UPDATING NUMERICAL SIMULATIONS FORTSUNAMI FORECASTING DATABASECONSIDERING SOURCES ALONG THE MANILATRENCHFatimah Zaharah Saleh
MEE10519

Supervisor:

Yushiro FUJII
Bunichiro SHIBAZAKI

ABSTRACT
We consider a method to update tsunami database in order to enhance the capability of Malaysia
National Tsunami Early Warning System. We identify the Manila trench to be the location of potential
earthquake sources which can generate a hazardous tsunami in South China Sea region and thesurrounding countries including Malaysia. The source points are located along the Manila trench with
4 depths (0, 10, 20 and 30 km). Fault parameters are set using a scaling law for 3 magnitudes ( 7.5,
8.0 and 8.5). Numerical simulations of tsunami propagation for 108 cases are performed using asoftware called TUNAMI-N2. Our target area is the coastal region of the east part of Malaysia, andforecast points are set along this area. There are two groups of forecast points; forecast points with afixed distance of 5 arc-minutes and forecast points along the bathymetry contour depth of 50 m. The*UHHQ¶VODZLVDSSOLHGLQRUGHUWRHVWLPDWHUHOLDEOHWVXQDPLKHLJKWVIRUWKHFRDVWDODUHD7KHUHVXOWVRI
the tsunami simulation showed similar tsunami waveforms pattern between the source points with thesame earthquake scenario. In terms of tsunami amplitude, the results indicate that higher tsunami
heights is originated from the source point with larger magnitudes. The factor of depth at the source
point also could contribute to the amplitude of tsunami height. This can be explained by the conditionof ocean bottom deformation. Finally, all the results will be additional information for the purpose to
update tsunami database.
Keywords: Tsunami height, source points, tsunami simulation, arrival time.

1. INTRODUCTION
Malaysia is located relatively close to the boundary between the Eurasian plate in the northern sideand the Australian plate in the southern side. Although the Malay Peninsula is located on a stable partof the Eurasian plate (Balendra et al., 2008), tremors are still felt due to large earthquakes from theactive seismic area of Sumatra and Andaman Sea. The Malaysia National Tsunami Early Warning
System, (MNTEWS) was established as national monitoring centre for all earthquake activities andtsunami around Malaysia. The implementation of tsunami database for the Malaysia National Tsunami
Early Warning system (MNTEWS) is needed to ensure a proper dissemination of tsunami warning.
Thus, updating the tsunami database has to be one of the purposes of this study. The numericalsimulation for the computation of tsunami propagation will be carried out and the results of thesimulation will be used as input data to be stored in tsunami database.

Malaysian Meteorological Department Malaysia.
International Institude of Seismology and Earthquake Engineering, Building Research Institude, Japan.

― 103 ―

2. DATA AND METHODOLOGY
2.1 Location of potential rupture area
We choose the Manila trench as a potential rupture area which can generate a hazardous tsunami inSouth China Sea region. According to the study by Kirby et al. (2006), there are 6 fault segments
identified along the Manila trench which are shown in Figure 1. According to the study, the coastal
regions of Malaysia are significantly affected by tsunamis generated from the fault plane segment E5.
Therefore we decided to choose the segment E5 as the location of source point. The fault parameters
for the segment E5 suggested by Kirby et al. (2006) are listed in Table 1.
Table 1: List of fault parameters suggested by Kirby et al.
(2006)

Figure 1. Suggested fault plane segments
along the Manila Trench (Kirby et al.,2006).

