andaman.


172

CAR NICOBAR

The tsunami survey was carried out along Kankana Air Base-Mus sector on the eastern coast of the island. On the basis of the survey an inundation map of the study area has been prepared (Plate-4). The area wise details of the survey is as follows:

Malacca

The Malacca is a residential area near seashore located to the east of the Administrative Headquarters of Car Nicobar. The ground height is less than 10 m. above sea level. According to local people, three pulses of tsunami waves attacked the area three times. The first wave that came 5 minutes after the earthquake was preceded by recession of the seawater up to 600-700 meters, exposing the seabed. The second and third waves came with a 10 minutes interval after the first and second waves respectively. The third wave was the strongest (maximum tsunami wave height of 11m.) and was accompanied by a loud noise. The landward flow direction measured from bent rods was towards S80

0W (Fig.15) and the back flow was towards east direction. The inundation

limit is 1.125m from the sea water/land contact (on the date of measurement) towards west and restricted up to 10 m. contour line of Survey of India toposheets. The main road runs on the axis of sand spit. Most of the house constructed over this sand spit, was destroyed (Fig.16). Some of the residential buildings were submerged and not destroyed. Traces of water level marks were visible on the walls of residential houses (Fig.17). Fine to medium grained yellowish white coloured sand deposition was recorded upto a height of 0.8 to 1.0 m above ground level. The advancement of sea towards land by upto 60-70 m. as noticed at places (Fig.18), and is most likely to be related to the coseismic land subsidence.

Air force colony, Kankana

Located just south of Malacca, the ground height is less than 10 m. above sea level. The tsunami waves attacked the area three times with a maximum tsunami wave height of 11 m (Fig. 19). Inundation limit was found to be up to 1.25 km inland. The landward tsunami wave direction was towards N75

0W; the measurements were taken from bent rod, fallen lamppost, alignment of

grass etc. (Fig.20). Fine to medium grained yellowish sand deposition up to a maximum height of 0.8 to 1.0 m from ground level observed. Watermarks up to a height of 5 m were recorded at residential building, Ramps etc.

The northern part of the area being situated at a lower elevation than that of the southern part was much more devastated but the inundation limit did not crossed the 10 m contour line of Survey of India toposheet. The residential buildings, hospital etc. were almost reduced to rubbles but some round shaped structures like water tank, primary school, shopping complex etc. were eitherrelatively less damaged or remained intact (Fig.21).

The impact of the waves was so severe that four Oil tankers of IOC were thrown almost 800 m from the seashore near Malacca to Air force colony main gate (Fig.22). The Ramp, which saved almost 250 people, has been broken in its southern and northern ends (Fig.23). Series of E-Wtrending cracks were observed on the metalled main road of the Air Force Colony area.

ChuckchuchaThis area is located north of Malacca. The maximum run up distance in the area has been

measured to be 1.25 km. from the seawater/land contact. Here also it was a three wave cycle; the


173

Fig. -15: Bent rods by the forceof tsunami at Malacca, Car Nicobar, indicate landward flow direction.

Fig. -16: Nature of devastation atMalacca, Car Nicobar.

Fig.-17: Damaged houses during high tide (24.03.2005) near Malaccajetty, Car Nicobar. Watermarks (shown by arrow) on the walls are visible.

Fig. -19: Devastation around Air ForceColony, Car Nicobar. (Tin roof damaged by tsunami waves indicated by the arrow,

implying tsunami wave height). Fig. -20: Bent lamppost indicatinglandward tsunami flow direction at

Air Force Colony, Car Nicobar.

Fig.-18: Aerial view showingadvancement of sea at Malacca, Car Nicobar. Inundated localities shown

within circle.


174

maximum tsunami wave height of about 12.0 m. was observed by the local people during the third cycle.(Fig.24). At places, coconut trees were uprooted from the eastern side of the road and dumped against structures and buildings on the other side of the road due to the impact of the tsunami wave. The water level marks recorded in EHL Building = 5.25 m. The ceiling fan of the EHL hall was twisted by the impact of the tsunami wave (Fig. 25). At places, uprooted coconut trees are aligned in a westerly direction, provided an indirect evidence of landward flow direction (Fig.26). Huge quantity of sand deposited all over the place from east to west (up to a max. height of 1.0 m)

Lapati

Located to the north of Chuckchucha the area also experienced a three-wave cycle with the maximum tsunami wave height of 12. m. Here, The frontal flow direction has been measured to be S70

0W (from bent bolt and rod) (Fig. 27). Seawater penetrated 1.125 Km. inland. Most of the

single storied buildings on the eastern and western side of the road were ripped away leaving only the foundations intact (Fig.27). Some of two storied RC buildings were also damaged. The debris materials from the eastern side has been dragged and thrown all over towards the western side of the road. Fewer trees were found amongst the debris. The deposition of fine to medium grained sand was found all over the places. At places scouring of sand has been noted.

Some mangled cars were also noticed among the debris. Still northward at Mus jettybreakwater was damaged (Fig. 28). Also a hundred ton pontoon has been washed ashore bytsunami wave near Mus jetty (Fig. 29). The result of the tsunami survey in Car Nicobar along selected profiles is given in the Table -3.

Table 3: Summarised result of tsunami survey in Car Nicobar

AREA Date ofSurvey

Run uplength

Maximum run uplevel measuredfrom Land-seawater contact

Maximumtsunami waveheight

LandwardFlowDirection

Air force colony

28.03.2005 1.25 km. 5.0m 11.0m N75oW

Malacca 26.03.2005 1.125 km. 5.5m 11.0m S80oW

Chuckchucha 27.03.2005 1.250 km. 5.25m 12.0m WesterlyLapati 27.03.2005 1.125 km. 5.20m 12.0m S70

oW

It has been observed that the inundation limits from the Air Force colony area to Kinyuka and the area around Mus are restricted below 10 m contour of the toposheet. On the other hand the stretch between Chukchucha and Kinmai, the inundation limit has gone either up to 10 m or is restricted between 10 m and 20 m contours.


175

Plate 4: Tsunami inundation map, Eastern Coast, Car Nicobar

(Inset showing run-up elevation measurements along profiles)


176

Fig. -21: A lone water tank standing amongst ruins opposite to hospital

at Air Force Colony, Car Nicobar.

Fig.-22: Large oil tank ripped apart from its foundation and carried 800m towards Air Force Colony fromMalacca side, Car Nicobar.

Fig. -23: Broken southern part of the ramp at Air Force Colony, CarNocobar.

Fig.-24: Twigs of remainingcoconut trees ravaged bytsunami indicating tsunamiheight at Chukchucha, CarNicobar.

Fig.-25: Twisted ceiling fan at about 5 m height due to impact of tsunami at

Chuckchucha, Car Nicobar.

Fig. -26: Uprooted coconut treesdumped against a damaged building at Chukchucha, Car Nicobar.


177

Fig.-30: Prostrated fence treesindicating landward tsunami flowdirection at Campbell Bay, GreatNicobar.

Fig.-31: Remains of a habitated area opposite to school, Campbell Bay,Great Nicobar.

Fig. -27: Flattened rows of houses at Lapati, Car Nicobar. The bent rod (shown by arrow) indicates landward tsunami flow direction.

Fig.-28: Damaged break water at Mus jetty, Car Nicobar.

Fig. -29: A hundred ton Pontoondrifted on land by tsunami near Mus jetty, Car Nicobar.

Fig.-32: Deposition of tsunami sand at

Campbell Bay, Great Nicobar.


178

GREAT NICOBAR

The tsunami survey was carried out in and around Campbell Bay and Joginder Nagar area. On the basis of the survey an inundation map of the study area has been prepared (Plate-5).

Campbell Bay

Tsunami had caused extensive damages to this main locality of Great Nicobar Island. According to the local information, the tsunami waves hit the area three times. The first wave came within 5 minutes of the earthquake. The second and third waves came10 minutes after first andsecond waves respectively. The second wave was the strongest with a loud noise. The landward tsunami wave flow direction was towards N25

0W, as indicated by bent rods, fallen lamppost, aligned

trees etc. (Fig.30). The return flow direction was towards S100E. The inundation limit varies from 250-550 m. within the study area. The buildings (mostly

made up of wood and concrete) between the road and sea were highly damaged (Fig.31). The water level marks recorded at Airport building (2.32 m) Joseph Nursery School (2.52 m) and stadium (0.90 m). Many fishing boats were found strewn around among the debris. Yellowish white, medium to coarse-grained sand with variable thickness (upto a max. of 0.8 m) has been deposited parallel to main road (Fig.32).

During the course of investigation, an advancement of sea towards land by 100-120m.havebeen noticed. As a result a vast area along the coastal tract that has been developed over the years are now remaining submerged during high tide (Fig. 33). At places, sea walls have been broken and many dug wells found to be submerged. Nearly 80 m. of the approach jetty was highly damaged andwashed away.

Jogindar Nagar area

Deadly tsunami waves wreaked havoc in this densely populated area, situated 13 km. south of Campbell Bay. According to local information, tsunami waves attacked the areathrice. The first wave came 5 minutes after the main shock (0629 hrs.) with a marginal drop in sea level. Second wave came 10 minutes after the first one with a maximum height of4.84 m and caused the major destruction. The third wave came within 15 minutes after thesecond one with a lower wave height. The coastal road was damaged heavily and at places was totally washed away. Most of the houses were damaged beyond recognition with onlybasement remaining intact (Fig. 34). The dense coconut plantation along the coast failed toprovide any protection whatsoever. The maximum inundation limit due to tsunami waterintrusion has been found to be about 500 m. The front flow direction measured from the bent bolt, bent rod and lamp posts etc was. Found to be towards N500W (Fig.35) while the return flow direction is towards N350E (Fig.36). The maximum run up level in the area measured from traces of water level in house was 3.5 m. Yellowish white to white colour sanddeposits (up to 0.8-1.0m thick) were found on both sides of road and inside damagedbuildings. At some places along the shore, drifted logs from uprooted trees were found. Anumber of vehicles were also found to be damaged. The Bihari basti on the beach wascompletely wiped out. At places seawalls were breached. An advancement of seawater

during high tide up to 40-50m inland have been recorded. The result of the tsunamisurvey along selected profiles in Great Nicobar is given in Table-4.


179

Fig.-33: Inundated area during hightide (24.03.2005) near zero point,Campbell Bay, Great Nicobar.

Fig.-34: Devastations at Joginder Nagar,

Great Nicobar.

Fig.-36: Bent lamppost towards sea indicating return flow direction,Joginder Nagar, Great Nicobar.

Fig.-35: Bent bolts indicatinglandward flow direction, JoginderNagar, Great Nicobar.

TABLE: 4 Summarized result of tsunami survey in Great NicobarAREA Date of

SurveyRunup

length

Maximum run up level measured from Land-seawater contact

MaximumTsunamiheight

LandwardFlow

Direction

Air strip, C’ Bay

22.03.2005 500 m 2.32 m 3.0 m N250W

Stadium, C’ Bay

22.03.2005 400 m 2.52 m 3.0 m N600E

AHWColony, C’

Bay

24.03.2005 250 m 1.50 m 2.2 m NorthEasterly

Oppositepower house,

C’ Bay

24.03.2005 550 m 3.00 m 3.5 m NorthEasterly

JogindarNagar*

24.03.2005 500 m 3.00 m 4.84 m N50oW

*Near Gram Pradhan, Abtar Singh’s house


180

Plate 5: Tsunami inundation map, Campbell Bay, Great Nicobar

(Inset showing run-up elevation measurements along profiles)


181

DISCUSSION

Because of their physiographic characters (surrounded by sea on all sides and narrow coast line on which most of the developmental activities are concentrated) the islands are very vulnerable to tsunami hazards. Our study has shown that there is a distinct spatial variability of tsunami damage as one goes from north to south. Due to their proximity to the epicenter, the magnitude of tsunami impact was more severe in the islands south of ten degree channel (Nicobar group of islands) than those situated to the north of the channel (Andaman group of islands). As a result, the damage and run up level in Nicobar group of islands are greater than those of Andaman group of islands. Also the western coastline (where the impact was more due to the wrap-round effect) got less affected than the eastern coastline (hit by large primary waves). It has also been observed that areas of low elevation and having a wide and shallow estuary and/bay are affected greatly .On the other hand, the shores protected by landmass, cliffs and promontories are least affected by the t sunami waves. Some of the effects of tsunami on these islands are listed below

a) Coastal flooding: Vast areas along the coast have been found to be flooded during these coastal low lands into marshy lands (e.g. areas around Garacharma, Sipighat etc. around Port Blair, South Andaman).

b) Loss of standing crops: According to a source from Central Agriculture Research Institute (CARI), the total cultivated areas affected by tsunami are in the range of 4500-5000 hectres with loss of crops. Apart from damaging the standing crops, the silt and mud deposited along with the saline water have made crop production impossible in near future.

c) Loss of lives: The Nicobar group of islands were badly damaged due to the tsunami of 26.12.2004 and 1861 people were died and more than 5000 people were missing (as on January 23, 2005). According to the sources from A & N administration, a total of 1925 people are dead and 5555 are missing. The extent of loss of lives in Andaman & Nicobar group of islands is given in Table-6.

d) Loss of drinking water resources: Inhabitants along the coasts in these islands are dependent on dug wells that tap shallow aquifer (recharged mostly by rain water) over saline water front. After 26

th December, 2004 many of the coastal dug wells are flooded by sea water thereby

causing loss of precious sources of drinking water in these areas.

e) Increased salinity: Salinity level has increased in vast areas of agricultural land due to sea water invasion. According to soil scientists of CARI the intruded seawater has high salinity of about 35 ppt.

f) Coastal erosion: Elevated sea water levels may increase the coastal erosion and the loss of trees along the coasts by the tsunami may not be adequate enough to protect them from future storm surges and tsunamis.


182

Table 6: Number of people died/missing in A&N Group of islands.

Sl.

No.

Name of island Population (as

per 2001 census)

No of people

died

No of people

missing

Persons in

relief camp *NICOBAR DISTRICT:1.

2.

3.

4.

5.

6.

7.

Car Nicobar

Teressa

Katchal

Nancowry

Camorta

Great Nicobar

Other islands of Nicobar group (evacuated)

20292

2026

5312

927

3412

7566

2533

790

50

345

1

51

336

288

348

9

4310

2

387

219

266

15550

3296

1818

934

1476

4690

ANDAMAN DISTRICTS1.

2.

3.

Andaman(include Port Blair)

Little Andaman

Other islands of Andaman

181949

17528

114607

5

56

3

14

2833

6569

Total 356152 1925 5555 42166

Data source: Andaman and Nicobar Administration.* indicating persons from the affected areas.

MITIGATION MEASURES

Tsunamis are perhaps the most catastrophic of all coastal hazards. Prediction of tsunamis is always going to be problematic considering the fact that they are high magnitude but low frequency events. Therefore, any tsunami defense system has to be a long- term measure taking intoconsideration the political, socio-economic, cultural and engineering matters. The first priority is to delineate the areas at risk on the basis of historical records and/or direct monitoring. Combining this with detailed measurement of the shape of the sea floor and the coastal topography of the identified sector will help in revealing the extent to which tsunami can invade inland and where there will be flooding.

