Information message about the second catastrophic earthquake in the region of Northern Sumatra on March 28, 2005.

     Catastrophic earthquake has happened on March, 2005 near the North-West coast of Sumatra Island, Indonesia at 16:09 GMT with magnitude М=8.5. Epicenter of this earthquake was located at nearly 200 km to the South-East from catastrophic earthquake of December 26, 2004. Aftershock process from December earthquake is under way even this time, however it's aftershock area is located to the North-West from the reported here event.
     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 40 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).
     Fig. 1 presents fragments of records obtained from digital stations Ala-Archa (delta 45 degrees), Talaya (delta 50 degrees), Kurchatov (delta 51 degrees), South-Sakhalinsk (delta 60 degrees), Garni (delta 61 degrees). Fig. 2 presents fragments of records obtained from digital stations Arti (delta 62 degrees), Kislovodsk (delta 64 degrees), Yakutsk (delta 65 degrees), Magadan (delta 71 degrees), Obninsk (delta 72 degrees).

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 16-09-34.5 2 97  33  27  8.5/147.1/1410-10.5126 IPC GS RAS (Предварительный)
2 16-09-34.60 2.03 97.01  33  43  8.50/177.10/20 126 IPC GS RAS (Уточненный)
3 16-09-32.5 2.16 97.17  10  258  8.6Mw   68 CSEM
4 16-09-37.06 2.09 97.02  30  65   7.2/57  NEIC (Предварительный)
5 16-09-36.2 2.07 97.01  30  239  8.5/1297.2/64 25 NEIC (Уточненный)
6 16-09-38.01 2.3 97.03  30  43   7.2  297 ORFEUS
  • 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
  • ORFEUS - Observatories and Research Facilities for EUropean Seismology
    • Epicenter
         Epicenter of this earthquake was located between the islands Nias and Simelue near the North-Western coast of Sumatra Island. Location of epicenter with the map of seismicity of 2005 in background is shown on figure 3. This figure was downloaded from National Earthquake Information Center (NEIC) web site of the US Geological Service - http://neic.usgs.gov/neis/bulletin/neic_weax_h.html It is clearly seen that the location of this earthquake’s epicenter is in the calm zone. Origin area of this earthquake was not influenced by aftershock process of catastrophic earthquake which happened in December 26, 2004 and it was located to the South-East. In accordance with NEIC information a few World Centers which monitor tsunami processes have warned about potential threat of tsunami from this earthquake. From ITAR-TASS (http://www.itar-tass.com/level2.html?NewsID=1875844&PageNum=0) information three meter tsunami has fallen on Simelue Island. More accurate information is now obtained about the damage and losses. From information published at Indian site (The Amateur Seismic Centre (ASC) - Maharashtra, India), this earthquake was accompanied with big waves of tsunami, which have been registered by flux-reflux stations installed in Indian Ocean ( http://asc-india.org/events/050328_bob.htm).

    Figure 3
    Aftershock
         This earthquake was accompanied with aftershocks. In accordance with IPC GS RAS data by March 30 it was registered 44 aftershocks with magnitudes mb=5.0-6.3. Location of the main shock on March 28 with magnitude М=8.5 is shown on fig. 4 as a yellow star, epicenters of aftershocks from this earthquake are shown in yellow rounds; epicenters of the previous earthquakes for the period 1955-2004 in accordance with Seismological Bulletin of CEME GS RAS are shown in green rounds, the earthquakes of 2005 till March 28 are shown on this map in pink rounds.