Fault

E5

Longitude center of fault (deg)119.6

Latitude center of fault (deg)

13.7

Length (km)140

Width (km)35

Strike (deg)320

Dip (deg)

22

Rake (deg)90

Slip(m)7.63

Magnitude (Mw)

8.0

2.2 Data
We used the bathymetry data from the General
Bathymetric Chart of the Oceans (GEBCO)
with a spatial grid size of one arc-minutewhich is equivalent to 1850 m. A source point
is defined as a center of tsunami source. The
area of source points covers from 12.67϶N to
14.83϶N and 118.33϶E to 120.67϶E (Figure 2).
The source points are set on the grid with adistance interval of 40 arc-minute ~ (74 km).
In Figure 2, there are 9 source points (redcircle) with three magnitudes (7.5, 8.0,
and 8.5) and 4 depths of center fault (DCF) (0,10, 20, 30 km) for each source point. A
location of buoy is set up as the buoy point forthis study which is located at longitude of
113.78϶E and latitude of 7.37϶N (yellow
triangle). The purpose of setting up the buoy
point is to observe early passing of tsunami
waves. Then for the forecast points, we
decided to form 2 groups; one is locatedparallel to coastal point with a fixed distanceof 5 arc-minute ~ 9.25km (purple circle) andforecast points which located along thebathymetry contour depth of 50 m (green
circle).

Figure 2. Locations of 9 source points (red circles), 1
buoy point (yellow triangle), forecast points with distance
5 arc-minute (purple circle) and forecast points of contour
depth of 50 m (green circle)― 104 ―

2.3 Initial condition

2.5 Scaling law

In tsunami numerical simulations, fault
parameters are parts of the inputs of a tsunami
source. Fault parameters consist of the values ofstrike angle, dip angle, slip angle,
length (L), width (W) and slip amount (U).
According to Satake (2008), the slip amount (U)has the largest effect on the vertical seafloor
deformation and the tsunami amplitude. The dip
angle and fault depth also contribute to control
the size of a tsunami. The fault parameters were
set up at the top left corner (TLC) in Figure 3. In
setting the strike angle, we need to consider the
direction of the trench axis. We put the strike of350϶ and 300϶ at source points parallel to thetrench axis. We set up the dip angle of 22϶ for a
purpose to update the information in a databasesystem and the slip angle is 90϶ considering theseverest case for tsunami generation.

A scaling law is used to determine the fault
parameters such as length L, width, W and slip
amount, U. The formula of the scaling law by
Tatehata (1997) is used for calculating the fault
parameters. The parameters of earthquakes canbe determined by the moment magnitude, Mw
and the scaling law formulas are expressed asfollows:

Table 2. Fault parameters with strike angle of 350϶ and dip
angle of 22϶.

*Depth of TLC had negative value and was forced to. zero

Figure 3. Fault plane parameters. Dotted line in
red indicates the depth of fault center (DCF)(Chai, 2008)

Table 3. Fault parameters with strike angle of 300϶ and dip
angle of 22϶.

In this study, we also categorized the magnitude
and depth into several cases for each source
point. The magnitude and the depth wereassumed based on historical earthquake records
from the Global Centroid Moment Tensor(CMT) catalog and the study by Liu et al. (2008)
about the potential tsunami hazards in the South
China Sea region. The lists of magnitude anddepth with fault parameters are shown in Tables
2 and 3.

― 105 ―

*Depth of TLC had negative value and was forced to zero

2.4 Numerical simulation by using TUNAMI-N2
TUNAMI-N2 (Tohoku UQLYHUVLW\¶V Numerical Analysis Model for Investigation of Near-fieldtsunamis, No.2) is used as a tsunami numerical simulation tool for this study, applying the shallow
water theory with the Cartesian coordinate system for calculating tsunami propagation. The process ofthe simulation requires several steps described by Fujii (2011). The area of computation covers from
102϶E to 123϶E in longitude and 1϶N to 21϶N in latitude with the grid points of 1260 and 1200
respectively. To stabilize the numerical computation, the temporal interval ( ) is set to 3s, satisfying
the C.F.L (Courant Friedrics Lewy) condition for stability criteria. The computation time is 8 hours
and the total number of simulation is 108 for all the source points.
*UHHQ¶VODZThe Green¶VOaw is used to estimate the height of tsunami at the coastal point from the forecast point at
the sea. 7KH*UHHQ¶VODZLVGHULYHGIURPWKHFRQVHUYDWLRQRISRWHQWLDOHQHUJ\DORQJWKHUD\ e.g. Satake,2008):

whereand
are the water depth at the coastal and the forecast point,tsunami at the coastal and the forecast point respectively.

