TSUNAMI SIMULATIONSFOR A PROTOTYPE OF TSUNAMI DATABASE
IN SOUTHWESTERN SUMATRA
Sugeng Pribadi ∗MEE06016

Supervisor :Yushiro Fujii**
Yohei Hasegawa***
Yosuke Igarashi***

ABSTRACTThe purpose of this study is to create a prototype of tsunami database for tsunami warning system. Firstly
we fix the locations of forecast and coastal points along the coast of Padang, Muarabunga and Bengkulu.
We also set the source points covering the deformation area of the 1833 Bengkulu, Sumatra earthquake(Mw 8.9) as the real case. The number of source points is 33 with 4 magnitudes (Mw 8.5, 8.0, 7.5 and 7.0)
and 2 depths (0 and 10 km) for each source point. The total number of computation is 231 for the source
points and 1 for the real case. We calculate a seafloor deformation due to the fault, which is assumed as
initial condition of tsunami source. For tsunami simulation, TUNAMI-N2 (Tohuku University’s
Numerical Analysis Model for Investigation of Near-field Tsunami, No-2) and TTT (Tsunami TravelTime) are used to obtain the estimation of tsunami heights and arrival times, respectively for quantitative
tsunami forecasting. The calculated tsunami heights by using Green’s Law show higher pattern than thoseat some coastal points and may give more realistic values for tsunami estimation. The computed results are
stored in appropriate file system for tsunami database. When an earthquake occurs, the values will beretrieved by the interpolation of the data from the database for the information of tsunami warning. We
have also made the message format which contains information of vulnerable coastal areas, predictedtsunami arrival times and tsunami heights.
Keywords: Tsunami Heights and Travel Times, Tsunami Simulation and Database, Tsunami Warning.
INTRODUCTION
Indonesia is one of the most seismically active countries. Some large earthquakes have generated tsunamis.
The huge tsunami generated by the 2004 Sumatra earthquake, caused more than 200,000 deaths. Since
2005, Indonesia Meteorological and Geophysical Agency (BMG) has been establishing Tsunami EarlyWarning System (TEWS) for giving fast warning by seismic auto-detection analysis. The system is still
under developing to reduce the false alarm. We refer to tsunami database by Japan Meteorological Agency(JMA) which contains tsunami simulation results to be used for tsunami warning system by calculatingtsunami heights and tsunami travel times from determined hypocenter.
Tsunami Simulation and Database∗Meteorological and Geophysical Agency (BMG), Jakarta, Indonesia
International Institute of Seismology and Earthquake Engineering (IISEE), BRI, Tsukuba, Japan***
Japan Meteorological Agency (JMA), Tokyo, Japan**1

The purpose of this study is to create a prototype of tsunami database. We select forecast and coastal
points as the output points along the coastal area, and then calculate a seafloor deformation due to fault,
which is assumed as initial condition (tsunami source). The tsunami simulation softwares of TUNAMI-N2
and TTT provide the estimation data of the tsunami heights and tsunami arrival times in those areas. Thenthe results are stored in tsunami database to be retrieved by interpolation method for tsunami warning
information.
Scope of Study Area
The scope of this study is coastal area of southwesternpart of Sumatra which covers the coordinates latitude 0°- 6° S, longitude 98° - 105° E (Figure 1). We concern thebig cities of Padang, Muarabunga and Bengkulu onsouthwestern coast of Sumatra, which are very close tothe 1833 Sumatra earthquake (Mw 8.9) source as theevidence of large tsunami may indicate high probabilityof tsunami in the future (Siripong, 2007).
METHOD OF ANALYSIS
Bathymetry Data

Figure 1 Location of 526 output points along
the coast of Sumatra and Java Islands withthe bathymetry grid contour of each city. Reddots are coastal points. Blue dots are forecast
points. Green lines box shows the site study.

The accurate bathymetric data is essential for tsunami
numerical simulation because the phase velocity oftsunami or long wave depends on the water depth. TheGeneral Bathymetric Chart of the Oceans (GEBCO) isavailable for global area and can provide the bathymetry
data for calculating tsunami travel times and waveforms.
The computation area is shown in Figure 1. The intervalof grid space is 1 arc-minute (∼1850 m).

Output points for Tsunami Simulation and Green’s Law
We fix the forecast points offshore along 50 m depth contour and coastal points near the land with random
interval distances. The total number of forecast and coastal points is 526 in 20 cities along west coast of
Sumatra and south coast of Java. The output point parameters include station name, latitude, longitude ongrid space. We concern only three vulnerable cities of Padang, Muarabunga and Bengkulu. The number ofoutput points is 33 for coastal points and 33 for forecast points.
We use the Green’s Law calculation to avoid the longer computational time with finer grid system.
The Green’s Law is needed to obtain the reliable tsunami heights for coastal point from that of forecast
point at the sea using energy conservation law along the ray (JMA, 2007). Tsunami height in the coast isdefined as,
H =4h1H1h, where H1 and h1 are tsunami height and sea water depth in the forecast point, H and h are tsunami heightand sea water depth in the coastal point.