Management of tsunami hazards can be taken broadly by two ways: i) the mega engineering approach i.e. by building concrete sea walls to hold back the waves or at least reduce their impacts and ii) by adopting geomorphologically focused natural defense system. Considering that the


183

Andaman & Nicobar group of islands is a tourist place with pristine natural beauty and have a low population density, it is both aesthetic and cost effective to adopt the second option. At a number of places within the study area presence of seawalls have failed to protect the onshore establishments. This is particularly true where the wave height was more than 2 meters. The present experience also reveals that the areas with a high density of mangroves are spared from much of the devastations. On the other hand, the areas where forest/mangrove cover is lost due to developmental activities bore the brunt of the damages caused by the tsunami waves. Also it was noted that the mangroves and the trees with low branches with a high density of leaves withstood the wave attack better than the coconut trees (see also Tsuji et al. 1995). Therefore, by conserving or replanting the coastal belts of forest and mangroves can offer a degree of protection. Also regular monitoring of beach sectors prone to erosion is required.

There should be no relocation of people in areas fronted by water and backed by estuaries, creeks and bays. In case of North, Middle and South Andaman, areas with an elevation of 10 m and above is recommended where as in case of Little Andaman as well as Nicobar group of islands, areas having an elevation of 15 m and above may be a suitable proposition. Local administration should ensure that all the critical facilities such as, hospitals, power plants, schools etc. are located outside the tsunami hazard zones. Also, banning buildings, hotels right on the shore is a measure to be strictly followed henceforth. Moving existing villages or settlements further back and upwards from the coasts is going to be unpopular because of the fact that many people in these islands depend on sea for their livelihood. In case of low lying areas in South Andaman like Sipighat, Bamboo Flat etc. it is necessary to shift population periodically to the upper elevated areas nearby, since these areas are vulnerable for flooding due to rain and tidal water invasion. For identifying areas for resettlement large-scale maps with contour interval of 5m or less should be prepared. Those maps used inconjunction along with the land use map on the same scale will help in selecting suitable areas for resettlement. The data given in the inundation maps generated through this work would help inplanning for future tsunamis in these Islands by better defining inundation zones and what segments of the coast were hardest hit by the tsunami.

It is also important to impart proper education to local people regarding the various aspects of tsunami, which is a less frequent event as compared to the earthquake. This will be the least expensive but most effective in mitigating the loss of human lives in case of a future tsunami. It has been learnt that in Car Nicobar many people ran towards the sea to see sudden retreat of seawater without knowing the consequences. The government official, schoolteachers etc. may be educated first in this regard so that they can take appropriate measures in case of an emergency. Memorials should be built at the worst hit sites like Car Nicobar, Katchal to remind future generations of this disaster and thus discourage resettlement within the hazardous zones.

Finally, authority should device some warning system to alert people in case of an impending tsunami. This involves planning and signposting evacuation routes, so that, people know which way to go to get to a safer place. Evacuation drills should be conducted annually, preferably on 26

th

December, the anniversary of the disaster.


184

ACKNOWLEDGEMENT

The authors are grateful to Dr. M. K. Mukhopadhyay, Deputy Director General, Eastern Region, GSI for his constant support, encouragement and overall guidance in the field and atheadquarters. Dr. M.M. Mukherjee, Deputy Director general, Operation: WB-Sik-A&N and the Director, Project Andaman, ER took keen interest and provided necessary logistic support during the second phase of the work. Cooperation received from the Chief Secretary and other officials of Andaman Administration is gratefully acknowledged. In this regard, special thanks are due to the Director and officials of Department of Science and technology (specially Mr. Hrishikesh, Senior Scientist), officials of APWD, Assistant Commissioner of Campbell Bay and Deputy commissioner and Assistant Commissioner of Car Nicobar. Sincere thanks are due to all the fellow scientists of GSI who have helped in different stages. Last but not the least, the cooperation received from the innumerable local people of all the islands visited by the authors at different stages of the work is sincerely appreciated. A study of this nature could not have been made without their help.

REFERENCES

Berninghausen, W.H. (1966): Tsunamis and seismic seiches reported from regions adjacent to the Indian Ocean. Bull. Seis. Soc. Am. V. 56 (1), p. 69-74.

Murthy, T.S. (1999): Tsunamis on the coastlines of India. Science of tsunami hazards. V. 17 (3), p. 167.

Ortiz, M. and Billham, R. (2003): Source area and rupture parameters of the 31st December 1881 Mw

7.9 Car Nicobar earthquake estimated from tsunami recorded in the Bay of Bengal. Jour. Geophys. Res. V. 108 (B4) [2002 JB 001941 RR 2003].

Tsuji, Y., Matsutomo, H., Imamura, F., Takeo, M., Kawata, Y., Matsuyama, M.,Takahashi, T.,Surarj and Harjadi, P. (1995). Damage to coastal villages due to the 1992 Flores island earthquake tsunami. PAGEOPH. V.144 (3- 4). p. 481-523.


185

TSUNAMI SURVEY IN THE SRIKAKULAM- PULICAT SEGMENT ANDHRA PRADESH

M. Raju, B.K. Bhandaru, V. Singaraju and B.M. Shah Geological Survey of India,

GSI complex, Bandlaguda, Hyderabad 500 068.

INTRODUCTION

Consequent to the tsunami that lashed the Indian coast on 26th

December 2004, field studies have been carried out along the 974 km long Andhra Pradesh coast (Plate 1)during 30

th December

2004 and 7th January 2005 to assess the impact of tsunami on coastal landforms and to make an inventory of damages. Data on loss of life, damages to the dwellings and structures, extend of inundation; wave height and run-up have been collected during fieldwork (see Tables 1- 7). In general, minor erosion has been observed south of Nellore whereas in Prakasam, Guntur, Krishna,West Godavari, East Godavari districts and Yanam, about 1 m thick sand was deposited at many places. In the northern districts of Visakhapatnam, Vizianagaram and Srikakulam, no visible changes in the coastline have been observed. Constructions in the beach near the waterfront have been generally affected. The creeks and rivers joining the sea helped to dissipate the energy of tsunami waves. As a result, water levels in those creeks and rivers rose to that extent. Plantations such as casuarinas present along the coast and mangroves in the swamps helped in dissipating wave energy and restricted inundation. As per available information, in Andhra Pradesh about 106 people died and 7 reported missing due to tsunami. About 301 villages have been hit affecting 2.11 lakh people. 1,557 dwelling units have been damaged; 195 cattle have been lost; 790 ha cropped area affected. The district-wise description of the impacts are given below:

NELLORE DISTRICT

The tsunami hit the Nellore coast around 0830 hrs and the wave action continued for about 3 to 4 hrs, mainly in three cycles. About 5m high water splashes have been reported during tsunami. The average run-up is about 1km. The stretch between Tada and Kavali has been worst affected in this district (Table-1). Vakadu, Tupilipalem, Ramudupalem, Mypadu, Gangapatnam, Pallepalem,Krishnapuram, Vottur, Lakshmipuram, Pudikuppam, Monapalem, Balireddipalem, Whitekuppamand Ramathirtham are some of the worst affected villages. Aquaculture ponds have been breached. Seawater has reached the vicinity of Sriharikota Rocket Launching Station. However no damage to the station is reported or observed. The first wave hit the Kottasatram coast at about 0900 hrs with swirling action carrying lot of silt. The second wave which was more damaging hit the coast around 0930 hrs. The sea regressed for about 100m in between. The seawater entered through the existing creek for about 1.5km. Few boats were pushed ashore for about 200m. At Mypadu Pallepalem (Fig.1 and 2), the first wave hit the coast around 0900 hrs with a splash of about 6m. The second one was slightly less in height and hit the coast around 0930 hrs. The sea has regressed for about 500m in between. Inundation was about 1km along the creek Damages to the thatched huts, fishing boats and nets have been reported. Gangapatnam Pallepalem has been surrounded by water from the two arms of the creek. The first wave hit the coast around 0830 hrs with 7-8m splash. The second one hit the coast around 1000 hrs and the wave action continued for about 3 to 4 hrs. The seawater has gone up to 2km along the creek. Few deaths have also been reported.


186

PRAKASAM DISTRICT

The tsunami hit the Prakasam coast three times in a span of 3-4 hours (Table-2). The second spell was the most furious. Water inundated the coastal belt that includes Mondivaripalem,Karlapalem and Pallepalem in Guntur Mandal. Thatched houses near the seafront (Fig.3), fishingboats and nets have been damaged. At Vadarevu, seawater inundated up to a maximum of 300m. Splash height up to 7m has been reported. Fluctuation in the sea level continued for 16 hours. Before the onset of tsunami, the sea retreated for about 300m exposing the seabed. At Pallepalem the seawater inundated up to 500m with a splash of 5m. The damage has been minimised by the presence of casuarinas plantation as bio-barrier. However, fishing boats and nets near the shore have been damaged. Kottapatnam Pallepalem located about 200m away from the seafront has been saved because of the coast parallel road. The first wave moved very slowly and hit the coast around 0900 hrs. The second wave with a splash of 5-6m hit the coast about 30 minutes latter. The sea has regressed for about 100m between the waves. The beach has been eroded by about 0.5 to 1m. The water went up to 1.5km along the creek. The waves hit the coast around 0900 hrs and continued for about 3-4 hrs at Pakala. About 500m run up has been recorded here. Formation of 1m vertical cliff in the shore has been noted. Few causalities and damage to boats have also been reported. At Rmnayapatnam Pallepalem the tsunami hit the coast around 0900 hrs with 5 to 6 m high splash and the activity continued till 1300 hrs. The waves reported to have come in 3 to 4 cycles and inundated about 1 km along an existing drain.

GUNTUR DISTRICT

Nizampatnam, Suryalanka beach, Nakshatranagar, Lankeyanidibba, Lakshmipuram are some of the prominent places affected in the district (Table-3). Minor sand deposition in tsunami struck areas has been observed. Thatched houses present in the coast have been damaged. Other prominent losses were damage to the fishing boats and nets and loss of cattle. Waves to the height of 2 - 3 m have been reported in Sllryaliualul beach near Bapatlll where the run up height was estimated around 2 m and the inundation extended up to 0.5 km. Rise in the sea level started around 0900 hrs and fluctuations in sea level continued till late evening. Thatched huts, compound wall ofguesthouses and other prominent constructions present right on the beach were damaged. Fishing boats and nets near the shoreline have been damaged. Dry fish catch stored on the beach were also lost. Minor causality has also been reported. The first tsunami wave hit the Nizampattnam coast around 0900 hrs. The run up height was about 2m. There has been a rise in water level and the inundation extended about 1.5 to 2 km in low-lying areas. The fluctuations continued for about 12 hours. The fishing harbor has not been affected. Huts in low-lying area have been damaged. Boats have been pushed inland and damaged. Tsunami also affected the East Tungabhadra Drain, which is joining the sea near Nizampatnam.

KRISHNA DISTRICT

This district includes part of Krishna Delta. Tsunami hit the coast around 0845 hrs and the wave action continued up to 1900 hrs (Table-4). Wave with a maximum height of about 4 m has been reported. Thatched houses present in the coast have been damaged (Fig.4-7). Other prominent loss includes damage to the fishing boats and nets, total loss of dry fish stored in the beach and lossof cattle. Water encroached up to Port Office in the Bandar Port (Fig.13) causing little damage. The run up height was estimated to be 2 m and fluctuations continued for about 12 hours. Boats present in the harbour were tossed by the waves and collided resulting in their damage. Slight deposition of sand has been observed in the tsunami struck areas of the district. About 2m run up has been observed in the Hamsala Divi (Divi Point). The inundation extended for about 2 km along the low-


187

lying tidal flat present near Polakaitippa. The road along the tidal flat has been badly damaged (Fig.8). Significant heavy mineral deposition has been observed associated with the fresh sand along the tidal flat. The tsunami hit Manginapudi Beach, Machilipatnam around 0845 hrs and the fury continued till 1900 hrs. Manginapudi beach is a low flat level beach adjacent to the creek, which suffered heavily (Fig.9-12). Waves to a maximum height of 4 m swept the beach. About 30 tourists who visited the beach for taking a holy dip in connection with Buddha Poornima were dragged away by the seawater. As the water spread for about 1 km on to the land forcefully, many constructions in the beach have been destroyed. Buildings have collapsed, electric poles twisted and RCC benches in the beach were broken. The seawater entered deep into a creek for about 1 km. About 0.5 to 1m thick heavy mineral layer has been deposited in the beach and the creek.

WEST GODAVARI DISTRICT

This district includes part of Godavari delta. During tsunami, the water level rose by 2 to 3 m (Table-5) above normal inundating low-lying areas, especially along creeks at their confluence with the sea. Many distributaries and creeks that joins the sea protected the coast by allowing seawater enter through them and thereby dissipating the energy. Slight deposition of sand in tsunami struck areas in the district has generally been observed. Thatched houses present in the coast have been damaged (Fig.16). Other prominent losses were damage to the fishing boats and nets (Fig.14 and 15), total loss of dry fish catch stored in the beach and loss of cattle.

EAST GODAVARI DISTRICT

This district includes part of Godavari delta. Bhairavapalem, Balusutippa, Edurlanka,Guttenadivi, Guttenadivi and Mulapalem (Table-6) are some of the places affected by tsunami(Table-6). The seawater has entered the distributaries of Godavari for a distance of 5 to 7 km. Water level in those distributaries and creeks rose by about 2 m. The fluctuations continued till 1400 hrs.The water level in the sea rose by 2 to 3 m above normal, inundating low-lying areas. Small culverts and thatched huts in the coastal area have been damaged. Other prominent losses were damage to the fishing boats and nets, total loss of dry fish stored in the beach and loss of cattle. Seiches reported in an irrigation tank near Guttenadivi Mulapalem. Water receded by about 200 m and after a period of 30 minutes to 1 hour, the water level rose by about 3 to 5 m above normal and touched the road level near Uppada beach. The embankment along the coast was slightly damaged due to water action. Minor but significant deposition of sand is observed along the tsunami struck area near Biyyaputippa in the district.

VISAKHAPATNAM DISTRICT

It is a rocky coast having a steep continental shelf. It was reported that the sea became very rough during the tsunami. Fluctuations in sea level commenced from 0900 hrs (Table-7) and continued till 1400 hrs. The sea was rough till late evening. Initially the water level has been reduced by about 2.5 m, then rose by about 2.5 m above the normal. No structural damages occurred along the coast. Boats present in the harbor and near to the coast were tossed up and collided with each other resulting in minor damage. Fishing nets were damaged. Fishermen, who went into deep sea for fishing much before the occurrence of tsunami, were unaware of the incident until their return.


188

VIZIANAGARAM DISTRICT

It is mostly a rocky coast having steep continental shelf. Neither deposition nor erosion was significant in this district. Fluctuations in sea level were reported from 0900 hrs to 1300 hrs. It was reported that sea water receded for about 300 m from the normal level and returned back up to about 200 m inland. The fluctuations were reported to have repeatedly occurred in a span of every 15 minutes for a period of 2 to 3 hours. However, the sea was rough till evening. It was reported that the water pipeline laid for about 100 m into the sea has been exposed during the recession. No structural damages occurred along the coast. Fishing nets in the near shore area have been damaged. Fishing boats collided with each other and got damaged.

SRIKAKULAM DISTRICT

This district has about 190 km long coastline, the longest in Andhra Pradesh. At

Bhavanapadu Fishing Harbour near Santabommali Mandal, seawater receded for about 300m initially. The furious waves hit the coast in three spells from 0900 hrs to 1400 hrs. The

waves dragged several boats and fishing nets deep into the sea. Fluctuations in sea levelwere reported from 0900 hrs to 1300 hrs. Sea was rough till evening. Seawater receded for about 100 to 300 m from normal around 0900 hrs for about 30 minutes.