andare the height of

3. RESULTS AND DISCUSSION
3.1 Different types of forecast points with
*UHHQ¶VODZ
Based on Figure 4, the tsunami heights at coastal
point between both forecast points are different.
The tsunami heights at coastal points from theforecast points with depth of 50 m depth arehigher than the results from forecast points at 5
arc-minute off shore. The distribution of tsunami
heights along the coastal points depend on thevariation of bathymetry. Thus, application of
GreeQ¶VODZfor an evaluation of tsunami heightat coastal points is required instead ofcomputations with finer bathymetry in order toobtain reliable results. In this study, we selecteda group of forecast points at depth of 50 m for an
estimation of tsunami height at coastal points
XVLQJ WKH *UHHQ¶V ODZ FDOFXODWLRQ 7KHQ WKHresults will be stored into the database.

Figure 4. Tsunami heights from the coastal points
REWDLQHG IURP *UHHQ¶V ODZ DW VRXUFH SRLQW 
Mw8.0, depth (DCF) of 0 km with different types offorecast points

3.2 Tsunami heights of different magnitudes and depths
A comparison between the results from tsunami simulation and calculation using GreeQ¶V ODZ ZLWK
different magnitudes and depths (DCF) at the fixed source point 4 is shown in Figure 5. Tsunami heights
DUHPDLQO\FRQWUROOHGE\WKHHDUWKTXDNH¶VPDJQLWXGH 7DWHKDWD 7KHODUJHUPDJQLWXGHFRQWULEXWHVto larger tsunami heights. The value RIWVXQDPLKHLJKWVFDOFXODWHGXVLQJ*UHHQ¶VODZIRUFRDVWDOSRLQWVLVKLJKHU WKDQ WKH UHVXOWV IURP GLUHFW WVXQDPL VLPXODWLRQ 7KH FDOFXODWLRQ XVLQJ *UHHQ¶V ODZ SURGXFHV D
significant value as tsunami height increases as the magnitude becomes larger. The factor of depth cangive different values of tsunami heights at coastal points. From the result of analysis on Figure 5, thetsunami heights from the deeper depth are higher than the shallow depth with the same magnitude.

― 106 ―

Figure 5. Tsunami heights at coastal point are
obtained directly from tsunami simulation (CP)DQG FDOFXODWLRQ XVLQJ *UHHQ¶V ODZ */  E\
different magnitudes and depths of center offault (DCF) at source point 4.

Figure 6. Vertical cross section of ocean
bottom deformation for magnitude 8.0 with
DCFs of 0 (red line), 20 (green line) and 30 km(blue line)

An inspection for this condition was carried out on
the ocean bottom deformation at the source point 4.
The vertical cross section across the center of fault
with depth of center of fault (DCF) of 0, 20 and 30
km are shown in Figure 6. DCFs of 0, 20 and 30 km
correspond to 0, 8.219, 18.219 km in depth of top ofleft corner (dTLC). Based on Figure 6, the crosssection of fault with depth of 30 km represented byblue line is wider than the cross section of fault withdepth of 0 km (red line).

The vertical sea floor deformation on depthsof 30 km and 20 km (green line), create
uplifts higher than the source depth of 0 km.
In this case, the vertical displacement ofwater surface affects the tsunami height at
the coastal point. The larger amount of uplift
will cause the higher amplitude of tsunami
height.

