Information message about destructive earthquakes on the shore of South Sumatra, Indonesia, September 30 and October 1, 2009

     Destructive earthquake with M=7.4 has occurred on September 30, 2009 at 10:16 GMT (14:16 Moscow time) at the western shore of South Sumatra, Indonesia. Another less strong shock with M=6.7 has occurred on October 1, 2009 at 01:52 GMT (05:52 Moscow time) at the western shore of South Sumatra, Indonesia.
     Alert message has been sent in 19 min. after the first earthquake to EMERCOM duty staff of Russia. The same meesage about the second earthquake has been sent in 18 minutes after it's registration.
     Summary processing of the first earthquake has been done with data from 48 stations, of the second earthquake - with data from 45 stations.
     Fig. 1 presents fragments of records obtained from digital stations Talaya (∆ 52.4º), Arti (∆ 66º), Kislovodsk (∆ 67.6º), Petropavlovsk (∆ 72.5º), Obninsk (∆ 75.8º) for the first earthquake. Fig. 2 presents fragments of records obtained from digital stations Ala-archa (∆ 51º), Kurchatov (∆ 56.4º), Erimo (∆ 58º), Arti (∆ 68.2º), Obninsk (∆ 77.9) for the second earthquake.

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:
Note: [1]- data for the first earthquake [2]- data for the second earthquake
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 01-52-29.8 -2.36 101.56  33  43  6.7/246.2/237.5-8 134 IPC GS RAS ([2])
2 10-16-08.6 -0.84 99.88  90  48  7.3/257.4/247-7.5 103 IPC GS RAS ([1])
3 01:52:28.9 -2.52 101.66  10  195  6.8 Mw   35 CSEM ([2])
4 10:16:09.8 -0.79 99.819  80  485  7.8 Mw   45 CSEM ([1])
5 10:16:09.9 -0.789 99.961  80  42  7.6 Mw 7.1/32 47 NEIC ([1])
6 01:52:29.9 -2.589 101.546  15  197  6.6 Mw 6/70 36 NEIC ([2])
  • 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 yellow star epicenter of the first earthquake, which was located near the western coast of South Sumatra Island, Indonesia, at the depth of 90 km, in 55 km W-N-W from Padanga, Indonesia, in 235 km S-W from Pekanbaru, Indonesia, in 508 km S-S-E from Medan, Indonesia, in 488 km S-S-W from Kuala-Lumpur, Capital of Malaysia and in 966 km N-W from Jakarta, Capital of Indonesia. Epicenter of second earthquake is shown with red star, which was located at the western shore of South Sumatra Island, Indonesia, at the depth of 33 km, in 252 km S-S-E from the first shock, in 176 km N-N-W from Bengkulu, Indonesia, in 247 km W-S-W from Jambi, Indonesia, in 361 km W-N-W from Pelembanga, Indonesia, in 480 km S-W from Singapore and in 715 km N-W from Jakarta, Capital of Indonesia.

    Figure 3
    Aftershock
         GS RAS registerd 1 aftershock with М=5.8, which occurred in 22 minutes after the first more strong shock and 1 aftershock with М=5.3, which occurred in 28 minutes after the second strong 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
    200931862009-09-30 10:38:48.0-0.86100.038026-5.8/ 224-4.5 Southern Sumatera, Indonesia
    200932002009-10-01 02:20:31.0-2.32101.583322-5.3/ 104-4.5 Southern Sumatera, Indonesia
    Macroseismic manifestations
         The first earthquake in accordance with data from 1 TV Channel, Russia destroyed dozens of settlements, and almost fully destroyed one of the biggest Indonesian cities - Padang. There are numerous injured people in overcrowded hospitals and camp hospitals. Destiny of thousands of people is unknown. Local residents try themselves to fight fires. The earthquake caused a few land slides, which cut the roads. Phone lines are broken between settlements. The strong shocks were felt even in country’s capital Jakarta located in thousand kilometers from the earthquake, as well as in neighboring countries – Malaysia and Singapore. From the latest data ITAR-TASS the number of victims reached 1100 people. Representative of crisis center of Health Ministry claimed that thousands of people are under the debris. Thus the score of victims continue to grow.

    Figure 4
    Figure 5
    Historical records
         Indonesia is located in one of the most seismically intensive zones of the planet, it is part of so called Pacific Fire Ring. This region holds active tectonic Australian and Sunda plates. In last five years more then 200 thousand people were killed in Indonesia after catastrophic earthquakes. Thus in December 2004 (see. Information message about catastrophic earthquake in the region of Northern Sumatra – December 26, 2004 ) the strongest tsunami felt on the North-Western shore of Sumatra Island, it killed 168 thousand people. Another 40 thousand people were moved into the sea. In March 2005 (see. Information message about second catastrophic earthquake in the region of Northern Sumatra – March 28, 2005 ) nearly thousand of people were killed after the earthquake in the region of Nias Island near Sumatra. May 26, 2006 in central part of Java Island the third catastrophic earthquake has occurred which killed more than 5000 people. The last destructive earthquake in Indonesia has occurred at Java Island on September 2, 2009 .
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism solutions for the earthquake which occurred on September 30, 2009 at 10:16 GMT 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. 6,7. These solutions are almost similar. The earthquake has occurred under the action of N-W oriented compression forces. Both nodal planes are rather steeply falling (DP=51º-57º), one of them – NP1 – has nearly along meridian direction of propagation, another – NP2 – propagates in N-E direction. The type of motion along both planes – uplift with drift components (left side along NP1 and right side along NP2). Averaged value of seismic moment Мо for the earthquake which happened on September 30, 2009 obtained in IPC GS RAS with P-wave spectra at four stations: Talaya (Δ34..2°), Arti (Δ66.1°), Kislovodsk (Δ67.6º), Obninsk (Δ75.7º), makes Мо=3.5* 10** 20 n*m, the value of moment magnitude calculated from Kanamori formula makes Mw = 7.7. The value od seismic moment Мо for the earthquake which happened on September 30, 2009 in accordance with USGS data makes Mo=2.6* 10** 20 n*m, the value of moment magnitude Mw = 7.5; in accordance with data from Global CMT Catalog – Mo= 2.64* 10** 20 n*m, Mw=7.5.
    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
    57431311 32220194554970 52132NEIC
    56474311 34216193584972 51136Quick CMT
  • NEIC - National Earthquakes Information Center of US Geological Service
  • Quick CMT - Quick CMT catalog

    • Figure 6
    Figure 7


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