REPORT

Field visit to Nepal

Lessons learnt from of 7.8 M on 25 April 2015

And 7.3 M 12 May 2015 Disastrous Earthquake

Submitted to

Seismology Division

Ministry of Earth Sciences

Government of India, New Delhi

Submitted by

Manipur University, Imphal 795003

July 2015

REPORT

Field visit to Nepal

Lessons learnt from Disastrous Earthquake of 7.8 M on 25 April 2015

Background

Large to Great earthquakes are disastrous for the life of people and their properties,

but beside that there are ample opportunities to seismologists, earth scientists and engineers

to understand the type of damages and sustainability of existing infrastructures and

preparedness for future. Every earthquake has its unique characteristics that may be

evidenced by damages to the existing infrastructures. Now a days, we have modern

earthquake instruments network global level to records the various earthquake parameters.

The April 25th and May 12th, 2015 earthquakes in Nepal present themselves as the two

major post-instrumentation era events in the Himalayan region and they provide an

opportunity to study the earthquakes in relation to the seismotectonics of the Himalayan

terrain. In order to carry out field studies and learning from the earthquake effects, the

Ministry of Earth Sciences provided us an opportunity to learn from the actual effects of a

large Nepal Himalayas earthquake.

7.8 M Earthquake

A large earthquake of magnitude Mw7.8 occurred in central Nepal on April 25th,

2015 (Fig 1). The April 25 earthquake has been followed by many aftershocks that

followed the main shock. Most of the aftershocks are close to edges of the ruptured zone

as it may be approximately delineated from seismological observations. Based on

geological cross-sections, crustal structure model, and the preliminary seismological data

available few days after the main shock, it appears that the earthquake has ruptured a piece

of the Main Himalayan Thrust (MHT). The rupture started at the epicentre, about 80 km

to the northwest of Kathmandu and propagated eastward for about 130 km, rupturing the

area directly located under the capital city of Nepal. The focal mechanism derived from

the analyses of seismological data shows a fault plane striking N143°E, with a very shallow

dip of 7° towards the North.

Tectonic Summary

The April 25, 2015 M 7.8 Nepal earthquake occurred as the result of thrust faulting

on or near the main frontal thrust between the subducting India plate and the overriding

Eurasia plate to the north. At the location of this earthquake, approximately 80 km to the

northwest of the Nepalese capital of Kathmandu, the India plate is converging with Eurasia

at a rate of 45 mm/yr towards the north-northeast, driving the uplift of the Himalayan

mountain range. The preliminary location, size and focal mechanism of the April 25

earthquake are consistent with its occurrence on the main sub-duction thrust interface

between the India and Eurasia plates ( Fig 2).

Although a major plate boundary with a history of large-to-great sized earthquakes,

large earthquakes on the Himalayan thrust are rare in the documented historical era. Just

four events of M6 or larger have occurred within 250 km of the April 25, 2015 earthquake

over the past century. One, a M 6.9 earthquake in August 1988, 240 km to the southeast of

the April 25 event, caused close to 1500 fatalities. The largest, an M 8.0 event known as

the 1934 Nepal-Bihar earthquake, occurred in a similar location to the 1988 event. It

severely damaged Kathmandu, and is thought to have caused around 10,600 fatalities.

May 12, 2015 M 7.3 Nepal earthquake

The May 12, 2015 M 7.3 Nepal earthquake (SE of Zham, China) occurred as the

result of thrust faulting on or near the decollément associated with the Main Himalayan

Thrust, which defines the interface between the underthrusting India plate and the

overriding Eurasia plate to the north. At the location of this earthquake, approximately 80

Fig 1 Damaged areas around epicentral of 7.8 M and 7.3 M

earthquakes in Nepal Laprak village (7.8 M Earthquake) and

Singati village (7.3M Earthquake)

km to the east-northeast of the Nepalese capital of Kathmandu, the India plate is

converging with Eurasia at a rate of 45 mm/yr towards the north-northeast a fraction of

which (~18 mm/yr) is driving the uplift of the Himalayan mountain range. The May 12,