    Figure 4
    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
    200509242005-03-28 16:38:41.01.2397.493322-6.3/ 146.5-7 Northern Sumatera, Indonesia
    200509252005-03-28 16:44:05.0-1.3495.553316-6.3/ 126.5-7 Southwest of Sumatera, Indonesia
    200509262005-03-28 17:03:30.01.7796.413317-5.2/ 104-4.5Off w coast of Northern Sumatera
    200509272005-03-28 17:11:39.00.4397.173310-5.2/ 84-4.5Northern Sumatera, Indonesia
    200509282005-03-28 17:24:12.01.3397.033313-5.8/ 115.5 Northern Sumatera, Indonesia
    200509292005-03-28 17:29:01.00.7596.653314-5.4/ 114.5 Off w coast of Northern Sumatera
    200509302005-03-28 17:39:51.00.9196.563310-5.0/ 73.5-4 Off w coast of Northern Sumatera
    200509312005-03-28 17:59:47.01.3497.633310-5.6/ 95 Northern Sumatera, Indonesia
    200509322005-03-28 18:30:41.00.7897.83318-6.2/ 146-6.5Northern Sumatera, Indonesia
    200509332005-03-28 18:48:48.02.2695.93316-5.9/ 125.5-6 Off w coast of Northern Sumatera
    200509342005-03-28 19:02:17.00.8697.813316-6.1/ 126-6.5Northern Sumatera, Indonesia
    200509352005-03-28 19:26:39.01.9798.573312-5.1/ 93.5-4 Northern Sumatera, Indonesia
    200509462005-03-28 20:06:24.01.0697.373314-5.4/ 74.5 Northern Sumatera, Indonesia
    200509472005-03-28 20:23:19.00.8197.73315-5.4/ 94.5 Northern Sumatera, Indonesia
    200509482005-03-28 20:35:15.01.6296.943313-5.9/ 75.5-6 Off w coast of Northern Sumatera
    200509362005-03-28 23:12:58.00.1497.0333215.4/ 126.0/ 145.5-6 Northern Sumatera, Indonesia
    200509372005-03-28 23:37:29.02.9296.4733225.5/ 135.9/ 135.5-6 Northern Sumatera, Indonesia
    200509382005-03-28 23:39:47.0396.12338-5.9/ 75.5-6 Northern Sumatera, Indonesia
    200509392005-03-29 00:56:02.01.56973317-5.6/ 105 Northern Sumatera, Indonesia
    200509402005-03-29 02:22:54.02.7396.073311-5.4/ 64.5 Northern Sumatera, Indonesia
    200509412005-03-29 03:44:33.01.2496.93314-5.2/ 84-4.5Off w coast of Northern Sumatera
    200509422005-03-29 04:09:12.01.5497.013317-5.7/ 105-5.5Northern Sumatera, Indonesia
    200509432005-03-29 04:19:00.01.1697.183317-5.6/ 115 Northern Sumatera, Indonesia
    200509442005-03-29 04:50:01.0-0.8695.81339-5.4/ 64.5 Southwest of Sumatera, Indonesia
    200509452005-03-29 05:16:27.02.696.583320-6.2/ 126-6.5Northern Sumatera, Indonesia
    200509492005-03-29 05:35:35.00.6197.283310-5.0/ 63.5-4 Northern Sumatera, Indonesia
    200509502005-03-29 06:16:13.01.7799.273314-5.3/ 74-4.5Northern Sumatera, Indonesia
    200509512005-03-29 07:16:49.01.4997.563315-5.0/ 93.5-4 Northern Sumatera, Indonesia
    200509522005-03-29 09:15:55.00.897.273315-5.2/ 74-4.5Northern Sumatera, Indonesia
    200509532005-03-29 09:28:21.01.3397.143315-5.1/ 63.5-4 Northern Sumatera, Indonesia
    200509542005-03-29 09:42:57.01.2497.383311-5.1/ 73.5-4 Northern Sumatera, Indonesia
    200509562005-03-29 10:56:53.02.496.653319-5.4/ 94.5 Northern Sumatera, Indonesia
    200509572005-03-29 11:28:04.01.5496.343314-5.0/ 73.5-4 Off w coast of Northern Sumatera
    200509582005-03-29 12:56:02.05.4693.363312-5.2/ 84-4.5 Off w coast of Northern Sumatera
    200509602005-03-29 13:35:57.02.5997.373313-5.0/ 53.5-4 Northern Sumatera, Indonesia
    200509612005-03-29 14:16:04.02.6396.263314-5.2/ 64-4.5 Northern Sumatera, Indonesia
    200509622005-03-29 16:21:11.01.7497.683317-5.4/ 84.5 Northern Sumatera, Indonesia
    200509652005-03-29 17:20:48.02.6597.153315-5.1/ 93.5-4 Northern Sumatera, Indonesia
    200509662005-03-29 17:40:09.00.5597.213313-5.0/ 63.5-4 Northern Sumatera, Indonesia
    200509672005-03-29 18:06:34.02.4396.773316-5.1/ 83.5-4 Northern Sumatera, Indonesia
    200509682005-03-29 18:29:45.00.697.523312-5.0/ 73.5-4 Northern Sumatera, Indonesia
    200509692005-03-29 20:41:35.02.397.293318-5.6/ 95 Northern Sumatera, Indonesia
    200509702005-03-30 01:13:15.01.8997.0233175.5/ 105.8/ 95.5-6 Northern Sumatera, Indonesia
    Macroseismic manifestations
         From ITARR TASS information http://www.itar -tass.com/level2.html?NewsID=1875844&PageNum=0 –this earthquake has killed from one to two thousand people, mainly in Nias Island (fig.5 – ITARR TASS). As it is supposed in the Indian Center (http://asc-india.org/events/050328_bob.htm ) significant destructions caused numerous victims in the region of Gunungsitoli at the Northern caast of Nias Island. The witness reported that the shocks there were so big, that people could not stand on the ground. From information obtained in NEIC by March 29 -http://pasadena.wr.usgs.gov/shake/ous/STORE/Xweax_05/ciim_display.html this earthquake has been felt in 70 cities of Indonesia in Sumatra Island, Singapore and Malaysia on Malacca peninsula - fig.6. The most powerful event known for this area had intensity of VI MSK (Banda-Aceh, Bukkitingi, Malacca).

