NUMERICAL MODELING ANALYSIS FOR TSUNAMI
HAZARD ASSESMENT IN WEST COAST OF
SOUTHERN THAILAND
Sorot Sawatdiraksa∗
MEE07174

Supervisor: Fumihiko IMAMURA∗∗

ABSTRACTThis study is intended to know the tsunami effect on the west coast of southern Thailand frompotential fault locations in and around Andaman Sea. Four cases of fault were simulated as thetsunami source models. TUNAMI code (TUNAMI-N2) used to compute tsunami propagation in theocean. For large area (region 1), tsunami was computed using GEBCO 1 arc minute bathymetry bythe linear theory in spherical coordinate system with Coriolis force. Finer spatial bathymetry grids
resample from GEBCO, 15, 5 and 1.67 arcs second in small area, were used in regions 2, 3 and 4 andthe tsunami propagation was computed by the non-linear theory in Cartesian coordinate system withbottom friction term. Calculated tsunami heights and travel times were obtained at following output
points namely: two existing DART buoys, eight existing tide gauges, four TMD planning tide gauges
and forty assumed tide gauges.
The results of Case 1 from linear long wave numerical model have shown that tsunami wave
heights were larger than observed data. The results of the non-linear long wave numerical model
demonstrated a good agreement with the observed data for tsunami heights and travel times.
The results of numerical simulations have shown that the Thai DART buoy is useful toindicate a generation of tsunami. Tsunami arrived at the Thai DART buoy in Cases 1, 2 and 3 before
the other tide gauges. This result can be used to improve accuracy of tsunami warning system forpreventing false alarm. Moreover, maximum tsunami heights were larger in the Phangnga and Phuket
provinces then integrated countermeasures and city planning must be set up to prevent communities
along coastal line.

Keywords: Tsunami simulation, Potential earthquakes, Southern Thailand.
INTRODUCTION
The 2004 Indian Ocean tsunami has made us understand more about the characteristics of tsunami. As
the Indian Ocean tsunami occurred in technology age, new information and physical data of tsunami
image were observed from satellite altimeters, water level recorded by coastal tide gauge stationsaround Indian Ocean, tsunami inundation and run-up height measured by field survey including
waveforms recorded by many seismographs. However, lack of tsunami early warning system,
countermeasures and knowledge caused severe damages along the Indian Ocean coast.
Historical record of tsunami event in Thailand is unclear because there is no evidence ofPaleo-Tsunami and effect of tsunami. Some villages have legends related to tsunami events. Morgan
people who roam freely from one island to another of the Andaman Sea have been keeping theirlegend that they must escape to high ground when abnormal sea drag appeared. It is said that Morganpeople survived from the Indian Ocean tsunami on 26th December 2004.

∗Thai Meteorological Department, Thailand.
Disaster Control Research Center, Tohoku University, Japan.

∗∗1METHOD OF COMPUTATION FOR TSUNAMI HAZARD ASSESSMENT
To simulate tsunami propagation in the open sea, we used a linear equation to describe ashallow-water wave on the spherical earth with the Coriolis force, and to simulate tsunami in thecoastal zone and the inundation area, we used a non-linear equation in a Cartesian coordinate system
for a shallow-water wave with bottom frictions (Goto et al., 2007).
Target Area
We selected wider coarse grid area for far-field tsunami simulation. The position started from latitude
0º N to 25ºN and longitude from 75ºE to 110ºE. This area was called region 1 with bathymetry datafrom GEBCO (General Bathymetric Chart of the Oceans) and spatial grid size of 1 arc minute.
Computation domains in region 1 were 2101 x 1501 grid points and the temporal grid size was set to1.5 s which satisfied a C.F.L. stability condition and the computation time was 12 hours. Computation
domains in region 2 was 825 x 905 grid points which covered area between latitude 5º59’00”N to9º45’15”N and longitude 96º29’00”E to 99 º55’15”E with a finer spatial grid size of 15 arc seconds.
Region 3 with a finer spatial grid size of 5 arc seconds covered the area between latitude
7º45’25”N to 8º12’39”N and longitude 97º59’55”E to 98 º20’00”E, and had 241 x 325 grid points.
Region 4 with the finest spatial grid size of 1.67 arc seconds in this study focused on Kamala andPatong beach in Phuket province and covered the area between latitude 7º50’58”N to 8º00’00”N andlongitude 98º5’28”E to 98º19’00”E with 487 x 325 grid points. Non-linear long wave model withbottom friction term was used in region 2, 3, and 4. The coverage areas of region 1, 2, 3 and 4 areshown in Figure 1.

