DEVELOPING PROBABILISTIC SEISMIC HAZARD MAPS OF SAGAING, SAGAING REGION, MYANMAR · In developing...
Transcript of DEVELOPING PROBABILISTIC SEISMIC HAZARD MAPS OF SAGAING, SAGAING REGION, MYANMAR · In developing...
DEVELOPING PROBABILISTIC SEISMIC HAZARD MAPS OF SAGAING, SAGAING
REGION, MYANMAR
December, 2015
CONTENTS EXECUTIVE SUMMARY ....................................................................................................... 3
1. INTRODUCTION ............................................................................................................ 5
1.1 Objectives of the project ............................................................................................. 6
1.2 Structure of report ........................................................................................................... 7
2 SEISMOTECTONICS AND GEOLOGY .............................................................................. 9
2.1 Seismotectonics of the region .......................................................................................... 9
3 METHODOLOGY AND USED DATA ............................................................................... 14
3.1 Methodology of Seismic Hazard Assessment ................................................................ 14
3.2 Applied Data ............................................................................................................. 15
3,2,1 Seismic Sources Identification and Characterization ............................................... 15
3.2.2 Site Investigation .................................................................................................... 16
3.3 Regional Geological Setting ...................................................................................... 18
3.4 Ground Motion Prediction Equations (GMPEs) .............................................................. 20
4 RESULTS ........................................................................................................................ 21
4.1 Site Condition ........................................................................................................... 21
4.2 Seismic Hazard ........................................................................................................ 25
4.2.1 Seismic hazards for 475 years recurrence interval .................................................. 26
4.2.2 Seismic hazards for 2475 years recurrence interval ................................................ 31
Bibliography ........................................................................................................................ 38
APPENDICES ..................................................................................................................... 41
Appendix A .......................................................................................................................... 42
Appendix B .......................................................................................................................... 43
Appendix (C) ....................................................................................................................... 44
Appendix (E) ....................................................................................................................... 50
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EXECUTIVE SUMMARY
Sagaing City is one of the cities that is passed through by the most active fault in Myanmar,
the right-lateral, strike-slip, Sagaing Fault. The city has experienced many large earthquakes
since 14th century. The earliest record of the historical earthquakes is the 1429 ear thquake
and t his earthquake caused several walls were dam aged i n Sagaing – Innwa region. The
historical ear thquakes h appened i n and round this r egion ar e t he ev ents o f 1429 , 1467 ,
1501, 1602, 1696, 1771, 1776 1830 and 1839.
Among those earthquakes, 1839 Innwa (Ava) earthquake is likely to be the largest event and
the magnitude is currently assumed as > 7.5. This earthquake struck on March 23 at 4:00
am. Due to this earthquake the city wall of Amarapura, and several buildings were collapsed.
The ground surface fractures were formed in the cities of Amarapura, Innwa and Sagaing,
together with the ground water poured out. According to the records, nearly all of the
houses, pagodas, and monasteries were completely damaged in Innwa. At least 300 to 400
casualties w ere r esulted in I nnwadue t o t his e vent. The g round surface f ractures were
formed al ong t he A yeyarwady R iver, bet ween I nnwa and A marapura and s ome ground
subsidence w ere al so occurred i n t he w idth o f 5 t o 20 feet. S everal af tershocks al so
happened i n t he nex t s ix m onths. T he most recent ev ent happened i n t his ar ea is t he
magnitude 7 .0, 1956 S againg E arthquake and i t s truck on J uly 16 at 9: 40 pm . This
earthquake c aused s everal pa godas, and bui ldings w ere da maged an d about 40 dea ths
happened in Sagaing.
According to the above mentioned earthquakes histories, Sagaing can be regarded
as one of the cities that have high probability of the large earthquake (≥ 7.0 magnitude)
potential in the f ugure. T herefore, Myanmar G eosciences S ociety ( MGS), M yanmar
Engineering Society (MES) and Myanmar Earthquake Committee (MEC) conducted the
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seismic risk as sessment for S againg C ity ( Sagaing R egion)in 2013 , w ith t he ai d of t he
United Nations Human Settlements Programme (UN-HABITAT). This project includes two
parts: the seismic hazard assessment (SHA) and seismic risk assessment (SRA), MGS and
MEC conducted SHA, while MES performed SRA. This report is for SHA for Sagaing City,
Sagaing Region.
In dev eloping the s eismic haz ard maps for S againg, pr obabilistic s eismic ha zard
assessment (PSHA) method is used. We developed the seismic hazard maps – peak ground
acceleraiton (PGA) map, spectral acceleration (SA) maps for the natural periods of 0.2 s, 0.3
s and 1.0 s and peak ground velocity (PGV) maps - for 10% probability of exceedance in 50
years (475 years return period) and 2 % probability in 50 years (2475 years return period).
These hazard maps are hopefully used for the purposes to mitigate the effects of the
earthquakes, es pecially in des igninng for t he seismic s afety for the current and future
constuction o f varioius sorts o f bui ldings, planning o f the retrifiting o f t he ex isting bui lding,
land-use planning of the city, and all of the preparedness schemes for the city.
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1. INTRODUCTION
Sagaing is the previous capital of Sagaing region, Myanmar, located in the southern end of
the region. The population of the city is about 100,000 according to 2014 census. According
the historical earthquake records, the city has experiences several large magnitude
earthquake as l isted i n Table ( 1). The events happened i n Sagaing – Innwa ar ea ar e t he
earthquakes happened i n 1429, 1467, 1485, 15 01, 1620, 1646, 1648, 1660, 1690, 1696,
1714, 1771, 1776, 1830 and 1839. The most recent earthquake and the most affected one is
the Sagaing earthquake that struck on July 16, 1956. This magnitude 7.0 earthquake caused
several pagodas, and buildings were damaged and about 40 deaths happened in Sagaing.
