TSUNAMI SIMULATION AND HAZARD ASSESSMENT
ON THE BANGLADESH COAST
Netai Chandra Dey Sarker*

Supervisor:

Yushiro Fujii**

MEE06008
ABSTRACTThe study was aimed to assess tsunami hazard on the Bangladesh coast, particularly to estimate
tsunami heights as well as tsunami arrival times considering three tsunami source models. The 2004
Sumatra earthquake (Mw 9.1) source and several scenario earthquakes with Mw 8.0 and Mw 8.5 wereconsidered along the pre-assumed trench. For Sumatra case fault parameters were used similarly to avery recent study. For scenario earthquakes with Mw 8.0 and Mw 8.5, 10 (Case1 – Case10) and 6(Case01 – Case06) tsunami sources were considered, respectively, where tsunami source parameters
for a rectangular fault model and slip amount were estimated for each case using scaling laws. It was
found for the 2004 Sumatra case that tsunami arrived first after the earthquake within 2.2 hours withthe maximum height of 31 cm at St. Martin Island. For scenario earthquakes, case9 and case05 where
sources exist nearby the coast of Cox’sbazar were identified as the most severe cases with Mw 8.0 andMw 8.5, respectively. Tsunami arrived within several tens of minutes after the earthquake with themaximum height of 110 cm and 184 cm for the case9 and case05, respectively, at the coast ofCox’sbazar. Case8-case10 of scenario earthquakes with Mw 8.0 and case05-case06 of scenario
earthquakes with Mw 8.5 may appear as threat to local tsunami at Meghna estuarine-ChittagongCox’sbazar cost of Bangladesh in future.
Keywords: Tsunami Source Model, Tsunami Simulation, Tsunami Height, Travel Time

INTRODUCTION
Considering the potential seismic sources and high density of population (741/sqkm) with more than70 percent vulnerable population, the coastal belt of Bangladesh can be identified as susceptible risk
areas for tsunami. In fact, the coastal belts lacking all sorts of physical and non- physical measures towithstand the tsunami devastation, in case of future occurrence of tsunami in Indian Ocean, might
create more devastation. It is well known that Bangladesh narrowly escaped from the 2004 SumatraTsunami. This escape was only for the some reasons, so far identified. Though the 2004 Sumatra
Tsunami did not affect Bangladesh directly, it fits with nation’s vision of comprehensive disastermanagement especially in tsunami hazard mitigation.
Objectives of the StudyInfrequent occurrence of tsunamis in the Bay of Bengal kept the geoscientists of this region almost
unconcerned about the potentiality of tsunami hazard. There are some evidences of Paleo-Tsunamis
and low height tsunamis (Aung et al., 2006). So far evidences of devastating tsunamis are not available
but threats of tsunamis in the coastal belt of the country cannot be ruled out. The study addressedtsunami hazard assessment with the following objectives:o Compute tsunami propagation numerically to obtain tsunami wave forms, and travel time;o Analyse tsunami waveforms in terms of tsunami heights and tsunami arrival times to investigate thetsunami threats at Bangladesh coast.
***

Disaster Management Bureau, Government of the People’s Republic of BangladeshInternational Institute of Seismology and Earthquake Engineering, BRI, Tsukuba, Japan1

METHODOLOGY OF THE STUDY
Data Source and Collection
Tide Gage Stations and Bathymetry data
Tsunami propagation was calculated at 39 tide gauge
stations as outpoints along the Bangladesh coast (Figure1). Out of 39 stations 33 are assumed at front face of sea
using Google Earth and GMT (Generic Mapping Tools)
and 6 are operated by Bangladesh Inland Water
Transport Authority (BIWTA). The stations operated by
BIWTA demanded very minor correction of locations
due to bathymetry grid resolution during preparation oflocation data on bathymetry grid using GMT. GEBCO
bathymetry data which is available in the internet(www.ngdc.noaa.gov/mgg/gebco) is used in this study.
This is 1 arc-minute grid size data digitized from contourmap.

B a y of B e n g a l
Operated by BIWTA
Assumed by Study

Figure 1 Tide Gauge Stations as Outpoints at
Bangladesh Coast.