2015 event was located 150 km to the west, and which ruptured much of the decollément

between these two earthquakes (Fig 1). Events of the size of the May 12, 2015 earthquake

are typically about 55x30 km in size (length x width). The April 25, 2015 M 7.8 main

shock had approximate dimensions of ~120x80 km, directed from its hypocentre

eastwards, and towards Kathmandu. The May 12, 2015 earthquake is located just

beyond the eastern end of that rupture (NOAA 2015). It is not considered as aftershocks

of 7.8 M.

Historical Earthquakes in Nepal

The Himalayan front has been the location of many large earthquakes in the past.

Although they are not all well documented, recent paleoseismological investigations

provided a better idea of the past seismicity of the area, and more precisely of the lateral

extent of the Mw8.2 event that devastated Kathmandu in 1934. In the same study, the

penultimate event has also been identified, in 1255AD, and the series of previous events,

yielding a return time close to 700 – 800 yrs (Sapkota et al., 2013, Bollinger et al., 2014).

The most recent work by the international team formed of French researchers (L. Bollinger

and Y. Klinger for CEA and IPGP respectively), Singaporian researchers (P. Tapponnier

and his team, EOS) and Nepalese researchers (S. Sapkota and his team, DMG) has shown,

based on the balance between the energy dissipated by past

earthquakes and the long term tectonic loading, that the area located between the

Fig.2 Epicenters of significant earthquakes in central Himalayan region based on data from

NCEI (2015), Rao et al. (2006) and Gahalaut (2009)

earthquake of 1934, to the east, and the event of 1505, to the west, that did rupture last in

1344 AD, was very close to rupture, as proved by the event of April 25th, 2015 (Fig 2).

This earthquake induced many mass movements in mountainous areas and resulted

in landslide lakes, which could be another cause of secondary disasters. The mass

movements and deformation of weathered soft soil cover are the main causes of the

collapse or heavy damage to buildings and heavy casualties in mountainous areas. In

addition, the earthquake also triggered a major avalanche on the south slopes of Mt.

Everest, located approximately 160 km east-northeast of the epicentre. The avalanche

destroyed the base camp of climbers.

Aftershocks on 7.8 M Earthquake

The aftershocks are distributed in an area roughly 150 km long and 50 km wide,

with the majority of the aftershocks located in the eastern part of the ruptured area. At first

order, the area defined by the bulk of aftershocks corresponds to the ruptured area on the

fault plane. The location of the ruptured area, together with the shallow dip of the focal

mechanism, suggest that it is most probably the sub-horizontal part of the MHT that has

ruptured, mostly the deeper part of it. The absence of aftershocks to the south of the valley

of Kathmandu suggests that the rupture has not propagated southward to reach the surface

along the Main Frontal Thrust. The aftershocks of 7.8 M earthquake continued up to 11

May 2015 and 7.3 M earthquake continued up to 29 June 2015. The rapture of the 7.8 M

earthquake was extended towards east which is evident from the 158 aftershocks (Fig 4

and Fig 5). 7.3 M earthquake on 12 May 2015 was the new rapture and after continued

further SW and NE direction (Fig 4). 54 aftershocks recorded up to 19 June 2015. It seems

that rapture of both the earthquake was on HFT and MBT in Kathmandu Himalaya but the

7.3 M earthquake was not the aftershock of 7.8 M earthquake.

Fig. 3 Epicenters of main shock and aftershocks of 2015 Nepal earthquake series (USGS

Earthquake Hazards Program)

Fig 4 158 aftershocks after the main shock and 54 events after the 7.3 shock

Fig 5 Number of aftershocks observed per day since the main shock (7.8M)

Brief Geology of Nepal:

