Synopses of Master Papers

Bulletin of IISEE, 47, 133-138, 2013

STUDY ON TSUNAMI INUNDATION SIMULATION IN
THE NORTHWESTERN COAST OF SABAH,MALAYSIASiti Nurhaida Basri ∗MEE11624

Supervisor:

Yushiro FUJII ∗∗Bunichiro SHIBAZAKI∗∗
Hideaki YANAGISAWA∗∗∗ABSTRACTTsunami simulations and inundation analyses are conducted on the northwestern coast ofSabah by assuming earthquake along the Manila Trench (MT) proposed by Salcedo (2010). TUNAMI(Tohoku University’s Numerical Analysis Model for Inverstigation) code is used. To calculate tsunami
propagation and inundation we perform numerical simulations of linear and nonlinear shallow water
wave equations in a spherical coordinate system with four different spatial grid sizes of 60, 20, 6.6667
and 2.2222 arc-sec. As output points, 24 tide gauge stations are assumed along Kudat coastal areas.
Seven scenarios with different moment magnitudes are considered to perform tsunami simulations.
Earthquake source regions are divided into four segments, MT1, MT2, MT3, and MT4. Single andmulti segmentation are used to assess the scenario earthquakes for all three target areas, Kudat
Peninsula, Balambangan Island and Banggi Island. Computation results show that the tsunami heights
are larger with large slip on the fault. We found that the slip on the segment MT1 is not sensitive forthe tsunami height to the coastal area of northwest Sabah. We also found that the most significant
tsunami is expected from MT4, as well as MT3 and MT2 cause large tsunamis.
Keywords: Scenario earthquakes, Manila Trench, Tsunami height and travel time, Inundation, Sabah,Kudat.

1. INTRODUCTION
Seismic zones in Indonesia and the Philippines bordering Malaysia are active with frequent
earthquakes and have significantly put Malaysia at risk of earthquakes from far field. Since theconvergence rate related to the subduction zone of the Manila Trench is high, the potential of larger
tsunamigenic earthquakes cannot be neglected. Megathrust earthquakes from the Manila Trench withlarge scale of magnitude 9.0 or greater can lead to an extremely large thrust fault that could generate awidespread tsunami which can cause tsunami to reach the northwestern part of Sabah.

2. DATA
Bathymetry and Topography Data
Bathymetry data are obtained from General Bathymetric Chart of the Oceans (GEBCO)∗Malaysian Meteorological Department (MMD), Malaysia.
International Institute of Seismology and Earthquake Engineering(IISEE), Building Research Institute (BRI),Japan.
∗∗∗Tohoku-Gakuin University, Japan.
∗∗

(https://www.bodc.ac.uk/data/online_delivery/gebco/) of 30 arc-second grid size and from digitizednautical chart (Ridzuan, 2010) for the finest computational regions. Topographic data were obtained
from Shuttle Radar Topography Mission (SRTM) for all three selected target areas, Kudat Peninsula,
Balambangan Island and Banggi Island.
Scenario Earthquakes and Computational Dimensions
Seven scenarios are considered to perform tsunami simulation for all three target areas. From the studyby Salcedo (2010), earthquake source region in the Manila Trench (MT) is divided into four segments,
MT1, MT2, MT3 and MT4 given by Bautista (2001), as shown in Figure 1. Table 1 shows the list of
scenario earthquakes using single fault and multi segmentations for this study. The top depth for all
scenarios is assumed to be 0 km. We used a nested grid system with four layers (Figure 1). The grid
sizes used for regions Region 1 (R1), Region 2 (R2), Region 3 (R3) and Region 4 (R4) are 60, 20,6.6667 and 2.2222 arc-second, respectively. Temporal grid size (∆t) of 1.0 s is used to stabilize thenumerical computation. Total duration of calculation is 480 min with 28,800 number of time steps.

Figure 1. Earthquake source region in the Manila Trench (MT) andcomputational domain Regions 1 (R1), 2 (R2), 3 (R3) and 4 (R4a, R4b, R4c).
Scen.

SingleSegmentation

1a1b1c

MT4
MT4MT4Table 1. Parameters for the scenario earthquakes.
Mw
SlipScen.
Multi Segmentation
Mwamount(m)8.1
2.63
2aMT4+MT3+MT2
8.8
8.4
10.0
2bMT4+MT3+MT29.0
8.6
20.0
3aMT4+MT3+MT2+MT1 8.9
3bMT4+MT3+MT2+MT1 9.1

Slip amount(m) for allsegments
10.0
20.0
10.0
20.0

Figure 2 shows the 24 tide gauge stations along target coastal area settings for computational
dimensions in each region.

Figure 2. Tide Gauge location along coastal area Kudat Peninsula for R4a (left),
Balambangan Island for R4b (center) and Banggi Island for R4c.

3. THEORY AND METHODOLOGY
3.1. Shallow Water Equations (SWE)
Governing equations in linear shallow water with spherical coordinate system are expressed by(Nagano et al., 1991)∂MgD ∂η1  ∂M∂η∂
(1)+− fc N = 0( N cos θ ) = 0++∂t
R cos θ ∂λ∂t R cos θ  ∂λ ∂θ∂N gD ∂η++ fcM = 0∂tR ∂θ
The momentum equations in non-linear shallow water with spherical coordinate system are expressedbygD ∂η∂M∂ M2 MN  gn 211∂ 
 +++M M2 + N2 =0 cos θ+∂tR cos θ ∂λ R cos θ ∂λ  D  R cos θ ∂θ D  D 7322gD ∂∂N(cos θη ) + 1 ∂  cos θ N  + 1 ∂  MN  + gn7 N M 2 + N 2 = 0+
∂t R cos θ ∂θ
R cos θ ∂λ D  R cos θ ∂λ  D  D 3(2),where θ is latitude, λ is longitude, M and N are discharge fluxes in the direction of latitude θ andlongitude λ, D is the still water depth, η is the elevation of the water surface, g is the gravitational
acceleration, R is the radius of the earth, f c is Coriolis parameter of f c = 2ω sin θ, ω is the rate ofangular rotation and n is Manning’s roughness (n = 0.025 in this study).

