TSUNAMI PROPAGATION AND INUNDATIONMODELINGS ALONG SOUTH-EAST COAST OFPAPUA NEW GUINEAMartin WAREK ∗MEE12620

Supervisor:

Yushiro FUJII ∗∗Bunichiro SHIBAZAKI ∗∗ABSTRACTThis study covers tsunami generation, propagation and inundation using eight earthquake scenarios
along the New Britain Trench and Ramu-Markham Fault zone in the south-eastern region of Papua
New Guinea. The tsunami propagation and inundation modeling, based on the TUNAMI-N2hydrodynamic computational model, was used in this study. The computational domain ranges from141o to 158o longitude and negative 1o to negative 12o latitude. The GEBCO 30 arc-second data andcoastal topography data from SRTM were utilized in the computation of tsunami waves and theinundation study in the target areas. Eight earthquake scenarios comprising of two Mw8.6 segments,
an Mw8.7 segment, and five Mw8.1 magnitudes were selected along the Ramu-Markham Fault zone
and the New Britain Trench for computing tsunami height, travel time and inundation of the target
areas. Geographically assuming tidal gauge stations at desired coastal points within the computational
domain, tsunami heights and travel time to these coastal points were computed and results obtained.
The earthquake scenarios, Mw8.6 segment_1 and Mw8.1 segment_A, with the highest tsunami heightto the target areas were selected as computational model for tsunami inundation study. The tsunami
travel time from fault segments covering both the sea and the land produced 0 min to 20 min travel
time. The maximum tsunami heights of 3 to 4 m were recorded for Mw8.6 segment_1 and Mw8.7
segment_2 in Woodlark Island, Kiriwina Island, and Finch coastal points. The inundation study reveals
Lae City observing negligible inundation, while Salamaua Coast was inundated with tsunami
inundation height of 3 m.
Keywords: Tsunami Waveforms, Tsunami Heights, Tsunami Travel Time, Inundation

1. INTRODUCTION
The complex seismic zone, active and frequent seismic activities in the region of Papua New Guinea
has significantly put the country at risk of seismic induced tsunami. In 17th July 1998, seismic induced
submarine slump caused tsunami off the coast of Aitape claiming more than 2,200 lives and left morethan 10,000 homeless. Several tsunamigenic earthquakes following the year caused recorded tsunami
heights as far as 3 m along the coast and the coastal islands of Papua New Guinea. The high seismicity
observed along New Britain Trench axis and Ramu-Markham Fault zone, where Solomon Sea andAustralian Plates subduct South Bismarck and Pacific Plates, are potential tsunami source areas. In
this study, tsunami heights and travel time of earthquake scenarios placed along the Ramu-Markham
and New Britain Trench were assessed along the south-east coast of Papua New Guinea. Lae City andSalamaua coast in Morobe Province were selected as the target areas of tsunami inundation.
∗Department of Works, Government of Papua New Guinea, Port Moresby, Papua New Guinea.
International Institute of Seismology and Earthquake Engineering (IISEE), Building Research Institute (BRI),
Japan.

∗∗12. THEORETICAL CONSIDERATION
2.1 Shallow Water Equations
The theory considers trans-oceanic tsunami of long wavelength against shallow water depth. The
governing equations in spherical coordinates system are as follows.
(1)
(2)
(3)
where θ and λ denote longitude and latitude respectively, 𝜂 denotes elevation of water surface, D is thetotal water depth (h+𝜂), h is the still water depth, t is time, R is the earth’s rotational axis, ρ is density,
M and N are flux (discharge) along the θ longitude and λ latitude while τx/ρ and τy/ρ are bottom friction
terms. The fundamental continuity and momentum equations expressed in a Cartesian coordinate
system are as follows (Koshimura, 2013).
(4)
(5)
(6)

The discharge flux M and N are given in Eq. (7) and (8).
(7)(8)
where u and v are water particle velocities in direction x and y respectively.