Nepal is located in the centre of the Himalayan mountain belt, and is almost

rectangular in shape with about 870 km length in the NWW-SEE and 130-260 km in N-S

direction. The Main Frontal Thrust (MFT) system consists of two or three thrust sheets

composed entirely of Siwalik rocks, from bottom to top mudstone, multi-storied sandstone

and conglomerate (Chamlagain and Gautam, 2015). These sedimentary foreland basin

deposits form an archive of the final stage of the Himalayan upheaval and record the most

recent tectonic events in the entire history of Himalayan evolution since ~14 Ma. The

northernmost thrust sheet of the MFT is truncated by the Lesser Himalayan sequence and

overlain by unmetamorphosed to weakly metamorphosed rocks of the Lesser Himalaya,

where the Lesser Himalayan rock package is thrust over the Siwalik Group along Main

Boundary Thrust (MBT). In western Himalaya crystalline thrust sheets are frequently

observed within the Lesser Himalaya (LH). The Lesser Himalayan zone generally forms a

duplex above the mid crustal ramp (Schelling and Arita, 1991; Srivastava and Mitra, 1994;

Decelles et al., 2001). The Main Central Thrust (MCT) system overlies the Lesser

Himalayan MBT system and was formed in ca. 24 Ma. This MCT system consists of high-

7.8 (25th April 2015)

7.3 (12th May 2015)

7.8 (25th April

2015)

7.3 (12th May

2015)

grade rocks, e.g. kyanite-sillimanite gneiss, schist and quartzite and is mostly characterized

by ductile deformation.

Fig. 6 Geological map of Nepal (LH: lesser Himalaya; HH: higher Himalaya;

TTS: Tibetan-Tethys sequence; STDS: South Tibetan detachment system)

Nepal has been divided into three major tectonic zones (Figure 6), namely, Main

Central Thrust (MCT), Main Boundary Thrust (MBT) and Himalayan Frontal Fault (HFF)

(Piya, 2004). According to Nakata and Kumahara (2002), many active faults are distributed

along the major tectonic boundaries. These faults were produced by the collision of the

Indian Plate with the Eurasian Plate. A cross-section of the Nepal Himalayas running from

Fig 7 Major faults in the Himalayan region and rupture zones of earthquakes of 25

April 2015 and 12 May 2015 as shown by USGS (2015a) on a generalized cross-section

after Lavé and Avouac (2000) and Kumar et al. (2006) (MFT: main frontal thrust;

MBT: main boundary thrust; MCT: main central thrust)

SSW-NNE is shown in Figure 7. Saijo et al. (1995) and Yagi et al. (2000) reported the

existence of active faults in the SW part the Kathmandu basin and they are cutting the Late

Pleistocene sediments and have a vertical displacement rate of 1 mm/yr.

The Kathmandu valley, where the 2015 Nepal earthquake caused heavy damage,

comprises of thick semi-consolidated fluvio-lacustrine Quaternary sediments on the top of

basement rocks. Piya (2004) reports that the maximum thickness of the valley sediments

reaches up to 550 m at the central part of the valley and the basement rocks composed of

Precambrian to Devonian rocks, such as limestone, dolomite, slate, marble, schist, meta-

sandstone, phylitte, quartzite. The shear wave velocity of the soft sedimentary deposits

ranges between 167 m/s and 297 m/s and ground amplification may be ranging between 1.9

and 7.9 according to Chamlagain and Gautam (2015). There are number of damages

observed due to Recent Nepal earthquake in Kathmandu valley. Since, the rapture of the 7.8

M earthquake did not extend towards south of its epicentre where the Kathamndu valley is

located, therefore, observed damages in the Kathmandu city were not very significant.

Another reason is the type of construction of the buildings in the Kathmandu city.

Tectonic Setting

The east-west trending plate boundary between India and Eurasia comprises several

major and minor faults distributed on a roughly 200 km wide strip between the Himalayan

front and the main central thrust to the north. The seismic activity is caused by the

convergence of the Indian tectonic plate to the north towards the Eurasian plate with a

relative rate of approximately 40 mm per year. The shortening is accommodated by several

parallel faults; hence we speak of a diffuse plate boundary. The plate boundary at the foot

of the Himalaya is one of the most active continental boundaries worldwide and host of the

largest earthquakes in the region.