2Source Points
We fix the source point which is located in thecenter of tsunami source area (fault). In thisstudy, we define the source points covering
seafloor deformation caused by the 1833
Sumatra earthquake as the real case. The
number of source points is 33 with 4
magnitudes (Mw 8.5, 8.0, 7.5 and 7.0) and 2
depths (0 and 10 km) for each source point.
The total number of computation is 231 for thesource points and 1 for the real case (Figure 2).
Initial Condition
An initial profile of tsunami source can beconsidered to be the same as a deformation ofsea bottom (Okada, 1985) due to earthquake.
We refer the source model by Borero (2006),
and Natawidjaja (2006) to determine the realcase fault parameters such as coordinate of thetsunami source point, depth and angle of strike,
Figure 2 Source points (green dots) location
dip and slip. For the real case, Natawidjaja
covering the crustal deformation area of the 1833
(2006) mentioned that the 1833 Sumatra
Bengkulu, Sumatra earthquake (Borero, 2006).
earthquake (Mw 8.9) had 3 subfaults with
Red triangles denote cities. Contour interval isdifferent rupture sizes. For the other 33 source
0.2 m. Red contour is uplift area. Blue contour ispoints, we used single segment. For the realsubsidence area.
case, all of the strike angles are parallel to thedirection of Sunda trench axis that is assumed as 325 degree from the north clockwise. All of the dip andslip angles are assumed as 10 and 90 degree, respectively. The depth of top left corner is 5 km. For eachsource point, we assume the same strike angle of 325 degree, dip angle of 45 degree, slip angle of 90
degree, and two depths of 0 and 10 km for top left corner.
For each source point to calculate fault parameter, we use Scaling Law is controlled by magnitude(Tatehata, 1997). The formulas are:log L = 0.5M w − 1.9 ,

W=L,2log U = 0.5M w − 1.4, where L is length (km), W is width (km), U is slip (m), Mw is moment magnitude.
For calculation of depth of fault center (DFC), we use depth of top left corner (TLC) of fault,
which is input of tsunami simulation. Here, δ is dip angle which is assumed as 45 degree. The equation isdefined as:
DFC = cos δ ⋅W+ TLC .
2Basic Equations
We use near field tsunami propagation theory in shallow sea (non-linear) with constant grids of Cartesian
coordinates. The governing equations of 2-D shallow water theory are denoted by two basic equations ofcontinuity and momentum equations (Koshimura, 2007) as follows.

3∂η ∂M ∂N++=0∂t∂x∂y∂η gn 2∂M ∂ ⎛⎜ M 2 ⎞⎟ ∂ ⎛ MN ⎞−M M2 + N2= − gD+ ⎜+⎟∂x D 7 / 3∂t ∂x ⎜⎝ D ⎟⎠ ∂y ⎝ D ⎠gn 2∂ ⎛ MN ⎞ ∂ ⎛⎜ N 2 ⎞⎟∂N∂η+− 7/3 N= − gD⎜⎟+
∂ x ⎝ D ⎠ ∂ y ⎜⎝ D ⎟⎠∂y D∂tη

