Information message about sensitive earthquake in Georgia on September 7, 2009

     The sensitive earthquake with М=6.1 has occurred in Georgia on September 7, 2009 at 22:41 GMT (September 8, 2:41 Moscow time).
     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 13 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).
     Preliminary processing has been done with data from 60 stations, accurate processing - with data 67 stations.
     Fig. 1 presents fragment of three component record obtained from digital station Kislovodsk (∆ 1.4º). Fig. 2 presents fragments of records obtained from digital stations Obninsk (∆ 13.2º), Arti (∆ 16.9º), Lovozero (∆ 25.7º), Talaya (∆ 40.9º), Yakutsk (∆ 51.9º).

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 22-41-34.9 42.63 43.33  10  67  6.1/256.1/248.5-9 73 IPC GS RAS (Accurate)
2 22-41-35.4 42.68 43.38  10  60  6.1/246.2/208.5-9 90 IPC GS RAS (Preliminary)
3 22:41:36.5 42.66 43.42  10  591  5.9Mw   16 CSEM
4 22:41:36.9 42.712 43.483  10  146  6.2 Mw 5.7/105 32 NEIC
5 22:41:36.9 42.55 43.51  10    6 Ml    UNSSPG
  • 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
  • UNSSPG - United National Survey for Seismic Protection , Georgia
    • Epicenter
          Fig.3 depicts with yellow star epicenter of this earthquake, which was located at the north of Geogia - in high maoutainous region at the depth of 10 km, 27 km N-W from Kvaisi (South Osetia), 40 km N-N-E from Sachkhere (Georgia), 68 km N-W from Tshinval - capital of South Osetia, 155 km N-W from Tbilisi - capital of Georgia and 93 km S-S-W from Nalchik (Russia).

    Figure 3
    Aftershock
         By 19:00 Moscow time GS RAS has registered 23 aftershocks with magnitudes from 3.7 till 5.1 on September 9.
    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
    200929102009-09-07 22:49:29.042.5543.611019-5.1/ 55.5-6 Western Caucasus
    200929032009-09-07 23:21:02.042.643.491022-4.4/ 74 Western Caucasus
    200929042009-09-07 23:33:49.042.6543.691015-4.3/ 43.5-4 Western Caucasus
    200929052009-09-07 23:36:06.042.6543.511010-4.2/ 33.5 Western Caucasus
    200929082009-09-07 23:40:50.042.6143.38107-3.7/ 12-2.5 Western Caucasus
    200929092009-09-07 23:57:57.042.6443.4109-4.1/ 23-3.5 Western Caucasus
    200929112009-09-08 00:07:18.042.5943.461013-4.1/ 33-3.5 Western Caucasus
    200929122009-09-08 00:18:40.042.5743.41010-4.0/ 13 Western Caucasus
    200929132009-09-08 00:58:56.042.6443.541011-4.0/ 33 Western Caucasus
    200929142009-09-08 01:24:55.042.5543.4108-3.7/ 12-2.5 Western Caucasus
    200929152009-09-08 02:03:27.042.6143.47107-3.7/ 12-2.5 Western Caucasus
    200929162009-09-08 02:11:20.042.5543.471010-3.9/ 32.5-3 Western Caucasus
    200929062009-09-08 02:57:53.042.6243.681014-4.2/ 43.5 Western Caucasus
    200929182009-09-08 03:26:40.042.5243.531013-4.0/ 23 Western Caucasus
    200929212009-09-08 06:24:34.042.5843.341011-3.9/ 32.5-3 Western Caucasus
    200929222009-09-08 10:10:36.042.6443.541012-3.9/ 22.5-3 Western Caucasus
    200929252009-09-08 17:50:48.042.6143.531028-4.8/ 64.5-5 Western Caucasus
    200929292009-09-08 22:33:55.042.643.641015-4.2/ 63.5 Western Caucasus
    200929372009-09-09 02:37:54.042.6243.51011-4.1/ 13-3.5 Western Caucasus
    200929342009-09-09 04:54:11.042.6243.481010-3.9/ 12.5-3 Western Caucasus
    200929382009-09-09 07:11:23.042.6143.371011-3.7/ 12-2.5 Western Caucasus
    200929392009-09-09 08:36:16.042.5443.571036-4.7/ 84.5-5 Western Caucasus
    200929402009-09-09 09:44:21.042.5443.541020-4.3/ 53.5-4 Western Caucasus
    Macroseismic manifestations
         This earthquake has been felt in Georgia – in Tbilisi with intensity of 5 MSK, in Oni with 6 MSK, in South Osetia – in Tshinval with 4-5 MSK. Underground shocks were felt in Armenia, in towns Gumri, Vanadzor and Alaverdi in particular, as well as in Tovuz, Gazakh, Agstafinsk and Shamkirsk region of Azerbaijan, in Abkhazia and Turkey. On the territory of Russia it was felt in North Osetia, Chechen Republic, Ingush Republic, Kabardino-Balkaria and Stavropol Region.
    Historical records
         In accordance with the map of seismic activity of Caucasus CP-91 [Earthquakes in USSR in 1991, M. GS RAS. 1997] and the general map of Seismic activity OCP-97 (Dr. Ulomov and others. 1997) this region belongs to 9 MSK active zone. Dr. E.A.Rogozhin (2002) determined seismic dangerous zone in this region with Мmax=6.7-6.9 based on the method of seismic regionalization of seismic potential with maximum potential magnitude Ммах of forcasted earthquakes and location of potential seismic origins using Reisner and Iohanson technique (1993). Fig.4 demonstrates it’s fragment and location of epicenter of this earthquake. This earthquake has occurred on September 7 in the region of Rachi (so called historical province of Georgia, which occupies territory of upper and middle parts of Rioni river) in th north of Georgia. In accordance with tectonic regionalization of Caucasus [composed by Dr. Bogachkin, Borisov, Rogozhin, 1992] this territory belongs to Chiatursky flysch syncline of Big Caucasus, joint with Gagro-Java tectonic zone, where, as it is known, one of the most significant earthquakes of Caucasus in XX century has happened on April 29, 1991 with magnitude Мw=7.0 and intensity in epicenter 8-9 MSK. The earthquake on April 29, 1991 has been accompanied with powerful series of secondary shocks, spatial distribution of them is shown on fig.5 in accordance with information of Dr. S.S.Arefieva [2003]. As one can see the aftershock process had spatial propagation in certain directions different from direction of the main process associated with Gagro-Java deep rupture. Epicenter of reported here earthquake is located at the north end of brunch to the upper side of Rioni river, this is approximately in 35 km from the main shock of Racha-Java earthquake, which occurred on April 29, 1991. On February 6, 2006 the earthquake with M=5.1 has occurred in this zone. At that time the strong shocks were felt in Georgia - in Kutaisi, Sakhchere, Tskaltubo, Lentekhi. In Armenia – it was felt in Gumri, Noyembriane, Stepanovan. On the territory of Russian Federation the earthquake of February 6, 2006 was felt in Kabardino-Balkaria and North Osetia.