However, the most deadliest event happened in this area is 1839 Innwa (Ava) earthquake
that struck on March 23 at 4:00 am. This earthquake is likely to be the largest event and the
estimated magnitude is > 7.5 (~8.0). This earthquake caused several buildings including the
city wall of Amarapura were collapsed. According to the records, near ly al l of t he houses,
pagodas, and monasteries were completely damaged in Innwa. At least 300 to 400
casualties were resulted in Innwa due to this event. The fractures were formed in the cities
of Amarapura, Innwa and Sagaing, especially along the Ayeyarwady River between Innwa
and Amarapura, together with the ground water poured out. Some ground subsidence were
also occurred in the width of 5 to 20 feet. Several aftershocks also happened in the next six
months.The other event not happened near Sagaing area, but happened within the 250 km
radius, is May 23, 1912 Maymyo earthquake.
The main seismogenic active fault that can contribute the major seismic hazard is the right-
lateral, strike-slip Sagaing Fault that is passing through the city. Kyaukkyan Fault, Nampon
Fault, Shweli Fault, Moemeik Fault, West BagoYoma Fault and Gwegyo Fault are the other
seismogenic s ources for S againg.Therefore, t he c ity c an ex pect the l arge ear thquake t o
happen in the future and its effects can be large for the city.
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In recent year 2012, the magnitude 6.8 Thabeikkyin Earthquake happened on November 11
in the north of Sagain at about 125 km. Various kinds of buildings such as pagodas, houses
and schools, about 500 were destroyed by this event, resulting 26 de aths and 231 injuries.
This earthquake also affected Sagaing City and one building damaged and walls of several
pagodas were fractured.
On the other hand, the urban development of Sagaing is also increasing along the
Sagaing Faul t. M oreover, new pr ojects of i nfrastructures c onstruction and bui lding
construction are c ontinuing. Therefore M EC, MGS and M ES i mplemented t o dev elop t he
seismic hazard maps and risk maps of Sagaing, with the aids of the United Nations
Development Programs (UNDP).
1.1 Objectives of the project
The main goal of the project is to construct the seismic hazard maps and seismic risk maps
of Sagaing, Sagaing Region. The objectives of the project of seismic hazard assessment of
Sagaing include the following:
1. To develop the probabilistic seismic maps of the city, the seismic hazard maps will
show t he hazard par ameters o f peak ground acceleration (PGA); s pectral
acceleration (SA) at the periods of 0.2 s, 0.3 s and 1.0 s; and pea k ground velocity
(PGV). These seismic hazard maps will correspond to 10% probability of exceedance
in 50 y ears ( 475 y ears return per iod) and 2% probability i n 50 years ( 2475 y ears
return period).
2. To contribute these seismic hazard assessment results to the corresponding
organizations that will include the civil societies, the ministries and depar tments that
will have to use for seismic safety des igns development, retrofitting for the seismic
unsafe buildings and land-use planning, etc.
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3. To pr ovide t he r esults t o t he r espective depar tments and or ganizations ( probably
publics) for earthquake disaster education and preparedness purposes.
By s eeing t he abov e m entioned obj ects, the mitigation o f ea rthquake effects o n t he
peoples of Sagaing, and build-in environment is the major purpose of this project.
1.2 Structure of report
The r eport i s composed of five chapters and t he chapter 1 i ntroduces the s ituation o f t he
seismicity and t ectonics s ituation with respect to t he current s ituation o f the c ity, Sagaing,
together with objectives of the project. The chapter 2 discusses the seismicity of the city and
its region, correlating with the regional tectonics, and the geology of the area, since the
surface geology is one of the important parameters that strongly influence on the earthquake
damage p roperties. The m ethodology and research p rocedure appl ied i n t his p roject work
comprise o f t he chapter 3. The dat a appl ied i n the seismic hazard assessment works a re
discussed i n t his c hapter t o under stand the a dvantages o f the us age and i ts l imitation.
Chapter 5 presents the results of seismic hazard assessment, and the seismic hazard maps
of Sagaing for 10% and 2% probabilities o f exceedance in 50 y ears (475 years and 247 5
years return periods). The PGA maps, SA (0.2 s, 0.3 s and 1.0 s) maps, and PGV maps are
the main outputs of the project and the average shear wave velocity to the upper 30 m (Vs30)
contour map is also included. As a final chapter of the report, the discussion on the results of
the project and the recommendation for the earthquake disaster mitigation for Sagaing are
presented in chapter 5.
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Figure (1) Map of the location of the project Sagaing City.
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2 SEISMOTECTONICS AND GEOLOGY
2.1 Seismotectonics of the region
When the seismicity of Myanmar is observed as the whole country, most of the crustal faults
such as the major right-lateral s trike-slip faults o f Sagaing Faul t, Kyaukkyan Faul t (KK F .)
and Nampon Fault (NP F.); the left-lateral strike-slip faults in Shan-Tanintharyi Block such as
Moemeik Faul t, S hweli Faul t; and t hrust s ystems o f West B agoYoma Faul t, and
Gwegyomostly generate the shallow focus earthquakes (≥ 40 km in focal depth).
Among them, the Sagaing Fault is the major active fault, running through or near the
major cities such as Yangon, Bago, Taungoo, Naypyitaw, Pyinmana, Meikhtila, Sagaing,
Mandalay, Wuntho and Myitkyina. The length of the fault is above 1200 km as the total, and
the s lip r ate i s from 18 – 22 mm/yr (Wang Y u et al ., 2013) . The m ajor ev ents ( M > 7. 3)
generated by t his f ault ar e t he w ell-known 1 839 Ava ( Innwa) earthquake, 1929 S wa
earthquake, 1930 B ago ear thquake, 1930 P hyu ear thquake, 1931 H tawgaw ear thquake,
1946 two continuous Tagaung earthquakes, and 1956 Sagaing earthquake. The slip rate of
West BagoYoma Fault is 5 m m/yr, as the largest rate, while that of other faults is around 1
mm/yr (SoeThuraTun et al., 2011).