YANAM (PONDICHERRY)

It is a flat coast, mostly covered with thick sand. No rock outcrops are present nearby coast.Part of the Godavari distributary system joins the Bay of Bengal in the area. The effects of tsunami were felt in this stretch between 0800 hrs and 1500 hrs. Initially the water levels receded in the distributary system for a couple of meters and latter rose by about 5 m above the normal. At Dariyalatippa, a small place in Yanam, it has been reported that the sea initially receded back by about 500 m and again transgressed for about 500 m.

ACKNOWLEDGEMENTS

The authors thank Shri S.D. Pawar, Deputy Director General (Retd.), Southern Region, Geological Survey of India, Hyderabad for his encouragement and suggestions while carrying out the studies. The authors thank Dr.K.S.Misra, Dy.Director General, Shri P.F. Augustine, the thenDirector, Engineering Geology Division, and Director, Technical Coordination Division, and Shri M. Mahesh Babu, Director, Earthquake Geology Division, Geological Survey of India, SouthernRegion, Hyderabad for extending their guidance and valuable suggestions.


189

______________________________________________________________________________________________


Table - 1CHARACTERISTICS AND IMPACT OF TSUNAMI IN NELLORE DISTRICT

Run-upSl.No

Location Arrivaltime

(hrs)Elevation

(m)

Distance

(m)

No.of pulses (strongest

pulse)

Height of wave

splash (m)

Maximumretreat of sea

(m)

Remarks

01 Sriharikota

(13°42′ 30 ″ : 80° 14 ′)0830 1.5- 2.0 100 3-4 (2) 4 Not reported

No damage. Casuarina plantation

acted as a bio -barrier

02 Mypadu Pallepalem

(14°30 ′ 35 ″ : 80°10′ 45 ″)0845 1.5- 2.0 1000* 2-3 (2) 4-5

500 Damage to the property, fishing boats

and nets reported

03 Gangapatnam Pallepalem

(14°31 ′ 50 ″ : 80°10′ 50 ″)0830 1.5- 2.0 1000* 2-3 (2) 7-8 Not reported

Few deaths reported. Villagecompletely inundated by the two

arms of a creek

04 Kottasatram

(14°56 ′ 30 ″ : 80°05′ 30 ″)0900 1.5- 2.0 1000* 2-3 (2) 6-7 100

The villa ge is located on a palaeo-

dune. Damage to the fishing boats,

nets reported

Table - 2CHARACTERISTICS AND IMPACT OF TSUNAMI IN PRAKASAM DISTRICT

Run-upSl.No Location Arrival

time

(hrs)Elevation

(m)Distance

(m)

No. of

pulses

(strongest

pulse)

Height

of wave

splash

(m)

Maximum

retreat of

sea (m)

Remarks

05 Ramayapatnam Pallepalem

(15°02′ 45 ″ : 80° 03′ )0900 1.5-2.0 1000* 3-4 (2) 5-6 Not

reported

Village situated over barrier ridge. Damage to the fishing boats and

nets

06 Karedupalem

(15°10 ′ 45 ″ : 80°04′ )

0900 1.5-2.0 2000-

3000*

2-3 (2) 3-4 Not

reported

Saltpan and fishing boats damaged

07 Pakala

(15°16 ′ 30 ″ : 80°05′ )0900 1.5-2.0 500 2-3 (2) 3-4 Not

reported

Few deaths reported. 1m vertical

cliff formed in the beach.

08 Kottapatnam Pallepale m

(15°16 ′ 15 ″ : 80°10′ 55 ″)0900 1.5-2.0 1500* 2-3 (2) 5-6 100

Coast parallel road saved damage. Beach eroded to the tune of 1m.

09 Peddaganjam Pallepalem

(15°38 ′ 30 ″ : 80°15′ )

0900 1.5-2.0 500 2-3 (2) 2-3 Not

reported

Casuarina plantation acted as a

b io -barrier

* Run-up along the creek

Table - 3

CHARACTERISTICS AND IMPACT OF TSUNAMI IN GUNTUR DISTRICT

Run-upSl.No Location Arrivaltime

(hrs)

Elevation

(m)

Distance

(m)

No. of pulses

(strongestpulse)

Heightof wave

splash(m)

Maximumretreat of

sea (m)

Remarks

10 Vadarevu

(15°47 ′ 30 ″ : 80°24′ 50 ″)0900 2 300 2-3 (3) 3-4 300

Erosion and deposition recorded in the beach

11 Suryalanka

(15°50 ′ 25 ″ : 80°30′ 35 ″)0900 2 500 2-3 (3) 2-3 300

One person died. Thatched huts

compound wall of guesthouses and

other prominent constructions on the beach damaged.

12 Nizampatnam

(15°55 ′ 30 ″ : 80°41′ 30 ″ )0900 2 1000* 2-3 (2) 2-3

Not

reported

Harbor unaffected. Fishing boats and

nets damaged.

13 Lankevanidibba

(15°47 ′ 30 ″ : 80°15′ 45 ″ )0900 2 1000* 2-3 (2) 2-3

Notreported

Damage to the property reported.

Table - 4

CHARACTERISTICS AND IMPACT OF TSUNAMI IN KRISHNA DISTRICT


time

(hrs)

Elevation

(m)

Distance

(m)

No .of

pulses

(strongestpulse)

Height

of wave

splash(m)

Maximum

retreat of

sea (m)

Remarks

14 Polakayalatippa Hamsaladivi

(15°58 ′ 30 ″ : 81° 07 ′ 30 ″ )0900 2 2000* 2-3 (3) 3-4

Not

reported

Road in the tidal flat badly damaged

15 Machilipatnam Port

(16°19 ′ : 81°19 ′ 30 ″ )0845 3 1000* 2-3 (3) 3-4

Notreported

Minor sand accretion noted in the beach. Boats tossed up during

tsunami.

16 Manginapudi Beach

(16°13′ 30 ″ : 81°12′ 30 ″)0845 2.5 1000* 2-3 (3) 3-4

Not

reported

About 30 deaths reported. Many

tourist constructions in the beach destroyed.

* Run-up a long the creek

Table - 5

______________________________________________________________________________________________


CHARACTERISTICS AND IMPACT OF TSUNAMI IN WEST GODAVARI DISTRICT


time(hrs)

Elevation(m)

Distance(m)

No. of pulses

(strongestpulse)

Height

of wave splash

(m)

Maximum

retreat of sea (m)

Remarks

17 Bolugunta

(16°23 ′ 15 ″ : 81°23′ 50 ″)

0900 2.0 1000* 2-3 (2) 2-3 Not

reported

The distributaries and creeks dissipated

the wave energy. Thatched huts damaged.

18 Mailavanilanka

(16°19 ′ 45 ″ : 81°40′45″)

0900 2.0 2000* 2-3 (2) 2 Not

reported

Thatched huts, fishing boats and nets

damaged. Road and culverts covered

with sand.

19 Chinnalanka

(16°20 ′ 30 ″ : 81°38′ 45″)

0900 1.0 2000* 2-3 (2) 2 Not

reported

Damage to the property reported

20 Biyyaputippa

(16°19 ′ 30 ″ : 81°42′ 30″)

0900 2.0 1500* 2-3 (2) 2 Not

reported

The foot bridge over the creek and

thatched huts damaged* Run-u p a l o n g t h e c r e e k

Table - 6CHARACTERISTICS AND IMPACT OF TSUNAMI IN EAST GODHAVARI DISTRICT

Run -upSl.No Location Arrival

time

(hrs)Elevation

(m)Distance

(m)

No. of

pulses

(strongest

pulse)

Height

of wave

splash

(m)

Maximum

retreat of

sea (m)

Remarks

21 Guttenadivimulapalem

(16°42 ′30 ″ : 82°15)0900 2.0 500 2-3 (2) 1

Notreported

Effects of earthquake felt in the form minor trembling. Wooden shop settled.

22 Guttinadivi

(16°41 ′ : 82°14′ 30 ″)0900 2.0 500 2-3 (2) 1

Notreported

Effects of earthquake felt in the form minor trembling. Seiches reported.

Fishing boats and nets damaged.

23 Gadimoga

(16°45 ′ : 82°17′ )0900 1.0 200 3-4 (2) 2

Not

reported

Effects of e arthquake felt in the form

minor trembling. Seiches reported. Fishing boats and nets damaged

24 Dariyalatippa

(16°42 ′ 30 ″ : 82°16′ 30 ″)0800 2.0 200 3-4 (2) 2

Not

reportedCoastal embankment damaged

25 Uppada

(17°04 ′ 40 ″ : 82°20′ 35 ″)0900 2.0 200 3-4 (2) 2 200 Fishing boats and nets damaged

Table - 7

______________________________________________________________________________________________


CHARACTERISTICS AND IMPACT OF TSUNAMI IN VISAKAPATTINAM DISTRICT


time(hrs)

Elevation(m)

Distance(m)

No.of

pulses(strongest

pulse)

Height

of wave splash

(m)

Maximum

retreat of sea (m)

Remarks

26 Bhuminipatnam

(18°53 ′ 15 ″ : 82°27′ 30 ″)0900 2.0 200 2-3 (2) 3 200 Fishing boats and nets damaged.

Fig. 1: Scouring of beach and scarp formationLoc : Mypadu (Nellore district)

Fig. 2: A breach in the beach barrierLoc : Mypadu (Nellore district)

Fig. 3: Destructed thatched huts Loc : Vodarevu near Chirala (Prakasam district)

Fig. 4: Damaged structure on the beach Loc : Suryala nka (Krishna district)

______________________________________________________________________________________________


Fig. 5: Collapsed compound wall Loc: Suryalanka (Krishna district)

Fig. 6: Destruction of thatched hutsLoc: Suryalanka (Krishna district)

Fig. 7: Erosion of barrier beach Loc: Suryalanka (Krishna district)

Fig. 8: Damage to the road in the tidal flatLoc: Hamsala Deevi (Krishna district)

______________________________________________________________________________________________


Fig. 9: Scouring in the beachLoc: Manginapudi (Krishna district)

Fig. 10: A part of the damaged tourist center Loc : Manginapudi (Krishna district)

Fig. 11: Scouring of the beach Loc : Manginapudi (Krishna district)

Fig. 12: Scouring of the beachLoc : Manginapudi (Krishna district)

______________________________________________________________________________________________


Fig. 13: Area about 1km away from the sea inundatedLoc: Bandar Port (Krishna district)

Fig. 14: Damaged nets entangled in palm trees Loc: Chinna Lanka (West Godavari district)

Fig. 15: Damaged fishing netsLoc: Chinna Lanka (West Godavari district)

Fig. 16: Inundation and damage to the hutments. Loc: Biyyaputippa (West Godavari district)


197

TSUNAMI SURVEY IN THE CHENNAI – NAGAPATTINAM SEGMENT TAMIL NADU COAST

R. Srinivasan and K. Nagarajan

Geological Survey of India, A2-B wing, Rajaji Bhavan, Chennai 600 090.

INTRODUCTION

This chapter includes the results of post-tsunami studies carried out in the 305 km long

Chennai – Nagapattinam segment spread between lat.10°46’ to 13°25’ and long.79°51’ to 80°19’.The area is characterized by a broad bay, between Marakkanam and Parangipettai, connecting the NNE trending Pulicat – Marakkanam and NS trending Parangipettai – Nagapattinam stretches. For convenience of description this segment has been sub-divided into five sectors based primarily on geomorphology of the coastal tract.

1) Pulicat – Palar River (100 km)2) Palar River – Pondicherry (60 km)3) Pondicherry – Cuddalore (25 km)4) Cuddalore – Tirumullaivasal (60km)5) Tirumullaivasal – Nagapattinam (60 km)

1. Pulicat- Palar River Sector:

The 100 km long Pulicat– Palar River sector is characterised by dune complex of lesser height (1-3m) and larger width (0.75 – 1.5 km), very large tidal and palaeotidal flats, smaller bays and strand line. Chennai, the capital of Tamil Nadu and Mahabalipuram, with the famousWorld Heritage Centre is situated in this sector. The impact of tsunami has been moderate in this sector (Table-1). Minor tremor (felt intensity III) was felt in Chennai city and surrounding areas (up to Mahabalipuram) at 0645 hrs on 26.12.2004. Tsunami induced breaches in the beach ridges and inundation of inter dune and tidal flat area is prominent in the coastal zone. Breaches, 3 to 15m wide, are common between Nemeli (Fig.1) and Mahabalipuram. Sea water has inundated the world famous Marina beach (Fig.2) for a short period triggering panicky among the tourists and morning walkers and caused life and material loss (Plate-2). However, the shallow ground water (perched aqufer) in the dune complex remained unaffected. The partially opened mouths of Korthalaiyar and Coovam Rivers, Pulicat lagoon, Ennore and Kalpakkam (Fig.3) creeks have been forcefully opened further by the tsunami wave that has flushed out some of the stagnated urban waste. The 1.5 km long Palar river mouth has been opened at number of places (for widths ranging from 200 to 300 m) and sea water has ingresses up to 1.75 km inland. The big channel bar deposits (tidal islands – Vengad islands) have been dissected and eroded. In the Pulicat, Ennore and Adyar creek / lagoon, water level has increased nearly 1 to 2 m above the normal level and flooded the adjacent areas. In addition, theestuaries and lagoons have also been silted due to the deposition of significant amount of littoralsediment (Fig.4). The water level in the coast parallel Buckingham Canal rose about 1 m to 1.5 m flooding the embankment areas.

All man made structures including fishing hamlets located near the shore have beenextensively damaged particularly the settlements (Foreshore Estate, Sadras and Oyyalikuppam) that are located near the river mouths. Small coastal strip between Ennore and Pulicat juxtaposed


198

between open sea and coast parallel aqua system have been overrun by the waves during tsunami (Plate-1). The theme parks and beach resorts in the Chennai – Mahabalipuram area have been damaged partly in the form of inundation and collapse of compound wall. However, those located on high dunes have been saved. The presence of fairly dense vegetation over a short stretch north of Ennore and between Kalpakkam and Sadras (Plate-3) has visibly reduced the tsunami impact. The damage to the Royapuram Fishing Harbour north of Chennai is less because of wave breakers (Plate-2). The impact on the salt panes and aqua ponds located in the Ennore and Kovalam tidal flats are also less because of lean season. The coast parallel wave breakers provided between Royapuram and Ennore to control sea erosion have immensely minimized the damage due to tsunami (plate-2). At places, a small height reduction (30 – 40 cm) and resettling of boulders in the wave breakers have been noticed due to toe erosion. In addition, the existing groynes appeared to have deflected the tsunami and reduced its force as per eyewitness accounts. The undisturbed nature of the small beach under development in these areas also vouches this. In spite of wave breakers, the seawater has entered the shore temple at Mahabalipuram, the World Heritage Centre, from the southern side beyond the protected area (Fig.5). The removal of beach sand in the area south of shore temple has exposed a few more archeological sites. The Dutch Cemetery at Pulicat and the Danish Fort at Sadras have been least affected.

2. Palar River- Pondicherry Sector:

The 60km long Palar River – Pondicherry sector is characterised by wide dunes (0.4 – 0.8 km) with heights ranging from 4 m to 20m in the northern part up to Marakkanam. The width and height of the dunes falls rapidly afterwards. This is flanked in the west by pediplain formed over the Archean and Tertiary rocks. The impact of tsunami has been moderate in this sector (Table-2).Alteration in the beach zone, concentration of beach placers in the high tide line and leveling of inter dune areas are prominent in the coastal zone. The concentration of heavies is marked inEggiyarkuppam (Fig.6). The partially opened mouths of Cheyyar, Yedanthittu Kaliveli and Kaliveli lagoons have been wide opened by the tsunami waves. Water level in the lagoons has risen by 1m to 1.5 m above normal (Fig.7) during tsunami inundating the adjacent agricultural lands. Tsunamideposits in the form of silt and sand bars are observed in Kaliveli channel as well as in parts of lagoons which chocked the aqua system for the deformed / dwarfed mangrove plants. This has also affected the internal navigation. Saltpans at Marakkanam and Cheyyur are not much affectedbecause of lean season and in fact, the incursion of additional seawater is likely to be useful during the ensuing season. The prominent silica sand deposits in the Mugaiyur – Marakkanam andAnumandai-Kalapettai areas are located just beyond maximum run-up distance and left undisturbed.

