2009 Samoa earthquake and tsunami ‐
Preliminary modeling results
Hong Kie Thio, URS corp
Rupture parameters:
M=8.0 (from Polet pers. comm.), M
0
=1.17x10
28
dyne.cm = 1.17x10
21
Nm
L=131 km
W=45 km
Slip = 7 m
Modeled using nested grids, dx=8 arcsec. Although the current grid is more accurate
than the previously used (24 arcsec) grid, there are still some issues with the
accuracy, expecially in Pago Pago, with the harbor not extending as far inland as it
should. Compared to the 24 arcsec results, the peak amplitudes are lower, which is
to be expected. We are also attempting to model a finer grid, 1.6 arcsec (~50 m).
Tables
M
W
Lat
Lon
Dep Str/Dip/Slip L
W
8.000 -15.321 -172.104 30.0 138.7/40/-90 131.0 45.0
Figures
Figure 1. Maximum waveheights in Samoa and American Samoa.
Figure 2. Detailed map of American Samoa (Tutuila).
Figure 3. Detailed map of Samo, Upolu Island.
Figure 4. Detailed map of Samoa, Savai’I island.
Figure 5. Comparison of observed (green) and modeled (yellow‐ish) marigrams at
Apia, Upolu island, Samoa.
Appendix
Location from the NEIC (as of 2009/09/30 12:33:00)
Magnitude
8.0
Date-Time
Tuesday, September 29, 2009 at 17:48:11 UTC
Tuesday, September 29, 2009 at 06:48:11 AM at epicenter
Time of Earthquake in other Time Zones
Location
15.559°S, 172.093°W
Depth
18 km (11.2 miles) set by location program
Region
SAMOA ISLANDS REGION
Distances
185 km (115 miles) ENE of Hihifo, Tonga
200 km (125 miles) S of APIA, Samoa
700 km (435 miles) NNE of NUKU'ALOFA, Tonga
2700 km (1670 miles) NNE of Auckland, New Zealand
Location Uncertainty horizontal +/- 6.5 km (4.0 miles); depth fixed by location program
Parameters
NST=291, Nph=291, Dmin=>999 km, Rmss=1.05 sec, Gp= 32°,
M-type=teleseismic moment magnitude (Mw), Version=9
Source
USGS NEIC (WDCS-D)
Event ID
us2009mdbi
Mechanism from J. Polet:
General region : 2009mdbi SAMOA ISLANDS REGION
surface waves (3.0,3.5,7,7.5 mHz)
Stations used : AAK BFO CASY CTAO DGAR ESK FFC GNI HKT INCN KEV KIP KMBO KONO
KURK LSZ LVC MAJO OTAV PMG PMSA SDV S
Origin time: 2009 272 17 48 19
Original location (lat,lon,depth) : -15.6000 -172.300 85
Moment tensor (x1.e26 dyncm) :
Mrr : -122.572960 Mtt : 47.130367
Mff : 75.442596 Mrt : 0.368360
Mrf : -24.089439 Mtf : -43.425598
T-axis: moment= 108.657 plunge= 4.916 azimuth= 54.761
N-axis: moment= 16.946 plunge= 5.500 azimuth= 145.236
P-axis: moment= -125.602 plunge= 82.613 azimuth= 283.198
best double couple: Mo= 117.130(x1.e26 dyncm) Mw=8.0 tau= 27.1
nodal planes (strike/dip/slip): 329.84/ 50.16/-82.83 138.73/ 40.37/-98.51
Centroid location : -15.321 -172.104 29.946
Centroid time : 19.832
Variance reduction (%) : 61
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0- 30- 60- 90- 120- 150- 180- 210- 240- 270- 300- 330-
z-comp: 1 0 2 2 4 3 3 6 1 3 2 3
r-comp: 1 0 0 2 2 3 2 5 1 2 2 1
t-comp: 1 0 0 1 1 3 2 5 1 3 2 1
Total number of traces used = 71