Data Processing and Analysis
Tsunami Source Model
The extent, geometry and slip distribution of a fault rupture and other parameters of a fault play
important roles in tsunami generation. It is envisaged that a tsunamigenic earthquake would be ofmagnitudes 8.0 and greater, however, local tsunami may occur with magnitudes 7.0-8.0 provided
necessary conditions are fulfilled (Khan, 2005). A recent study also predicts that a major earthquake of
Mw 8.5 may occur every century on this segment of the subduction (Socquet et al., 2006).
Due to lack of historical data and previous study of the area, in this study, the 2004 Sumatra
earthquake source and several scenario earthquakes (Figure 2, 3) sources are considered from
Bangladesh coast to north Andaman Island along the pre-assumed Arakan trench alignment (Socquetet al., 2006; Nielsen et al., 2004) to estimate the extent of tsunami source and slip distribution. For
Sumatra case, the geometry of each subfault, slip amount and other fault parameters are used similarly
to the study by Fujii and Satake (2007) where tsunami source is divided into 22 subfaults covering theaftershock area for a day after the mainshock. For scenario earthquakes with Mw 8.0 and Mw 8.5, 10
and 6 tsunami sources were considered respectively. Tsunami source parameters for a rectangular fault
model (Okada, 1985) andslip amount (Table 1, 2)
were estimated for each
Case06case using scaling laws
Case10Case9
based on the Okal’s (2006)
Case05
Case8equations. The depths andCase7
Case04
dip angles are assumed toCase6
be 3 km and 10°
Case03
Case5
Case4
respectively, for all theCase02
Case3cases. Strike angles are
Case2
Case01
based on pre-assumed
Case1
trench alignment (Socquetet al., 2006) and rake
angles (slip) are based on
Figure 2 Tsunami Source Models (Mw 8.0).
Figure 3 Tsunami Source Models (Mw 8.5).
the averaged compressional
axis direction.

2Table 1 Tsunami Source Parameters for Scenario Earthquakes (Mw 8.0)
Case
No.
Case1
Case2
Case3
Case4
Case5
Case6
Case7
Case8
Case9
Case10Length(km)120.22120.22120.22120.22120.22120.22120.22120.22120.22120.22

Width(km)
60.11
60.11
60.11
60.11
60.11
60.11
60.11
60.11
60.11
60.11

Depth(km)3333333333

Strike(°)
3036
37
5330
330
330
328
348
345

Dip(°)
10101010101010101010Rake(°)
160
166
167
154
120120120118
130
127

Longitude(°)
92.10092.66493.32894.00794.10593.53992.97392.40791.80891.572

Latitude(°)
13.00013.94114.82015.68816.77017.71018.65019.59020.511
21.573Slip(m)
3.48
3.48
3.48
3.48
3.48
3.48
3.48
3.48
3.48
3.48

Table 2 Tsunami Source Parameters for Scenario Earthquakes (Mw 8.5)
Case
LengthWidth Depth
StrikeDipRakeLongitude
LatitudeNo.
(km)(km)(km)(°)
(°)
(°)
(°)
(°)
Case01
213.79106.89332
10160
92.10013.000
Case02213.79106.89332
10160
93.164
14.639Case03213.79106.893335
10120
94.22816.278Case04213.79106.89333010115
93.37718.028Case05213.79106.893337
1012592.37119.700
Case06213.79106.893345
10127
91.58421.478Latitudes, Longitudes and Depths indicate the left bottom corner of each fault of scenario case.

Slip(m)
6.19
6.19
6.19
6.19
6.19
6.19

Computational Domain
The 1min grid spacing computational domain is derived from the 1min GEBCO bathymetry extending
from 0° - 24° North in latitude and 82° - 100° East in longitude for the Sumatra case and from 10° 24° North in latitude and 85° - 99° East in longitude for the scenario earthquakes in all cases (Figure 2,3). There are 1441×1081 and 841×841 grid points for Sumatra case and scenario cases (Mw 8.0 and8.5) along the latitude and longitude directions respectively. A time
step of 0.5 sec is used to satisfy the stability condition. Total numberof time steps is 72,000 for computation (10 hours).
Tsunami Simulation
Tsunami propagations were simulated with a view to obtain tsunami
waveforms and tsunami travel times at coast for all the cases. To
calculate tsunami propagation initiated at each case, the nonlinearshallow water long wave equations were numerically solved by theTUNAMI code (TUNAMI-N2) developed by Disaster Control
Research Center of Tohoku University, Japan. For the initialcondition, static deformation of the sea floor is calculated using thethree source models’ parameters for all the cases (Figure 4).