    Figure 5
    Figure 6
    Historical records
         The map on figure 7 (downloaded from NEIC site) illustrates historical events known for this region, one can see from this map that epicenter of reported earthquake has fallen in "window" between break zones from the strongest earthquakes, which have happened in 1833, 1861 and 2004.

    Figure 7
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism solution of the earthquake 28.03.2005 has been calculated with TMC method in National Earthquake Information Center (NEIC), USA and in Harvard Center (HARVARD), USA. It is presented in table 2 and shown on figures 8, 9. IPC GS RAS has obtained statically stable solution from the first signs of Р wave arrivals (with 75, d 8) and records obtained from 83 stations of Global Network IRIS (http://www.iris.edu/cgi-bin/wilberII_page1.pl). This solution is also presented in table 2 and shown on figure 10. Solutions obtained by different centers are rather identical and it is very important – they are similar to the focal mechanism of the earthquake, which happened in that region on December 26, 2004. The motion in origin has occurred under the action of the same value compression strengths oriented to the South-West direction and expansion strengths oriented to the North-East direction. One of the nodal planes has South-East - North-West spread direction and steep falling angle. The type of motion - thrust. The other nodal plane is flat and from NEIC data it is latitudionally oriented, and from Harvard data – it is oriented to the North-West - South-East. Type of motion along this plane - overthrust. The value of seismic moment Мо in accordance with NEIC made 1.5* 10** 21 n*m, the value of moment magnitude - Mw = 8.1. The value of seismic moment Мо in accordance with Harvard made 1.1* 10** 22 n*m, the value of moment magnitude - Mw = 8.6. The value of seismic moment Мо obtained in GS RAS with data from 3 stations OBN, KIV and TLY made 1.2* 10** 21 n*m, the value of moment magnitude - Mw = 8.0.
    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
    514439226 11353257100135 8489IPC GS RAS
    474543219 3312251429132 8893NEIC
    513738222 21303297109130 8388HARVARD
  • IPC GS RAS - Informational Processing Center, Geophysical Survey, Russian Academy of Sciences
  • NEIC - National Earthquakes Information Center of US Geological Service
  • HARVARD - Harvard Geophysical Center (USA)

    • Figure 8
    Figure 9

    Figure 10


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