STUDY ON TSUNAMI NUMERICAL MODELINGFOR MAKING TSUNAMI HAZARD MAPSIN INDONESIA
Athanasius Cipta*
MEE07172

Supervisor: Fumihiko IMAMURA**
ABSTRACT

Five source models along west coast of Sumatra and one for the south coast of Java were conducted
for tsunami simulations. Based on those results, waveform characteristics were analyzed. We chosethe west coast of Sumatra for waveform analysis because the coast has variation in water depth,morphology and shoreline shape.
For making tsunami hazard map, we chose source parameters from the 2006 south Java tsunami
event. The target area is Pangandaran Peninsula, one of the most damaged areas attacked by the 2006
event. We will compare the simulation results with the field survey results by Kongko et al. (2006).
We want to know how appropriate the simulation results are for the tsunami earthquake event.
To simulate near field tsunami propagation, numerical modeling was used. We considerednested areas, in limited area around Padang (Sumatra cases) and Pangandaran (Java case). Fromsimulations, we got results such as tsunami waveforms, run-ups, tsunami heights and inundations.
Based on these results, field surveys, and some pictures taken from AMS (American Marine Survey)
and Google Earth, we made tsunami hazard maps.
Keywords: Tsunami, Simulation, Inundation, Hazard Map.
INTRODUCTION
The northern Sumatra and the south coast of Java Island were hit by tsunamis which led to wave runups and landward inundations. The devastation at any particular location is caused by a function of thevelocity, acceleration, and elevation of the water as it interacts with natural and man-made coastal
objects. Clear understanding of tsunami wave behavior is indispensable to tsunami hazard assessment.
Decisions affecting human safety require systematic methods for evaluating the tsunami events.
DATA AND METHOD OF COMPUTATION
Bathymetry and Topography Data
Bathymetric and topographic spatial data are the basic data for tsunami simulation, as we know
tsunami wave propagates over the sea bathymetry and when tsunami wave inundates inland, floods
over land topography.
For Sumatra cases, we used GEBCO (GEneral Bathymetric Chart of the Ocean) 1 arc min
bathymetry for region1, nautical chart 20 arc seconds for region 2 and nautical chart 5 arc seconds forregion 3. SRTM (Shuttle Radar Topographic Mission) is also used for topographic data in region 3.
For Java case, GEBCO is used for both of the bathymetric and topographic data. We used 1 arc
min grid size of bathymetry and topography for region 1 and grid size of 15 arc seconds for region 2.
∗

Volcanological Survey of Indonesia
Professor, Disaster Control Research Center, Tohoku University, Japan.

∗∗

1Tsunami Simulation
Tsunami simulation is recognized to be an essential tool to explain the observations and records of atsunami (tsunami heights, travel times etc.), and to assess tsunami hazard, vulnerability and risk.
Tsunami simulation can be used to provide tsunami assessment and prediction of arrival times,
expected wave amplitude and coastal effects.
For these purposes we use tsunami simulation program named TUNAMI code, developed by
Tohoku University (Imamura et al., 2006; Koshimura, 2008) and the Boussinesq approximation model.
Cartesian coordinate system will be used in numerical simulation and the shallow water theory withbottom friction in the near-shore region in which water depth is shallower than 50 m (Nagano et al.
1991).
The most popular stability criterion is Courant-Friedrich-Levy number (C.F.L. condition) whichstates that the time step must be smaller than the time it takes for a wave to propagate from one grid
point to the next. Spatial and temporal grid sizes are set to satisfy this stability condition in the
numerical computation to avoid instability results.
The fault size parameter such as length, width, and slip amount (dislocation) can be determinedby using scaling law theory for dip-slip fault in subduction region (Papazachos et al., 2004). Scaling
law is useful for calculating fault parameters which is controlled by magnitude (Mw).
For Sumatra cases, we assumed four sources at 102.1oE and 6.39oS (fault 0), 100.25oE and4.25oS (fault 1), 98.48oE and 2.14oS (fault 2), 96.71oE and 0.03oS (fault 3). All the cases haveparameters: Mw 9.0, fault length 575.44 km, fault width 144.54 km, slip 2.5 m, top depth of fault 10km, strike 320o, dip 10o and rake 12o. Fault 4 is assumed at 100.0oE and 1.0oS with the fault
parameters: Mw 8.5, fault length 300 km, fault width 79 km, slip 6.0 m, top depth of fault 10 km,
strike 320o, dip 10o and rake 12o, although the fault 4 is not a realistic case and only for simulation.
Tsunami propagation was calculated for 24 assumed tide gauge (TG) stations as outpoints along thewest coast of Sumatra. Tsunami sources from fault 2 and fault 3 are used because of the biggest effects
to Padang City (target area) and Mentawai Islands, off Padang shoreline.
For Java case, we assumed an earthquake source at 107.82oE and 10.285oS, Mw 7.7, fault length
80.9 km, fault width 40 km, slip 2.5 m, depth of fault 20 km, strike 289o, dip 10o and rake 95o(Yukselme, 2006). Tsunami propagation was calculated for 13 assumed TG stations, along theaffected area by the 2006 South Java tsunami.
RESULT AND DISCUSSION
Sumatra Cases
Tsunami Wave and Water Depth
Figure 1 shows the location of TGs and assumed
faults. Each TG is located at the different depththat will affect to calculated tsunami waveform.
In the shallow sea, amplitude of tsunami
wave is getting higher, wavelength and celerity
are decreasing. Figure 2 right (shallow water)shows that amplitude is higher than in Figure 2
left (deep sea). These oscillations are the resultof reflection. Padang TG is located inside thechannel, between mainland and islands arc westof Sumatra, tsunami wave that goes inside thechannel approaches mainland and is trapped
inside the channel. Direct wave resonances withreflected wave, second reflected and so on. In
this case shoreline acts as wave reflector.
Figure 1. Location of the assumed faults.