Figure 4 Sea Floor Deformation for
Case05 of Scenario EQs (Mw 8.5).

Travel Time Calculation
Tsunami travel time was calculated both from waveforms for the most severe cases of scenario
earthquakes including Sumatra case and by TTT for all the cases of scenario earthquakes. In order tocalculate tsunami travel times using TTT software developed by Geoware, inverse refraction diagram
was prepared for each outpoints. The grid points which have absolute value of greater than 0.1 m areconsidered as the source points inside the seafloor deformation area. Then using the source points,
tsunami travel times are extracted from inverse refraction diagram for each outpoint. Finally, theminimum values are taken as the tsunami travel times for each outpoint.

3

RESULTS AND DISCUSSIONS
Maximum Tsunami Heights
0.35

Tsunami Height (m)0.30.250.2
0.15
0.1
0.05
0TG
01
TG03
TG05
TG07
TG
09
TG
11TG
13TG
15TG
17TG
19TG
21TG
23
TG
25TG
27
TG
29TG
C. 31
Bazar
TG
35
TG
37
TG
39

2004 Sumatra Earthquake (Mw 9.1)
Figure 5 shows that for this devastating event,maximum tsunami height was limited only in thesouth-east and western part of the coast of
Bangladesh. Tsunami height rose over 20 cm only
at 6 outpoints where maximum tsunami height was
31 cm. Because of lack of the observation data, itis quite difficult to compare the results obtainedfor this study. However, this result is very similar
to the eyewitness which was 25-30 cm as
published in the media and mentioned in theseveral national dialogues.

Tide Gauge Stations

Figure 5 Maximum Tsunami Height at 39 Outpoints
for Sumatra Earthquake (Mw 9.1).

Scenario Earthquakes (Mw 8.0)
Figure 6 shows the tsunami height at 39 outpoints for 10 cases of scenario earthquakes with Mw 8.0.
Case9 is the most severe case for which maximum tsunami height rose 1.1 m according to thewaveform data. Tsunami height rose bellow than 20 cm in the Meghna Estuarine Coastal Belt (TG2027) for all the cases except case10 (Figure 6). For case10 tsunami height rose over 80 cm. Tsunami
height varied at some adjacent outpoints in the western part of the coast probably due to location far
from the coast. Only 4 sources (case7-10) may appear as threat to local tsunami at Bangladesh coast
for which tsunami height has risen over 50 cm at maximum.
Scenario Earthquakes (Mw 8.5)
Figure 7 shows the tsunami height at 39 outpoints for 6 cases of scenario earthquakes with Mw 8.5.
Case05 is the most severe case for which maximum tsunami height rose 1.84 m according to thewaveforms. Tsunami height rose bellow 40 cm in the Meghna Estuarine and Chittagong Coastal Belt
(TG20-31) for all the cases except case06 (over 130cm). Out of 6 sources 4 sources (case03-06) may
appear as threat to local tsunami at Bangladesh coast for which tsunami height has risen maximum
over 50 cm.

Tsunami Height (m)

12
case1

case2

case3

case4

case5

case6

case7

case8

case9

case101.8
1.6
Tsunami Height (m)1.20.80.60.4

case01

case02case03case04

case05

case06

1.4
1.2
10.8
0.6
0.4

0.2

0.20TG
01
TG03
TG05
TG
07
TG09TG
11TG
13TG
15TG
17TG
19TG
21TG
23TG
25TG
27TG
29TG
C. 31Bazar
TG
35TG
37TG
39TG
01
TG
03
TG
05
TG
07
TG
09TG
11TG
13TG
15TG
17TG
19TG
21TG
23TG
25TG
27TG
29TG
C. 31Bazar
TG
35
TG
37TG
39

0Tide Gauge Stations

Tide Gauge Stations

Figure 6 Maximum Tsunami Heights at 39 Outpoints
for 10 cases of Scenario Earthquakes (Mw 8.0).

Figure 7 Maximum Tsunami Heights at 39 Outpoints
for 6 cases of Scenario Earthquakes (Mw 8.5).