Rather than the seismicity related to the crustal faults, the other seismogenic sources are the
subduction z one of I ndian P late beneat h B urma P late i n t he west of Myanmar and t he
collision zone of Indian Plate with Eurasia Plate in the northwest. While the rate of collision is
about 50 m m/yr, t he s ubducted r ate i s 36 m m/yr(Socquet et al ., 2006 ). Other t ectonically
seismogenic source Adaman spreading region. The spreading rate is about 37 mm/yr and
the s eismicity happened i n t his r egion mostly c omprises the s hallow f ocus ev ents. 1762
Arakan ear thquake i s pr obably t he subduction r elated event and t he m agnitude i s around
7.5M. From t he c ollision z one of I ndian and E urasia P lates, t he l argest ev ent i s t he
magnitude 8.6, August 8, 1950 earthquake.
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The seismicity of Myanmar is depicted in Figure (2) and Figure (3) i llustrates the seismicity
of Sagaing area. Figure ( 4) p resents the magnitude > 7.0 earthquakes happened in and
around the city. Table (1) lists the previous historical and instrumental recorded significant
events, describing the respected properties of damages and casualties.
Figure (2) Seismicity map of Myanmar (ISC earthquake catalog, 1906 – 2011)
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Figure (3) Seismicity map of Sagaing area.
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Figure (4) Map of the previous magnitude ≥ 7.0 events happened around Sagaing
area
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Table (1) List of the previous earthquakes happened in and around Sagaing Date Location Magnitude or brief description
1429 Innwa Fire-stoping enclosure walls fell
1467 Innwa Pagodas, solid and hollow, and brick monasteries destroyed
24, July, 1485 Sagaing 3 well-known pagodas fell
1501 Innwa Pagodas, etc. fell
6, June, 1620 Innwa Ground surface broken, river fishes were k illed af ter quake
10, Sept, 1646 Innwa
11, June, 1648 Innwa
1, Sept, 1660 Innwa
3, Apr, 1690 Innwa
15, Sept, 1696 Innwa
8, Aug, 1714 Innwa 4 well-known pagodas destroyed
15, Jul, 1771 Innwa
9, June, 1776 Innwa A well-known pagoda fell
26, April, 1830 Innwa
21, Mar, 1839 Innwa Old palace and many buildings demolished; pagodas and city walls fell; ground surface broken; the river’s flow w as r eversed f or sometime; M ingun P agoda shattered
23, May, 1912 Taunggyi M = 8. 0, al most al l of c ities i n Myanmar w ere shocked
16, July, 1956 Sagaing Several pag odas and b uildings severely dam aged, about 40 deaths
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3 METHODOLOGY AND USED DATA
3.1 Methodology of Seismic Hazard Assessment
In conducting seismic hazard assessment for Sagaing, pr obabilistic methodology is used
and it includes four steps (Cornell, 1968, McGuire, 1976, Reiter, 1990 and Kramer, 1996).
The following the basic steps of probabilistic seismic hazard assessment (PSHA):
1. Identification of seismic sources: the seismic sources such as the fault sources, areal
or volumetric sources from t hose the ear thquake pot entials o f l arge magnitude can be
expected to happen in the future and can generate the significant ground motion at the
city are identified in this stage.
2. Characterization of seismic sources: the seismic source parameters for each identified
seismic s ources (fault, ar eal or v olumetric s eismic source) ar e calculated and the
parameters es timated ar e t he s patial and temporal oc currence pa rameters s uch as a-
and b- values, the annual recurrence of the earthquake of the certain magnitude, and the
maximum earthquake potential. For fault seismic sources, the fault parameters such as
the its geometry and geological parameters such as the dip, fault length, slip rate, etc.
are also needed to estimate.
3. Choosing the ground motion prediction equation (GMPE): the predictive ground
motion equations are commonly applied in PSHA. By them, the ground motion at a s ite,
that c an be gener ated by an y pos sible s ized ear thquake ar e es timated. The m ost
suitable GMPEs are need to choose for the city based on the tectonic environments and
fault types, etc.
4. Integration of va riables t o es timate the se ismic ha zard: the s eismic haz ards, i .e.
PGA, SA (at the periods of 0.2 s, 0.3 s and 1.0 s) and PGV are estimated by considering
the unc ertainties o f t he location, t he m agnitude o f t he ear thquake, and ground m otion
parameters, with the combination of the effects of all the earthquakes with the different
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magnitude from t he l ower bound m agnitude, di fferent di stance and di verse occurrence
probability.
In P SHA, t he t hree input par ameters: 1 ) s eismic s ources da ta t hat include t he f uture
earthquakes related parameters such as the maximum earthquake magnitude, the (temporal
and spatial) occurrences of the earthquakes with certain magnitude, etc., 2) the parameters
and coefficients o f the chosen G MPE, and 3) t he par ameters o f s ite condition, m ostly t he
average shear wave velocity to the upper 30 m (Vs30).
3.2 Applied Data
3,2,1Seismic Sources Identification and Characterization
In 2011, Myanmar Earthquake Committee (MEC) carried out the probabilistic seismic hazard
assessment for Myanmar and developed the PSHA maps of the country. In that assessment,
the s eismic s ources i dentification and characterization of the ac tive faults w as done by
SoeThuraTun et al. (2011) and they constructed the active fault database for Myanmar. In
the same work, Myo Thant et al. (2012) conducted the areal seismic sources identification
and characterization f or each t ectonic domain such as t he subduction zone o f I ndia P late
beneath B urma P late, i n t he w est of t he c ountry; t he c ollision z one o f India P late w ith
Eurasia Plate in the north and nor thwest, and the Andaman spreading center in the south.
While S oeThuraTun et al. ( 2011) c onstructed t he ac tive f aults dat abase, t he geological
information and paleoseismologic data such as the geometry of the fault, dip and strike of
the fault, fault displacement, fault s lip (slip per event or annual s lip rate), etc. are appl ied,
Myo T hant e t al . (2012) appl ied t he s eismological and geological i nformation s uch as
instrumental ( ISC ear thquake c atalog, 1900 – 2011; A NSS c atalog 19 36 – 2011) and
historical records of the previous events and t he geological parameters such as the rate of
subduction, collision, and spreading, and the age of subducted slab, etc.