Figure 1. Computation area for numerical model regions 1, 2 (left) and regions 3, 4 (right).
Target Points
We calculated tsunami heights
and travel times at 54 stations
including the Thai DART buoystation and the Indonesia DART
buoy station. Eight tide gauge
stations are presented. Withinthese tide gauges, Taphaonoi andTarutao tide gauge stations wereoperated
byHydrographic
Department Royal Thai Navy.
Ranong, Kuraburi, Krabi, andKantang tide gauge stations wereoperated by Marine Departmentof Thailand. At four tide gauge

Figure 2. Locations of DART buoys (red stars), existing tidegauge stations (pink circles), and TMD planned installation tidegauge stations (blue triangles). Locations of virtual tide gauge
stations (red triangles) along the west coast of southern
Thailand.

2stations the installation is underway by Thai Meteorological Department. Another tide gauge stations
assumed along west coast of southern Thailand near the famous beaches and important residential
areas in the provinces. Locations of all tide gauge stations are shown in Figures 2.
Source Model in Andaman Sea
Fault parameters such as fault mechanism, location, and magnitude of earthquake are significant tomake generation of tsunami. Tsunami power is related to volume of water change which depends on
fault parameters of earthquake. We considered fault locations around Andaman Sea which potentiallygenerate tsunami along Sunda trench and Burma ridge. The source models include 4 cases namely;
Case 1 is real tsunami case of the 2004 Sumatra Indian Ocean tsunami in which fault model parameterfrom DCRC (Disaster Control Research Center, Tohoku University, Japan) were used. Magnitude forthis event was estimated to be 9.3 and its fault was divided into 6 sub faults. For second case, weconsidered height potential seismic gap in north Andaman Sea and the fault area was located fromnorthern part of Andaman Island along Sunda trench. The empirical formula introduced byPapazachos et al. (2004) was used to the estimate fault parameters for an assumed magnitude of 9.0.
The Same earthquake magnitude of 9.0 was used in Case 3. Location of fault along trenchline in western side of Andaman Island was similar to that of Fujii and Satake (2007). For Case 4,
historical earthquake records were used to provide fault parameters and assumed magnitude was 7.5 incentral Andaman Sea. Mechanism of fault was different from the other cases because it wascategorized in normal fault. All the fault parameters for four cases are shown in Table 1.
Table 1. Tsunami source parameters for scenario earthquakes in and around Andaman Sea
Parameter

Case 1Case 2

Case 3

Case 4Magnitude

9.3

9.0

9.0

7.5

Sub Fault

12

3

4

5

6---

Length (km)

200

125

180

145

125

380

575.4

575.4

77.6

Width (km)

150

150

150

150

150

150

144.5

144.5

25.1

Displacement (m)1412.6101177

9.55

9.55

3.80

Depth (km)1010101010103335

Strike (º)

3233353403403457258254

Dip (º)1515151515

15101056

Slip (º)

90

90

9090

90

90

90

115

-90

Latitude (ºN)

3.03

4.48

5.51

7.14

8.47

9.63

11.8

8.60

10.95

Longitude (ºE)

94.90

93.82

93.30

92.74

92.28

91.97

91.0

91.64

95.05

RESULTS AND DISCUSSION
Scenario Case 1
The first tsunami wave that reached to the Thai DART buoy (by23401) took approximately 27.75 minafter the earthquake. The wave was a positive wave with the maximum wave height of 1.055 m.
Miang, TMD planning station (tmd007) was the second tide gauge station where the first tsunami
wave arrived at approximate time of 62.25 min. Tsunami wave reached Miang station about 34.75 minlater than the Thai DART buoy. Simulated tsunami travels time for all the stations are shown in Figure
3.

3

350

300

First positive wave Travel time
Tsunami wave Travel TimeTime (min)

250

200

150

100

50

by23401
by53401
tmd006tmd007tmd008tmd009
md001
md002
md003
md004
md005
md006
ny001
ny002
tg102
tg103
tg104
tg105
tg106
tg202
tg203
tg204
tg205
tg206
tg207
tg208
tg209
tg210
tg302
tg303
tg304
tg305
tg306
tg307
tg308
tg309
tg310
tg311
tg312
tg313
tg402
tg403
tg404
tg405
tg502
tg503
tg504
tg505
tg506
tg603
tg604
tg605
tg606
tg607

0

Tide Gauge Stations

Figure 3. Tsunami travel times and first positive wave travel
times (Case 1).