Tsunami Travel Times at Coast

Tsunami travel times were obtained at 39 outpoints along the Bangladesh coast for the 2004
Sumatra earthquake with Mw 9.1 and scenario earthquakes with Mw 8.0 (10 cases) and Mw 8.5 (6cases). In order to calculate travel time it was compared with the result calculated by TTT and thoseobtained from waveforms at first for the most severe cases. It is found that travel times are almost the4same between the both methods. Sometimes, it is also quite confusing and time consuming to obtain
travel time using waveforms. Therefore, tsunami travel times were calculated by TTT for all the casesof scenario earthquakes with Mw 8.0 and Mw 8.5 except Sumatra case. For Sumatra case, travel time isobtained from tsunami waveforms.

Tsunami Travel Time (hour)

9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
TG
01
TG
03
TG
05
TG
07
TG
09
TG
11TG
13TG
15TG
17TG
19TG
21TG
23TG
25TG
27TG
29TG
C. 31
BazarTG35TG37
TG
39

2004 Sumatra Earthquake (Mw 9.1)
Tsunami arrived first at St. Martin Island (TG39)
southernmost part of Bangladesh coast within 2.2
hours after the occurrence of earthquake. In thesouthern part of the coast- near cox’sbazar (TG3337) tsunami arrived approximately within 2.5
hours and in the western part of the coast- near
Sundarban (TG01, TG03) tsunami reached within
3.0 hours after the Sumatra earthquake (Figure 8).
Tsunami arrived earlier in the southern andwestern part than the Meghna estuarine coast line(TG21-30) of the coast of Bangladesh. In theMeghna estuarine coast line tsunami arrived morethan 6 hours after the earthquake.

Tide Gauge Stations

Figure 8 Tsunami Travel Times at 39 Outpoints along theBangladesh Coast for Sumatra Earthquake (Mw 9.1).

Scenario Earthquakes (Mw 8.0)
Tsunami arrives spending no time at Bangladesh coast for 3 sources (Case8-10) specifically in theeastern part of Meghna estuarine and Chittagong coast line (TG20, TG23-32) for Case10, and in theCox’sbazar-Teknaf coast line (TG32-39) for Case7 and Case8 (Figure 9). In general tsunami reaches
earlier in the western part of coast- near Sundarban (TG01-07) and in the south-eastern part of coastalong cox’sbazar coast line (TG34-37, TG39) approximately 2.0-3.5 hours and 1.5-3.0 hours
respectively than Meghna estuarine and Chittagong coastline (TG20-30) after the earthquake. In theMeghna estuarine and Chittagong coast line tsunami arrived 5.0-7.5 hours after the earthquake.
Scenario Earthquakes (Mw 8.5)
Tsunami arrives spending no time at Bangladesh coast for 2 sources (Case05-06) specifically in theeastern part of Meghna estuarine and Chittagong-Cox’sbazar coast line (TG20, TG23-34) for Case06,and in the Cox’sbazar-Teknaf coast line (TG30-39) for Case05 (Figure 10). In general, tsunami
reaches earlier the western part of coast- near Sundarban (TG01-08) and the south-eastern part ofcoast- along cox’sbazar coast line (TG34-37, TG39) approximately 2.0-3.5 hours and 1.0-3.0 hours
respectively than Meghna estuarine and Chittagong coastline (TG19-32) after the earthquake. In theMeghna estuarine and Chittagong coast line tsunami arrived approximately 4.0-7.0 hours after theearthquake except case05 and case06.

6.00

Case1
Case3
Case5
Case7
Case98.00

Case2
Case4
Case6
Case8
Case10

Tsunami Travel Time (hour)

7.00

5.00
4.00
3.00
2.00

Case01
Case02
Case03
Case04
Case05
Case06

7.00
6.00
5.00
4.00
3.00
2.00

1.00

1.00

0.00

0.00
TG01
TG03
TG05
TG
07
TG
09
TG
11TG
13TG
15TG
17TG
19TG
21TG
23TG
25TG
27TG
29TG
C. 31Bazar
TG
35TG
37TG
39TG01
TG03
TG05
TG
07TG
09
TG
11TG
13TG
15TG17TG
19TG
21TG
23TG
25TG
27TG
29TG
C. 31Bazar
TG
35TG
37TG
39Tsunami Travel Time (hour)

8.00

Tide Gauge Stations

Tide Gauge Stations

Figure 10 Tsunami Travel Times at 39 Outpoints along theBangladesh Coast for 6 Cases of Scenario EQs (Mw 8.5).

