Information message about destructive earthquake in Pacific Ocean, region of Samoa Islands, September 29, 2009 |
| The earthquake with М=8.2 has occurred on September 29, 2009 at 17:48 GMT (at 21:48 Moscow time) in Pacific Ocean, the region of Samoa Islands. This earthquake has originated destructive waves of tsunami, which caused victims. |
| Parameters of the earthquake
have been determined in the Alert Service (AS) of Information
Processing Center (IPC) of Geophysical Survey of RAS in Obninsk with station data
obtained from digital and analog seismic stations of Russia, countries of CIS
and from abroad. Alert message on this earthquake has been delivered in 17 min after
registration to the Ministry of Emergency of the Russian Federation (EMERCOM). |
| Preliminary processing has been done with data from 35 stations, accurate processing - with data 45 stations. |
| Fig. 1 presents fragments of records obtained from digital stations Tennant Creek (∆ 51º), Erimo (∆ 70.4º), Petropavlovsk (∆ 72.6º), Albuquerque (∆ 79.9º), Seimchan (∆ 82.8º). Fig. 2 presents fragments of records obtained from digital stations Hockley (∆ 86.2º), Falkland Islands (∆ 92.2º), Tiksi (∆ 95.3º), Ulan-Bator (∆ 95.2º), Talaya (∆ 98.4). |
Figure 1
| 
Figure 2
|
|
| IPC GS RAS also has obtained information with parameters of this event from some seismological centers, these data are given in table 1: |
| Table 1 |
| NN |
Time in origin h-min-s (GMT) |
Lat degr. |
Lon degr. |
Depth km |
N s/st |
Ms/ N |
mb/ N |
I0 calc |
GAP |
Center | | 1 |
17-48-11.0 |
-15.4 |
-172.16 |
20 |
45 |
8.2/32 | 7.1/18 | 10.5-11 | 58 | IPC GS RAS (Accurate) | | 2 |
17-48-13.3 |
-15.4 |
-172.14 |
33 |
35 |
8.3/28 | 7.2/14 | 10-10.5 | 81 | IPC GS RAS (Preliminary) | | 3 |
17-48-11.0 |
-15.4 |
-172.16 |
20 |
45 |
8.2/32 | 7.1/18 | 10.5-11 | 58 | IPC GS RAS (Accurate) | | 4 |
17-48-13.3 |
-15.4 |
-172.14 |
33 |
35 |
8.3/28 | 7.2/14 | 10-10.5 | 81 | IPC GS RAS (Preliminary) | | 5 |
17-48-17.9 |
-15.43 |
-172.2 |
60 |
187 |
8.1 Mw | | | 54 | CSEM | | 6 |
17-48-17.9 |
-15.43 |
-172.2 |
60 |
187 |
8.1 Mw | | | 54 | CSEM | | 7 |
17-48-19.6 |
-15.55 |
-172.3 |
85.4 |
77 |
7.9 Mw | | | 55 | NEIC (Preliminary) | | 8 |
17-48-11.4 |
-15.55 |
-172.07 |
18 |
293 |
8 Mw | 7.1 | 186 | 32 | NEIC (Accurate) | | 9 |
17-48-19.6 |
-15.55 |
-172.3 |
85.4 |
77 |
7.9 Mw | | | 55 | NEIC (Preliminary) | | 10 |
17-48-11.4 |
-15.55 |
-172.07 |
18 |
293 |
8 Mw | 7.1 | 186 | 32 | NEIC (Accurate) | |
| IPC GS RAS - Informational Processing Center, Geophysical Survey, Russian Academy of Sciences |
| CSEM - European - Mediterranean seismological center |
| NEIC - National Earthquakes Information Center of US Geological Service |
| Epicenter |
| Fig. 3 depicts with red star epicenter of this earthquake, which was located in Pacific Ocean, in the region of Samoa Islands, at the depth of 33 kilometers, in 184 km S-S-W from Apia, Capital of Western Samoa, in 200 km S-W from Pago-Pago, American Samoa, in 460 km N-W from Alofi, Niue, in 490 km E-S-E from Mata-Utu, Wallace and Futuna Islands and in 711 km N-E from Nukulofa, Capital of Tonga. |
Figure 3 |
|
| Aftershock |
| GS RAS registered 22 aftershocks with magnitudes М>=5 whithin 15 hours after the main shock. |
| N |
Date & Time (GMT)
yy-mm-dd hh:mm:sec |
Lat
degr. |
Lon
degr. |
Depth
km |
N
station |
Ms/ N |
mb/ N |
Io
calc. |
Region |