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For the present seismic hazard assessment, from the seismic sources identified by
SoeThuraTun et al. (2011) and Myo Thant et al. (2012), those lie within 250 km in radius are
obtained as t he m ost p ossible s eismic s ources ( fault and ar eal) t hat c an c ontribute t he
seismic hazards to Sagaing.
3.2.2 Site Investigation
The s ite geology dat a pl ays an i mportant r ole f or t he s ite s pecific s eismic haz ard m ap
development. In the site investigation of Sagaing, the borehole drilling is performed in four
locations in the city with reference to the geology and geomorphology. The SPT test and soil
sampling a re c arried o ut w hile t he bor eholes ar e dr illing. Labo ratory t ests o f s ome s oil
samples are also conducted in this project.
As t he o ther s ite i nvestigation m ethod, we conducted the microtremor surveying in
Sagaingduring 7 – 11 July, 2013 as geophysical s urvey. T he s ite par ameter i n seismic
hazard c alculation by us ing the selected G MPEis t he av erage s hear wave v elocity t o t he
upper 30 m, Vs30 and the H/V spectral technique is used to calculate Vs
30.
The l ocations o f bor eholes and m icrotremor s urvey s ites i n S againg are s hown i n
Figure (5).
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Figure (5) Map depicting the locations of boreholes and microtremor survey points
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3.3 Regional Geological Setting
It can be generally said that Sagaing City is bounded by Minwun range in the west and
Sagaing Hill in the east. While Minwun Range is covered by Minwun Metamorphics
composed mainly of m etapelite and m etabasite, S againg H ill i s oc cupied by S againg
Metamorphics that are mainly gneisses and Calciphyres with white marble bands
(MyintThein, 2009) . R ather t han M inwun Metamorphics, I rrawaddy Fo rmation and U pper
Pegu Group can also be seen in Minwun Range.
Most parts of Sagaing are covered by alluvium, and river terrace, especially in the southern,
central, western and eas tern parts of the city. The north-western part of the city is covered
by Minwun Metamorphics and north-eastern part by Sagaing Metamorphics. Regional
geological map of the Sagaing City is shown in Figure (6).
The c ity i s m oreover pas sing t hrough(the c enter of the c ity) by right-lateral, s trike-slip
Sagaing fault;and bounded by Kyaukkyan Fault and Nampon Faul t, and West BagoYoma
Fault and Gwegyo Faultin the west.
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Figure (6) Regional geological map of Sagaing
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3.4 Ground Motion Prediction Equations (GMPEs)
After t he g round motion v alues ( peak ground ac celeration (PGA), s pectral
acceleration (SA) at the periods of 0.2 s, 0.3 s and 1.0 s, and peak ground velocity
(PGV)) calculated by using the several different ground motion prediction equations
(GMPEs) are correlated, the GMPE of Boore et al. (1997) is used for seismic hazard
calculation of PGA and SA, and Boore and Atkinson (2008) NGA is applied for PGV
calculation.
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4 RESULTS
4.1 Site Condition
From borehole drilling, SPT and Labor atory analysis, the N-values and dens ity of each soil
layer ar e obt ained. T hese par ameters a re t he bas ic par ameters for H /V s pectral r atio
analysis f or mircrotremor dat a. A s i n al l t he g eophysical m ethods, the ac tual g eological
condition c an be appl ied as t he m odel f or m icrotremor dat a anal ysis. T he s hear w ave
velocity s tructure o f eac h s urvey s ite i s c onstructed bas ed on t his m odel and f inally we
estimate the average shear wave velocity to the upper 30 m, Vs30. For example, Figure (8)
shows t he H /V spectral r atio o f t he m icrotremor s ite SG-30 and Figure (9) r epresents t he
shear wave velocity structure. The average shear wave velocity to the upper 30 m, Vs30 of
this site is obtained as 195.64 m/s.
The o ther ex ample i s t he s hear w ave v elocity o f s tructure der ived from t he H /V
spectral ratio analysis of the microtremor measurement at the site SG-13. While Figure (10)
shows the H/V spectral ratio of the site SG-13, Figure (11) illustrate the shear wave velocity
structure of the site. The average shear wave velocity to the upper 30 m, Vs30 is deduced as
382.69 m/s.
From about H/V spectral ration analysis of about 39microtremor survey sites, the
shear wave velocity structure of all sites are developed and Vs30 of all sites are estimated.
The Vs30 contour map of Sagaing city is f inally developed by interpolating these Vs
30 values
of 39 sites. Figure (12) shows the Vs30 contour map of Sagaing and this map is applied as
the parameter o f s ite condition f or t he seismic hazard calculation.Most of the soil t ypes in
Sagaing can be classified as very dense soil (i.e. B class) based on the Vs30 values (Uniform
Building Code, UBC and Eruocode 8, EC8). Soft soil (D) can only be obs erved in southern
and western margin of the city. As mentioned in previous session of regional geology of the
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city, t he nor th-western and nor th-eastern par t o f t he c ity is covered by hard r ock, i .e. s ite
class A.
The V s30 value i s t he m ain i nput par ameter o f t he site c ondition, for t he s eismic
hazard (peak ground acceleration (PGA); spectral acceleration (SA) at the periods of 0.2 s,
0.3 s and 1. 0 s ; and pe ak ground velocity ( PGV)) calculation by us ing t he gr ound m otion
prediction equation (GMPE).
