Information message about the strong earthquake near the western coast of Northern Sumatra on February 20, 2008 |
| The strong earthquake with М=7.6 has happened on February 20, 2008 at 8:08 GMT (11:08 Moscow time) near the western coast of Northern Sumatra. |
| 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 24 min after
registration to the Ministry of Emergency of the Russian Federation (EMERCOM). |
| Preliminary processing has been done with data from 33 stations, accurate processing - with data 45 stations. |
| Fig. 1 presents fragments of records obtained from digital stations Ala Archa (∆ 44º), Ulan-Bator (∆ 45.8º), Talaya (∆ 49.1º), Kurchatov (∆ 49.9º), Hailar (∆ 50.5º), Borovoe (∆ 54.3º). Fig. 2 presents fragments of records obtained from digital stations Arti (∆ 61.1º), Kislovodsk (62.2º), Yakutsk (∆ 64.2º), Obninsk (∆ 70.6º), Tiksi (∆ 71.8º), Seimchan (∆ 72.7º). |
Figure 1
| 
Figure 2
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|
| 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 |
08-08-30.0 |
2.88 |
95.99 |
33 |
45 |
7.6/18 | 6.6/17 | 9 | 83 | IPC GS RAS (Accurate) | | 2 |
08-08-29.8 |
2.86 |
96.02 |
33 |
33 |
7.6/13 | 6.6/15 | 9 | 83 | IPC GS RAS (Preliminary) | | 3 |
08-08-28.6 |
2.85 |
95.95 |
10 |
261 |
7.3Mw | | | 59 | CSEM | | 4 |
08-08-31.9 |
2.75 |
95.97 |
34 |
65 |
7.5Mw | 6.6/57 | | 61 | NEIC | |
| 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 has been downloaded from Geological Service, USA NEIC , it presents epicenter of this earthquake, which was located in the sea near the western coast of Northern Sumatra at 310 km to the south-south-east from Banda-Aceh. |
Figure 3 |
|
| Aftershock |
| Within 2 hours after the main shock Geophysical Survey of RAS registered 6 aftershocks: |
| 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 |
| 20080524 | 2008-02-20 08:28:18.0 | 2.69 | 96.22 | 33 | 18 | - | 5.7/ 9 | 5-5.5 | Northern Sumatera, Indonesia | | 20080525 | 2008-02-20 08:36:36.0 | 2.58 | 96.16 | 33 | 13 | - | 5.5/ 8 | 4.5-5 | Northern Sumatera, Indonesia | | 20080526 | 2008-02-20 09:05:05.0 | 2.59 | 96.28 | 33 | 21 | - | 5.6/ 13 | 5 | Northern Sumatera, Indonesia | | 20080527 | 2008-02-20 09:11:26.0 | 2.66 | 95.89 | 33 | 18 | - | 5.3/ 11 | 4-4.5 | Off w coast of Northern Sumatera | | 20080528 | 2008-02-20 09:32:04.0 | 2.64 | 95.91 | 33 | 14 | - | 5.1/ 8 | 3.5-4 | Off w coast of Northern Sumatera | | 20080529 | 2008-02-20 10:08:28.0 | 2.58 | 95.9 | 33 | 9 | - | 4.8/ 5 | 3-3.5 | Off w coast of Northern Sumatera | |
| Focal mechanism and seismic moment of the earthquake |
| Focal mechanism solution for the earthquake 20.02.2008 has been calculated with TMC method in National Center of information about the earthquakes USGS, USA, it is presented in table 2 and shown on fig. 4. This earthquake has occurred under the equal value compression and expansion forces oriented to the North-West– South-West. The motion along the flat nodal plane with latitudinal direction of propagation was characterized by the thrust (with components of left side drift), while along the steep falling plane oriented to the South-Eastern direction of propagation – it was characterized by uplift (with components of right side drift).
The value of seismic moment Мо of the earthquake 20.02.2008 in accordance with USGS made 6.8* 10** 19 n*m, the value of moment magnitude calculated with Kanamori formula made Mw = 7.2.
|
| 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 |
| 53 | 45 | 36 | 216 |
4 | 309 | 130 | 82 | 95 | 281 |
10 | 61 | IPC GS RAS | |
| IPC GS RAS - Informational Processing Center, Geophysical Survey, Russian Academy of Sciences |
Figure 4 |
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