| 20093155 | 2009-09-29 18:08:24.0 | -15.6 | -171.93 | 33 | 12 | - | 5.9/ 8 | 5.5-6 | Samoa Islands region | | 20093156 | 2009-09-29 18:21:41.0 | -16.16 | -173.05 | 10 | 17 | - | 5.9/ 11 | 7.5-8 | Tonga Islands | | 20093170 | 2009-09-29 18:34:29.0 | -14.97 | -172.63 | 10 | 8 | - | 5.1/ 2 | 5.5-6 | Samoa Islands | | 20093157 | 2009-09-29 18:40:16.0 | -15.09 | -173.04 | 50 | 22 | - | 5.8/ 11 | 4.5-5 | Tonga Islands | | 20093172 | 2009-09-29 18:46:00.0 | -15.11 | -173.31 | 10 | 10 | - | 5.2/ 1 | 5.5-6 | Tonga Islands | | 20093158 | 2009-09-29 18:58:03.0 | -15.81 | -172.81 | 33 | 14 | - | 5.6/ 10 | 5 | Samoa Islands region | | 20093159 | 2009-09-29 19:59:40.0 | -16.48 | -172.36 | 33 | 9 | - | 5.3/ 4 | 4-4.5 | Samoa Islands region | | 20093177 | 2009-09-29 21:27:46.0 | -16.41 | -173.2 | 10 | 9 | - | 5.0/ 4 | 5-5.5 | Tonga Islands | | 20093180 | 2009-09-29 21:29:02.0 | -14.61 | -173.44 | 10 | 8 | - | 5.1/ 4 | 5.5-6 | Samoa Islands region | | 20093182 | 2009-09-29 21:50:58.0 | -16.22 | -172.64 | 10 | 14 | - | 5.2/ 7 | 5.5-6 | Samoa Islands region | | 20093183 | 2009-09-29 21:52:24.0 | -16.16 | -172.82 | 10 | 10 | - | 5.4/ 7 | 6-6.5 | Samoa Islands region | | 20093160 | 2009-09-29 22:08:32.0 | -15.43 | -173.47 | 33 | 13 | - | 5.3/ 4 | 4-4.5 | Tonga Islands | | 20093162 | 2009-09-29 23:11:50.0 | -15.47 | -173.54 | 10 | 20 | - | 5.3/ 6 | 6-6.5 | Tonga Islands | | 20093163 | 2009-09-29 23:32:56.0 | -15.36 | -173.42 | 10 | 21 | - | 5.7/ 10 | 7-7.5 | Tonga Islands | | 20093164 | 2009-09-29 23:45:02.0 | -15.84 | -172.58 | 10 | 22 | - | 6.0/ 9 | 7.5-8 | Samoa Islands region | | 20093165 | 2009-09-30 01:05:33.0 | -14.94 | -173.37 | 10 | 15 | - | 5.4/ 9 | 6-6.5 | Samoa Islands region | | 20093166 | 2009-09-30 01:09:28.0 | -14.79 | -173.69 | 10 | 15 | - | 5.4/ 5 | 6-6.5 | Samoa Islands region | | 20093169 | 2009-09-30 01:39:48.0 | -15.63 | -173.38 | 10 | 11 | - | 5.3/ 6 | 6-6.5 | Tonga Islands | | 20093175 | 2009-09-30 05:24:49.0 | -15.48 | -173.53 | 10 | 10 | - | 5.5/ 7 | 6.5-7 | Tonga Islands | | 20093176 | 2009-09-30 05:25:46.0 | -15.56 | -173.49 | 10 | 15 | - | 5.7/ 7 | 7-7.5 | Tonga Islands | | 20093179 | 2009-09-30 07:32:12.0 | -15.11 | -173.6 | 10 | 7 | - | 5.0/ 4 | 5-5.5 | Tonga Islands | | 20093184 | 2009-09-30 09:05:10.0 | -16.06 | -173.18 | 10 | 10 | - | 5.2/ 7 | 5.5-6 | Tonga Islands | |
| Macroseismic manifestations |
| This earthquake was felt in Western Samoa and American Samoa with intensities from 2 to 7 MSK and caused the series of tsunami. In accordance with 1 TV Channel, Russia the waves of 5 meter height totally destroyed a number of villages. From preliminary calculations the number of victims is approximately one hundred. Dozens of people still are not found. Foreign citizens are among the victims. |
| Focal mechanism and seismic moment of the earthquake |
| Focal mechanism solutions of the origin for the earthquake which has happened on September 29, 2009 at 17:48 were obtained with CMT technique in NEIC USA, NEIC – USGS and in Global CMT Catalog, USA, they are presented in table 2 and shown on fig. 4,5. These solutions are almost similar.
The earthquake has occurred under the action of expansion forces oriented N-E-E. Nodal plane NP1 has nearly along meridian direction of propagation and was steeply falling (DP=52º-72º), another plane NP2 – lays more flat (DP=31º-46º) – it propagates S-E direction. The type of motion along both planes – fault with shift components (left side along NP1, right side along NP2).
The value of seismic moment Мо of the earthquake on September 29, 2009 in accordance with USGS makes Mo=1.2* 10** 21 n*m, the value of moment magnitude Mw = 8.0; in accordance with Global CMT Catalog – Mo= 1.82* 10** 20 n*m, Mw=8.1.
|
| Table 2 |
| Axes of main strengths |
Nodal planes |
Center |
| T |
P |
N |
NP1 |
NP2 |
| Pl |
Azm |
Pl |
Azm |
Pl |
Azm |
Stk |
Dp |
Slip |
Stk |
Dp |
Slip |
| 3 | 55 | 68 | 317 |
21 | 146 | 345 | 52 | -61 | 124 |
46 | -120 | NEIC | | 3 | 55 | 68 | 317 |
21 | 146 | 345 | 52 | -61 | 124 |
46 | -120 | NEIC | | 23 | 77 | 55 | 310 |
25 | 178 | 7 | 72 | -64 | 129 |
31 | -144 | Quick CMT | | 23 | 77 | 55 | 310 |
25 | 178 | 7 | 72 | -64 | 129 |
31 | -144 | Quick CMT | |
| NEIC - National Earthquakes Information Center of US Geological Service |
| NEIC - National Earthquakes Information Center of US Geological Service |
| Quick CMT - Quick CMT catalog |
| Quick CMT - Quick CMT catalog |
Figure 4 | 
Figure 5 |
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