FRAMEWORK FOR EARTHQUAKE HAZARD ASSESSMENT
SEISMIC HAZARD RISK ASSESSMENT OF BAGO, TAUNGOO
AND SAGAING CITIES, MYANMAR
Myanmar Geosciences Society (MGS)
16 July 2013
Contents
Background ............................................................................................................................................. 1
Objectives and Scope of the Project ....................................................................................................... 2
Methodology of the Project .......................................................................................................................... 5
Seismic Hazard Assessment .................................................................................................................... 5
Task 1. Seismic sources identification and characterization ............................................................. 5
Task 2. Estimating the temporal occurrence of earthquake and maximum magnitude ................... 6
Task 3. Attenuation relationship selection ........................................................................................ 6
Task 4. Calculation of the seismic hazards ........................................................................................ 6
Generation of Microzonation Map (Amplification Map or Map of Amplification Factor)...................... 6
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Seismic Hazard Assessment of Bago, Taungoo and Sagaing, Myanmar
Background
Situating in one of the two major earthquake belts, Myanmar is prone to earthquakes. Numerous
historical earthquakes recorded in damage of religious buildings since fifth century C.E. exhibit seismic
nature of almost all land of Myanmar. Since the 18th century, at least 15 major earthquakes including two
historical events in 1762 (northern Rakhine Coast) and 1839 (Innwa ancient capital) occurred in Myanmar
territory. Some recent earthquakes with smaller magnitude (more than 6.5 R.M.) occurred as strong
earthquakes in Central Myanmar i.e. 1975 Bagan Earthquake (M=6.5), 2003 Taungdwingyi Earthquake
(M=6.8) and in Eastern Myanmar like 2011 Tarlay Earthquake (M=6.8). Being its location at convergence
zone between Indian and Eurasian tectonic plates, western part of Myanmar lies on Burma Plate of which
Bengal subduction zone in the west and Sagaing transform fault in the east. As the tectonics is still active,
underthrusting, transcurrent and collisional structures overwhelmed the whole country and devastating
earthquakes have been subjected to the people and infrastructure of Myanmar.
Recent studies on earthquakes in Myanmar have been started since the event of 2003
Taungdwingyi Earthquake. Geologists from the Myanmar universities were later organized in Myanmar
Earthquake Committee and paleoseismological research began after 2004 Sumatra Earthquake and
Tsunami and the work was emphasized on marine terraces along the northern Rakhine Coast where
occurred 1762 Bengal Earthquake (M7). From early of 2007, studies on active faults in Myanmar became
a joint project among scientists of Myanmar, and its international partners like AIST (Geological Survey of
Japan), Kyoto and Hiroshima Universities (Japan), California Institute of Technology (USA), National
Taiwan University (NTU) and Earth Observatory of Singapore (Nan Yang Technological University,
Singapore). Works emphasized on interpretation of SRTM (Shuttle Radar Topographic Mission) imagery
and aerial photographs of Kabaw Fault, Sagaing Fault, Western Rakhine Coast, and Northern Yangon areas
and subsequent field observations. Activity of faults were determined through tectonic geomorphology
of Kyaukkyan Fault (Shan Plateau of eastern Myanmar) and along the Sagaing Fault (Central Myanmar).
On Sagaing Fault, paleoseismological trenching have been conducted in two southern segments like Bago
Segment at west of Payagyi Town and Phyu Segment at Taungthonlon (west of Phyu). Paleoseismic data
indicates that recurrence of surface rupturing earthquake is approximately 100 years in southern Sagaing
Fault.
Bago and Taungoo cities are the highly populated places of Bago region and the population is
above 300,000.They have being continually developed with the growth of population, various sorts of
builds and the infrastructures, etc. The deterministic seismic hazard map of Bago - Oakthar Myothit area
was developed by San Shwe and Maung Thein in 2007, and that of Taungoo by Aye Aye Myint in 2008 and
are the first seismic hazard maps of these cities and the seismic hazards were expressed in term of peak
ground acceleration (PGA). However, no systematic research on seismic hazard and risk assessment has
done. Therefore systematic seismic hazard and risk assessments are tended to carry out.