M =∫−hM2 +N2ηudz = u (η + h) , N =∫ vdz = v(η + h) , D = h + η−h, where u and v are water particle velocities in the x and y directions, u and v are average velocities, D is
total water depth, h is water depth, η is water elevation, M and N are discharge fluxes in x and y directions,g is gravitational acceleration, n is Manning roughness coefficient, t is time.
TUNAMI-N2 and TTT
TUNAMI-N2 developed at DCRC (Disaster Control Research Center, e.g. Imamura et al., 2006), is thenumerical analysis model for investigating near field tsunami. In this study, we use grid interval (Δx, Δy)of 1850 m, gravity acceleration (g) of 9.8 m/s2, and maximum bathymetry depth (hmax) of 7,271 meter. We
set the time temporal interval (Δt) as 2 seconds which is less than CFL condition. This temporal interval isused to define sampling time of waveforms and snapshot time for tsunami movie files. We can calculate
maximum heights of tsunami at the output points.
TTT developed by Paul Wessel, Geoware, can calculate tsunami travel times using Huygen’s
principle on a geographic latitude and longitude grid of each output point derived from a suppliedbathymetric data such as GEBCO. By using TTT software, we can prepare the inverse refraction diagram
to calculate inverse travel time of tsunami from the coastal point to the source. It is useful to determine theexact and minimum value of tsunami travel times from each output point into the outermost part ofdeformation area. We only take the minimum value as the fastest travel time to the coastal point by “minmax” commands of GMT. We extract all tsunami travel times from whole inverse refraction diagrams ofall output points.
RESULT AND DISCUSSION
From all of the tsunami simulation results, we chose several cases as the samples. We choose thevariation data of tsunami heights and tsunami travel times in each coastal point depending on different
source points, then compare with the Green’s Law calculation.
For tsunami heights (Figure 3A), tsunami sources closer to the coastal area cause higher tsunami
heights. The source of ZE (2.0° S, 100.5° E) makes tsunami amplitude higher in Padang and some part ofMuarabunga coastal points. The real case source and ZG source (3.5° S, 101.5° E) cause high tsunami
amplitudes half of the coastal points in Bengkulu city. For tsunami travel times (Figure 3B), the most offar source points into the coastal point give longer times of tsunami travel. The source ZE and E (2.5° S,100.5° E) cause longer tsunami travel time into almost Bengkulu city coastal points and real case makelonger tsunami travel time into almost Padang city coastal points.
For tsunami heights of Green’s Law calculation, more closed coastal point to the source givehigher value, like as Bengkulu coastal point. For the real case (Mw 8.9), the Green’s Law heights (greenline) is more stable by giving higher tsunami heights. However, the coastal calculation of Muarabunga cityand some part Bengkulu city, show the deviation (Figure 3C). This data indicate that we could not use theGreen’s Law at some forecast points for tsunami warning issue.

4TSUNAMI TRAVEL TIME BY DIFFERENT SOURCES
MAX TSUNAMI HEIGHT BY DIFFERENT SOURCES
100890

7

REAL_Mw8.9_DFC65.780
REAL_Mw8.9_DFC65.76

N_Mw8.5_DFC39.6

70

E_Mw8.5_DFC39.64

ZE_Mw8.5_DFC39.6

ZF_Mw8.5_DFC39.6

3

TIME (min)HEIGHT (m)N_Mw8.5_DFC39.6

5

E_Mw8.5_DFC39.6

60
ZE_Mw8.5_DFC39.6

50
ZF_Mw8.5_DFC39.6

40

ZG_Mw8.5_DFC39.6

30

ZG_Mw8.5_DFC39.6

2

Real_Coast_Mw8.9_
DFC65.7

6.0

Real_Green_Mw8.9_
DFC65.7

HEIGHT (m)5.0

N_Coast__Mw8.5__
DFC39.6

4.0

N_Green__Mw8.5__
DFC39.6
E_Coast__Mw8.5__
DFC39.6

3.0

E_Green__Mw8.5__
DFC39.6

2.0

1.0

Bengkulu-12

Bengkulu-11

Bengkulu-10

Bengkulu-9

Bengkulu-8

Bengkulu-7

Bengkulu-6

Bengkulu-5

Bengkulu-4

Bengkulu-3

Bengkulu-2

Bengkulu-1

Muarabunga-9

Muarabunga-8

Muarabunga-7

Muarabunga-6

Muarabunga-5

Muarabunga-4

Muarabunga-3

Padang-12

Muarabunga-2

Muarabunga-1

Padang-11

Padang-10

Padang-9

Padang-8

Padang-7

Padang-6

Padang-5

Padang-4

Padang-3

Padang-2

0.0
Padang-1

Bengkulu-12

Bengkulu-9

Bengkulu-11

Bengkulu-8

Bengkulu-10

Bengkulu-7

Bengkulu-6

Bengkulu-5

Bengkulu-4

Bengkulu-3

Bengkulu-2

Bengkulu-1

Muarabunga-9

Muarabunga-8

Muarabunga-7

Muarabunga-6

Muarabunga-5

Muarabunga-4

Muarabunga-3

Padang-9

Padang-12

Padang-11

Padang-8

Padang-10

Padang-7

Padang-6

Padang-5

Muarabunga-2

COASTAL POINT

Figure 3 Tsunami heights and travel times
in each coastal area, where vertical bars aretsunami height in meter and tsunami travel
time in minute, horizontal bar is coastal
point. (A) Tsunami heights by different
sources. (B) Tsunami travel times bydifferent sources. (C) Tsunami heights ofcoastal and Green’s Law calculation bydifferent sources.