3.2 Tsunami arrival time with different magnitudes and depths
The information of arrival time can be used fortime estimation of incoming tsunami reaching
to the land. An analysis of tsunami arrival timeat the buoy points and coastal points from thesource point 4 (SP4) with different scenarios ofmagnitude and depth are shown in Figure 7.
The pattern of arrival time is almost similar for
every case. The arrival time at coastal points forthe case ofis a slightly earlier than thecase of. Tsunami arrival time depends
on the size of earthquake slightly. The larger
earthquake causes, a little faster tsunami
arrivals. The analysis in cases of thesameshowed that the tsunami arrival
time was slightly earlier in the case with thesource depth of 30 km than the cases of thesource depths of 0 and 10 km. The initial waves
can be detected at the buoy point and thisinformation is needed in order to estimate thetsunami waves approaching to the coast.

Based on the analysis, the initial tsunami waves
from source point 4 (SP4) reached to the buoy
point in 103.1 min after the earthquake, while
the arrival time at coastal point Kudat 1 is after
119.9 min. Therefore, it can be estimated thattravel time of tsunami from the buoy point to
the land is approximately 17 min.

Figure 7. Tsunami arrival time at coastal points
according to different magnitudes and depths(DCF) at a fixed source point 4 (SP4).

― 107 ―

5. CONCLUSIONSIn this study, an effort to update the tsunami database was carried out. The initial attempt was to findon potential rupture locations. A part of the Manila Trench, located from 12.67϶N to 14.83϶N and
118.33϶E to 120.67϶E was chosen as a source points region considering the potential as highly
hazardous tsunamigenic earthquake source region (Liu et al., 2008) and the target location is at theeast part of Malaysia. A simulation of tsunami using the software TUNAMI-N2 was conducted withtotal of 108 cases as the initial conditions.
The results of simulation were analysed and the variation of tsunami waveforms in terms oftsunami heights and tsunami arrival times were discussed. To predict any possible tsunami amplitude
DW WKH FRDVW WKH *UHHQ¶V ODZ ZDV DSSOLHG $ FRPSDULVRQ EHWZHHQ WKH WVXQDPL KHLJKWV REWDLQHG E\DSSOLFDWLRQ RI WKH *UHHQ¶V ODZ DQG WKRVH REWDLQHG GLUHFWO\ IURP WVXQDPL VLPXODWLRQ LQGLFDWHV DQ
inconsistency. An inaccuracy of sea depth data of GEBCO could affect the result. Therefore, the useof an accurate bathymetry data is essential in numerical computation. Based on the result of analysis,
the distribution of tsunami height in the coast depends on magnitude, depth and location of thesources. The amplitude of tsunami height at coast is higher as the earthquake size increases. An
analysis on tsunami arrival time was performed and the data from the buoy point is important as we
can estimate the incoming tsunami from offshore.
A concept of tsunami database is exposed with the methods of retrieving the database.
Hopefully, all the obtained tsunami information can be the additional data to be stored in the existingtsunami database.
AKNOWLEDGEMENT
In this opportunity, I would like to express my gratitude and gratefulness to Allah for giving me
strength which is priceless. In this study, we used TUNAMI-N2 code for tsunami simulation andGeneral Mapping Tools (GMT) which was developed by Paul Wessel and Walter Smith for map
creation. This study is conducted in International Institute of Seismology and Earthquake Engineering(IISEE).

REFERENCES
Balendra, T., and Li, Z., 2008, EJSE International Special Issue. 1-63
Chai, M.F., 2008, Individual studies by participant at the IISEE. 1-65
Fujii, Y., 2010-2011, IISEE Lecture Note 2010-2011, IISEE, BRI.
Kirby, S. et al., 2006, In: USGS Tsunami Sources Workshop, April 21±22.
Liu, L.-F., Xiaoming, W., and Andrew J.Salisbury., 2008, Journal of Asian Earth Sciences 36, 2-12
Satake, K., 2008, Springer-Verlag, 2009, 1-16
Tatehata, H., 1997, The Japan Meteorological Agency (JMA), Tokyo, 39-49
Website: Global Centroid Moment Tensor Project catalog search, http://www.globalcmt.org/
Website: General Bathymetric Chart of the Oceans (GEBCO) http://www.ngdc.noaa.gov/mgg/gebco― 108 ―