Sagaing City, populated and also important for its accommodation of hundreds of monasteries of
Buddhist monks, is prone to large earthquake and is well-known for being reference place to Sagaing
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Fault. There has been no systematic research on seismic hazard and present study intends to fill the gap
in present day development work of the country.
Objectives and Scope of the Project
The fundamentals to evaluate the seismic hazard is for the invaluable information for
development work of the urban areas and for the background information in seismic risk assessment the
organization working cooperatively with Myanmar Engineering Society (MES).
i. To identify the most possible seismic sources for Bago, Taungoo and Sagaing Cities
ii. To assess the geological and seismological information related to the seismic sources
iii. To evaluate the ground motion parameters of the seismic hazards
iv. To appraise the site condition that influence the amplification of the ground motions
Specifically, the seismic hazard assessment will include
i. The seismic sources identification and characterization
ii. The seismicity or temporal distribution of earthquake recurrence characterization
iii. The site characterization
iv. The seismic hazard calculation
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Figure 1. Tectonic Map of Myanmar (Soe Thura Tun and Maung Thein 2012)
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Figure 2. Hypothetical earthquake segments of active faults threatening Sagaing City and central
Myanmar region.
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Figure 3. Map showing the relation of earthquake and surface fault trace of the part of Central
Myanmar.
Methodology of the Project
Since the project include the seismic hazard analysis, the methodology related with each portion
is discussed separately in brief. The seismic hazard assessment will be carried out by using the classical
probabilistic seismic hazard analysis of Cornell (1968). This method comprises of four tasks accounted by
Reiter (1990) and Kramer (1996).
Seismic Hazard Assessment
Task 1. Seismic sources identification and characterization
In the seismic source identification, the geometry and spatial distribution of seismic sources of
future seismicity (the earthquake potentials) in and around the proposed urban area (Bago, Taungoo &
Sagaing) area will be determined by reviewing the available literatures and unpublished documents
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related with the previous historical events and by using the image and air photo interpretation, especially
for the active fault sources.
Task 2. Estimating the temporal occurrence of earthquake and maximum magnitude
The paleoseismological investigation such as trenching are tended to carry out to obtain the
reasonable geological data related to those such as fault slip rate, fault geometry, and activity rate,
especially for Sagaing Fault.
Instrumental earthquake catalog and historical records of the previous earthquakes will be
analyzed to estimate the seismicity parameters such as estimation of a- and b- values for each seismic
source. The estimation of occurrence rate of the earthquake with the function of a magnitude for each
seismic source, and the maximum magnitude of the earthquake potential for each seismic source is
required to carry out with the cooperation of their uncertainty.
Task 3. Attenuation relationship selection
The attenuation relationships have been developed for various region and different sort of
tectonic setting. In Myanmar, there are no enough strong ground motion records to develop and even to
validate which one should be suitable for a certain region. Therefore, we will make comparative study on
several attenuation relations of the same tectonic setting by utilizing the seismic sources and site
parameters for Bago, Taungoo and Sagaing areas. Normally the attenuation relations of Boore et al. (1997)
and Takahashi et al. (2000) were applied in seismic hazard assessment for other areas or regions (even
national seismic hazard assessment of Myanmar).
Task 4. Calculation of the seismic hazards
The seismic hazards will be calculated by applying the EZFRISK computer program for firm rock
condition. The results will be represented in terms of peak ground acceleration (PGA) in g, peak ground
velocity (PGV) in cms-1 and spectral acceleration (SA) in g at the periods of 0.2s, 0.3s and 1.0s for 10%,
39%, 63%, 86% and 99% of probabilities of exceedance of 50 years.