Tsunamis propagate indeep sea faster than in shallow sea.
Therefore, waves reached the Thai
DART buoy in deep water before
they arriving at the other near shoretide gauges.
In this computation case,the maximum tsunami wave heightin far-field model was 15.419 m atKapoe Ranong stations (tg104) andin near-field model was 8.989 m at
Khao-lak Phangnga station (tg204).

Tsunami heights and arrival times: comparison between observed data and numerical result
The 2004 Indian Ocean tsunami was observed at six tide gauge stations in Thailand. Tsunami
waveforms comparisons between calculated data and observed data at existing tide gauges are shownin Figure 4. The results demonstrated that the tsunami of the far-field model reached to the Ranong,
Kuraburi and Kantang stations earlier than the observed data, but the tsunami travel times from
calculated data at Taphaonoi, Krabi and Tarutao stations are later than the observed data. For
near-field model, earlier tsunami wave reached to the Kuaraburi, Taphanoi, amd Kantang stations
before the observed data. However, simulated tsunami reached to the Krabi and Tarutao stations later
than the observed data.
Large bathymetry
grid size contains one valueof the depth, but it will havedifferent values when makea comparison with a finer
grid size in the same area.
When finer grid is used in
one large grid area, the same
area provides more detailed
values. Tsunami waves
which were computed by anon-linear model with afiner grid size and bottom
friction terms traveled faster Figure 4. Synthetic waveforms from far-field model (blue colors) andthan linear model with near-field model (green colors) compared with observed tsunami
larger grid size in a small waveforms (red colors) at existing Thai tide gauges for Case 1.
region. Wave turned toviscosity in large grid size that resulted in smooth waveform shape in far-field model.
Tsunami heights computed from the far-field model gave over estimated results comparedwith the observed data. However, computation results have shown a good agreement with observed
data in near-field simulation model. For tsunami propagation in the shallow water, where the depth isless than 50 m, bottom friction terms were included in model calculation. Selecting different
Manning’s roughness value for bottom friction terms can affect the computation result. The maximum
tsunami height can be higher or lower than observed data as well as difference of tsunami arrival times.
The results of the far-field model have shown that excluding bottom friction terms resulted overestimated tsunami heights compared with the observed data.

4Scenario Case 225

Latitude (N)Tsunami wave firstly reached to the Thai DARTbuoy about 38.5 min after the earthquake, which20
was 56.25 min earlier than the arrival at the secondtide gauges, Miang, TMD planning station. The first15
wave that reached to the Thai DART buoy was apositive wave with the height up to 0.256 m.
10
Tsunami wave reached to the Miang station at
approximate time of 94.75 min with the maximum
5wave height of 0.519 m. Kho-khao Island inPhangnga (tg203) has 2.769 m maximum wave
0height from far-field model simulation, which was
75
80
85
90
95
100
105110considered as the highest wave in Case 2. The
Longitude (E)result of the near-field model indicates the tsunami
height of 1.311 m at Khao-lak. The maximum wave
1.0
2.0
3.0
height distributions concentrate on Indian coastline
Height (m)and other sides as refracted to Myanmar coast.
Figure 5. Maximum wave height distribution
Tsunami energy was perpendicular to thein Indian Ocean after 12 hours (Case 2).
direction of the fault length. The initial wave wasseparated into two components and travelled to opposite directions. India is location perpendicular on
the major axis of the fault caused the maximum wave height at the coastal line as shown in Figure 5.
Tsunami wave can refract in both shallow and deep water. However, the effects of refraction would
become prominent near the coast because of the rapid decrease of depth towards the shore. This is oneof the reasons why tsunami energy was trapped in shallow water parts of Myanmar.
Scenario Case 3
8Similarly to Case 1 and Case 2,tsunami wave reached to the Thai
DART buoy firstly at approximate
30.5 min with positive wave andmaximum wave height of 0.479 m.
The second tsunami wave reachedto the Miang station within about
73.75 min. The maximum wave
height from the far-field tsunami
model appeared at Ban-thap-lamu
Tide Gauge Stations
Phangnga (tg205) with a height ofFigure 6. Maximum wave height in Case 3.
7.24 m as shown in Figure 6. The
result from the near-field model has shown the maximum height of 3.467 m at Kamala beach Phuket(tg305). The maximum wave height distribution shows energy concentration of India coastline and theopposite site, the north of west coast of the southern Thailand.
7Height (m)