2

Fault2, Mw 9.0

Fault 2, Mw 9.0

pariaman3

painan3

Padang

0.06

4

0.04

3
amplitude (m)amplitude (m)padang3

0.02
0
-0.02
-0.04

PainanPariaman

2
1
0
-1
-2
-3

-0.06
0

50

100

150
200
time (sec)

250

300

0

350

50

100

150

200

250

300

350

time (sec)Figure 2. Tsunami waveforms affected by water depths, calculated at Padang, Painan and Pariaman TGs.
Tsunami Wave and Seafloor Morphology
Figure 3 shows different tsunami waveforms, affected by seafloor variation. Sibarubaru TG is facing
to the open sea and located at shallow water. This conditions cause tsunami wave has higher amplitude
and shorter period. The first incoming tsunami wave was not the maximum tsunami, the maximum
one came later. The amplitude and period of tsunami wave changed after 225 min and amplitude
became lower and period became shorter. After 275 min, amplitude and period increased and tsunami
wave reached the maximum in height. The complexity of seafloor morphology causes oscillation wave,
amplitude change and period change.
MarlboroughFault 2, Mw 9.0

Sibarubaru Is.
Fault 2, Mw 9.0

amplitude (m)amplitude (m)

1
0.5
0
-0.5
-1
-1.5
-2
0

50

100

150

200

time (sec)

250

300

350

2
1.5
1
0.5
0
-0.5
-1
-1.5
-2

amplitude (m)

1.5

0

50

100

150
200
time (sec)

250

300

350

Pjg Saibi
Fault 2, Mw 9.0

8
6
4
2
0
-2
-4
-6
-8
0

100

200
time (sec)

300

Figure 3 Tsunami waveforms calculated at Sibarubaru Island, Marlborough and Pjg. Saibi.
Sibarubaru is located at the southernmost
2000
1000
of this passage, facing directly to the open sea
Sibarubaru
Sea Leveland Marlborough is located at the southernmost -10000
Marlboroughof the passage (Figure 4). Tsunami wave hits -2000
Sibarubaru and rapidly attenuates. After 150 -3000-4000
Vertical scale 1 : 158,000
min, amplitude of tsunami wave becomes lower -5000
Horizontal scale 1 : 4,560,000
-7
-6
-5
-4
-3
-2
-1
and lower. Marlborough TG shows that wave -6000
Latitudeperiods changes by time, from 100 to 150 min Figure 4 Cross section Sibarubaru-Marlborough,period is larger than before. After 150 min, passage between Sibarubaru and Marlborough.
period becomes smaller and increases again
after 250 min. First tsunami wave went inside
passage, hit Sumatra Island, reflected and resonance with next incoming tsunami wave. Amplitude oftsunami wave does not attenuate rapidly because tsunami wave is trapped inside the passage.
In front of Pjg. Saibi TG, there are 2 sea ridges, both on the right and left side, form a passage,
hereupon, tsunami wave is concentrated in this passage and propagate to Pjg. Saibi. After 150 min,tsunami wave amplitude tends to decrease and becomes lower gradually.
Tsunami Wave and Shoreline ShapeMaximum tsunami height varies depending on the location of each TG. Different location gives
different result as shown in Figure 5. In Padang, tsunami wave amplitude was slightly lower than in
Pariaman and Painan because Padang TG is located at the straight coast line, although Pariaman is
located at straight coastline but at the shallower water than Padang TG.
Maximum tsunami heights in Pariaman and Painan do not show significant difference even3though these cities are located in different shoreline shapes. Pariaman is located in straight shoreline
and Painan is located inside the shallow circular bay. Even Painan is located inside the bay, but
tsunami wave did not concentrate in this bay because this bay is too wide and beach slope is too steep.

