Information message about destructive earthquake in the area of Southern Sumatra, September12, 2007

     The destructive earthquake with M=8.3 has happened on September12, 2007 at 11:10 GMT (15:10 Moscow time) near the South-Western coast of Sumatra Island, Indonesia.
     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 22 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).
     Preliminary processing has been done with data from 37 stations, accurate processing - with data 49 stations.
     Figure 1 presents fragments of records obtained from digital stations Ulan-Bator (∆ 52.3º), Hailar (∆ 55.8º), Talaya (∆ 55.9º), Kurchatov (∆ 58.3º), Borovoe (∆ 63º). Figure 2 presents fragments of records obtained from digital stations Arti (∆ 70º), Kislovodsk (∆ 71.3º), Petropavlovsk (∆ 74.6º), Tiksi (∆ 78º), Obninsk (∆ 79.6º).

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 11-10-23.5 -4.4 101.48  30  49  8.3/187/2210-10.5112 IPC GS RAS (Accurate)
2 11-10-23.8 -4.34 101.49  30  37  8.3/157/2010-10.5112 IPC GS RAS (Preliminary)
3 11-10-21.5 -4.4 101.36  10  147  8.4Mw   41 CSEM
4 11-10-24.2 -4.37 101.56  16  30  7.9Mw 7.1/12  NEIC (Preliminary)
5 11-10-26.3 -4.52 101.38  30  175  8.4Mw 7.1/51 40 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
         Epicenter of this earthquake was located in the sea (at the depth of 30 km) near the south-western coast of Sumatra Island, Indonesia: at 130 km to the south-west from Bengkulu and at 620 km to the west-north-west from Jakarta Capital. Fig.3 was downloaded from NEIC site Geological Service NEIC, USA and presents epicenter of this earthquake with red circle.

    Figure 3
    Aftershock
         This earthquake was accompanied with numerous aftershocks. Within the first day after the earthquake GS RAS has registered 45 earthquakes with magnitudes M>5. The strongest aftershock with М=8.1 occurred in 12 hours after the main shock. Below one can find aftershocks with М>6.
    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
    200732972007-09-12 13:02:05.0-2.92101.373327-6.2/ 146-6.5 Southern Sumatera, Indonesia
    200733022007-09-12 14:40:03.0-3.08101.553332-6.5/ 147-7.5 Southern Sumatera, Indonesia
    200733062007-09-12 16:37:02.0-2.99101.473337-6.4/ 156.5-7 Southern Sumatera, Indonesia
    200733122007-09-12 23:49:01.0-2.54100.8533368.1/ 157.3/ 169.5-10 Southern Sumatera, Indonesia
    200733182007-09-13 01:26:35.0-1.7899.843330-6.1/ 146-6.5 Southern Sumatera, Indonesia
    200733222007-09-13 02:30:02.0-1.6299.753332-6.5/ 167-7.5 Southern Sumatera, Indonesia
    200733252007-09-13 03:35:28.0-2.0899.6733347.3/ 166.7/ 168.5-9 Southern Sumatera, Indonesia
    200733432007-09-13 13:10:15.0-2.6101.123320-6.1/ 126-6.5 Southern Sumatera, Indonesia
    200733472007-09-13 16:09:12.0-3.15101.563328-6.7/ 147.5-8 Southern Sumatera, Indonesia
    200733532007-09-14 01:02:05.0-3.59101.973326-6.3/ 126.5-7 Southern Sumatera, Indonesia
    Macroseismic manifestations
         State of emergency was announced in the regions of Indonesia affected by this earthquake. Authorities confirmed the death of thirteen persons. In accordance with official data 50 people were seriously injured, however medial staff reported about hundreds of injured. Now it is difficult to say about the size of disaster, because continued shocks cause new destructions. Fig.4. presents the map obtained from NEIC site Geological Service NEIC, USA , it presents instrumental intensity of this earthquake.

    Figure 4
    Historical records
         For the last three years more than 200 thousand people were killed in Indonesia as a result of catastrophic earthquakes. In December 2004 (see Information message about catastrophic earthquake in the area of Northern Sumatra – December 26, 2004 ) at the north-western coast of Sumatra the huge tsunami wave has killed 168 thousand people. In addition 40 thousand people were swept to the sea and they are known as "lost". In March 2005 (see Information message about the second catastrophic earthquake in the region of Northern Sumatra – March 28, 2005 ) nearly one thousand people were killed after the earthquake near Nias Island near Sumatra.
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism solution of the main shock 12.09.2007 0=11-10 М=8.3 has been calculated with method of centroid in Harvard Center, USA (HARVARD), it is presented in table 2 and shown on fig. 5. The earthquake has occurred under prevailing strengths of compression, oriented to the south-west. Both nodal planes propagate to the North-Western-South-Eastern direction. One plane (NP1) is flat, the type of motion along it – thrust with small right sided slide component. The other nodal plane (NP2) steeply falls, the type of motion – uplift with small left sided slide component. Averaged value of seismic moment Мо for the main shock 12.09.2007 0=11-10, the value obtained in GS RAS based on Р-wave spectra obtained from stations Talaya, Obninsk, Arti, Kislovodsk , makes 7.8* 10** 20 n*m, the value of moment magnitude - Mw = 7.9. The value of seismic moment Мо from HARVARD data makes 5.05* 10** 21 n*m, the value of moment magnitude - Mw = 8.4.
    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
    562734217 512432712114123 7985HARVARD
  • HARVARD - Harvard Geophysical Center (USA)

    • Figure 5


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