3. DATA AND METHODOLOGYThe Tohoku University’s Numerical Analysis Model for Investigation of Near-field Tsunami(TUNAMI-N2), the simulation code by Koshimura (2013) and Fujii (2013) was used for computing
tsunami heights and travel times, while inundation code by Yanagisawa (2013) was used for tsunami
inundation study. The bathymetry data from GEBCO 30 arc-second and SRTM 3 arc-second wereutilized for the computation. The computational domain at 141o to 158o longitude and 1o to 12o latitude
was set as region 1 of the study with the grid size of 1020 x 660. In the computation of tsunami heights
and travel times, GEBCO 30 arc-second data with 1 arc-minute spatial grid size was used for region 1.
In the inundation study of the target area, region 2, 3 and 4, the grid sizes are 390 x 300, 270 x 225 and459 x 243, respectively. The region 2 and 3 used GEBCO bathymetry data, while SRTM 3 arc-second
data was used as coastal topographic data in region 4. Figure 2 shows the location of the existing andassumed tidal gauge stations.

2Figure 1. Location of earthquake scenarios. Left: mega scenarios, right: Mw8.1 scenarios.
Earthquake scenarios with fault segments shown in Figure 1 were used for computation fortsunami waves and inundation. The fault parameters are shown in Table 1. The fault segments wereplaced along the subduction trench, and subducting plates based on Wallace et al., (2004). Theearthquake scenarios were two Mw8.6 segments (S1 and S3), an Mw8.7 segment (S2), and fiveMw8.1 segments (SA, SB, SC, SD, SE). Dip angles were obtained from USGS Slab 1 Interactive Map
data.
Table 1. Fault parameters for each earthquake scenario.
Scenario Mw
Lon.
Lat
Length, Width,Strike,Dip, δ Rake, λ Slip, u(deg.)(deg.)L (km)W (km) θ (deg.) (deg.)(deg.)
(m)
1
8.6
148.4
-7.6
426
146
300
2090
3.6
2
8.7
153.0
-5.7
536
146
248
2090
4.0
3
8.6
155.6
-8.0
426
146
312
2090
3.6
A
8.1
149.0
-7.3
169
117
283
2090
2.0
B
8.1
150.6
-6.8
169
117
253
2090
2.0
C
8.1
152.3
-6.0
169
117
246
2090
2.0
D
8.1
153.8
-6.2
169
117
290
2090
2.0
E
8.1
154.9
-7.4
169
117
3162090
2.0
The scaling law by Moritani at al. (2013) and the equations that follows were utilized for thecomputation of the fault parameters.

(9)
(10)
(11)
(12)
(13)
where W is the width area of the fault, Mo isthe seismic moment, u is the average slip, S is
the fault area and L is the length of the fault
segment.

Figure 2. Location of tidal gauge stations.

34. RESULTS AND DISCUSSION
Figure 3 shows the tsunami waveforms obtained from earthquake scenario Mw8.1 S1 for all coastal
points located around the Ramu-Markham and New Guinea Trench. The Finch and Voco Point coastal
points observed the first wave of 1 m amplitude at initial time of 0 min. Madang coastal point showedsimilar phenomenon. Arawe coastal point, however, received negative waves at the initial time of 0min. The other coastal points observed
tsunami waves after the initial time.
These waveform characteristics wereobserved in all earthquake scenarios.
Relating to Figure 3, tidal
gauge stations located within the fault
areas and uplift regions observed
waveforms characteristic similar toFinch, while those located outside fault
area but within subsidence observed
waveforms similar to Arawe. Positive
wave was read from tidal gauge within
the uplift region at the initial time,
while negative wave was read at initialtime for tidal gauge stations locatedwithin subsidence region.
Figure 4, the maximum
tsunami heights observed for the megaearthquake scenarios, Mw8.6 S1 and
Mw8.7 S2, were more than 3 m at
Finch, Woodlark Island and Kiriwina
Island coastal points. Maximum
tsunamiheightobservedfromearthquake scenarios Mw8.1 was fromSA. The maximum tsunami height at
Voco Point and Salamaua coastal points,
were obtained from Mw8.6 S1 andMw8.1 SA computation. Accordingly,
these two scenarios were used for theinundation study of the target area.
In Figure 5, tsunami travel
time less than 10 min for earthquake
Figure 3. Calculated tsunami waveforms for each scenario Mw8.6 S1 was observed at
Finch, Voco Point and Madang coastal
coastal point for the earthquake scenario Mw8.6 S1.
points. For earthquake scenario Mw8.7
S2, the tsunami travel time within 10 min was observed at Finch, Watta and Arawe coastal points. Thetsunami travel time less than 10 min for Mw8.1 SA was observed at Finch and Voco Point coastalpoints. For Mw8.1 SB, tsunami travel time less than 10 min was observed at Arawe coastal point,
while Mw8.1 SC was observed at Watta coastal point. The tsunami travel time less than 10 min forearthquake scenario Mw8.1 SD was observed at Madahas Island and Watta coastal points. For
earthquake scenario Mw8.1 SE, tsunami travel time less than 10 min was observed at Jaba andMadahas Island coastal points.
The inundation study in Figures 6 and 7 revealed negligible inundation in Lae City, while
inundation in Salamaua was observed with a height of 3 m from Mw8.6 S1. For Mw8.1 SA, only
Salamaua coast was inundated at 1.2 m height. Bathymetry and coastal topography of Lae City andSalamaua was responsible for the inundation pattern observed in the two target areas.