Figure 8: Historic earthquake locations along the Himalayas showing the seismic gaps as the well as

the patterns of temporal seismicity.

Along this Himalayan front, several large earthquakes occurred during the last

century. In the far East, along the border region of India, China and Bangladesh, the Assam

earthquake killed more than 1500 people and had a magnitude of 8.6. In the direct vicinity

of the 2015 earthquake, the Magnitude 8.1(Fig 8).

Bihar earthquake had an even stronger impact on Kathmandu and Nepal in 1934

than the most recent one. In the far West, in the years 1905 and 1803, the magnitude 7.8 and

8.1 Kangra and Uttarpradesh earthquakes occurred. Regarding the last 500 years of

seismicity, the location where the 1505 Lo Mustang earthquake happened is today

considered to be a seismic gap, a region where a future large earthquake is expected to

happen due to the on-going stress accumulation which hasn’t been released during the last

centuries. The seismic pattern of large earthquakes in the Himalayans indicates local

clustering. The M7.3 follow- up earthquake of May 12th shows a similar spatial pattern as

the sequences of 1905 – 1906 during the Kangra event; in 1991 & 1999 during the Uttarkashi

and Chamoli earthquakes; 1916 – 1926, 1926 – 1945 in Uttaranchal; and 1947 – 1950 for

the Assam earthquake. About 50% of all large earthquakes during the last century can be

accounted for using this pattern that strong earthquakes occur in the spatial and temporal

vicinity of each other, normally within years. Thus the recent May the vent was quite likely

additionally induced by slow static triggering of the M7.8 earthquake (Fig 8). It is also

inferred that the strain was build up and part of its energy was released in these recent

earthquakes (Fig 9).

Ground Motion

In many cases in rural towns, there was enough time for people to leave their houses

given the frequency content and shaking mechanism. A few reports from towns indicate that

only the elderly or pregnant women unfortunately were unable to run out in time. There is

a widely held notion among the general public that the intensity of ground shaking and hence

the destructive power of an earthquake generally decreases as the epicentral distance

increases. Thus, when a strong earthquake occurs, the location of the epicentre gets a lot of

Figure 9: Red arrow: tectonic

convergence. Black lines:

local stress orientation

(WSM, World Stress Map).

Additional literature:

Avouac, 2003; Bollinger et

al., 2006, 2014

attention in the press, with the earthquake location often depicted on a map as concentric

circles around the epicentre. This way of thinking may be also related to the fact that many

traditional attenuation laws, or ground‐motion prediction equations (GMPE), are empirical

relationships to represent a continuous reduction of the intensity of ground motion with an

increasing epicentral distance, implicitly assuming seismic waves to originate from a point

source. Such a model would be applicable only when the rupture zone is relatively small,

i.e. when the magnitude of an earthquake is not very high. The ground acceleration was

computed using the USGS data for the Nepal earthqualke. The acceleration ranges from

0.02 to0.74g, which is displayed in the Intensity map (Fig 10).

When a strong earthquake is caused by a dip-slip movement on a large and almost

horizontal fault, as in the case of the main shock of 25 April 2015, the epicentral distance is

not a very relevant parameter for the determination of the ground motion, because a large

portion of the affected area lies even directly above the rupture zone. Seismic waves arrive

at a given point from the whole of the rupture zone and not just from the epicentre. This

explains why the damage caused by the main shock of 25 April 2015 did not decrease with

an increasing epicentral distance, as evident from the intensity map shown in 9. In fact, the

largest damage and loss of lives occurred in the Sindhupalchok district, about 100 km to the

east of the epicentre in Gorkha. It is quite evident that 7.3 M earthquake has effcetd the

damages in Sindhupalchok district although it is located quite far from 7.8 M earthquake.