Figure 9 Tsunami Travel Times at 39 Outpoints for 10Cases of Scenario EQs (Mw 8.0).

5

CONCLUSION
In this study three source models were considered, mainly, the 2004 Sumatra tsunami source, scenario
earthquakes with Mw 8.0 sources (10 cases) and Mw 8.5 sources (6 cases) from Bangladesh coast to
Andaman Island along the assumed trench axis to assess the tsunami hazard on Bangladesh coast.
Tsunami height rose highest 0.31 m for Sumatra case, 1.1 m for case9 and 1.84 m for case05
of scenario earthquakes with Mw 8.0 and Mw 8.5, respectively. The maximum tsunami height rose over
50 cm for case7-10 and case03-06 of scenario earthquakes with Mw 8.0 and Mw 8.5, respectively. The
area with the maximum tsunami height of over 50 cm was limited along the Cox’sbazar-Chittagong,
the Meghna estuarine, and in the western part of the coast. It can be mentioned here that the limitations
were due to existence of tsunami source nearby the area and the direction of principal tsunami from thesource.
Tsunami first arrived within 2.2 hours after the earthquake at St. Martin Island for Sumatracase, spending no time for 3 sources (Case8-9) and 2 sources (Case05-06) of scenario earthquakes
with Mw 8.0 and Mw 8.5 respectively. In general tsunami arrived earlier in the south and south-easternpart of the coast than western and Meghna estuarine part of the coast for most of the cases except
case10 and case06 of scenario earthquakes with Mw 8.0 and 8.5, respectively. For those 2 cases
tsunami arrived earlier spending no time at Meghna estuarine part than other part of the coast. It can beassumed that if earthquake takes place in future with Mw 8.0 or Mw 8.5 at the sources described before
tsunami will not take time to reach Meghna estuarine, Chittagong and Cox’sbazar cost of Bangladesh.
Finally, considering the existence of Arakan trench, seismic gap and results of tsunamisimulation it can be assumed that those sources (case8-9 and case05-06 of scenario earthquakes with
Mw 8.0 and Mw 8.5, respectively) may appear as threat to local tsunami at Bangladesh coast in future.
The residents of these coastal areas will not get enough time to take shelter and escape from thedevastation of the first wave of local tsunami.

ACKNOWLEDGEMENT
I am very much grateful to my advisor Dr. Bunichiro Shibazaki, IISEE for his heartiest andspontaneous supports to provide some of relevant literatures and suggestions for many improvements
in terms of tectonic setting and assuming the sources of scenario earthquakes in this study. I would liketo extend my gratitude to Professor Fumihiko Imamura, Disaster Control Research Center of Tohoku
University, Japan; Professor Nobuo Shuto, Advanced Research Institute for the Sciences andHumanities (ARISH) of Nihon University, Japan and to Dr. Kenji Satake of Active Fault ReseachCenter, AIST, Japan supporting me in terms of research ideas. I also acknowledge my indebtedness toProfessor Sifatul Quader Chowdhury, Professor Syed Humayun Akhter and Professor Aftab AlamKhan, Department of Geology, University of Dhaka for their kindest supports and suggestions for thisstudy.

REFERENCES
Aung, T. T. et al., 2006, Annual Report on Active Fault and Paleoeartquake Researches, 6, 171-188.
Okal, E. A., 2006, Lecture Notes, UNESCO-IOC Int. Trg. Course, 2006, Ostend: Belgium.
Fujii, Y., and K. Satake, 2007, Bull. Seis. Soc. America, Vol. 97, No. 1A, 2007.
Khan, A. A., 2005, Key Note Paper, Bangladesh Geographical Society, University of Dhaka.
Nielsen, C. et al., 2004, Marine Geology, 209, 302-327.
Okada, Y., 1985, Bulletin, Seismological Society of America, 75, 1135-1154.
Socquet, A. et al., 2006, Journal of Geophysical Research, Vol.111, No.B4, 2215.

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