Though no major township exist in this sector, a number of villages are situated close to the sea. Houses that are very close to the sea front have been severely damaged. However bio-barrier(casuarinas plantation and coconut trees) has effectively reduced the tsunami impact at a number of places especially in the Tenpattinam Beach Resorts (Fig.9). The tsunami has aggravated the ongoing erosion in the Chinnakuppam and Periyakuppam villages located just south of Palar River mouth. Muthukadu and Alamparai located close to the lagoon openings have also been more affected. The bund in the southern banks of Palar River has been breached at a number of places inundating the surrounding areas. Though seawater has entered the dilapidated Moghul fort, the archaeologicalmonument situated at Alamparai has been spared.


199


200

3. Pondicherry-Cuddalore Sector:

The 25 km long Pondicherry - Cuddalore sector has a narrow strip (100 – 200 m) of coastal dunes of lesser height flanked on the west by pediments of Tertiary age. Tidal flats and lagoons are practically absent. However an intricate network of coast parallel aqua systemcharacterise this sector. Gully erosion and bad land topography are prominently exposed north of Pondicherry. The alluvial deposits of Gingee, Malattar, Ponnaiyar and Gadilam Rivers occur over the pediment between Cuddalore and Pondicherry. The entire coastline is thickly populated.Pondicherry and Cuddalore are the major townships in this sector.


201


202


203

The impact of the earthquake has been manifested in the form of strong seismic seicshereported in a number of water tanks located in the coastal area. The impact of tsunami has been moderate to severe in this sector (Table-3). Minor alteration in the beach zone and flattening of dune ridges and inter-dune flat area are observed in the coastal zone. The prograding beach atVirampattinam has been leveled. The partially opened mouths of Gingee, Ponnaiyar, Gadilam Rivers and Ariyankuppam Ar, a prominent creek were further wide opened. There was a marked increase in water level in these water bodies and the seawater reached much more inland than normal. Stray boats have been pushed in the estuaries as far as 2.5 Km from the sea. The creeks and estuaries are visibly silted, affecting the navigation (Fig. 10).

In general, most of the coastal villages in this sector have been protected by bio barrier (casuarinas and coconut) and hence escaped the fury of tsunami. However, unfavorable geomorphic conditions (narrow strip of low-elevation land juxtaposed between open sea and coast parallel aqua system) have made Thalanguda, Devanampattinam and Sonangkuppam villages around Cuddalore more vulnerable and hence suffered heavy life and property loss (Plate-4). Pondicherry town located in the northern part is relatively unaffected. Coast parallel wave breakers, heaped to a height of 2 to 2.5m have protected the entire township. The fishing harbour at Pondicherry situated in theAriyankuppam Ar estuary with its mouth protected by groynes and riprap has suffered minimumdamage. The fishing harbour at Cuddalore located in a coast parallel tidal creek (inland tidal jetty) is worst affected. The waves surged through the creek and as well as from the open sea and pushed the boats overland and above the bridges. In general, the damage to the jetty is minimal but the damage to the boats has been extensive. This is mainly because of collision among the boats as well as against the jetty (Fig.11).

4.Cuddalore – Tirumullaivasal Sector:

The 60 km long Cuddalore – Tirumullaivasal sector has a wide spread dune complex. About 100m wide recent dune complex has been followed by an older dune complex comprising a number of strandlines up to 9km. This has been flanked on the west by river alluvium. Cuddalore, the HQ of South Arcot district and Parangipettai are the major townships located in this sector.

The impact of the earthquake has been manifested in the form of strong seismic seiches reported in a number of water tanks located near Tirumullaivasal. The impact of tsunami is moderatein this sector (Table -4). Breaches of 3-15m in the beach ridges (Fig.12) and leveling of inter-duneflats are prominently observed between Cuddalore and Parangipettai. The inter-dune flats were prominently water logged for a brief period during tsunami (Fig.13) resulting in considerablepercolation and thus affecting the shallow ground water. The casurina plantations prevalent in this area show signs of distress in the form of withering of leaves. The remarkable alignment of casuarina trees in the inter dune flat has indicated a SSW propagation direction of the waterfront in the land.

The Parangipettai-Tirumullaivasal area is marked by a narrow strip of sandy flat juxtaposed between open sea on the east and intricate network of coast parallel aqua system in the west (Plate-5). A near marshy condition with mangrove swamps exists in this stretch. This has effectivelyminimised the wave energy. However, rapid movement of water along the canals has disturbed the boats that used to ply in the canals. The forceful entry of seawater and rise in the water level is likely to accelerate the luxuriant growth of mangroves in the near future. During Tsunami, the water level in the canals has increased by 1 to 1.5 m above normal. The mouths of Vellar and Kollidamrivers have been wide opened. The prominent spit developed at the Vellar river mouth and the cuspate lobe at Kollidam river mouth has been severely eroded and sand deposited in the river channel. Mudasalodai, Chinnavaikkal and Kodiyampalayam that have been located in narrow strip


204

juxtaposed between open sea on the east and the coast parallel aqua system on the west have been severely affected with heavy life and property loss (Plate-5). During tsunami the surging waves have practically run over the narrow strip of sandy flat and joined the aqua system on the west. The leeward elongation created by minor impediments preserved in the sandy flat beyond the high tide level indicate a SSW propagation direction for the water front in the land, south of Mudasalodai. The coastal road from Cuddalore to Parangipettai has been damaged at places. Minor damage to road bridges has also been noted.

5. Tirumullaivasal- Nagapattinam Sector:

The 60 km long Tirumullaivasal – Nagapattinam sector trends N-S in an otherwise NNE trending coastline. Narrow beaches followed by sandy flats characterise this low flat coast with deltaic alluvial sediments on the western side. As per the historic records, this sector is under severe sea erosion and submergence for the past 2000 years. Many ancient towns have been submerged.Tirumullaivasal, Tarangambadi, Karaikkal, Nagore and Nagapattinam are the major towns locatedalong the coastline.

This sector, located in the tail end of Cauvery delta has been worst affected (Table-5).Concentration of beach placers and breaching of barrier dunes are prominently observed in thecoastal zone. Black sand, 3 to 10 cm thick, occurs as thin layer over the normal greyish brown sand. The leeward elongation created by minor impediments preserved in the sandy flat beyond the high tide level in the near flat Karaikal beach indicate a SSW propagation direction of the water front on the land (Fig.14). Tsunami induced breaches on the shoreline (well depicted on high resolutionsatellite imageries) have weakened the natural frontline coastal defense system against the high tide and cyclone storm surges. The mouths of all water bodies have been opened during tsunami and rise in the water level up to 2m above normal has been reported. In contrast, areas far off from the sea, along river channels have been choked due to siltation by the sediments brought by tsunami.Villages situated close to the shore have invariably been affected. The impact was particularly more at Tirumullaivasal, Tarangambadi, Pattanacheri (Nagore), Kichchankuppam and Akkaraipettai due to their vulnerable geomorphic locations (low sandy flat area without any natural or artificial barrier and close to river mouths) and high population density. The seawater has entered parts of Nagoreand Nagapattinam towns (Plate-6). Even though parts of the segment have been protected by low-level embankment, it was ineffective and battered severely. The coast parallel segment of Uppanar River at Nagapattinam where the fishing harbour has been situated witnessed a steep raise in water level during tsunami resulting upstream drifting and smashing of boats. A few places likeKichchankuppam (Fig.15) and Akkaraipettai that are situated in low sand dunes in between open sea on one side (east) and creeks on the west have been marooned resulting in the demise of hundreds of people, besides loss of property. The inundation of the vast area in this sector due to flat terrain condition has affected the agricultural lands. The plants show distress signs in the form of withering and yellowing of leaves. The bridges across Arasalar (Karaikkal) and Uppanar (Akkaraipettai) have been damaged. The meter gauge railway line between Nagapattinam and Nagore and a few roads have also been damaged. Minor impacts have been inflicted in the recent constructions near the shore at Poompuhar and already affected Masilamani temple at Tarangambadi. Surprisingly the damage to the 16

th Century Danish Fort was minimal (Fig.16).


205

ACKNOWLEDGEMENT

The authors wish to record their sincere gratitude to Shri S.D. Pawar, DDG (Retd.), SR, Hyderabad, Dr. M.M. Nair, DDG (Retd.), Op:TNPK, Chennai, Dr. Sujit Dasgupta, Director(Monitoring), CHQ, Kolkata, Shri A. Sundaramoorthy, Director, Op:TNPK, Chennai and Shri G. Rajagopalan, Director, EG Division, Op:TNPK, Chennai in the execution of the project andpreparation of the manuscript.


206


207

________________________________________ ______________________________________________________


Table – 1

CHARACTERISTICS AND IMPACT OF TSUNAMI IN PULICAT – PALAR SECTOR

Tsunami Run-up

Sl.No. Name of the village ArrivalTime

(hrs)

No. of Pulses (with

relativelystrong pulse)

Elevation

(m)

Distance

(m)

Maximumretreat

between

waves (m)

Propagationdirection of waterfront in

land

Remarks

A . Pul icat

(13°25’: 80°19’) 8.45 3 (2nd) 1.5 250 150

- Lagoon mouth opened; lagoon channel

shallowed due to siltation; shallow aquifer una f f ec t ed .

B. Chenna i (Mar ina)

(13°05’: 80°16’30”)8.459.20

3 (2nd) 1.5 300 - - Sudden inundation caused panic among tou r i s t s . Pa rked veh ic l e s des t royed .

1. 1 km S of Vada Nemeli

(12°44’”: 80°14’30”)

09001200

1230

3 (2nd) 1.5 120 45- Rattl ing of art icles reported during the

earthquake; beach ridge breached; houses in

f ront row damaged,

2. Suler ikuppam

(12°42’30”: 80°13’30”)

0845

09201230

3 (3r d) 2.5 300 20- The earthquake has been felt in the morning;

beach ridges breached; houses located close to s e a i n u n d a t e d ; On e d e a t h r ep o r t e d .

3. New Nemeli Kuppam

(12°39’30”: 80°13’)

0855

09150940

1030

4 (2nd ) 1.7 350 30- Earthquake feebly felt; breaches in frontal

beach ridges; about 10m transgression of sea after Tsunami as reported by locals; 30 deaths

repor ted .4. Shore Temple

Mahabal ipuram

(12°37’: 80°11’45”)0845 3 (2nd ) 2.5 300 150

- Flattening of foreshore area prominent; houses

and boats damaged; 4 m high wave breaker has minimised damage .

5. Kokilame d u

(12°36’: 80°11’30”)0845 3 (3r d ) 1.5 300 400

- Earthquake feebly fel t ; heavy mineral deposition on beach prominent; houses

damaged .

6. M e y y u r

(12°32’: 80°10’)

09000920

0945

3 (3r d ) 2.0 - 2.5 300 425- -

7. Oyya l ikuppam

(12°29’: 89°30’)

0845

10301100

3 2.0 - 2.5 350 300- Palar river mouth breached at many places;

houses and boa ts damaged; 10 dea ths repor ted .

________________________________________ ______________________________________________________


Table - 2

CHARACTERISTICS AND IMPACT OF TSUNAMI IN PALAR-PONDICHERRY SECTOR

Tsunami Run -up

Sl .No.

Name of the village ArrivalTime

(hrs)

No. of Pulses (with

relatively

strong pulse)

Elevation(m)

Distance(m)

Maximum

retre atbetween

waves (m)

Propagation

direction of waterfront

in land

Remarks

8. Chinnakuppam

(12°26’45”: 80°08’30”)08401230

5 (3r d ) - 500 500- Beach r idges breached; huts damaged;

invading waves repor ted to be s lushy

9. T h e np a t t i n a m

(12°24’45”: 80°06’45”)

- -

1 300

- - Inundation of dune flat areas prominent; thin silt deposition noted; beach resorts damaged; casuar ina p lanta t ion ac ted as a buffer

10. P a ramankeni Bridge

(12°21’: 80°04’)

- - -

400

- - Water upsurge through the creek and tidal flat reported during tsunami; Inundation of salt pan reported; sil t ing of lagoon by thick t sunami depos i t

11. Pana iyurkuppam(12°18’: 80°02’) 0845

09453 2 750

- - Earthquake feebly felt; Houses damaged; 2 dea th s r ep o r t ed .

12. Eggiyarkuppam(12°11’: 79°57’45”)

08551000

4 - 150- - Black sand deposition on beach observed

13. Anumantha ikuppam

(12°07’30” 79°55’)0810 5 - 400

- - Beach ridges breach at number of p laces;

f ron t a l hu t s / houses damaged

14. N ochch ikuppam

(12°05’15” : 79°54’)

-3 (1s t ) - 150

- -Proper ty loss - few.

15. P u d u k u p p a m(12°03’: 80°52’30”)

08451230

5 - 300- - Development of new beach surface prominent

over the sandstone pediment; front line houses

af fec ted .

16. Chinna Kalape t

(12°01’30”: 80°52’)

08451000

3 (2nd ) 1 100 - - The tsunami impact has been less; coconut t r ee s ac t ed a s b io -barr ie r

________________________________________ ______________________________________________________


Table - 3

CHARACTERISTICS AND IMPACT OF TSUNAMI IN PONDICHERRY – CUDDALORE SECTOR

Tsunami Run-up

S l .No.

Name of the vil lage

ArrivalTime

(hrs)

No. of Pulses

(withrelatively

strongpulse)

Elevation(m)

Distance (m)

Maximum

retreatbetweenwaves (m)

Propagation


in land

Remarks

17. Pondicherry town

(12°56’30”:

79°50’)

0910 to 1200

3 (2nd ) 1.5 300 150- No earthquake impact; the tsunami impact was

less; 3 m high wave breaker has protected the

town.

18. Virampatt inam

(11°53’30”:

79°49’30”)

0830 3 (2nd ) 1.5 – 2.0 200 300- Strong seismic seiches reported in the water bodies

close to the shore in the morning; prograding coast (broad beach); flattening of foreshore area prominent; huts and boats damaged; 3 deaths

repor ted .

19. Pann i th i t tu

(11°49’30”:

79°48’)

0845 5 1.75 200 - -Leveling of dunes prominent; moderate damage to property; coconut grove acted as bio-barrier.

20. T h a l a n g u d a

(11°46’30”:

79°47’30”)

0845 3 (3r d ) - - 50 -Already facing erosion; Ponnaiyar river mouth

opened; flat dunes / beach inundated; houses and boats have been damaged; 36 deat hs reported.

21. Sonangkuppam

(11°43’30”: 79°47)0900 3 (2nd ) 2.0 – 2.5 350 - -

Village surrounded by seawater through creek and sea; submergence of low dune complex; heavy loss

o f l i f e and damage t o b oa t s and house s .

________________________________________ ______________________________________________________


Table - 4

CHARACTERISTICS AND IMPACT OF TSUNAMI IN CUDDALORE-TIRUMULLAIVASAL SECTOR

Tsunami Run -up

Sl .No.

Name of the village Arrival

Time (hrs)

No. of Pulses (with

relativelystrongpulse)

Elevation

(m)Distance (m)

Maximum

retreatbetween

waves (m)

Propagation


in land

Remarks

22. Kumarapa t t i

(11°33’ : 79°45’30”)

-150 - - A prominent breach in the beach ridge

n o t e d ; m o d e r a t e p r op e r t y l o s s .

