Information message about the strong earthquake in the region of Sumatra, April 6, 2010 . |
| A strong earthquake with M=7.8 occurred on April 6, 2010 at 22:15 GMT (7 April at 02:15 Moscow time) near the coast of North 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 15 min after
registration to the Ministry of Emergency of the Russian Federation (EMERCOM). |
| Preliminary processing has been done with data from 54 stations, accurate processing - with data 67 stations. |
| Fig. 1 presents fragments of records obtained from digital stations Diego Garcia (∆ 26.5º), Tennant Creek (∆ 42.6º), Taejon (∆ 43.9º), Ala-Archa (∆ 45º), Talaya (∆ 49.5º). Fig. 2 presents fragments of records obtained from digital stations Kurchatov (∆ 50.7º), Port Moresby (∆ 51.1º), Erimo (∆ 57º), Arti (∆ 62.2º), Yakutsk (∆ 64.3º). |
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 |
22-15-00.0 |
2.32 |
97.2 |
33 |
67 |
7.8/29 | 6.8/33 | 9-9.5 | 120 | IPC GS RAS (Accurate) | | 2 |
22-15-00.0 |
2.33 |
97.22 |
33 |
54 |
7.8/29 | 6.8/29 | 9-9.5 | 139 | IPC GS RAS (Preliminary) | | 3 |
22-15-02.8 |
2.218 |
97.033 |
48 |
123 |
7.8Mw | | | 67 | CSEM | | 4 |
22-15-02.1 |
2.36 |
97.132 |
31 |
240 |
7.7Mw | 6.8/145 | | 29 | NEIC (Accurate) | | 5 |
22-15-02.6 |
2.236 |
97.046 |
46 |
63 |
7.8Mw | 6.9/52 | | | NEIC (Preliminary) | |
| 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 |
| Red star in Figure 3 shows the epicenter of the earthquake, the focus of which was in the sea off the west coast of North Sumatra, at a depth of 33 km, 218 km south-west of Medan, Indonesia and 502 km north-northwest of Padang, Indonesia. |
Figure 3 |
|
| Aftershock |
| GS RAS registered 6 aftershocks with М>=4.8 within 10 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 |
| 20101300 | 2010-04-06 22:54:03.0 | 2.29 | 97.22 | 33 | 28 | - | 5.4/ 14 | 4.5 | Northern Sumatera, Indonesia | | 20101301 | 2010-04-06 23:35:36.0 | 1.97 | 97.13 | 33 | 23 | - | 5.2/ 9 | 4-4.5 | Northern Sumatera, Indonesia | | 20101304 | 2010-04-07 03:32:40.0 | 2.48 | 97.32 | 33 | 17 | - | 4.8/ 5 | 3-3.5 | Northern Sumatera, Indonesia | | 20101305 | 2010-04-07 04:22:14.0 | 2.82 | 97.22 | 33 | 33 | - | 5.3/ 19 | 4-4.5 | Northern Sumatera, Indonesia | | 20101308 | 2010-04-07 07:54:22.0 | 2.28 | 96.64 | 33 | 13 | - | 4.9/ 11 | 3-3.5 | Northern Sumatera, Indonesia | | 20101309 | 2010-04-07 08:16:59.0 | 2.2 | 96.53 | 33 | 20 | - | 4.9/ 9 | 3-3.5 | Northern Sumatera, Indonesia | |
| Macroseismic manifestations |
| According to RIA Novosti: "The national news agency Antara reports that according to the head of the Office of Disaster Simeulue Mr. Irwansyah there was rather serious damage in the south-east of the island, however it was not accompanied by the loss of life. At least a dozen people have been injured, but only in four cases quite serious. The victims were hospitalized. Dormitory for nurses partially collapsed in the area of Sinkey Aceh, and one of the women who lived there was slightly injured.
Governor Irwandi Yusuf confirmed insignificant damage. However, power outages are still observed in the neighboring province of North Sumatra. The earthquake and aftershocks were felt in almost all of northern and central parts of Sumatra, the sixth largest island of the world, and even in the largest city in neighboring Malaysia, Kuala Lumpur. This event caused panic in some towns of Sumatra, where there have been interruptions in power supply. Pacific Tsunami Warning Center and NUMKG announced a warning immediately after the strongest shock which was later canceled when it was found that the sea level changes are extremely low. Tsunami warning was announced in neighboring Thailand."
Fig. 4, obtained from USGS NEIC , presents the map of intensity based on phone calls to 186 residents living in 35 places.
|
Figure 4 |
|
| Historical records |
| Epicenter of this earthquake was located 35 km N-N-E from another catastrophic earthquake, which occurred in the region of North Sumatra on March 28, 2005.
|
| Focal mechanism and seismic moment of the earthquake |
| Focal mechanism solution of this earthquake (April 6, 2010 at 22:15 GMT) was calculated in IPC GS RAS with signs of initial arrivals of Р-waves at 118 stations, 106 of these stations registered the waves of compression (plus signs), 12 stations registered the waves of expansion (minus signs). These stations were located in the interval of epicenter distances of 4-100 degrees with rather dense distribution of these stations along azimuths. Origin’s mechanism in stereographic projection on lower hemisphere is presented in fig. 5, elements of this mechanism are presented in table. 2. Table. 2 and fig. 6, 7 also present focal mechanism solutions, calculated with CMT method by USGS NEIC, USGS and Global CMT Catalog, USA. Focal mechanism solutions are almost identical. This earthquake has occurred under the action of rather equal compression and expansion forces oriented N-E and S-W respectively.
Both nodal planes propagate N-W – S-E. One nodal plane is rather steeply falling (declination angle DP=78º-83º), another plane lays rather flat (DP=7º-12º). The type of motion along steeply falling plane – uplift, along another plane – thrust.
The value of seismic moment Мо of this earthquake (April 6, 2010) was obtained in IPC GS RAS with Р-wave spectra at four stations: «Arti» (delta 61.3 degrees), «Kislovodsk» (delta 84.4 degrees), «Talaya» (delta 84.9 degrees), "Obninsk" (delta 87.2 degrees), it makes Мо=1.2* 10** 20 n*m. Averaged value of moment magnitude Mw was calculated with Kanamori formula and it makes Mw = 7.4.
The value of moment magnitude Мо in accordance with USGS makes 3.9* 10** 20 n*m, the value of Mw = 7.7, in accordance with Global CMT Catalog – Мо= 5.56* 10** 20 n*m, Mw = 7.8.
|
| 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 |
| 51 | 44 | 39 | 226 |
1 | 135 | 325 | 7 | 100 | 135 |
84 | 89 | IPC GS RAS | | 57 | 40 | 32 | 221 |
0 | 130 | 312 | 12 | 91 | 130 |
78 | 89 | NEIC | | 54 | 41 | 36 | 220 |
0 | 311 | 308 | 9 | 87 | 131 |
81 | 90 | Quick CMT | |
| IPC GS RAS - Informational Processing Center, Geophysical Survey, Russian Academy of Sciences |
| NEIC - National Earthquakes Information Center of US Geological Service |
| Quick CMT - Quick CMT catalog |
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