4. RESULTS AND DISCUSSION
4.1. Seafloor Deformation
Sea surface deformation is assumed as the instant uplift or subsidence of the seismic deformation of
the sea floor. Figure 3 shows the initial tsunami height for some scenario earthquakes.

Figure 3. Seafloor deformation as initial tsunami height for Scenarios 1a (left), 2a(middle) and 3a (right). Contour interval of surface deformation is 0.2m.
4.2 Maximum Tsunami Heights and Tsunami Travel Time4.2.1 Region 4a - Kudat Peninsula
The maximum height of 1.6 m occurs at KDT2 for Scenario 2b and 1.4 m at KDT1 for Scenario 3b.
For the worse case scenarios of moment magnitude Mw more than 9.0, all tide gauge stations record
high tsunami waves of more than 0.8 m. Figure 4 shows the maximum tsunami heights and tsunami
travel times at all tide gauge stations in Kudat Peninsula corresponding to all the scenarios.

Figure 4. Maximum tsunami heights at tide gauge stations for all earthquake scenarios in R4a ( left)
and tsunami travel times (right).
4.2.2 Region 4b – Balambangan Island
Figure 5 shows the maximum tsunami heights and tsunami travel time at all tide gauge stations inBalambangan Island corresponding to all the scenarios. The maximum wave height calculated for
Scenario 2b and 3b are 2.7 m and 2.6 m, respectively, at tide gauge station BLM8.

Figure 5. Same as Figure 4, but in R4b.
4.2.3. Region 4c – Banggi Island

The maximum wave height for Scenarios 2b and 3b is about 1.8m at station BGG2. Figure 5 shows themaximum tsunami heights and tsunami travel times at all tide gauge stations in Banggi Islandcorresponding to all scenarios.

Figure 6. Same as Figure 4, but in R4c.
4.3.Inundation Area
4.3.1 Region 4a – Kudat Peninsula
Figure 7 shows three selected locations namely Kudat Airport, Tanjung Kapor and Kampung Air. For
the Scenario 3b, the highest inundation 1.9 m reaches Tanjung Kapor, followed by Kudat Airport up to1.8 m and Kampung Air at 0.9 m. Kudat Airport is located at the open coast where direct tsunami
waves may approach. A narrower bay may cause greater amplification in the case of Tanjung Kapor.
Kampung Air which is more secluded and far from tsunami source, has lower result of the maximum
inundation height.

Figure 7. Location of target points and maximum inundation height for R4a. Red, blue andgreen corresponds to Tanjung Kapor, Kampung Air and Kudat Airport, respectively (left).
Region 4a (right).
4.3.2 Region 4b – Balambangan Island
Figure 8 shows two locations of the selected villages namely Kampung Kok Simpul and Kampung
Batu Sirih. For worst case Scenario 3b, Kampung Kok Simpul reaches the highest inundation height to
3.0 m and Kampung Batu Sirih at 1.3 m. Kampung Batu Sirih is located at open coast which direct
tsunami waves may approach the coast. It is also closest to the Philippines which may be the first area
to be affected by a megathrust earthquake tsunami. Tsunami inundation may be governed by theshoreline shape.

Figure 7. Same as Figure 7, but in R4b. Red and blue corresponds to Kampung KokSimpul and Kampung Batu Sirih, respectively.
4.3.3 Region 4c – Banggi IslandFigure 9 shows the location of the selected area Molbog village. For the worst case Scenario 3b,Molbog village reaches the highest inundation height to 1.68 m. Molbog Village is another selected
place located close to the Philippines at open coast, in which direct tsunami waves may approach thecoast.

Figure 8. Same as Figure 7, but in R4c. Blue corresponds to Molbog Village,respectively.
5. CONCLUSIONS
We found that the slip on the segment MT1 is not sensitive for the tsunami height to the coastal area ofnorthwest Sabah. We also found that the most significant tsunami is expected from MT4, as well as
MT3 and MT2 cause larger tsunamis. The result shows that under the worst case scenario, target
points Kampung Air, Tanjung Kapor and Kudat Airport located in Kudat Peninsula of Region 4a areaffected by the tsunami inundation with height of approximately 1 m or more. In Region 4b most areas
along Balambangan Island are significantly inundated with height of more than 1.3 m for thecatastrophic event of Mw 9.1. Balambangan Island located closest to the Philippines is the first
affected area with target point Kampung Kok Simpul, and is directly approached by tsunami waves.
Kampung Batu Sirih is affected with greater inundation height as its shoreline shape has bay along thecoast. Based on the result of tsunami simulation, the maximum inundation height more than 1.5 m wascalculated in target area Region 4c for the worst case scenario Mw 9.1. Molbog Village located at thenorthern part of Banggi Island is hit with direct tsunami waves as it is located at open coast.
REFERENCES
Bautista, B. C., et al., R. S., 2001, Tectonophysics, 279-310

Nagano, O., Imamura, F. and Shuto, N., 1991, Natural Hazards 4, 235-255
Ridzuan, M. A., 2010, GRIPS, Tokyo, Japan.1-36.
Salcedo, J. C., 2010, GRIPS, Tokyo, Japan. 1-38.