23. P u d u k u p p a m

(11°31’30”: 79°46’)

0855 2 (2nd ) 1.0 450 - - Houses /boats damaged; 126 deaths repor ted .

24. MGR Thi t tu

(Mudosa loda i )

(11°29’: 79°47’)

4.0 400 - S20°WThis village is situated in the narrow strip

of land juxtaposed between sea and coast parallel aqua system; entire village

overrun by sea water; life loss reported; severe damage to houses / boats; wave propagation direction well preserved in

the sandy f l a t .

25. Thirumullaivasal

(11°14’: 79°50’30”)

0900 3 1.0 – 1.5 1000 m

through creek

300 m through land

- Oscillation of water in ponds (seismic seiches) during the earthquake reported;

creek mouth widened; silting inside; shallow ground water salinity reported;

150 deaths reported; houses and boats d a maged .

________________________________________ ______________________________________________________


Table - 5

CHARACTERISTICS AND IMPACT OF TSUNAMI IN TIRUMULLAIVASAL-NAGAPATTINAM SECTOR

Tsunami Run-upSl .No.

Name of the vil lage

ArrivalTime(hrs)

No. of Pulses (with relatively strong pulse)

Elevation(m)

Distance (m)

Maximum

retreatbetween

waves (m)

Propagation


in land

Remarks

26. P o o mp u h a r

(11°07’30”:79°51’30”)

0840

1000

5 (3r d ) 1.5 – 2.0 350 150SSW

Water reportedly poured on its own from hand

pumps during earthquake; deposition of heavy

sand prominent in the beach; dunal flat area inundated; damage to houses and boats; the

tsunami was mainly a water boar with lot of slurry; limited wave breaker protection has

been e f fec t ive .27. Tharangambadi

(11°02’:

79°51’30”)

0900 3 - 400 - -Oscillation of water in ponds (Seismic seishes)

reported during earthquake; the coast is

already under erosion; huts, boats damaged the 16th Centuary Danish Fort has been breifly inundated and silted; coast partially protected b y w a v e b r e a k e r s .

28. Karaikkal(10°55’:79°50’)

09101100 5 (3r d ) - 250 350 SSW

Low flat coast; inundation of vast area; buildings, boats destroyed; the bridge over

Arasalar River in the East Coast Road damaged .

29. Nagore

(10°49’: 79°51’)0915 4 - 750 -

Low flat coast; Inundation of vast area; heavy loss of life and property; Railway line and roads damaged

30. Nagapattinam

(10°46’: 79°51’)0920 6 (2nd & 3 r d ) 2.5 (3 m

near boat j e t t y )

250After 1 s t

spell 1000 m, 100 m la te r on

- Low flat coast and shallow off-shore areas; the beach ridge has been breached at many places; a sheet of sea water, bubbling and frothing, has inundated vast coastal area; severe damage;

heavy loss of life (more than 4000 people). B o a t s a n d h o u s e s w a s h e d a w a y .

________________________________________ ______________________________________________________


Fig.1: A major breach in the frontal beach ridge

Loc: Nemili

Fig.2: A panoramic view of Marina Beach during tsunami

Loc : Chennai

Fig.3: Creek mouth opening Loc: Kalpakkam Fig.4: Silting of the estuary Loc: Palar River (about 1.5km inland from open sea)

Creek mouth

________________________________________ ______________________________________________________


Fig.5: Sea water entered the World Heritage Center resulting in temporary inundation.

Loc: Mahabalipuram

Fig.6: Heavy minerals concentrated near the hightide line. Loc: Eggiyarkuppam

Fig.7: Raised water level in the creek indicated by the precariously perched boat in the bridge. Loc : Paramankeni Bridge

Fig.8: Presence of bio-barrier reduces tsunami impact. Loc: Tenpattinam

________________________________________ ______________________________________________________


Fig.9: Siltation in the Ariyankuppam Ar creek posingproblems for navigation. Loc: Pondicherry

Fig.10: Boats lifted over the jetty by the wave surge. Loc: Cuddalore Harbour

Fig.11: A major breach in the frontal beach ridge Loc: Kumarapatti

Fig.12: Withered plantation and drifted boatindicating inundation in the inter-dune area

Loc: Pudukuppam

________________________________________ ______________________________________________________


Fig.13: Leeward elongation of sand ridges created by minor impediments indicating propagation direction of water front

in the land. Loc : Karaikal

Fig.14: A panoramic view of the worst affected Kichchankuppam Village – a case of unfavorablegeomorphic location. Loc: South of Nagapattinam

Fig.15: A road damaged due to tsunami. Loc : Nagapattinam Fig.16: Relatively unaffected 16t h Century Danish FortLoc : Tarangambadi

SSW

___________________________________________________________________________________________REPORT ON SUMATRA -ANDAMAN EARTHQUAKE & TSUNAMI, 26 DEC ’04

217

TSUNAMI SURVEY IN THE NAGAPATTINAM-KANYAKUMARI SEGMENT

TAMILNADU COAST

B. Kanishkan and B. Lakshminarayanan

Geological Survey of India, Chennai 600 090.

INTRODUCTION

The December 26th

2004, Indian Ocean tsunami that struck the coasts of Indian sub-continenthad shell shocked everyone with a pall of gloom by its unimaginable devastation, causing huge loss of life and livelihood besides damage to properties. The tsunami survey between the coastal stretch of Nagapattinam and Kanyakumari, one of the severely damaged segments, has been dealt in this section (Segment-3 of the Indian coast; see Index Map). The coastline between Nagapattinam and Kanyakumari, Tamil Nadu fringing the east coast extends for about 480 km (Plate I). Considering the vast stretch, varied geomorphology/ bathymetry (Plate II) and variable impact of tsunami, the area has been subdivided into the following five sectors (Plate-I) for the convenience of description and better understanding.

i) Nagapattinam – Point Calimere (57 km)

ii) Point Calimere – Ramanathapuram (190 km)

iii) Ramanathapuram – Rameswaram – Tuticorin (113 km)

iv) Tuticorin – Tiruchendur (35 Km)

v) Tiruchendur – Kanyakumari (85 km)

A succinct account of the Tsumami survey carried out during 05.01.2005- 14.01.2005 between Nagapattinam –Kanyakumari segment, Tamil Nadu is documented below. The data pertains tolocation wise tsunami survey is summarized in Tables 1-5. Arrival times, number of pulses and the strongest pulse given in the tables are from eyewitness accounts except for Tuticorin, where there is tidal gauge record. Predominant tsunami wave directions are based both from ground indicators and eyewitness observations.

1. Nagapattinam- Point Calimere Sector:

This is a 57 km N-S coastal stretch lying to the south of Pondicherry. The coastline consists of 10-30m wide sandy beach; 1.5 to 3.0 km wide recent dune complex seen well developed along the Nagapattinam- Topputurai stretch; two to three dune ridges of 3-5 m height run along the coast and coalesce to form compound dune complex (Krishnan and Srinivasan, 1999). A huge loss of life and property has been reported in this sector particularly in the Pattanchcheri (Nagore)-Nagapattinam–Kitchankuppam-Akkaraipettai-Velanganni backshore/foreshore stretch wherein 8000+ people have simply been washed away. Flattening of beach due to tsunami is common. Heavy siltation (tsunami deposit) is noted in Vettar, Uppanar and Vellar rivers. The closely berthed boats in the fishing jetty collided due to the tsunami waves and many lif ted and perched over the bridge, some thrown inside the adjoining fisherman colony. At the Velanganni pilgrimage center, post-Christmas Sundaytourists in the beach mainly bore the attack of tsunami. Loss of life and damage to property was comparatively less between Velanganni and Point Calimere due to the presence of linear/wide


218

barrier sand dunes along the coast, wide beach and thick belt of plantations near Pattanavarnattam and Point Calimere sanctuary. The cause behind the major tragedy in this sector is mainly due to the dense population/inhabitations seen along coast especially between Nagore in the north andVelanganni in the south (Fig.1 to 6) and geomorphic setup conducive to inundation. The tsunami wave arrived by 09: 20 hrs and hit the coast at an acute angle (Table- 1& Plate-I). As reported by the locals, the tsunami wave splash on hitting the coast rose up to 8-10m. Post- tsunami survey indicates that run-up elevation varies from 2 to 3m while the run-up length varied within 0.2 to 1.25 km depending on the coastal geomorphology. Maximum inundation by seawater of the order of 0.5 to 1.2 km was observed in the low-lying stretch between Pattanchcheri and Nagapattinam causing damage to topsoil and ground water. The shoreline also appears to have transgressed a few meters inland in this segment.

2. Point Calimere – Ramanathapuram Sector:

The Point Calimere – Ramanathapuram sector forms the southern extension ofNagapattinam coast. It is a long (190km) and curvilinear coast encompassing the Palk Bay, the bathymetric data of which indicates a shallow nature of sea with a maximum depth of 150m (Plate-II). The coastal tract essentially consists of Quaternary sediments and the major landformsencountered are 15-20 m. wide beaches, recent dune complex, tidal inlets, lagoons, mangrove swamp (mangrove swamps seen near Attirampattinam; Erippurakkarai lagoon near Agniar river mouth and Talainayar), deltas of rivers Cauvery, Agniar, Vellar, Vaigai etc. The post-tsunamiimpact on this coast is comparatively less as compared to the previous sector. The impact profile broadly includes opening of river mouths along deltas and lagoons followed by seawater ingression and siltation; less impact on recent dune complex. Tidal flat / agricultural lands fringing the coast ofAgniyar-Vellar rivers is damaged moderately due to saline water ingression; quality of ground water also deteriorated by the influence of sea water. Geothermal springs in Vellar-Tondi stretch, Tanjore district has not indicated any significant change. The wide spread aqua culture farms (Fig.7) seen along the coastal tract of Tanjore district and saltpans is marginally affected. As reported by the locals, the arrival time of strong tsunami waves was between 14.00 and 14:15 hrs and the wave splash attained a height of 2 to 5 m. The survey has indicated a run-up elevation of waves varying between 0.5 and 2 m and the inundation by seawater for a length of 25 to 100m (Table-2 & Plate-I).The presence of a number of deltas, tidal inlets and two major lagoons with mangrove swamps/ Casuarinas (Fig.8) has protected against major devastation.

3. Ramanathapuram – Rameswaram – Tuticorin Sector:

This sector comprises the famous Rameswaram island and Dhanushkodi besides the coastal stretch of Mandapam and Tuticorin stetching for about 85 Km. The cuspate foreland of Vaigai between Uchipuli and Mandapam and the Rameswaram island lying further east, separated by the sea over a distance of 2 Km, forms the divide between the Palk Bay in the north and Gulf of Mannar in the south. The coastline exhibits discontinuously calcareous sandstone and shell limestone of Quaternary period and occurs as abrasion platforms. The shoreline is covered mostly by beach sand and oxidized ‘teri’ sand. The major landforms include beach, recent dune complex (Fig.9), wave cut platform (Fig.10), tidal inlets, bay, tombolo etc. The landform connecting the mainland of Tuticorin with the Pandiyan Tivu (Hare island) is the only tombolo present in the entire coast of Tamil Nadu (Krishnan and Srinivasan, 2000). The impact of tsunami waves within the long coast betweenRamnanathapuram and Rameswaram (Fig. 11) and Mandapam and Tuticorin, manifested in terms of coastal erosion and destruction to the existing landforms. The significant impacts are the widening of river mouths in Gundar, Vembar and Vaippar rivers resulted in backflow of seawater into the river and tidal inlets, depositing sand and clay inside lagoon and lakes. No major effect to recent sand dune complex is noticed. The tip of Dhanushkodi shows erosion along the coast, at the contact of beach and berm crest (Fig.12). Impact to Vaigai cuspate foreland and Rameswaram island is


219


220

marginal. No major enrichment of heavies (ilmenite and garnet) noticed in Vembar-Vaipparsections. Presence of small islands and coral reefs along the coast partially diminished the energy flux of the waves. The quality of ground water occurring within the coastal stretch is generally saline and hence no major variation could be found. Saltpans located close to the coast of Tuticorin are damaged by inundation (Fig. 13). Damage to the major Port Tuticorin is minimum. The post-tsunami survey in this sector revealed that there were four major pulses of tsunami waves that struck the coast at 10:00,13:00,16:20 and 17:40 hrs (Tide gauge data of Tuticorin Port) out of which the pulse at 13:30 was most severe. The run-up elevation of waves varied between 0.5 and 2m with a resultant run-up length inundation between 25 and 500m inland depending on coastal morphology. The wave splash ranged between 2 and 6 m depending on the obstruction it encountered. The withdrawal of sea (ebbing) exposing the sea bed hitherto uncommon in the sector was prominently seen between the pulses of tsunami waves and it ranged from 20 to 500m ((Table-3 & Plate-I).Natural speed breakers in the form of 21 islands and coral reefs present diminished the energy flux of waves. Tsunami deposits with coral fragments is characteristic to this sector (Fig. 14).

4.Tuticorin – Tiruchendur Sector:

This sector falls within the Gulf of Mannar and extends for about 35 km along NNE-SSWand N-S directions. The major coastal landforms observed are the beach; recent dune complex, Tambraparni estuary, etc. The beach is narrow with 10-15 m width except in Tambraparni estuarine delta, where it is between 15 and 25 m. Tuticorin-Tiruchendur sector is essentially made up of Tambraparni estuarine delta, which has three major tidal inlets. Dense Mangrove vegetations are seen in all these channels. The general elevation of the coast ranges between 2 and 5 m above m.s.l. The N-S coastal stretch extending between Virapandianpattinam and Kayalpattinam is devoid of any distinct dune barriers resulted in seawater inundation. The impact on tidal inlets of Tambraparniestuary is characterised by way of opening of its mouths and sea water ingress besides silting of sand (tsunami deposit) far inside for about 2-3 km. No significant change in quality of ground water along the coastal zone is observed. The impact on mangrove cultivations within Tambraparni estuary and on saltpans is negligible. The post-tsunami survey in this sector documented the arrival time of the most destructive waves between 13:00 and 13:30 hrs, with a run –up elevation of 1.5 to 2 m and a wave splash of 3 to 6 m. Further the inundation of sea water inland (run-up length) was between 25 and 500m and withdrawal of sea during the pulses of tsunami waves was 50 –1000 m (Table- 4 & Plate-I).

5. Tiruchendur – Kanyakumari Sector:

The Tiruchendur – Kanyakumari sector extends for about 85 km and lies in the lower segment of Gulf of Mannar, protruding into Indian Ocean. The various land forms observed in the sector are the beaches, recent dune complex, wave cut platforms, abrasion platforms, shore platforms by quarrying, bay, etc. The lithounits present in the coastal sector are sand (younger coastal dunes and the older red coloured ‘teri’ sand), calcareous sandstone and limestone of Recent to Sub- Recent period and the rocks of migmatite complex, charnockite and khondalite groups. Wide beach of 15 to 25 m width seen between Tiruchendur and Kulasekarapattinam and Periyatalai and Nambiyar river mouth while it is narrow of less than 15 m width in the rest of the coast. In Tiruchendur – Manappad coast, the recent dune complex is about 1 km wide but is poorly developed between Manappad and Kanyakumari. Wave cut shore platform occurs discontinuously near Tiruchendur, Manappad,between Baradar Ovari and Maraikkattuvilai, Nambiyar river mouth, Kuttankuli, Vijayapati and Idindakarai – Kudankulam area. The post-tsunami survey recorded (Table- 5 & Plate-I) a run-upelevation of waves between 1 m and 3 m, run-up length between 10 m and 250 m, wave splash rose maximum up to10m at Vivekananda rock memorial, Kanyakumari and the withdrawal of sea between the pulses of tsunami waves ranged from 250 to 1000m. The withdrawal of sea both at Tiruchendur (Fig.15&16) and Kanyakumari was quite conspicuous. Heavy loss of property mainly to the fishing boats, nets, and hutments etc, reported in this sector.