    Figure 4
    Figure 5
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism solution for the earthquake which occurred on September 7, 2009 at 22:41 GMT was calculated in GS RAS with use of initial arrivals of Р-waves at 95 stations, 78 of these stations registered the waves of compression (plus signs) and 17 stations the waves of expansion (minus signs). These stations are located in the interval of epicenter distances of Δ=1.37-95.2º with rather uniform distribution along the azimuths. Focal mechanism for Р-waves in stereographical projection at lower hemisphere is shown on fig.6, element of focal mechanism of the origin are presented in table 2. Solution obtained with CMT technique in NEIC USA – USGS and in Quick CMT Catalog, USA are also presented in table 2 and shown on fig. 7, 8. All solutions are almost identical. The earthquake has occurred under the action of compression forces oriented to S–W direction, both nodal planes have N-E direction of propagation and are rather steeply falling in case of Р-waves and USGS (falling angles of these planes change in the interval DP=32º-58º). Type of motion along both planes – «pure uplift» – in case of Р-wave solution, and in case of USGS –uplift with left side shift components for NP1 and – right side shift components for NP2. From Quick CMT Catalog solution one of the nodal planes is flat and the type of motion along it – overthrust with right side shift components, while for steeply falling plane – uplift with left side shift components. The value of seismic moment Мо of the earthquake on September 7, 2009 was obtained in GS RAS from spectrum of Р-wave at Talaya station (Δ 40.9º) and it makes 3.8* 10** 18 n*m, the value of moment magnitude was calculated with Kanamori formula and it makes Mw =6.3. The value of seismic moment Мо in accordance with USGS makes 7.8* 10** 17 n*m, the value of moment magnitude makes Mw = 5.9 and in accordance with Quick CMT Catalog – Mo=1.33* 10** 18 n*m, Mw = 6.0
    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
    774013225 11351345889317 3292IPC GS RAS
    8633214 11241234887307 4293NEIC
    67220210 101171126679317 26112Quick 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

    • Figure 6
    Figure 7

    Figure 8


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