It is thus clear that the attenuation laws employing the epicentral distance as a

parameter should not be used in an earthquake hazard analysis in the Himalayan region, as

the rupture zone of a strong seismic event in this region tends to be large and almost

horizontal. It is necessary to resort to a more modern attenuation law that uses the minimum

distance from the causative fault as a parameter. There could still be a research need to

develop or refine a representative attenuation model suitable for an earthquake hazard

analysis in this region.

Intensity of 7.8 M Earthquake

It is based upon the observation of earthquake damage at a particular location. The

intensity of a quake differs greatly from place to place. It depends upon such factors as the

distance from the epicenter, the design and quality of construction of local buildings, and

the type of surface beneath the buildings. The intensity of an earthquake at a particular

locality indicates the violence of earth motion produced there by the earthquake. It is

determined from reported effects of the tremor on human beings, furniture, buildings,

geological structure, etc. is variable over the area affected by the earthquake, with high

intensities near the epicentre and lower values further away. This phenomenon is the result

of seismic-wave attenuation, which is the reduction in wave amplitude and wave energy as

they travel away from their source.

On 25th April, 2015, at 11:56 local time, a massive 7.6 magnitude earthquake struck

Nepal, with the epicentre in Gorkha District (north-west) of Kathmandu and south of the

China border. Dozens of aftershocks followed, including a 6.7 magnitude earthquake on

26th April 2015 at 12:54 local time. The earthquake has been found with a maximum

Mercalli Intensity of IX (Violent) (Fig 10).

Epicentre of main shock is approximately 34 km east-southeast of Lamjung, Nepal,

and its hypocentre at the depth of approximately 15 km. These areas are densely populated,

including remote villages perched on hilly areas.

The hypocenter of the Mw 7.3 earthquake on May 12th, 2015 at 7:05 UTC (12:50

local time) was located around 80 kilometers northeast of Kathmandu, Nepal at 10 kilometer

depth (GEOFON). The rupture plane strikes parallel to the Himalayan Belt WNW to ESE,

dips with 10° to the North and extends about 60 km along strike and 20 km perpendicular

to it. The maximum PGA was estimated at 0.4g( Fig 11).

Fig. 10 Intensity of ground shaking produced by 7.8 Mw main shock of 25 April 2015

(Source: USGS, 2015a)

Fig 11 Intensity map of Nepal earthquakes ( 7.8M and 7.3M)

Observations about earthquake damage to structures

Building Typology

Most of these buildings were also built of unreinforced masonry (although in a

slightly different style) and caused similar fatality rates. In 1.7 million destroyed houses (ca.

5 million rooms), 65,000 died. As a ratio this is 1 death per ca. 250 destroyed houses. In the

current event, the ratio is in the order of 1 death per 350-400 destroyed houses (however, it

is important to take the time of day difference into account). Thus both earthquakes have

similar ratios.

In Kathmandu, from photos seen from the field, it appears as though low quality

building and material (i.e. concrete strength), additional rebar and other safe building

practices saved many catastrophic collapses, thus reducing the death toll.

Earthquake damage to temples and heritage structures

The earthquake of 25 April 2015 had a devastating effect on the ancient temples and

heritage structures, many of which are parts of the UNESCO World Cultural Heritage sites

in the Kathmandu Valley. A disproportionately high percentage of such structures collapsed

during to the 2015 earthquake shaking, compared to the brick masonry and reinforced

concrete frame buildings in their immediate neighbourhood, most of which did not collapse

and mostly suffered only minor visible damage.

Various possible explanations for the higher level of earthquake damage to the

temples and the heritage structures are the age of the heritage structures, which are generally

older than the surrounding buildings. There was a lack of maintenance of these historical

buildings. There is unusual structural systems (higher flexibility, larger masses). There is a

pre-existing damage and cracks due to past strong earthquakes of 1833 and 1934 Hasty and

poor-quality reconstruction after collapse caused by the 1934 earthquake. The natural

frequencies of these monumental structures usually differ significantly from those of normal

brick masonry buildings. This could also have made them more vulnerable to the ground

motion of the main shock dominated by long period motions.