221


222

The significant observations made during the survey are the coastal erosion in Manappad and Vattakottai bays. The villages of Kulasekarapattinam and Manappad (Fig. 17 & 18) wereprotected against major devastation by the wave breakers (groynes) already erected; impact on placer deposits between Kuttam and Ovari was not significant except for enrichment of Ilmenite near Vattakkottai (Fig.19). The famous Tiruchendur temple located right on the shore was protected by the barrier dune and by the shore platform (Valli cave) and the wave breakers erected along the coast. The other impacts include opening of river mouth of Nambiar and seawater ingression and silting. Further, the quality of potable water springs occurring along the slopes of shore platform of Manappad and near the coast of Tiruchendur have not been affected by the tsunami waves. Damage to Chinna Muttam Fishing Harbor near Kanyakumari was almost total. Boats berthed inside the harbor were dragged out by currents and some were perched on the groynes (Fig.20) erected on the bank. Tossing of loose boulders by wave splash was conspicuous at Kanyakumari (Fig. 21-24).

ACKNOWLEDGEMENTS

The authors are thankful to Shri S.D. Pawar and Dr M.M. Niar Deputy Director General, GSI, Southern Region for their guidance during the work and preparation of the report. The authors also gratefully acknowledges the help and logistic support provided by the Directors of variousDivisions of GSI and other officials. Acknowledgement is also due to Port authorities and local administration for the support provided during the course of study.

REFERENCE

Krishnan, V &Srinivasan, R

1999 Geoenvironemntal Resources Appraisal and impactassessment studies along Tamil Nadu coast betweenNagapattinam and Ramanathapuram (FS 1994-95)


2000 Report on the Geoenvironemntal Resources Appraisal andimpact assessment studies along Tamil Nadu coast beltbetween Ramanathapuram and Kollankod (FS 1995-96)


2000 Geoenvironemntal Resources Appraisal and impactassessment studies in Uchpuli-Mandapam area andRameswaram island, Ramanathapuram district, Tamil Nadu (FS 1995-96)


223

TABLE-1

TSUNAMI SURVEY DATA IN NAGAPATTINAM – POINT CALIMERE SECTOR

Run-upSl No + Location

(Toposheet no.)

Arrival

time of

strongest

wave

Elevation

(m)

Distance

(m)

No. of pulses

(Strong pulses)

Predominant wave

direction (Height

of wave splash due

to obstruction)

Maximum

seaward

retreat (m) of

shoreline

between wave

pulses

Remarks

1

Pattanchcheri

10º 49'16''

79º51'09''

(58 N/13)

09:20 3.0 500 4 (2nd & 3rd) WNW (10m) -

Casualty: 460+;

damage to property

within back/fore-

shore region; ingress

of tsunami water 3-4

km along Vettar

river.

2

Samandampettai

10º47'48''

79º51'08''

(58 N/13)

09:20 3.0 1250 4 (2nd & 3rd

) WNW (10m) -

Casualty: 140+;

damage to property

within back/fore-

shore region.

3

Nambiarkuppam

10º46'45''

79º51'08''

(58 N/13)

09:20 2.0 750 4 (2nd & 3rd

) WNW (8m)-

Casualty: 300+;

foreshore area

washed off.; dunes

restricted damage in

backshore.

4

Nagapattinam

10º45'53''

79º51'07''

(58 N/13)09:20 3.0 750 4 (2nd & 3

rd) WNW (10m) -

Casualty 500+;

foreshore area

washed off.

Table1 continued


224

TABLE-1

TSUNAMI SURVEY DATA IN NAGAPATTINAM – POINT CALIMERE SECTOR


(Toposheet no.)

Arrival

time of

strongest

wave

Elevation

(m)

Distance

(m)

No. of pulses

(Strong pulses)

Predominant wave

direction (Height

of wave splash due

to obstruction)

Maximum

seaward

retreat (m) of

shoreline

between wave

pulses

Remarks

5

Kichchankuppam

& Akkaraipettai

10º44'32''

79º51'09''

(58 N/13)

09:20 3.0 750 4 (2nd & 3rd) WNW (10m) -

Casualty 5000+;

maximum

devastation to life

and property in the

entire tsunami hit

Indian coastline

6

Velankanni

10º40'43''

79º51'17''

(58 N/14)

09:20 3.0 750 4 (2nd & 3rd) WNW (10m) -

Heavy loss of life;

damage to

kiosks/hutments on

the back/foreshore

area;

7

Pattavarnattam

10º37'12''

79º51'18''(58 N/14)09:20 2.0 300 4 (2nd & 3rd) WNW (8m) -

Shelter bed

plantations restricted

damage.

8

Vanavanmahadevi

10º31'47''

79º51'39''

(58 N/14)09:20 2.0 500 4 (2nd & 3rd) WNW (8m) -

Foreshore area

washed off.

9

Point Calimere

(Kodiyakarai)

10º16'23''

79º49'30''

(58 N/15)

09:20 3.0 200 4 (2nd & 3rd) WNW (10m) -

Casualty: 27+

Foreshore area

washed off; bird

sanctuary saved due

to shelterbelt

plantations.

+ Refer Plate- 1 for locations


225

TABLE-2

TSUNAMI SURVEY DATA IN POINT CALIMERE –RAMANATHAPURAM SECTOR


(Toposheet no.)

Arrival

time of

strongest

wave

Elevation

(m)

Distance

(m)

No. of pulses

(Strong pulses)

Predominant

wave direction

(Height of wave

splash due to

obstruction)

Maximum

seaward retreat

(m) of shoreline

between wave

pulses

Remarks

10

Mallipattinam

10º16'29''

79º19'07''

(58 N/7)

14:15 1.5 100 3 (2nd) NNW (5m) 50

Casualty: Nil

Damage to property –

minimum.

11

Ammanichattram

10º11'34''

79º15'42''

(58 N/4 & 8)

14:15 1 25 3 (2nd) NNW (2m) 30

Dune complex

protected the place;

no damage reported.

12

Adipattiman

10º00'33''

79º13'50''

(58 N/4 & 8)

14:15 2 50 3 (2nd) NW (3m) 25No damage to life

and property

reported.

12(a)*Kottaipattinam

(58 O/1 & 2)14:15 2 75 3 (2nd) WNW (3m)

-

No damage to life

and property

reported. Aqua farms

unaffected.

12(b)*Mimisal

(58 O/1 & 2)14:15 1.5 50 3 (2nd) WNW (3m)

-

No damage to life

and property

reported.

Table 2 continued



226

TABLE-2

TSUNAMI SURVEY DATA IN POINT CALIMERE –RAMANATHAPURAM SECTOR


(Toposheet no.)

Arrival

time of

strongest

wave

Elevation

(m)

Distance

(m)

No. of pulses

(Strong pulses)

Predominant

wave direction

(Height of wave

splash due to

obstruction)

Maximum

seaward retreat

(m) of shoreline

between wave

pulses

Remarks

13

Pasipattinam

09º48'35''

79º04'56''

(58 O/1 & 2)

14:15 1.5 50 3 (2nd) WNW (3) 10

Elevated beach

protected the place.

No damage to life

and property

reported.

14

Tondi

09º44'28''

79º01'24''

(58 O/1 & 2)

14:00 0.5 50 3 (2nd) WNW (2m) -

Elevated beach


No damage to life

and property

reported.

15

Devipattinam

09º28'46''

78º53'57''

(58 K/15)

14:00 1.0 50 3 (2nd) WNW (2m) 50

Elevated beach


No damage to life

and property

reported.

16

Ariyaman

09º17'48''

79º04'14''

(58 O/3 & 4)

14:00 1.5 100 3 (2nd) S (2m)

-

Wide beach and thick

belt of plantations

(Casuarinas) along

the coast. No damage

reported.

*12( a & b) are locations between 12 and 13.



227

TSUNAMI SURVEY DATA IN RAMANATHAPURAM-RAMESWARAM-TUTICORIN SECTOR TABLE-3


(Toposheet no.)

Arrival

time of

strongest

wave

Elevation

(m)

Distance

(m)

No. of pulses

(Strong pulses)

Predominant

wave direction

(Height of wave

splash due to

obstruction)

Maximum

seaward retreat

(m) of shoreline

between wave

pulses

Remarks

17

Thonithurai

09016'52''

79011'05''

(58 O/3 & 4)

14:00 2 50 3 (2nd) N (2m) 20m

Location protected by

wave cut platform.

18

Rameswaram

09017'14''

79019'20''

(58 O/7 & 8)

14:00 0.5 25 3 (2nd) WNW (2m) 25

Raised beach and wave

cut platform saved the

location and the temple

19

Dhanushkodi

09010'33''

79025'01''

(58 O/7 & 8)

14:00 1 50 3 (2nd) N (2m) 100

Erosion of berm crest

20

Mandapam camp

09016'14''

79008'19''

(58 O/3 & 4)

14:00 1 50 3 (2nd) N (2m) 20

Wave cut platform and 21

small islands fringing the

coast protected the zone

21

Kilakarai

09013'35''

78047'17''

(58 K/16)

14:00 1 25 3 (2nd) N (2m) 25

Elevated beach protected

the location.

22

Chinna Ervadi

09011'47''

78043'15''

(58 K/12)

14:00 1 200 3 (2nd) N (2m) 500

Casualty: 2

Damage: marginal

23Valinokkam

09º09'48''

78039'01'' (58 K/12)

14:00 1 100 3 (2nd) N (3m) 100

Wave cut shore platform

and elevated beach

minimized damage.

+ Refer Plate- 1 for locations Table 3 continued


228

TABLE-3

TSUNAMI SURVEY DATA IN RAMANATHAPURAM-RAMESWARAM-TUTICORIN SECTOR


(Toposheet no.)

Arrival

time of

strongest

wave

Elevation

(m)

Distance

(m)

No. of pulses

(Strong pulses)

Predominant wave

direction (Height

of wave splash due

to obstruction)

Maximum

seaward retreat

(m) of shoreline

between wave

pulses

Remarks

24

Melmundal

09007'50''

78034'28''

(58 K/12)

14:00 1 100 3 (2nd) N (3) 100

Long and wide beach

minimized damage

25

Terku Mukkaiyur

09007'33''

78028'48''

(58 K/8)

14:00 0.5 50 3 (2nd) N (6m) 50

Elevated beach

protected the

location. Silting

(tsunami deposit)

along Gundar river.

26

Terku Naripaiyur

09006'46''

78025'16''(58 K/8)

14:00 1 50 3 (2nd) N (2m) 50

Elevated and wide

beach protected the

location

27

Vembar

09004'29''

78021'59''

(58 K/8)

13:30 1 50 3 (2nd) N (5m) 300

Casualty: 1 Elevated

beach minimized the

damage.

28

Sippikulam

08059'33''

78015'14''

(58 L/1 & 5)

13:30 1 250 3 (2nd) N (3m) 250

Elevated beach

protected the

location. Minimum

damage; heavy silting

(tsunami deposit)

along Vaippar river.

29

Pattanamarudur

08055'15''

78011'14''

(58 L/1 & 5)

13:30 1.5 100 3 (2nd) N (3m) 500

Elevated beach

protected the

location.

Table 3 continued



229

TABLE-3

TSUNAMI SURVEY DATA IN RAMANATHAPURAM-RAMESWARAM-TUTICORIN SECTOR


(Toposheet no.)

Arrival

time of

strongest

wave

Elevation

(m)

Distance

(m)

No. of pulses

(Strong pulses)

Predominant

wave direction

(Height of wave

splash due to

obstruction)

Maximum

seaward retreat

(m) of shoreline

between wave

pulses

Remarks

30

Taruvaikulam

08053'23''

78010'35''

(58 L/1 & 5)

13:30 2 200 3 (2nd) N (3m) 300

Elevated beach

protected the location

31

Vellaipatti

08051'19''

78010'04''

(58 L/1 & 5)

13:30 1.5 500 3 (2nd) N (3m) 25

Elevated beach


32

Tuticorin

08048'34''

78009'56''

(58 L/1 & 5)

13.30 2 100 3 (2nd) N (5m) 250

Erosion along

Tuticorin north bay.

33

Pandiyan Tivu

08047'11''

78011'56''

(58 L/1 & 5)

13.30

1.5 100 3 (2nd) N (5m) 100

Tombolo – protected

the damage. Tsunami

deposit viz. broken

corals are seen along

the shore.



230

TABLE-4

TSUNAMI SURVEY DATA IN TUTICORIN-THIRUCHENDUR SECTOR


(Toposheet no.)

Arrival

time of

stronges

t wave

Elevation

(m)

Distance

(m)

No. of pulses

(Strong pulses)

Predominant

wave direction

(Height of wave

splash due to

obstruction)

Maximum

seaward retreat

(m) of shoreline

between wave

pulses

Remarks

34

Tuticorin Harbour

08044'58''

78011'40'' (58 L/2)

13:30 2 200 3 (2nd) N (3m) 1000

South bay-- lowlying

area, plantation

destroyed

35

Muthaiyapuram

08044'18''

78010'02'' (58 L/2)

13:30 2 200 3 (2nd) N (5M) 50

Low lying industrial

zone flooded

36

Punnaikayal

08038'08''

78007'20'' (58 L/2)

13:15 1.5 100 3 (2nd) N (5M) 500

Damage to fishing

harbour, heavy silting

along Tambraparni

river delta.

37

Kayalpattinam

08033'39''

78008'03'' (58 L/2)

13:00 2 500 3 (2nd) N (3m) 50

Channels aided

ingression of tsunami

water.

38

Veerapandiya

pattinam

08030'58''

78007'26'' (58 L/2)

13:00

2 150 3 (2nd) N (6m) 25

Flattening of beach;

low lying area

inundated

39

Thiruchendur

08029'31''

78007'47'' (58 L/3)

13:00

2 25 3 (2nd) N (5m) 500

Barrier dune and

wave cut platforms


and Temple;

withdrawal of sea

conspicuous.



231

TABLE-5

TSUNAMI SURVEY DATA IN THIRUCHENDUR - KANYAKUMARI SECTOR


(Toposheet no.)

Arrival

time of

strongest

wave

Elevation

(m)

Distance

(m)

No. of pulses

(Strong pulses)

Predominant

wave direction

(Height of wave

splash due to

obstruction)

Maximum

seaward retreat

(m) of shoreline

between wave

pulses

Remarks

40

Alantalai

08027'49''

78006'09''

(58 L/3)

12:45 2 100 3 (2nd) N (10m) 250

Ingression along

inter-dune

depressions

41

Kallarmozhi

08026'24''

78004'57''

(58 L/3)

12:45 1 250 3 (2nd) N (10m) 250

Barrier dune


42

Kulasekara

pattinam

08023'36''

78003'35'' (58 L/3)

12:45 1.5 60 3 (2nd) N (6m) 250 Groynes protected

the erosional coast.

43

Manapad

08022'20''

78003'48''

(58 L/3)

12:45 1.5 60 3 (2nd) WNW (10m) 250

Sand bar, shore

platform and groynes

protected location.

Quality of potable

water springs along

the ridge unaffected

44

Periyathalai

08020'05''

77058'42''

(58 H/15)

12:45 1.5 80 3 (2nd) N (5m) 250 Casualty: 1; damage

to property reported.