Figure (8) H/V spectral ratio of the microtremor survey site, SG-30
0
1
2
3
0.1 1 10
H/V
Spe
ctra
l rat
io
Frequency [Hz]
observed data
initial model
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Figure (9) Shear wave velocity structure of the microtremor survey site, SG-30 (Vs30-195.64 m/s)
Figure (10) H/V spectral ratio of the microtremor survey site, SG-13
-70
-45
-20
0 100 200 300 400
Dep
th (m
)
Vs (m/s)
0
1
2
3
4
0.1 1 10
H/V
Spe
ctra
l rat
io
Frequency [Hz]
observed data
initial model
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Figure (11) Shear wave v elocity s tructure of the microtremor survey s ite, SG-13 (Vs30 -382.69 m/s)
-200
-175
-150
-125
-100
-75
-50
-25
0
0 300 600 900 1200
Dep
th (m
)
Vs (m/s)
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Figure (12) The Vs
30 contour map of Sagaing
4.2 Seismic Hazard
The seismic hazard assessment is carried out for 10% and 2% probabilities of exceedance
in 50 years (475 years and 2475 years recurrence intervals) by using PSHA. The results of
seismic hazard assessment will be discussed in this session.
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4.2.1 Seismic hazards for 475 years recurrence interval
The s eismic haz ard p resented by m eans o f pe ak ground ac celeration (PGA) i n g for t he
recurrence interval (10% probability of exceedance in 50 years) is shown in Figure (13). The
maximum seismic hazard area is in the west of the city and the PGA ranges from 0.65 g to >
1.0 g. The eastern part of Zayar Ward, the western part of Thaw Tar Pan are in the highest
seismic z one, P GA > 1 .0 g. H owever, m ost par ts o f t he S againg s uch as t he wards o f
Takaung, Poe Tan, More Zar, Aye Mya Wati, Nanda Wun, PannPae Tan, Seingone, Myothit,
Htone B o, P arami, Y warHtaung, Zay ar ( western par t), Thaw T ar P an ( eastern par t),
MeeYahtar, Shweminwun, and Patamyar comprise the second most highest seismic hazard
zone (PGA – 0.9 g – 1.0 g).
From Figure (14) to (16) depict the probabilistic seismic hazard maps presented in
terms of spectral acceleration at the periods of 0.2 s, 0.3 s, and 1.0 s, for 10% probability of
exceedance in 50 years (475 years recurrence interval). The range of SA is from 1.4 g to 2.2
g for 0. 2 s pe riod and 0 .5 g to 1 .8 g for 0. 3 s period. H owever, S A at the per iod o f 1. 0s
ranges f rom < 0. 6 g t o >1.4 g. The S A v alues of these nat ural per iods f or 475 y ears
recurrence interval can be used for developing the seismic safety design for the (ordinary)
buildings and structures.
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Figure (13) P robabilistic s eismic h azard m ap o f S againg, S againg Region, f or 10% probability of exceedance in 50 years (475 years recurrence interval), in terms of peak ground acceleration (PGA) in g.
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Figure ( 14) Probabilistic s eismic haz ard m ap o f S againg c ity, S againg Region f or 10% probability of exceedance in 50 years (475 years recurrence interval), in terms of spectral acceleration (SA) at the period of 0.2 s, in g.
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Figure ( 15) P robabilistic s eismic haz ard m ap o f S againg c ity, S agiang Region f or 10% probability of exceedance in 50 years (475 years recurrence interval), in terms of spectral acceleration (SA) at the period of 0.3 s, in g.
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Figure ( 16) P robabilistic s eismic haz ard m ap o f S againg city, S againg Region f or 10% probability of exceedance in 50 years (475 years recurrence interval), in terms of spectral acceleration (SA) at the period of 1.0 s, in g.
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4.2.2 Seismic hazards for 2475 years recurrence interval
Figure (17) shows the probabilistic PGA map of Sagaing for 2% probability of exceedance in
50 years (2475 years recurrence interval). The seismic hazard zones are trending in NW-SE
and the PGA values range from 0.8 g to > 1.5 g. The highest PGA is contributed to some
portions of the city with the ground motion level of > 1.5 g and it includes Htone Bo, Parami,
Thaw Tar Pan, Zayar, MeeYahtar, Shweminwun and Patamyar Wards. Some parts of wards
such as Aye Mya Wati, Poe Tan also fall in this seismic hazard zone. The rest wards of the
city – Takaung, Seingone, Myothit, Moe Zar, Nanda Wun, Aye Mya Wati, DarwaeZay,
PannPae Tan, YwarHtaung, Tat Myae and Nilar – belong to the second highest seismic
hazard zone and t he PGA of this zone is f rom 1.35 g to 1.5 g. For 2,475 years recurrence
interval, the city falls in these two zones.
Probabilistic SA maps for the periods of 0.2 s, 0.3 s, and 1.0 s are illustrated in Figures (18-
20). The hazard distribution patterns of these ground motion parameters are also nearly the
same w ith each ot her. To dev elop t he s eismic r esistance des ign for l ong t erm projects
(buildings and structures), t he S A for 2475 y ears r ecurrence i nterval c an be us ed for t his
city.
31
Figure (17) Probabilistic seismic hazard map of Sagaing, Sagaing Region, for 2% probability of exceedance in 50 years (2475 years recurrence interval), in terms of peak ground acceleration (PGA) in g.
32
Figure ( 18) P robabilistic s eismic haz ard m ap o f Sagaing c ity, S againg Region f or 2% probability of exceedance in 50 years (2475 years recurrence interval), in terms of spectral acceleration (SA) at the period of 0.2 s, in g.
33
Figure ( 19) P robabilistic s eismic haz ard m ap o f Sagaing c ity, S againg Region f or 2% probability of exceedance in 50 years (2475 years recurrence interval), in terms of spectral acceleration (SA) at the period of 0.3 s, in g.
34
Figure ( 20) P robabilistic s eismic haz ard m ap o f Sagaing c ity, S againg Region f or 2% probability of exceedance in 50 years (2475 years recurrence interval), in terms of spectral acceleration (SA) at the period of 1.0 s, in g.