It is interesting to note that some old temples that have survived the 2015 earthquake

are also known to be those that suffered the least damage in the 1934 earthquake disaster,

for example the Akash Bhairav Temple at Indrachowk, Kathmandu, the Pashupatinath

Temple in Kathmandu and the Nyatapole Temple at the Taumadhi Square, Bhaktapur

(Shakya, 2000). In the Nyatapole Temple, the highest pagoda temple in Nepal, only the

uppermost storey shows externally visible damage, which seems to a re-run of the 1934

earthquake damage to this temple, as recalled by some elderly people in Bhaktapur. An

investigation of the possible reasons (e.g. more robust structural system, better maintenance,

etc.) for the apparent earthquake resilience of these temples could provide valuable hints for

the earthquake-resistant redesign of the collapsed temples.

Earthquake damage to stone rubble masonry houses

In the mountainous regions of Nepal, a majority of people live in houses made of

stone rubble masonry held together with mud mortar. Such structures are inherently

vulnerable to sudden brittle failure when subjected to strong earthquake shaking. In some

mountainous regions of Nepal, almost 100% of such stone masonry buildings collapsed

during the 2015 earthquake sequence. This is the main factor behind the high death toll in

the mountainous Sindhupalchok district, where 3423 deaths were confirmed as of 17 May

2015, accounting for about 40% of the total number of 8567 people killed in the 2015 Nepal

earthquake disaster. Also in other mountainous districts, such as Nuwakot, Dhading,

Rasuwa, Gorkha, Kavrepalanchok, etc., many stone rubble masonry buildings failed,

causing numerous injuries and deaths. To minimize losses of lives and property in the rural

area during inevitable future earthquakes, it is urgently necessary to spread the knowledge

about cost-effective means to improve the earthquake resistance of stone masonry buildings.

It would be a mistake if the collapsed buildings are hastily rebuilt without incorporating

earthquake-resistant features.

Numerous landslides triggered by the earthquake have also proven to be deadly in

the mountainous regions with unstable slopes. Hence, it is necessary to make detailed

geological hazard surveys to identify zones particularly vulnerable to rockfalls and

landslides. Such locations have to be officially declared as danger zones where building

activities are no longer permitted.

Worst affected Sindhupalchok District after the 7.8 and 7.3 M earthquake

Sindhupalchok is one of the worst-affected districts as a result of the earthquake that

took place on the 25th April. Buildings in these areas are less damaged than in other parts

of the district (Fig 12). In the belt to the north of this well accessible area including Chautara,

the district capital, damages are greater. In these areas there is higher population density and

major landslides have blocked roads. In a word, the area was devastated. 80-90% of

buildings have been rendered uninhabitable; 20-30% were razed to the ground. Pillared

concrete buildings (accounting for less than 5% of the total) appeared to be intact. Almost

no stone/brick/mortar buildings are now inhabitable. Many village roads, asphalt and

cinder, have long cracks 3-6” wide. Only a few roads have craters large enough to prevent

driving, but many are blocked by rock landslides. Sections of roadway will be pried away

by the coming monsoon rains. Along our route, all bridges were intact with no overt signs

of damage.

Earthquake damage to Reinforced Concrete Buildings

Concrete buildings are relatively new in Nepal and have been built mainly since the

1960s. Such a building consists typically of a reinforced concrete (RC) skeletal frame with

brick infill walls. The performance of the RC frame buildings in the 2015 earthquake was

not necessarily superior to that of well-constructed traditional brick masonry structures.