Generation of Microzonation Map (Amplification Map or Map of Amplification Factor)
It is also need to account the effect of local site condition on the seismic hazards since the
amplification characteristics (site effect) of local soil has a great influence on the damage intensity during
an earthquake. To understand the amplification characteristics of underlying soil deposit, linear or non-
linear response analysis has to be conducted. 1D dynamic response analysis which is based on equivalent
linear method will be performed in this project by using DYNEQ program coded by Nozomu Yoshida, 2004.
A first level seismic microzonation map of three cities have been produced with a GIS platform using the
themes, viz, Peak Ground Acceleration (PGA), Shear wave velocity at 30 m, Geology, Ground water
fluctuation and bed rock depth. For that purpose, the following measurements and data collection will be
carried out.
Geotechnical site investigation: Drilling at least 30m depth will be conducted in three cities together with
Standard Penetration Test (SPT) and samplings. The number of proposed boreholes was presented in
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figures 5 to 7 and Appendix 1. 2-D soil profile of each borehole will be constructed based on drilled log,
SPT values and laboratory results. Shear wave velocity structure of each borehole will be estimated based
on SPT data. The delineation of bedrock profile, the mapping of subsoil strata, and the associated soil
structure, fluctuations of ground water table, determination of soil properties, and understanding of site-
effects represent routine elements of the microzoning exercise. Soil-foundation-structure interaction,
which turns crucial during an earthquake, depends in a big way on the quality of soil characterization.
Microtremors survey: It will be conducted for a number of sites (100 or more) including drilling sites to
determine horizontal to vertical spectral ratio (H/V ratio) which is mainly related to sediment thickness
and average shear wave velocity at upper 30m (vs30). Earthquake effects are usually quantified on the
basis of degree of damage and the recorded ground motions at a site. Beside the building quality and
desing, the local soil conditions dominate the damage and loss of life in earthquakes. Therefore, it is
needed to investigate the site condition of the three cities. In this project, we conducted the microtremor
survey before borehole logging. Microtremor survey method is rapid, cost effective and efficient method
for delineating the site condition by estimating the average shear wave velocity of the soil layers occurred
at the site, especially for the upper 30m, Vs30.
Construction of Subsurface soil Model and S-wave velocity structure: Based on S-wave velocity
structures from SPT results, and microtremors survey, final S-wave velocity structure of each site (drilled
site, microtremors site) will be constructed. Moreover, 2-D soil profiles of each site (drilled site,
microtremors site) will be constructed based on S-wave velocity structure, soil profiles of boreholes,
laboratory results, and H/V ratios from microtremors survey.
Generation of Synthetic Bedrock Motion: The required bedrock motion will be generated based on
earthquake source parameters for a point source (historical earthquake) or a line source (Sagaing fault
segment).
1D Equivalent Linear Seismic Response Analysis: Based on 2-D soil profile, engineering properties and S-
wave velocity of each soil layer, and synthetic bedrock motion, response analysis will be performed for all
investigated sites.
Amplification map, PGA map, PGV map, maps of fundamental frequency and predominant period, and
map of sediment thickness above engineering bedrock (vs = 500 m/s) will be final outcomes.
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Figure 4. The map of proposed Borehole locations for Bago city (across those locations
microtremor survey to be carried out).
Figure 5. The map of proposed Borehole locations for Taungoo city (across those locations
microtremor survey to be carried out).
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Figure 6. The map of proposed Borehole locations for Sagaing city (across those locations
microtremor survey to be carried out)
Table 1. Activity for Seismic Hazard Assessment at 3 Cities in Central Myanmar
Sr. Activity Sub-Activity Month
1 2 3 4 5 6 7 8 9
1 Seismic Source Identification
Air Photo Purchase
Image/ Photo Interpretation
Field Survey
Trenching
Data Analysis and Reporting
2 Probabilistic Seismic Hazard Assessment
Area Source Classification
Line Source Classification
Seismic Hazard Analysis
Spectral Analysis
PSHA Map Output
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Data Analysis and Reporting
3 Site Amplification Assessment
55 mm Drilling up to 30m
Microtremor Survey
Data Analysis and Reporting