35
5 DISCUSSION AND RECOMMENDATION
With t he ai ds o f U NHABITAT, Myanmar E arthquake C ommittee (MEC), Myanmar
Geosciences Society (MGS) and Myanmar Engineering Society (MES) carry out the seismic
hazard and r isk assessment for three cities: Sagaing City (Sagaing Region), and B ago and
Taungoo Cities (Bago Region). This report is prepared for the probabilistic seismic hazard
maps of Sagaing. While MES develops the seismic risk maps of Sagaing, MEC and MGS
develop the seismic hazard maps of the city by using the probabilistic seismic hazard
assessment m ethodology ( PSHA). We c onstruct t he s eismic haz ard m aps of S againg for
475 years recurrence interval (10% probability of exceedance in 50 years) and 2475 y ears
recurrence interval (2% probability of exceedance i n 50 years. The hazard maps include
probabilistic peak ground acceleration (PGA) map, and spectral acceleration (SA) maps of
0.2 s, 0.3 s and 1.0 s. There are, therefore, four seismic hazard maps for each recurrence
interval level.
Instead o f al l s eismic haz ard m aps, t he di scussion will m ainly c oncern t o P GA gr ound
motion l evel of t he c ity, f or bot h 475 y ears and 2475 years r ecurrence i ntervals. For 475
years r ecurrence i nterval, t he P GA l evel of the c ity i s in t he r ange o f 0 .6 g t o > 1. 0 g.
Therefore, it can be regarded as the city is in violent zone of perceived shaking, heavy zone
of potential damage, and instrumental intensity zone IX. However, for 2475 years recurrence
interval, the PGA level of most parts of the city is in the range of 0.8 g to > 1.5 g. It means
that the city comprises the extreme zone of perceived shaking, very heavy zone of potential
damage, and X+ zone of instrumental intensity.
The s eismogenic s ource t hat can m ainly c ontribute t he seismic haz ard t o S againg is t he
right-lateral, s trike-slip S againg Faul t which i s pas sing through the c ity. T herefore, the
seismic hazard level is very highfor the center of city, trending NS direction. This is the key
point to be considered for land-use planning or urban development.
36
We develop the seismic hazard m aps o f S againg city by us ing t he c urrent available dat a
such as the seismic sources data, and s ite data, etc. However, i t is needed to update and
modify these maps based on the availability of more data, especially on the seismic sources
data such as the active fault data, paleoseismological data, etc. These maps can be used for
developing the seismic resistance designs of buildings, structures, infrastructures for certain
projects. But it should be noted that it is need to adjust what hazard maps, i.e. the different
recurrence interval level (either 475 years recurrence level or 2475 years recurrence level)
should be us ed bas ed on t he pr ojects pu rposes. H owever, al l m aps c an be used for
earthquake disaster preparedness purposes.
For special or major project, it might be needed t o conduct the site specific seismic hazard
analysis for that site or location.
37
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confidence limits, Bull. Earthq. Res. Inst., Univ. Tokyo, 43, 237-239.
Ambraseys, N . N . 1988 . Magnitude – Fault Lengt h R elationships f or Earthquakes i n t he
Middle East, In: Lee, W.H., Meyers, H. &Shimazaki, K. eds, Historical Seismograms
and Earthquakes of the World, Acad. Press Inc., 309-310.
Atkinson, G. M . 1984. Attenuation o f S trong Ground M otion i n C anada from a R andom
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Cornell, C. A. 1968. Engineering Seismic Risk Analysis, Bulletin of the Seismological Society
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Gutenberg, B., and R ichter, C. F. 1944. Frequency of Earthquakes in California, Bulletin of
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KhinThetSwe and Myo Thant, 2012. Probabilistic Seismic H azard Maps of B ago R egion,
Myanmar, 1 st International C onference on R egional G eology, S tratigraphy and
Tectonics o f M yanmar and N eighboring C ountries and E conomic G eology
(Petroleum and Mineral Resources) of Myanmar
38
KhinThetSwe, 2012. Seismic H azard A ssessment of B ago R egion by using P robabilistic
Seismic Hazard Analysis (PSHA). Department of Geology, Yangon University. 16-18
p.
Kijko, A. 2004. Estimation of the Maximum Earthquake Magnitude, mmax, Pure and A pplied
Geophysics, Vol.161, No.8. pp. 1655-1681.
McGuire, R. K. 1976. Fortran computer program for seismic r isk analysis, US. Geol. Surv.,
Open - File Rept 76-67, 90 pp.
MaungThein and T int Lw inSwe, 2005. The S eismic Zone M ap of M yanmar, Myanmar
Earthquake Committee, Myanmar Engineer Society.
Myo T hant, 2010 . Lecture N otes o f E arthquake E ngineering ( Part-1). Department o f
Engineering Geology, Yangon University. 32 p.
Myo T hant, Nwe Le′ Nge, SoeThuraTun, MaungThein,WinSweand ThanMyint, 2012.
Seismic H azard A ssessment M yanmar, Myanmar E arthquake C ommittee(MES),
Myanmar Geosciences Society(MGS).
Nwe Le′ Nge, 2010. Evaluation of Strong Ground Motion for the Central Portion ofYangon.
Department of Geology, Yangon University. 62 p.
Papazachos B. C., Scordilis E. M., Panagiotopoulos, D. G., Papazachos, C. B. and
Karakaisis G . F . 2004 . Global R elations be tween S eismic Faul t P arameters an d
Moment M agnitude o f E arthquakes, Proced. of 10 th International C ongress,
Thessaloniki, April, pp. 1482-1489. (in Appendix A)
Reiter, L 1990. Earthquake H azard A nalysis- Issues and I nsights, C olumbia University
Press, New York, 254pp.
San Shwe&MaungThein, 2011. Seismic Microzones of Bago-OaktharMyothit Area, Journal
of the Myanmar Geoscience Society, 66 p.
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Steven L. Kramer, 199 6. Geotechnical E arthquake E ngineering, Civil E ngineering and
Engineering Mechanics, University of Washington. 19-20, 45-50 p,595p.
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Commission for Asia and the Pacific. 183 p.
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Geoscience Society, Yangon, Myanmar.