Many people are surprised that quite a few of these modern-looking structures also collapsed

during the earthquake shaking. Quite a few recently built apartment blocks and shopping

malls also suffered heavy damage, leading in some cases to a total loss of substantial

Fig.12 Aerial footage shot on Tuesday of Chautara in Nepal’s

Sindhupalchowk District shows the extent of damage from the two

major earthquakes in the region.

investments of the owners of these expensive structures. The reinforced concrete (RC)

structures were built in Nepal in many cases without performing proper structural analysis

and design by a qualified structural engineer. Even when a structural analysis was carried

out, more often than not the earthquake load considered in the design was too low, usually

not more than about 0.1 g. Poor concrete quality and deficient reinforcement detailing are

further factors that make the reinforced concrete structures in Nepal vulnerable to

earthquake damage.

While an RC skeletal frame efficiently supports the static vertical gravity forces, it

is not suitable to resist the substantial horizontal shear forces occurring during a strong

earthquake. Many building owners are not aware of this fact, due to which a vast majority

of the reinforced concrete buildings in Nepal have been built without proper shear walls,

which would ideally be in the form of adequately reinforced concrete walls. As a result, the

horizontal shear forces due to an earthquake would be carried primarily by the brick infill

walls.

Damage to Bridges

There is no report yet about the damage to bridges. Figure 13 and 14 shows damaged

bridges at along Arniko Highway near Lokanthali Bus stand at Kathmandu. The bridge in

Kathmandu City is a two span-simply supported reinforced concrete structure. The bridge

appears to be functional despite a nearby reinforced concrete building collapsed in a pan-

cake mode. We suspect that the E-W trending lineament in Kathmandu valley is responsible

for the damage of the bridge. Most of the bridge are not damaged after the Gorkha

earthquake. The Bridge in Gorkha district is a single-span truss bridge. This bridge is also

not damaged despite of its location is in the epicentral area. We also noticed that in Balua

village the newly constructed bridge is also intact, although it is very near to the epicentral

area.

Fig 13 Number of roads

bridges are damaged in

Nepal

3ft

Fig. 14 Severe cracks developed over a road bridge in Kathmandu after

the 7.8 M earthquake. A vertical slip of 1 meter along the E-W trending

fault in Kathmandu valley, which seems to be activated after the 7.8 M

earthquake and damaged the bridge

Summary

The seismotectonic setting of Nepal Himalays is known better after the two large Nepal

earthquakes. The following are emerged:

1. The large earthquakes caused by the dip slip movement along a thrust fault HFT and

MBT between sybducting Indian plate and over ridden Eurasian plate forms a

horizontal plane (dip 70 and strike N 1430 E) with a very shallow depth.

2. The epicentre of these recent earthquakes are not located within the rupture zone of

great earthquake of Nepal Bihar of 1934.

3. The damages of these earthquake area does not decrease with the epicentral distance

from the earthquake. It is due to the triggering of another 7.3 earthquake to the east

of 7.8 M earthquake. Damages patterns of many villages of Sindhupalchok have

been effected worst due the second earthquake. Another reason is the horizontal

rupture in a very shallow depth also effected the damages for large distances from

the epicentre of 7.8 M earthquake.

4. The ground motion records available from a USGS seismograph at Kathmandu. It

reveals that ground motion

5. It is difficult to predict the future large/great earthquake, however, preparedness is

very essential besides the rehabilitation work. Even an existing building that has

suffered only minor but still seems to be structurally deficient such as many tall

storied building and commercial complexes in Laltipur and Bhaktapur districts. Such

buildings need to be identified and retrofitted.

6. There are chances for large number of landslides which may again trigger during the

monsoon season along the highways above the tributaries of Kosi river in Nepal as

these are triggered due to the two earthquakes may become vulnerable in the next

few months. There is need for a contingency plan to be ready for its immediate

implementation. If the damming of these tributaries takes place, the Nepal as well as

North Bihar mat become vulnerable.

7. Since, there was no earthquake triggered on the west of 7.8 m Earthquake after 1505

AD, this region is now considered as “Seismic gap” with an enhanced earthquake

risk. Unfortunately, if the same patterns of earthquake epicentre of 7.8 M takes place

(west of Great earthquake of 1934), it may be in either western Nepal or Uttarakhand

state of India in the future.