45

Kuduthalai

08017'51''

77055'48''

(58 H/15)

12:45 3 15 3 (2nd) N (5m) -

Elevated beach.

Placer garnet

concentrate washed

off

+ Refer Plate- 1 for locations Table 5 continued


232

TABLE-5



(Toposheet no.)

Arrival

time of

stronges

t wave

Elevation

(m)

Distance

(m)

No. of pulses

(Strong pulses)

Predominant

wave direction

(Height of wave

splash due to

obstruction)

Maximum

seaward retreat

(m) of shoreline

between wave

pulses

Remarks

46

Nadar Ovari

08016'59''

77054'06''

(58 H/15)

12:45 2 60 3 (2nd) N (5m) -

Elevated beach.

47

Bardar Ovari

08016'38''

77053'44''

(58 H/15)

12:45 2 10 3 (2nd) N (6m) 500

Groyne erected

across coast

facilitated formation

of beach with garnet

deposition.

48

Karikovil

08015'28''

77051'37''

(58 H/15)

12:45 1.5 100 3 (2nd) N 750

Barrier dunes. Placer

garnet concentrate

washed off

49

Kuttankuli

08012'53''

77047'01''

(58 H/16)

12:45 1.5 100 3 (2nd) N (10m) 750

Casualty: 1;

damage to property

marginally high;

placer garnet

concentrate washed

off.

49(a)#

Avudayalpuram

08011'35''

77018'16''

(58 H/16)12:30 3 10 3 (2nd) N (10) 500

Wave cut platform

and barrier dunes


+ Refer Plate- 1 for locations Table5 continued


233

TABLE-5



(Toposheet no.)

Arrival

time of

stronges

t wave

Elevation

(m)

Distance

(m)

No. of pulses

(Strong pulses)

Predominant

wave direction

(Height of wave

splash due to

obstruction)

Maximum

seaward retreat

(m) of shoreline

between wave

pulses

Remarks

50

Idindakarai

08010'28''

77044'39''

(58 H/12)

12:30 1.5 50 3 (2nd) N (10m) -

Casualty: 3; damage

to property

marginally high;

flattening of beach

observed.

51

Chinna Muttam

08005'40''

77033'58''

(58 H/12)

12:30 2 100 3 (2nd) N (10m) -

Damage to fishing

harbor severe.

52Kanyakumari

08005'16''

77033'31''

(58 H/12)

12:30 3 100 3 (2nd) N (10m) 1000

Damage to property

and jetty severe;

rocky coast;

enrichment of

ilmenite deposits.

Vivekananda

memorial and

Valluvar statue

withstood the

onslaught.

Withdrawal of sea

from coast was

conspicuous.


____________________________________________________________________________________________REPORT ON SUMATRA -ANDAMAN EARTHQUAKE & TSUNAMI, 26 DEC ’04

234

Fig 1. Backshore with coconut groovesshowing boat hit marks at Pattancheri

Fig 2. Back/foreshore with ruins of Pattancheri where about 400+ casualty reported; damaged oil jetty at the background

Fig 3. Damaged jetty at Nagapattinam ; boatsdamaged due to collision

Fig 4. Opening of the river mouth of Vettar near Nagapattinam causing ingression of sea water

Fig 5. Run up length of Tsunami wavesat Velanganni wherein heavy casualtyreported on post Christmas day

Fig 6. Post Tsunami reclaimed backshore / foreshore area of Velanganni beach

Boat hit mark

Run up length


235

Fig 7. Aqua culture farm near Kottaipattinam showing no impact

Fig 8. Elevated beach with bio-shield Plantation (Casurina) near Ariyaman, Ramanathapuram coast

Fig 9. Barrier Dune with vegetation near Pudumadam, protected the coast

Fig 10. Wave cut Platform near Mandapam acted as natural barrier

Fig 11. Post Tsunami Scene between the coastsof Ramanathapuram andRameswaram

Fig 12. Dhanushkodi coast unaffected by Tsunami waves


236

Fig 13. Saltpan near Tuticorin less damaged byTsunami ingression

Fig 14. Tsunami deposits consistingmainly corals strewn near Hare Island(Tuticorin)

Fig15. Unprecedented withdrawal of the seabetween the pulses of Tsunami waves atTiruchendur showing temple at background

Fig16. Post Tsunami scene at Tiruchendur coast unaffected by Tsunami

Fig-17 A view from Manapad shore platformshowing the erosional front and Groynesprotecting the village

Fig –18 Rubble mounted seawall (RMS)/ Groynes erected near Kulasekarapattinam protected the inhabitants in thebackground

Shoreline

Groynes


237

Fig 19. Tsunami deposits of ilmenite placersnear Vattakottai, Kanyakumari coast

Fig 20. A scene at Chinnamuttam harbour, Kanyakumari showing perched boats on the Tetrapods

Fig 21. Tossed boulders by the surge ofTsunami waves near Kanyakumari

Fig.22. Live photograph showing the bore of Tsunami waves at Kanyakumari

Fig 23. Live photograph showing wave splash at Kanyakumari

Fig24. Post Tsunami scene at Vivekananda rock memorial, Kanyakumari

____________________________________________________________________________________________REPORT ON SUMATRA -ANDAMAN EARTHQUAKE & TSUNAMI, 26 DEC ’04 239

TSUNAMI SURVEY IN THE KANYAKUMARI - COCHIN SEGMENT

IN PARTS OF TAMIL NADU AND KERALA

K. Jayabalan and U. Durairaj

Geological Survey of India, Chennai

INTRODUCTION

The tsunami generated due to the great Sumatra earthquake of 26th December 2004 hit the Indian main land with devastating effects. This document deals with the results of studies carried out between 5

th and 13

th January 2005, in Kanyakumari - Cochin segment in parts of Tamil Nadu and

Kerala covering about 300 km. Considering the vast stretch, varied geomorphology, bathymetry and variable impact of tsunami, the entire study area (Plate I) has been subdivided into the following four sectors for the convenience of description:

1. Kanyakumari - Thiruvananthapuram (100 km)2. Thiruvananthapuram - Quilon (60 km)

3. Quilon - Alleppy (75 km) 4. Alleppy - Cochin (80 km)

Distribution of run up elevation and run up distance in all the above sectors are shown in Plate II.

Kanyakumari - Thiruvananthapuram Sector

This sector, located in the southern part of the Indian sub-continent covers a stretch of about 100 km. Thiruvananthapuram, the capital of Kerala and Kanyakumari, the famous tourist center are located in this sector. The coastal stretch between Kanyakumari and Kolachal is oriented in WNW-ESE direction, after which it swerves to NNW-SSE. Khondalite and Charnockite Group of rocks are exposed intermittently as rocky knobs in this coastal stretch with cover rocks of Tertiary andQuaternary sediments. In this Sector, 1.5 to 2m sand ridges/ dune complexes usually protect the coast. Beaches, sand dunes/ ridges, wave cut platforms and shore platforms characterize thissegment. Intensity of tsunami including causalities decreases from south to north (Table 1). AtKanyakumari, sea level fluctuations have been reported from 0930 hrs with rough sea, though the first wave hit the coast around 1030 hrs followed by a series of waves at 10-15 minutes intervals.Around 1200 hrs, seawater receded for a distance of 300 - 500m from the shoreline exposing the seabed. A huge wall like water column (water bore) with tremendous speed and terrific noise hit the coast at 1215hrs with the flash rising up to 10m. At Manakkudi, sea level fluctuated from 0940 hrs; the first wave hit the coast at 1025 hrs followed by a series of waves with 10 - 15 minutes interval;seawater receded in between the pulses exposing the seabed up to 300 - 500 m around 1215 hrs. The killer wave rushed towards the land with an approximate height of 7 - 9 m devastating coastalvillages and newly constructed concrete bridge (Fig. 1) across the Pazhayar River. Breaches in the coastal ridges/ dune complexes (Fig.2 and 3) are also noticed in the area from Melmanakudi toPillaithoppu. Around Melmanakudi and Pallom, houses built parallel to the beachfront werecompletely destroyed (Fig.4) with heavy loss to life and property. At Kadiappattanam, the first wave hit the land at 1030 hrs with devastating effect. The approximate run up elevation of 4m has caused


inundation of vast area along the coast. The Valliyar river mouth has been widened (Fig. 5) with heavy deposition of black sand. The entire Kottilpad village located just east of Kolachel has been swept away causing severe damage to life and property. A thick blanket of placer deposits covers the beach after tsunami. At Kolachel, around 0945 hrs, seawater gradually increased and suddenly hit the land with the maximum speed and energy, submerging the low-lying areas all along the coast. The seawater later vigorously receded for about 200 - 300m. These fluctuations in the sea level have been reported for 5 - 6 times. When the tsunami hit the land, it breached the coastal ridges and canal banks. A thick column of seawater entered through the canal and surrounded the villages located nearby. From Kolachal to Thiruvananthapuram the destructions are comparatively less due to higher elevation of the beaches and the steep gradient of the continental shelf. At Villinjam, initial surge was reported around 0930 hrs while the main wave hit the coast around 1250 hrs causing severe damage to the fishing boats and settlements located in the nearby areas. At Kovalam, sea levelfluctuated around 0930 hrs creating panic among the tourists. The first wave hit the coast around 1245 hrs; then the sea progressively receded for a distance of 100 to 150 m exposing the seabed and again hit the coast around 1300 hrs with run-up elevation of 1.5 to 2m.

Thiruvananthapuram - Quilon Sector

This 60km long coastal stretch is almost a NW-SE trending plain country. Vertical cliffs can be seen at places along the coast. These cliffs vary in height from 3m to 20m, capped by laterite. This sector is less affected by tsunami (Table 2). The initial surge in this sector has been reported between 0930 hrs and 10.20 hrs. Recessions during the repeated pulses have also been reported. The run-up elevation in this sector ranges from 0.75 to 1m and the run-up distance from 50 to 200m.

Quilon - Alleppy Sector

This 75km long NNW trending sector is characterized by the presence of prominent coast parallel water bodies. A narrow stretch of land separates the open sea and the kaya1 (backwaters). Post -tsunami data (Table 3) indicated a maximum run-up distance up to 1.5 km, along the creek, TS canal being primarily responsible for the inundation. At Azhikkal, the first wave hit the coast at around 1145 hrs, followed by series of waves with 10-15 minute intervals. The sea receded in between successive waves exposing the seabed up to l km around 1300 hrs. The largest wave with an approximate height of 7m hit the coast at 1310 hrs with devastating effect. This has causedinundation of vast area along the coast. Higher run up distance of 2.5km has been observed along a 10km stretch. The maximum damage has occurred between open sea and TS canal. Most of the concrete houses, property, fishing vessels and automobiles on the coast parallel road have beenuprooted and thrown to a distance of 100 to 200m (Fig.6, 7, 8, 9 and 10). The width of the barrier beach is between 100 - 500 m and in general the land slopes towards the kayal. Wave breakers protect most part of the kayal. The rubbles/ blocks from the wave breakers have been lifted and thrown ashore up to a distance of 100m by tsunami waves. At places, these blocks, fishing vessels and trucks got struck in the coconut groves, while some were washed over into the neighboring TS canal. The waves have destroyed the roads and scoured the basement of the houses. A thick pile of beach placers (ilmenite and rutile) have been deposited in the area between the sea and TS canal (Fig.11, 12, 13, 14 and 15). About 60cm thick heavy mineral layer has been noticed for a stretch of 2km in the Azhikkal and Taraikaduvtura area. A thick blanket of (70-90 cm) heavy mineral has been deposited over the coastal road at Valliya Azhikkal area. An acute shortage of drinking water is reported in the area around Alappad, where the inundation of wells has resulted salinity. Heavy loss of men and material has been reported from Alappad Panchayat. At Valliyattukaltura, sea levelfluctuation started around 1000 hrs. Just before the major wave, seawater receded for a distance of 500m exposing the seabed. During the retreat, people who entered the sea to collect the fishes lying


on the seabed have been engulfed by the tsunami in no time along with the rescuers. The causality figures were higher in this area because of dense population. At places, the concrete houses have also damaged due to under scouring. Low foundation depth and poor construction were responsible for damages to the constructions. At Anthakaranahalli, the tsunami hit the coast around ll00 hrs. The seawater receded up to a distance 500m. Around 1115 hrs a giant wave (bore type) hit the coast with devastating fury. The beach is very gentle with an elevation of less than a meter. The river mouth is breached at Manakkodam (Fig.16). The bore about 1.5m high, had rushed through the estuaries,spilling over the existing sand bar causing severe damage to the light house.

Alleppey - Cochin Sector

This 80km long sector comprises two distinct geomorphic units viz. Kadapuram and Viyam formations (tidal flats). In this sector, 8 km stretch between Cherai - Edavanakkad has been badly damaged. Cherai resorts and fishermen colonies located in the narrow strip of barrier beach have been fully damaged. Heavy causalities have also been reported from this stretch. The first wave hit the coast at 1110 hrs followed by a series of waves with 10 - 15 minutes interval. After devastating the coastal villages, the sea receded for about 500- 1000m exposing the seabed around 1315 hrs. At 1430 hrs, all of a sudden, a big wave rushed towards the land with tremendous force along with unusual noise and hit the coast inundating vast area. The run up of largest wave is more than a kilometer along this stretch. Most of the well-built concrete houses, valuable property, mechanised fishing boats and the automobiles on the coast parallel road have been thrown to a distance of 50-100m. Wave breakers (made up of granite blocks) without gabions provided along the shoreline were fully damaged. The haphazardly placed granite blocks were lifted by the waves and thrown ashore up to a distance of 100m. These granite boulders acted like canon balls and caused severe damages to the life and property. At places, fishing vessels and catamarans got struck into the coconut groves, while some were washed into the kayals (backwater). Tsunami brought huge volume of beach placer (ilmenite and rutile) and blanketed the roads and other nearby areas (Table 4).

ACKNOWLEDGEMENT

The authors express their sincere thanks to Shri S.D. Pawar and Dr. M.M. Nair, DDG, GSI. The authors are also thankful to Shri G. Rajagopalan, Director, for his guidance in thepreparation of this report. We sincerely thank Shri R.S.Nair, Dr. P.K. Muralidharan, Directors and S/Shri. Koshy John, C. Muraleedharan, B. Nageswaran, Dr. Mathew Joseph, Geologists and other colleagues for active support. The authors are grateful to the Port Trust officials, Cochin, for providing tidal gauge data.

__

__

__

__

__

__

__

__

__

__

__

__

__

__

___

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

_

RE

PO

RT

ON

SU

MA

TR

A-A

ND

AM

AN

EA

RT

HQ

UA

KE

& T

SU

NA

MI,

26

DE

C ’

04

242

__

__

__

__

__

__

__

__

__

__

__

__

__

__

___

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

_

RE

PO

RT

ON

SU

MA

TR

A-A

ND

AM

AN

EA

RT

HQ

UA

KE

& T

SU

NA

MI,

26

DE

C ’

04

243

__

__

__

__

__

__

__

__

__

__

__

__

__

__

___

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

_

RE

PO

RT

ON

SU

MA

TR

A-A

ND

AM

AN

EA

RT

HQ

UA

KE

& T

SU

NA

MI,

26

DE

C ’

04

244

TA

BL

E-1

TS

UN

AM

IS

UR

VE

Y D

AT

A I

N K

AN

YA

KU

MA

RI

– T

HIR

UV

AN

AN

TH

AP

UR

AM

SE

CT

OR

Sl.

No.