40
APPENDICES
41
Appendix A The maximum magnitude of earthquake potential expected to happen by fault specific
sources c an be det ermined by us ing t he following relationships of earthquake m agnitude
and fault length.
Inoue et al., AIJ (1993); 0.5M = Log L + 1.9 (A-1)
Ambraseys’s equation (1988); Msc= 1.43 logL + 4.63 (A-2)
in which Msc is the expected surface wave magnitude and L is the fault length.
Mohammadioun&Serva (2001); Ms= 2 log L + 1.33 log ∆σ + 1.66 (A-3)
where, Msis t he surface wave m agnitude, L is t he f ault r upture l ength ( km) and ∆σ is t he
stress drop released by the earthquake (in bars) that depends on the width of the faults and
type ( kinematics) o f t he faults. S tress d rop pa rameters for eac h fault are c alculated by
applying the following relationships (Mohammadioun and Serva, 2001);
∆σN = 10.6 x W0.5 (A-4)
∆σSS = 8.9 x W0.8 (A-5)
∆σR = 4.8 x W1.6 (A-6)
in w hich ∆σN,∆σSS and ∆σRare stress drop (in bars) for normal, strike-slip and reverse
faults and W is the fault width (km) which is also determined by utilizing the relation of fault
length and fault width; L = 2W (Bormann and Baumbach, 2000).
M = (LogL+6.4)/1.13 (Ambraseys and Zatopek, 1968) (A-7)
M = 2.0 logLmax+ 3.6 (Otsuka, 1964) (A-8)
M = 2.0 logLmax+ 3.5 (Iida, 1965) (A-9)
M = 2.0 logLmax + 3.7 (Yonekura, 1972) (A-10)
in which L maxis the maximum earthquake fault length,
42
M = 1.7 LogL + 4.8 (Matsuda, 1977) (A-11)
and, 0.5 M = Log L + 1.86 for oblique faults (A-12)
0.59 M = Log L + 2.3 for Strike slip faults (A-13)
(Papazachos et al., 2004)
Appendix B
The maximum magnitude of the earthquake potentials which can be originated from all areal
seismic sources are determined by using the relationship of Kijko (2004);
)exp()}]exp(/{)}()([{ min22211maxmax nmnnEnEmm obs −+−−+= β (B-1)
where, E1(z) = {(z2 + a1z + a2)/ [z (z2 + b1z + b2)]} exp (-z) (B-2)
n1 = n / {1 - exp [-β(mmax - mmin)]} (B-3)
n2= n1exp [-β(mmax- mmin)] (B-4)
in which n is the number of earthquakes greater than or equal mmin, a1 = 2.334733,
a2 = 0.250621, b1 = 3.330657, and b2 = 1.681534.
It must be noted that Equation 2.23 does not constitute a direct estimator formmax since
expressions n1and n2, which appear on the right-hand side of the equation, also contain
mmax. Generally the assessment of mmax is obtained by the iterative solution of Equation (B-
1).
However, when mmax- mmin ≤ 2, and n ≥ 100, the parameter mmax in n1 and n2 can be
replaced by mmax(obs), pr oviding mmax estimator which can be obt ained w ithout iterations
(Kijko, 2004).
43
Appendix (C)
The mathematical expression of the probability of the ground motion parameter Z will exceed
a specified value z, during a specified time period T at a given site is as follow:
tzvezZP ⋅−−=> )(1)( (C.1)
wherev(z) is the mean annual rate of events from which the ground motion parameter Z will
exceed z at a certain site resulting from the earthquakes from all seismic sources in a region.
It can be calculated by applying the following equation:
∫ ∫∑ >⋅==
drdmrmzZPrfmfmzv RM
N
ni ),/()()()()(
1λ
(C.2)
where )( imλ = t he frequency of ea rthquakes on s eismic s ource nabove a m inimum
magnitude of engineering significance, mi ;
)(mfM = t he pr obability dens ity f unction o f ev ent s ize on s ource nbetween m0 and
maximum earthquake size for the source, mu;
)(rfR = t he pr obability dens ity f unction for di stance to ear thquake r upture o n s ource n,
which may be conditional on the earthquake size; and
P(Z>z|m,r)= the pr obability t hat, at a given a magnitude mearthquake and at a di stance
rfrom the site, the ground motion exceeds value z.
Therefore the calculation of the seismic hazards will be included the following steps;
1) Calculating the frequency of the occurrence of the event of magnitude m on source n,
2) Computing the probability density function of event size on source n
betweenm0 and mu,
3) Computing the probability distribution for the distance from the site to source n where the
event with the magnitude m will occur, and
44
4) Calculating, at each distance, the probability that an event with magnitude m will exceed
the specified ground motion level z, i.e. calculating the ground motion amplitude parameters
for a certain recurrence interval.
The seismic hazard values can be obtained for individual source (zones) and then combined
to express the aggregate hazard. The pr obability of exceeding a particular value Z, of a
ground m otion par ameter, z, is calculated f or on e pos sible ear thquake at one pos sible
source location and then multiplied by the probability that the particular magnitude
earthquake w ould oc cur at that par ticular l ocation. The p rocess i s t hen r epeated for al l
possible m agnitudes an d l ocations, and t hen summed al l o f t he pr obabilites on t hese
variables (Kramer, 1996).
Calculation of the Event Rate
The first step is the computation of the rate of occurrence of events of magnitude m.
The annual rate of exceedance for a pa rticular magnitude can also be determined by using
Gutenberg-Richter recurrence law.
Log Nc(m) = a – bm (C.3)
where Nc(m) is the yearly occurrence rate of earthquakes with magnitude ≥ m in a particular
source zone, a and b are constants specific to the seismic source zone, and t hese can be
estimated by a l east s quare anal ysis of the da ta bas e o f t he pas t s eismicity from eac h
seismic s ource. These values m ay v ary i n s pace and time. While the a-value g enerally
characterizes the level of seismicity in a given area i.e. the higher the a-value, the higher the
seismicity, the b-value describes the relative l ikelihood of large and s mall earthquakes, i .e.
the b-value increases, the number of larger magnitude earthquakes decreases compared to
smaller.