Figure 5. Tsunami waveforms calculated in Pariaman, Padang and Painan TGs.
Tsunami Wave and Location of Fault
Tsunami wave calculated in Afulu TG has
Afulu (Nias)very high amplitude for fault 3 case. One
Afulu (Nias Is.)
Fault 2, Mw 9.0
Fault 3, Mw 9.0of the reasons is that the position ofearthquake source is located parallel toAfulu, and tsunami wave propagated fromsouth to the north, then many times
tsunami waves reflected on beach of
Sumatra, reflected wave resonance withlater incoming wave and produced higher Figure 6. Tsunami waveform recorded in Afulu TG.
amplitude wave. Figure 6 shows thatmaximum tsunami height came later andtsunami wave did not attenuate rapidly.
Tsunami wave has short period because it propagated in shallow water. Tsunami wave did notattenuate rapidly because the reflected wave came, reflected and came again and sometimes maderesonance with later incoming wave
15

4
3
2
1
0
-1
-2
-3
-4

a m p litu d e (m )am p litu d e (s )

10

5
0

-5

-10
-15

0

50

100

150
200
time (sec)

250

300

350

0

50

100

150
200
time (sec)

250

300

350

Java Case
Tsunami Travel Time
Tsunami travel time (Figure 7) is time between earthquake
occurrence time and tsunami wave arrival time. The shorter thetsunami arrival time, the nearer the coastal area, many evacuation
facilities should be built. Tsunami travel time is important also forpeople to decide to evacuate themselves as soon as possible.
Tsunami wave hit Pangandaran about 30 min after theearthquake occurred. If tsunami early warning was issued 5 minafter the earthquake, it would mean that people near coastal area
have only 25 min for evacuation.

Figure 7. Tsunami travel time.

Inundation Area
Naturally, inundation area breadth is controlled by tsunami height, force of tsunami, inlandmorphology, and stream pattern. Variation of feature of earth surface gives various possibilities forinundation.
The coastal areas are lying below the mean waterline due to its down sloping characteristics.
Furthermore, the back water system is generally running parallel to the shoreline and the coastal areas
are like a narrow lane of land (barrier beach) lying between the backwater and sea. This condition
caused tsunami inundated farer and wider inland because tsunami wave inundated through streamline.

4

Maximum Inundation Height
Maximum inundation height is controlled by shoreline shape and beach slope. Figure 9 and 10 show
maximum inundation heights. Maximum inundation height got up to 1.32 m in Nusa Kambangan thatis located perpendicular to the fault length.

Figure 10. Inundation heights
at several villages.

Figure 9. Maximum inundation heights.

Tsunami Hazard Map
Tsunami hazard map contains information about damages of tsunami, affected area, emergency
information, other information and graph, depend on purpose.
In tsunami hazard map, we put some important area that may be inundated, like business center,
airport and area with special feature that could be flooded by tsunami wave higher than other area. We
also put tsunami waveform and tsunami height in some TGs. Based on simulation data such as,
waveform, travel time, inundation height, and another data, such as survey data, photograph, map
image, we can make tsunami hazard map (Figure 11).
Some pictures in Pangandaran tsunami hazard map (Figure 11) show interesting places thatwere attacked by the 2006 tsunami. Pangandaran coast, the most valuable tourism destination in WestJava Province is the interesting place that was attacked by tsunamis twice in last hundred years (Tedy
Eka Putra, LIPI, personal communication). Based on field survey (Kongko et al., 2006), 2 tsunami
deposit layers are found in Cikembulan Village, Pangandaran.

Figure 11. Example of tsunami hazard map, Pangandaran area, West Java Province.

5CONCLUSION
In this study non-linear theory model based on nested grid system computations of tsunami
propagation is conducted. The precise and finer (< 3 arc seconds) bathymetry and topography data areimportant as basic input for simulation, especially for complicated shoreline shape.
Tsunami height at tide gauge stations, tsunami travel time, inundation height and inundation
area are some of many factors to be considered in making tsunami hazard map. Tsunami hazard map isthe first step in effort to minimize tsunami disaster.
FUTURE WORKS
There are still broad possibilities to improve tsunami simulation based on the nested grid systemtechnique in this paper. The important things to be done in the future are:
• Improvement of computed results for tsunami travel times, tsunami heights and inundation
heights in the model, the detailed and accurate bathymetry data is essential for tsunami
numerical computation.
• Improvement of modeling by using more accurate and effective input source parameters.
• Topography data should be concerned in the numerical computation where interaction with thestructure as well as vegetation or buildings should be taken into consideration in calculation oftsunami coastal effect.
ACKNOWLEDGEMENT
We would like to express our sincere gratitude to advisor Dr. Y. Fujii of IISEE, BRI for continuous
support, valuable suggestion and guidance during study.
REFERENCES
Imamura, F., et al., 2006, Tsunami Modelling Manual (TUNAMI model).
Mofjeld H.O., 2000, Analytic Theory of Tsunami Wave Scattering in the Open Ocean with
Application to the North Pacific, NOAA Technical Memorandum OAR PMEL-116.
Kongko, W., et al., 2006, Rapid Survey On Tsunami Jawa 17 July 2006, BPDP-BPPT & ITS.
Koshimura, S., 2008, Lecture Note on Theory of Tsunami Propagation and Inundation Simulation,
IISEE/BRI.
Nagano, O., et al., 1991, Natural Hazards 4, 235-255.
Papazachos B.C., et al., 2004, Bulletin of the Geological Society of Greece vol. XXXVI, 2004,
Proceedings of the 10th International Congress, Thessaloniki.
Yukselme D., 2006, July 17, 2006 Indonesia Java Tsunami, Middle East Technical University, Civil
Engineering Department, Ocean Engineering Research Center, Ankara.

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