6

5

4

3

2

1

by23401
by53401
tmd006tmd007tmd008tmd009
md001
md002
md003
md004
md005
md006
ny001
ny002
tg102
tg103
tg104
tg105
tg106
tg202
tg203
tg204
tg205
tg206
tg207
tg208
tg209
tg210
tg302
tg303
tg304
tg305
tg306
tg307
tg308
tg309
tg310
tg311
tg312
tg313
tg402
tg403
tg404
tg405
tg502
tg503
tg504
tg505
tg506
tg603
tg604
tg605
tg606
tg607

0

Scenario Case 4
The simulation results in this case were interesting because of the change of the first station’s location.
Tsunami wave arrived at the first station at Similan island station (tg210) in about 72 min, which wasvery close to 72.25 min, the arrival time at the Thai DART buoy. It took about 72.5 min to reach thethird station (Miang station) as shown in Figure 7. The maximum wave height distribution is alsointeresting because tsunami energy was released along large stretches of the coastline in the Andaman
Sea. The maximum wave height from the far-field model was 1.632 m at Kamala beach Phuket(tg305) and the wave height from the near-field model was 2.436 m at Naihan beach Phuket (tg309).

525

Latitude (N)

2015

10

5075

80

85

9095

100105

110

Longitude (E)Figure 7. Snapshots of a tsunami wave inCase 4 at time of 72 min after the earthquake.

The tsunami waves in three cases (Case 1,2, and 3) that reached to the Thai DART buoy atfirst were positive waves before they arrive atanother tide gauges. However, tsunami wave inCase 4 reached to another tide gauge before theThai DART buoys with negative wave.
The results of the four TMD planning tidegauge stations have indicated that tsunami wave
reached Miang Phangnga station earlier than theother stations. The first waves of tsunami thatreached to the four TMD planning tide gauge
stations were negative in all the cases. Themaximum wave height in Case 1 is larger than thatin the other cases and the smallest maximum wave
height was calculated in Case 4.

CONCLUSIONS
The results of TUNAMI model simulation with the sources around Andaman Sea have shown that thetsunami travel time and wave height in Case 1 gave good agreement with those from near-field model
when a comparison was made with observed data. Scenario simulation Cases 1, 2, and 3 presented
tsunami waves first reach to the Thai DART buoy before the other tide gauge stations. For TMD
planning tide gauge, tsunami first arrived at Miang stations in all the cases.
Even if tsunami cannot be prevented or precisely predicted but damages can be reduce throughundertaking various countermeasures and mitigation plans. Moreover, integrated measures are needed
to take in to account the achievement of the mission. Adjusting integrated countermeasures must be
considered for a suitable area with maximum efficiency. As the results of this study, tsunami heights
were larger in Phangnga and Phuket provinces. Therefore, people who live in these areas and along
coastal line should be protected from tsunami disaster by the government.
Because the simulated tsunamis reach to the Thai DART buoy at first as mentioned in theresult, we can use the Thai DART buoy data as reference in order to assure generation of tsunami forpreventing false alarm for tsunami early warning system. However, we must be careful about its use
for some cases because in Case 4 the tsunami reached to some tide gauges before the Thai DARTbuoy.
AKNOWLEDGEMENT
The author would like to express thanks to Dr. Yushiro Fujii, my advisor for reviewing themanuscripts and giving valuable comments.
REFERENCES
Fujii, Y., and K. Satake, 2007, Bulletin of the Seismological Society of America, 97, S192-S207.
Goto, K., S. A. Chavanich, F. Imamura, P. Kunthasap, T. Matsu, K. Minoura, D. Sugawara, and H.
Yanagisawa, 2007, Sedimentary Geology 202, 821-837.
Papazachos, B. C., E. M. Scordilis, D. G. Panagiotopoulos, C. B. Papazachos, and G. F. Karakaisis,
2004, Bulletin of the Geological Society of Greece, Vol. XXXVI, Proceedings of the 10th
International Congress, Thessaloniki, April 2004.

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