45
Probability of the Event Magnitude
The second step of the seismic hazard analysis is the calculation of the probability
that the magnitude will be within an interval of the lower bound magnitude ml and the upper
bound magnitude mu. It can be calculated by the following relation:
)()](exp[1
)](exp[)/()( 0max
0luul
M mmmm
mmmmmmPmf −−−−
−−=<<=
βββ
(C.4)
where, β = 2. 303b, mmax is t he m aximum magnitude o f t he ear thquake pot ential for a
specific seismic source (Kramer, 1996).
Probability of the Source-to-site Distance
The probability for the source-to-site distance can be computed as the same in the
second step and can be expressed by the following equation:
)()](exp[1
)](exp[)/()( 0max
0luul
R rrrr
rrrrrrPrf −⋅−−−
−−=<<=
βββ
(C.5)
in which rmax is t he l ongest source-to-site di stance, r0 is t he shortest distance, rl is t he
lower bound source-to-site distance, andru is the upper bound distance.
Probability of Ground Motion Parameter
The probability for a c ertain ground motion parameter, Z that will exceed z from the
specified magnitude, m and at the specific location (source) with the distance r, can be
calculated by utilizing the following relation:
))ln()ln((1),/(ln y
PHAzFrmzZPσ−
−=> (C.6)
46
where PHA is t he peak hor izontal ac celeration and σlny is t he s tandard dev iation of t hat
attenuation relation.By multiplying these probabilities from each sources and repeated again
for all possible seismic sources together with the above mentioned steps, the Probabilistic
PGA map can be developed for a certain area of interest or region.
Probability of Exceedance
The assumption called no memory (Poisson Model) is used the occurrence of certain
magnitude ear thquake i n any par ticular y ear, t he r eturn per iod ( T) of an ev ent
exceeding a par ticular ground m otion level i s r epresented by t he mathematical
expression as:
T = 1/v = - ∆t / ln (1 - P(Z>z)) (C.7)
In this equation, P(Z>z) is the desired probability of exceedance during the time T.
Appendix (D)
0
0.5
1
1.5
2
2.5
1906
1911
1916
1921
1926
1931
1936
1941
1946
1951
1956
1961
1966
1971
1976
1981
1986
1991
1996
2001
2006
2011
33.544.555.566.577.58
47
Figure (D-1). D iagram representing the relationship of normalized frequency of events of certain m agnitude w ith respect t o t ime ( year) for M yanmar r egion ( in w hich magnitude roundness is 0.25).
Table ( D-1). Time o f c ompleteness for t he ev ents w ith c ertain m agnitude for M yanmar region.
Magnitude Incremental Frequency
Time of
Completeness
3.0 791 1992
3.5 876 1992
4 1055 1978
4.5 541 1966
5 266 1964
5.5 89 1964
6 60 1933
6.5 33 1925
7 23 1925
7.5 6 1918
8 1 1906
8.5 1 1906
48
Figure (D-2). The Gutenberg-Richter relation for Myanmar region.
Figure (D -3). T he di agram i llustrating t he ann ual r ate o f ex ceedance o f c ertain magnitude earthquake for Myanmar region.
Log Nm = 4.744 - 0.8083m
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
0 2 4 6 8 10
Log
Nm
Mw
0.001
0.01
0.1
1
10
4.0 5.0 6.0 7.0 8.0 9.0
Annu
al ra
te o
f exc
eeda
nce
Mw
49
Appendix (E)
Table (E-1) Ground profile (soil) types or classification of subsoil classes according
to UBC (Uniform Building Code) and EC8 (Eurocode 8) standards based ontheVs
30 values (modified from Sˆeco e P into 2002; Dobryet a l. 2000; Sabetta&Bommer 2002). (Source-Kanl1 et al., 2006).
Ground profile (Soil) type (UBC) or Subsoil Class (EC8)
Ground description (UBC)
Description of s tratigraphic pr ofile (EC8)
Shear wave velocity 𝑉𝑉𝑠𝑠30 (m s-1)
SA(UBC) Hard rock — >1500 (UBC)
SB(UBC) o r A (EC8)
Rock Rock or ot her rock-like geol ogical formation, including at most 5m of weaker material at the surface
760–1500 ( UBC) or >800
(EC8)
SC(UBC) o r B (EC8)
Very dense s oil and soft rock
Deposits of v ery de nse s and, gravel or v ery s tiff c lay, at l east several t ens of m i n thickness, characterized b y a gradual increase of m echanical pr operties with depth
360–760 ( UBC) or 36 0–800
(EC8)
SD(UBC) or C (EC8)
Stiff soil
Deep de posits of den se or medium-denses and, gravel or stiff clay with thickness from several tens to many hundreds of m.
180–360 (UBC and EC8)
SE(UBC) o r D (EC8)
Soft soil
Deposits of l oose-to-medium cohesionless s oil ( with or w ithout some s oft c ohesive layers), or of predominantly s oft-to-firm cohesive soil
<180 (UBC and EC8)
SF(UBC) or E (EC8)
Special soils
A s oil profile c onsisting of a surface —alluvium layer with V30s values of c lass C or D an d thickness varying between about 5 m and 20 m , under lain b y s tiffer material with
—
50
𝑉𝑉𝑠𝑠30 >800 m 𝑠𝑠−1
S1 (EC8) —
Deposits consisting—or containing a layer at least 10 m thick—of soft clays/silts with high plasticity index (PI >40) and high water content
<100 (EC8)
S2 (EC8) —
Deposits of l iquefiable s oils, of sensitive c lays, or an y ot her s oil profile not included in classes A–E or S1
— (EC8)
51
Photos of some pagodas affected by 2012 Thabeikkyin Earthquake
52
Photos of microtremor surveying
53
Microtremor instrument and its parts
54