Lo

ca

tio

nL

at/

Lo

ng

Tsu

na

mi

arri

val

tim

e

Sea w

ate

r

recess

ion

Ru

n-u

p

ele

va

tio

nR

un

up

dis

tan

ce

Rem

ark

s

1K

an

yak

um

ari

08

°0

4’4

1”

77

°3

2’5

6”

09

.30

hrs

10

.00

hrs

.1

2.1

5h

rs.

> 1

00

m4

m1

00

m.

Wa

ve

fro

nt

mo

ve

d d

ue

no

rth

2M

an

ak

ku

di

08

°0

5’2

4”

77

°2

9’0

2”

09

.40

hrs

10

.25

hrs

.

12

.30

hrs

.

> 5

00

m3

m>

2.5

km

(alo

ng

cre

ek

)

He

av

y c

asu

alt

ies.

Ro

ad

s a

nd

ho

use

s

dam

ag

ed

. New

ly c

on

stru

cte

d b

rid

ge a

cro

ss

the

Pa

lay

ar

riv

er

bro

ke

n i

nto

pie

ce

s.

Se

aw

ate

r e

nc

roa

ch

ed

th

e b

ea

ches

. Wel

l

wate

r b

ecam

e s

alt

y.

Wav

e d

irecti

on

du

e

N60

0E

.

3M

utt

om

08

°0

7’2

0”

77

°1

9’2

5”

09

.40

hrs

.

10

.20

hrs

.1

2.3

0 h

rs.

50

0m

2.5

m7

5m

4K

ad

iya

pa

ttn

am

08

°0

8’3

0”

77

°1

8’1

7”

09

.15

hrs

.1

0.2

0 h

rs.

12

.30

hrs

.

>6

00

m2

m>

25

0m

5S

ou

th

of

Man

av

ala

ku

rich

i

08

°08’1

0”

77

°1

8’0

9”

09

.30

hrs

.

10

.20

hrs

.

11

.10

hrs

.1

2.0

0 h

rs.

>6

00

m2

m>

30

0m

6K

ott

ilp

ad

u0

8°1

0’1

8”

77

°1

5’5

9”

09

.30

hrs

.1

0.3

0h

rs.

11

.10

hrs

.1

2.1

5h

rs.

>6

00

m3

m4

00

mH

eav

y c

asu

alt

ies.

En

tire

vil

lag

e w

as

swep

t

aw

ay

.

7E

of

Ko

lac

he

l0

8°1

0’2

2”

77

°1

5’1

1”

09

.30

hrs

.

10

.30

hrs

.1

1.1

0h

rs.

12

.20

hrs

.

>6

00

m3

-4m

>5

00

mS

eaw

ate

r en

tere

d t

hro

ug

h t

he A

VM

can

al

an

d s

urr

ou

nd

ed

th

e n

ea

rby

vil

lag

es.

8K

ola

ch

el

08

°1

0’2

2”

77

°1

4’4

9”

10

.30

hrs

.1

1.1

0h

rs.

12

.15

hrs

.

>3

00

m3

.5m

>5

00

mH

ea

vy

ca

su

alt

ies.

9V

izh

inja

m P

ort

08

°2

2’3

1”

76

°59’2

0”

10

.30

hrs

. 1

1.1

5 h

rs.

12

.50

hrs

.

>1

50

m2

-2.5

m>

20

0m

A f

ew

mech

an

ized

fis

hin

g b

oats

dam

ag

ed

.

10

Ko

va

lam

be

ac

h

--0

9.3

0h

rs.

10

.30

hrs

.1

2.4

5h

rs.

> 3

00

m2

m>

10

0m

__

__

__

__

__

__

__

__

__

__

__

__

__

__

___

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

_

RE

PO

RT

ON

SU

MA

TR

A-A

ND

AM

AN

EA

RT

HQ

UA

KE

& T

SU

NA

MI,

26

DE

C ’

04

245

TA

BL

E-2

TS

UN

AM

I S

UR

VE

Y D

AT

A I

N T

HIR

UV

AN

AN

TH

AP

UR

AM

– Q

UIL

ON

SE

CT

OR

Sl.

No

.L

oc

ati

on

La

t /

Lo

ng

Tsu

na

mi

arr

iva

l

tim

e

Sea w

ate

r

rec

ess

ion

Ru

n-u

p

ele

va

tio

nR

un

up

dis

tan

ce

Rem

ark

s

11

San

ku

mu

gam

08

°2

8’4

4”

76

°5

4’3

3”

10

.20

hrs

.

12

.10

hrs

.

<1

00

m1

m2

50

m

12

Vel

i0

8°3

0’0

5”

76

°5

0’3

0”

09

30

hrs

.

10

.20

hrs

.

12

.10

hrs

.

50

m0

.5m

50

m

13

Th

an

ga

se

ri

(Du

tch

Fo

rt)

08

°5

2’5

6”

76

°3

3’5

9”

10

.30

hrs

.

11

.10

hrs

.

13

.00

hrs

.

> 2

00

m2

.5m

25

0m

Hig

h l

an

d

top

og

rap

hy

.

Wa

ve

dir

ec

tio

n

SS

W-N

NE

14

Qu

ilo

n (

lig

ht

ho

use

)

--1

1.5

0 h

rs.

13

.10

hrs

.1

4.1

0 h

rs.

> 1

50

m1

.5m

17

5m

__

__

__

__

__

__

__

__

__

__

__

__

__

__

___

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

_

RE

PO

RT

ON

SU

MA

TR

A-A

ND

AM

AN

EA

RT

HQ

UA

KE

& T

SU

NA

MI,

26

DE

C ’

04

246

TA

BL

E-3

TS

UN

AM

I S

UR

VE

Y D

AT

A I

N Q

UIL

ON

– A

LL

EP

PE

Y S

EC

TO

R

Sl.

No

.L

oc

ati

on

La

t /

Lo

ng

Tsu

na

mi

arri

val

tim

eS

ea

wa

ter

rec

essio

nR

un

-up

ele

va

tio

nR

un

up

d

ista

nc

eR

em

ark

s

15

Ala

pp

att

utu

ra0

9°0

4’0

0”

76°2

9’3

0”

10

.30

hrs

.1

1.4

5 h

rs.

13

.10

hrs

.

50

0m

1.7

m4

50

m

16

S o

f A

zh

ikk

al

09°0

7’0

1”

76°2

8’1

2”

10

.30

hrs

.1

1.4

5 h

rs.

12

.15

hrs

.1

3.1

0 h

rs.

>5

00

m1

.75

m>

50

0 m

Heav

y c

asu

alt

ies.

Gra

nit

e b

lock

s (s

ize 0

.5 c

um

) p

hy

sicall

y

lift

ed

an

d t

hro

wn

fo

r 5

0-1

00

m f

rom

th

e s

ho

reli

ne. H

eav

y

min

era

ls d

ep

osit

ion

(3

-4m

). W

av

e d

irecti

on

SS

W-N

NE

.

17

Az

hik

ka

l0

9°0

7’2

5”

76°2

8’0

2”

10

.30

hrs

.1

1.4

5 h

rs.

13

.10

hrs

.

0.5

-1k

m3

m2

.5k

mH

eav

y c

asu

alt

ies.

Hig

h s

peed

wit

h u

nu

sual so

un

d o

f w

av

es.

H

ea

vy

min

era

ls d

ep

osit

ion

(3

-4m

)

18

Va

lliy

atu

kk

al

Tu

ra0

9°0

8’2

3”

76°2

7’3

5”

10

.30

hrs

.

11

.30

hrs

.1

3.0

0 h

rs.

> 1

km

3m

> 1

.5 k

mA

s a

bo

ve

19

Re

lie

f c

am

p0

9°0

9’5

6”

76°2

7’0

1”

10

.30

hrs

.1

1.3

0 h

rs.

13

.00

hrs

> 1

km

2.5

m>

1.5

km

20

So

uth

of

Tar

aik

adav

u T

ura

09°0

9’0

0”

76°2

7’1

0”

10

.30

hrs

.1

1.3

0 h

rs.

13

.00

hrs

> 1

km

2.5

m>

1.5

km

He

av

y c

asu

alt

ies.

He

av

y m

ine

rals

de

po

sit

ion

(3

-4m

)

21

Tara

ikad

av

u T

ura

09°0

9’4

0”

76°2

7’0

0”

10

.30

hrs

.1

1.3

0 h

rs.

13

.10

hrs

.

> 1

km

2.5

m>

1k

mA

s a

bo

ve

22

Per

um

pal

li (

22

km

fro

m T

ho

ttap

all

i)

--1

0.3

0 h

rs.

11

.30

hrs

.1

3.0

0 h

rs.

--2

.5 m

> 0

.5 k

mH

ea

vy

ca

su

alt

ies

re

po

rte

d

23

Th

ott

ap

all

i0

9°1

8’4

0”

76°2

2’5

5”

10

.55

hrs

.1

2.2

5 h

rs.

12

.55

hrs

.

0.5

km

1.5

m>

1k

m

24

Pu

nn

ap

ra0

9°2

5’5

5”

76°1

9’5

4”

11

.10

hrs

.

12

.30

hrs

.1

3.0

0 h

rs.

0.5

-1k

m1

.5m

40

0m

Wa

ve

dir

ec

tio

n S

SW

-NN

E.

25

An

tha

ka

ran

az

hi

09°4

4’5

3”

76°1

7’0

2”

11

.10

hrs

.

12

.25

hrs

.1

3.0

0 h

rs.

>5

00

m2

m>

50

0m

__

__

__

__

__

__

__

__

__

__

__

__

__

__

___

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

_

RE

PO

RT

ON

SU

MA

TR

A-A

ND

AM

AN

EA

RT

HQ

UA

KE

& T

SU

NA

MI,

26

DE

C ’

04

247

TA

BL

E-4

TS

UN

AM

I S

UR

VE

Y D

AT

A I

N A

LL

EP

PE

Y –

NO

RT

H O

F C

OC

HIN

SE

CT

OR

Sl.

No

.

Lo

ca

tio

nL

at

/ L

on

gT

sun

am

i

arr

ival

tim

e

Se

a w

ate

r

rec

essio

n

Ru

n-u

p

ele

va

tio

n

Ru

n–

up

dis

tan

ce

Rem

ark

s

26

Ma

na

kk

od

am

(lig

ht

ho

use

)0

9°4

4’5

3”

76

°1

7’0

2”

11

.00

hrs

.1

2.2

5 h

rs.

50

0m

(11

.15

hrs

.)2

m>

50

0m

He

av

y c

asu

alt

ies.

Wid

en

ing

of

the r

iver

mo

uth

, h

eav

y s

ilta

tio

n

an

d f

orm

ati

on

of

sp

it.

27

Vy

pin

09

°5

9’8

2”

76

°1

3’3

4”

11

.10

hrs

.1

2.5

5 h

rs.

--1

.5m

20

0m

28

Ed

av

an

ak

ka

d1

0°0

5’0

9”

76

°1

1’3

0”

11

.10

hrs

.1

3.0

0 h

rs.

14

.50

hrs

.

0.5

–

1km

(1

1.3

0 h

rs.)

2.5

mC

ross

ed

th

e

ba

rrie

r

isla

nd

(>1

km

)

He

av

y c

asu

alt

ies.

Wa

ve

bre

ak

ers

wit

ho

ut

ga

bio

ns

– g

ran

ite

blo

ck

s (s

ize

0.2

5 c

um

)

ph

ysi

call

y lif

ted

an

d th

row

n a

sho

re a

dis

tan

ce

of

50

-10

0m

fro

m t

he

sh

ore

lin

e,

roa

d a

nd

ho

use

s d

am

ag

ed

an

d im

pact o

n a

qu

a c

ult

ure

.

29

Ch

era

i b

ea

ch

reso

rt

--1

1.0

0 h

rs.

13

.00

hrs

.1

5.0

0 h

rs.

0.5

- 1km

(12

.30

hrs

.)

1.5

m>

50

0m

30

Ka

da

pu

ram

10

°1

0’3

0”

76

°1

0’1

0”

11

.10

hrs

.

13

.00

hrs

.

14

.30

hrs

.

2m

>5

00

m

31

Mu

na

mb

am

ha

rbo

ur

(fis

hin

g y

ard

)

10

°1

0’4

0”

76

°1

0’2

5”

11

.10

hrs

.

13

.00

hrs

.

14

.30

hrs

.

1.5

- 2

m1

00

m 1

5-2

0 f

ish

ing

bo

ats

da

ma

ge

d

__

__

__

__

__

__

__

__

__

__

__

__

__

__

___

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

_

RE

PO

RT

ON

SU

MA

TR

A-A

ND

AM

AN

EA

RT

HQ

UA

KE

& T

SU

NA

MI,

26

DE

C ’

04

248

Fig

.1-

Dam

ag

ed

ro

ad

bri

dg

e o

ver

Pazh

ay

ar

Riv

er

Lo

c:

Man

ak

ku

di

Fig

.2-

Bre

ach

in

th

e co

asta

l ri

dg

eL

oc:

Ko

ttil

pad

Fig

.3-

Bre

ach

in

th

e fr

on

tal

dune

Lo

c:

Ko

vak

ula

mF

ig.4

- D

est

ructi

on

of

fro

nt

row

of

ho

use

sL

oc:

Ko

lach

el

__

__

__

__

__

__

__

__

__

__

__

__

__

__

___

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

_

RE

PO

RT

ON

SU

MA

TR

A-A

ND

AM

AN

EA

RT

HQ

UA

KE

& T

SU

NA

MI,

26

DE

C ’

04

249

Fig

.5–

Wid

enin

g o

f V

alli

yar

Riv

er m

ou

th L

oc:

Man

aval

aku

rich

iF

ig.6

– C

oll

ap

sed

ho

use

Lo

c:

Azh

ikk

al

Fig

.7–

Blo

wn

aw

ay

ro

of

top

Lo

c:

Ed

av

an

kk

ad

Fig

.8–

Rem

ain

s o

f a r

av

ag

ed

ho

use

Lo

c:

Tara

ikad

av

utu

ra

__

__

__

__

__

__

__

__

__

__

__

__

__

__

___

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

_

RE

PO

RT

ON

SU

MA

TR

A-A

ND

AM

AN

EA

RT

HQ

UA

KE

& T

SU

NA

MI,

26

DE

C ’

04

250

Fig

.9–

Tru

ck

tra

pp

ed

betw

een

th

e d

est

roy

ed

ho

use

sL

oc:

Azh

ikk

al

Fig

.10

– R

em

nan

ts o

f ra

vag

ed

ho

use

Lo

c:

Ed

av

an

kk

ad

u

Fig

.11

– H

eav

y m

inera

l d

epo

siti

on

Lo

c: V

alli

azh

ikal

Fig

.12

– H

eav

y m

inera

l d

epo

siti

on

Lo

c: A

zhik

al

__

__

__

__

__

__

__

__

__

__

__

__

__

__

___

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

__

_

RE

PO

RT

ON

SU

MA

TR

A-A

ND

AM

AN

EA

RT

HQ

UA

KE

& T

SU

NA

MI,

26

DE

C ’

04

251

Fig

.13

Heav

y m

inera

l d

ep

osi

tio

nL

oc:

Kay

amk

ula

mF

ig.1

4–

Heav

y m

inera

l d

epo

siti

on

Lo

c: V

alli

azik

al

Fig

.15

Heav

y m

inera

l d

ep

osi

tio

n

Lo

c:

Azik

al

Fig

.16

– B

reac

h i

n t

he

riv

er m

ou

th

Lo

c:

Man

ak

ko

dam

Sumatra-Andaman Earthquake and Tsunami 26 December 2004

Documents

Transcript of Sumatra-Andaman Earthquake and Tsunami 26 December 2004