4

Heights (m)

4.50
4.00
3.50
3.00
2.50
2.00
1.50
1.00
0.50
0.00

S1S2S3SASBSCSDSE

Time (min)Figure 4. Tsunami heights for each coastal point from the computation of theearthquake scenarios.
1009080706050403020
100S1S2S3SASBSCSDSEFigure 5. Tsunami travel time to various coastal points from respective
earthquake scenario source area.

Figure 6. Calculated tsunami inundation of the region 4 from earthquake
scenarios Mw8.6 S1 (left) and Mw8.1 SA (right).

5Figure 7. Magnified maps of rectangular areas in Figure 6. The left figure shows
negligible inundation in Lae City, while right figure shows inundation in Salamaua.

5. CONCLUSIONThe study covers simulations of tsunami propagation and inundation performed from earthquakescenarios along the New Britain Trench and the Ramu-Makharm Fault zone. Utilizing the GEBCO
bathymetry data and SRTM coastal topographic data, tsunami travel time for each scenario andtsunami inundation study of Lae City and Salamaua were investigated. The tsunami heights exceeded
3 m were observed from earthquake scenarios Mw8.6 S1 and Mw8.7 S2 at Finch, Kiriwina Island andWoodlark Island coastal points. Coastal points within the fault area, the uplift region and subsidence
region recorded tsunami travel time within 10 min. The inundation study of Lae City and Salamaua
revealed negligible inundation observed in Lae, while 3 m height tsunami inundation was observed atSalamaua. Similar studies are needed for coastal towns and cities in Papua New Guinea. To carry out
such study, the Department of Works must have tsunami disaster management policy as prerequisite toutilizing government resources (manpower and finance).

ACKNOWLEDGEMENTS
I would like to expresses my sincere gratitude to Dr. H. Yanagisawa for using his inundation modeland Dr. Hurukawa for his invaluable comments at the final stage of this study.

REFERENCES
Fujii Y., 2013, IISEE Lecture Note 2013, IISEE, BRI.
Koshimura S., 2013, IISEE Lecture Note 2013, IISEE, BRI
Murotani S., Satake K. and Fujii Y., 2013, GRL, under review.
Wallace L. M., Stevens C., Silver E., McCaffrey R., Loratung W., Hasita S., Stanaway R., Curley R.,
Rosa R. and Taugaloidi J., 2004, Geophys. J. Int., 109, B05404.
Website: General Bathymetric Chart of the Ocean (GEBCO), https://www.gebco.net/ .
Website: Shuttle Radar Topographic Mission (SRTM),
http://dds.cr.usgs.gov/srtm/version2_1/SRTM3/Eurasia/.
Website: United State Geological Survey (USGS), USGS Slab 1.0 Interactive Map data,(http://earthquake.usgs.gov/research/data/slab/map/.
Yanagisawa H., 2013, IISEE Lecture Note, IISEE, BRI.

6