If anything is not referred, it is not done intentionally and authors apologise for that.

Team Members

1. Prof Arun Kumar, Manipur University

2. Shri L. Someswar Roy, MU

3. Shri M. Devachandra Singh, MU

4. Meenal Adhikari TU Kathmandu, Nepal

ACKNOWLEDGEMENT

We thankfully acknowledge Seismology Division, Ministry of Earth Sciences

Government of India for providing the financial assistance to carry out the post-earthquake

survey at Nepal. Our thanks to Shri Deepak Adhikari, “Sangh Parivar Pracharak” at Nepal

and one of his associate Shri Meenal from Tribhuvan University to provide the suggestions

and guidance for visiting the earthquake damaged sites at Nepal. We also sincerely thanks

to Shri Ranjit Rae, Ambassador of India at Nepal and Dr. Brij Mohan Singh Rathore from

ICIMOD, Nepal for having discussions in their office with the team members. We also

acknowledge Dr. S. Manichandra to prepare the earthquake intensity map of large Nepal

Earthquake and useful discussions for the preparation of the report.

( Arun Kumar)

Team Leader

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Meeting with Officials in Nepal

Shri Ranjit Rae, Indian Ambassador, Nepal, Prof Arun Kumar, Devachandra Singh,

Someshwor Roy and Deepak Adhikari in Embassy of Indian, Kathmandu

Dr. Bri Mohan Singh, Rathore, ICIMOD Nepal, Prof Arun Kumar, Devachandra Singh,

Someshwor Roy and Deepak Adhikari in Kathmandu

FIELD PHOTOGRAPHS

GPS track from Kathmandu to 7.8 M and 7.3 M epicenter zones and other effected areas in Nepal.

Satellite image showing Bhaktapur (dotted red circled). 7.8M earthquake effected

photographs shown below.

Bhaktapur (Royal Durbar Square entrance)

ROYAL DARBAR SQUARE (Bhaktapur)

Dome of the Royal Durbar square temple was damaged and corridor was collapsed due to the 7.8 M Earthquake

Chautra, 328 km from Kathmandu (Highly damaged area)

Most of the houses collapsed in Chautara after 7.8 M and 7.3 M earthquakes

Lomasangu

Houses damaged due to the 7.3 M

Earthquake at Lomasangu village

after the 7.3 M earthquake

Barahbise

Barabise villages – Damaged houses in the village and large fissures developed on the hill

slope along the Kosi River due to 7.3M earthquake. The river is vulnerable for the ponding

during monsoon season.

Damaged in Lalitpur District

Beams and walls of the masonry collapsed due to the 7.8 M Earthquake at Lalitpur, near to

Kathmandu

Singati

Traverse to 7.3 M earthquake epicentre at Nepal China border at Singati village

Damaged houses in Singati village

with cracks on the bed rocks, rock

slides and fissures on the ground

near the epicentre of 7.3 M

Earthquake

Balua

Traverse from Kathmandu to Epicenter (7.8M) via Gorkha, Balua and Barpak.

Most of the houses are fully damaged at Balua village due to &.8M earthquake.

Barpak and Laprak villages (Epicentral areas 7.8 M Earthquake)

Damaged villages, School and houses (Barpak) and large fissures at the epicentral areas of 7.8

M Gorkha earthquake.

Basantapur (Kathmandu Durbar Square)

Satellite image showing Basantapur (dotted red circled). 7.8 M earthquake effected photographs shown

below.

Damaged building of Basantapur Durbar Square (with temporary supports) and cracks and

partially collapsed palace, Kathmandu due to 7.8 M earthqauke.

Before earthquake After earthquake

Photo 3 Dharahara tower in Kathmandu before and after the 25 April 2015 earthquake

Before earthquake After earthquake

Bhaktapur Durbar Square before and after the 25 April 2015 earthquake (the elegant Vatsala temple

collapsed during the earthquake)