Information message about the sensitive earthquake in Georgia on February 6, 2006

     Sensitive earthquake with magnitude М=5.1 has happened in the territory of Georgia on February 06 at 04:08 GMT (7:08 Moscow time). It occurred in the epicentral area of Racha-Java earthquake, known as one of the strongest earthquakes of previous century, which happened on April 29, 1991 with magnitude М=6.9.
     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 42 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).
     Data from 4 stations of the united national service of seismic protection at the Institute of geophysics of Georgia by the name of M.Z. Nodia have been used at getting accurate calculation parameters. This information was obtained by exchange. Total number of 14 regional distance (from 80 to 800 km) stations have been involved in data acquisition, they include the stations located in Vladikavkaz, Anapa, Sochi, Kislovodsk, Piatigorsk, Mahachkala – these are the stations of Geophysical Survey of RAN, and Simpheropol (station of Crimean network of Institute of Seismology of Ukraine).
     Fig. 1 presents fragments of records from digital stations: Ardon (0.8 degrees), Vladikavkaz (1 degrees), Sunzha (1 degree), Kislovodsk (1.5 degrees), Sochi (2.9 degrees), Mahachkala (3 degrees). Fig. 2 presents fragments of records from digital stations: Obninsk (13.3 degrees), Arti (16.9 degrees), Vasula (19 degrees), Ala-Archa (22.8 degrees), Kurchatov (25.2 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 04-08-00.6 42.61 43.61  15  30  5.1/105.7/86141 IPC GS RAS (Preliminary)
2 04-08-01.0 42.64 43.49  15  49  5.1/155.6/116114 IPC GS RAS (Accurate)
3 04-07-59.9 42.62 43.54  10  272   5.0  43 CSEM
4 04-08-04.3 42.67 43.59  25  20   4.9/8  NEIC
5 04-07-59.7 42.49 43.44  7  18  K13.3   122 NCOB GSRAS
  • 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
  • NCOB GSRAS - Northern Caucasus operative bulletin of GS RAS
    • Epicenter
         Epicenter of the reported here earthquake belongs to the origin area of the known strongest Racha-Java earthquake, which happened on April 29, 1991 with М=6.9 (fig.3). This area stayed highly seismic active in the recent yeas, however no earthquakes have been registered here with magnitude 5 and more since May 3, 1991. In the year 2005 in accordance with data from local networks of North-Osetian branch of GS RAS and Caucasian Mineral Waters laboratory nearly 60 earthquakes with magnitude from 1 to 3.5 have been registered here. The strongest of them with magnitude 3.5 have happened on January 27 at 07:04 and on November 2, 2005 at 02:17 (fig.4).

    Figure 3
    Figure 4
    Aftershock
         This earthquake has been accompanied with aftershocks and 7 most significant of them have been registered by Geophysical Survey of RAS. In accordance with data of North-Osetian branch of GS RAS by 12pm GMT nearly 20 aftershocks with magnitude М>1 have been registered.
    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
    200602962006-02-06 04:48:06.042.4743.461543.2/ 1-3.5-4 Western Caucasus
    200602972006-02-06 05:46:55.042.6743.721563.2/ 1-3.5-4 Western Caucasus
    200602982006-02-06 06:29:21.042.3743.491553.1/ 1-3.5 Western Caucasus
    200602992006-02-06 06:58:13.042.643.391532.7/ 1-2.5-3 Western Caucasus
    200603012006-02-06 07:14:43.042.543.41532.2/ 1-2-2.5 Western Caucasus
    200603022006-02-06 09:43:26.042.7843.7715204.0/ 64.6/ 54.5-5 Western Caucasus
    200603062006-02-06 13:23:31.042.4243.671542.8/ 1-3 Western Caucasus
    Macroseismic manifestations
         The strong strikes have been felt in towns Kutaisi, Sahchera, Tskaltubo, Lentehi. Because of the earthquake electricity supply has been terminated in Chiatura town. The earthquake lasted nearly 2 minutes. From preliminary information there were no destructions of victims. Undeground strikes were felt by residents of Rachinsk region, Lower Svanetti and Imeretti. Insignificant destructions were reported in villages of Ambrolaura region. Cracks in the walls have been seen in a few buildings after the strikes. (RIAN News Service, publish in "Газета.RU"). In accordance with message from National Service of Seimic Protection of Armenia this earthquake has been felt in the north of Armenia: in Gumri, Noemberian with intensity 3-MSK, in Stepanovan with intensity 3-4 MSK. On the territory of Russian Federation this earthquake has been felt in Kabardino Balkaria, from data of this republic’s EMERCOM in Nalchik and Alagire (Northern Osetia-Alania) this earthquake has been felt here with intensity of 3-4 MSK.
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism solution of this earthquake’s origin on 06.02.2006 at 04:08 is presented in accordance with data from European – Mediterranean Seismological Center (CSEM). Focal mechanisms are presented on fig.5 in their graphical representation in stereographical projection (lower hemisphere, waves of compression areas are shown in dark). Elements of mechanism are presented in table 2. One of nodal planes (NP1) has North-Western direction of propagation and flat deposition. The other nodal plane (NP2) spreads in latitudinal direction and has a steep falling angle. Investigated here earthquake has happened under the action of longitudinally oriented strengths of compression. The type of motion along the flat plane – thrust with components of right side drift, the type of motion along the other plane is uplift. The value of seismic moment Мо makes 6.9* 10** 16 n*m, the value of moment magnitude - Mw = 5.2.
    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
    6133020197 191003173013192 6869CSEM
  • CSEM - European - Mediterranean seismological center

    • Figure 5


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