7.0

(C)

Padang-4(B)

TSUNAMI HEIGHTS OF COASTAL AND GREEN'S LAW CALCULATION BY
DIFFERENT SOURCES

Muarabunga-1

COASTAL POINT(A)

Padang-3

Padang-1

Bengkulu-12

Bengkulu-9

Bengkulu-11

Bengkulu-8

Bengkulu-10

Bengkulu-7

Bengkulu-6

Bengkulu-5

Bengkulu-4

Bengkulu-3

Bengkulu-2

Bengkulu-1

Muarabunga-9

Muarabunga-8

Muarabunga-7

Muarabunga-6

Muarabunga-5

Muarabunga-4

Muarabunga-3Padang-12

Muarabunga-2

Muarabunga-1

Padang-9

Padang-11

Padang-8

Padang-10

Padang-7

Padang-6

Padang-5

Padang-4

Padang-3

Padang-2

0
Padang-1

100

Padang-2

201

COASTAL POINTTSUNAMI DATA BASE
Database Storing and Interpolation Method
Originally data format of simulation results are in the text format. Then, we put the data in Excel fileformat as the first database storing system. We have to change the data into MySQL format referring toJMA’s tsunami data base. Then, the data should be put in hypocenter table. Each hypocenter data (hyppoint) has some values of latitude and longitude coordinate, focal mechanism, magnitudes, depths, andsimulation results. Each simulation result contains the estimation values of tsunami heights and tsunami
travel times for all coastal points. We can retrieve the interpolated result by searching four closest hyppoints surrounding a present determined hypocenter. The interpolation method consists of epicenter
location interpolation, magnitude-depth interpolation, maximum risk interpolation, and magnitude-depthextrapolation (Kiyomoto, 2007).
Tsunami Warning Information
We made a message format for tsunami warning information, which contains tsunami arrival times, andtsunami heights for all vulnerable coastal areas. Tsunami arrival time is used to know when tsunami willreach to the coastal area in the exact local time after present origin time of earthquake. Arrival time issummation of tsunami travel time estimation and origin time, which is shown as hours, minutes andseconds unit. The tsunami warning message contains several types of tsunami warning information whichbased on tsunami height (H) criteria. Those information are major tsunami warning (H ≥ 2 m), tsunami
warning (1 ≤ H < 2 m), and tsunami warning advisory (H < 1 m).

5CONCLUSION
In this study we have created a prototype of tsunami database. We chose the 1833 Bengkulu earthquake as
the evidence of large tsunami that occurred in southwestern coast of Sumatra. The study started fromfixing a mount location of forecast points and coastal points as the output points along the coast of Padang,Muarabunga and Bengkulu, then calculating a seafloor deformation due to fault that is assumed for initialcondition of tsunami source. Tsunami simulation using the tsunami softwares TUNAMI-N2 and TTT
provided the estimation data of tsunami heights and tsunami arrival times in those areas for tsunami
forecasting.
According to the result of analysis, we found that the coastal points which are far from the source
have the smallest tsunami height and the longest tsunami travel time. On the other hand, most of thetsunami sources close to the coastal area cause higher tsunami height. Tsunami travel times almost havethe similar values between different magnitudes and depths at the same source points. The calculated
tsunami heights by using Green’s Law show higher pattern than those at some coastal points and may give
more realistic approximation for tsunami estimation.
The computed results are stored in appropriate file system for tsunami database. When an
earthquake occurs, the values will be retrieved by the interpolation of the data from the database for theinformation of tsunami warning. We have also made the message format which contains information ofvulnerable coastal areas, predicted tsunami arrival times and tsunami heights. The tsunami warning
information gives early warning for evacuation and precaution.

ACKNOWLEDGEMENT
We thank to Dr. B. Shibazaki (IISEE), Dr. T. Hara (IISEE), Mr. M. Kiyomoto (JMA), and all lecturers fortheir guidance to complete this study.

REFERENCES
Borrero, J.C., et al., 2006, PNAS, U.S.A., 103, 52, 19673-19677.
Imamura, F., et al., 2006, TSUNAMI MODELLING MANUAL, DCRC, Tohuku University, Japan, 72pp.
Japan Meteorological Agency (JMA), 2007, Lecture Note of JMA, Tokyo, Japan.
Koshimura, T., 2007, Lecture Note of IISEE, Tsukuba, Japan, 19pp.
Kiyomoto, 2007, Lecture Note of JMA, Tokyo, Japan.
Okada Y., 1985, Bulletin Seismological Society of America, 75, 1135-1154.
Natawidjaja, D.H., et. al., 2006, Journal of Geophysical Research, 111, B06403, 37pp.
Siripong, A., 2007, ICUS Newsletter, The Univ. of Tokyo, Japan, 6, 4, 1-3.
Tatehata, 1997, Perspectives on Tsunami Hazard Reduction, 175-188.

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