Information message about the strong earthquake on the territory of Koriak autonomous area being part of Kamchatka Region on April 21, 2006.

     On April 20, 2006 at 23:25 GMT (April 21, 12:25 local time) the strong earthquake with magnitude М=7.8 has happened in the ridge area of Koriak mountains, to the north-west from Goven peninsula. Calculated intensity of this earthquake in the epicenter area reached 8-9 MSK on the 12 MSK scale called MSK64. This earthquake has happened in the origin zone of the famous Koriak earthquake, which occurred on March 8, 1991 with magnitude М=7 and calculated intensity equal to 8 MSK.
     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 23 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 55 stations.
     Fig. 1 contains fragments of records obtained from digital stations Bilibino (∆ 7.1º), Magadan (∆ 8.2º), Petropavlovsk (∆ 9.2º), Yakutsk (∆ 17.7º), Tiksi (∆ 18.3º), Yuzhno-Sakhalinsk (∆ 19.8º). Fig. 2 contains fragments of records obtained from digital stations Talaya (∆ 35º), Borovoe (∆ 49º), Arti (∆ 50º), Ala-Archa (∆ 55º), Pulkovo (∆ 55º), Obninsk (∆ 58º).

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 23-25-03.0 60.96 167.06  45  55  7.8/186.8/258.5-968 IPC GS RAS (Accurate)
2 23-25-02.5 60.98 167.1  40  37  7.8/116.6/109-9.5127 IPC GS RAS (Preliminary)
3 23-25-02.8 61.1 167.2  40  416  7.7Mw   47 CSEM
4 23-25-05.4 61.09 167.1  43  172  7.7Mw   47 NEIC
  • 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 reported here earthquake almost coincided with epicenter of the earthquake which happened here on March 8, 1991 at 11:36 GMT with magnitude М=7.0 and called Kariak earthquake, because it’s epicenter was located in the ridge area of Koriak mountains (fig.3).

    Figure 3
    Aftershock
         This earthquake has been accompanied with numerous aftershocks. Parameters of 18 strongest aftershocks have been determined by 4 PM on April 21 in accordance with data of Alert Survey GS RAS.
    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
    200611152006-04-20 23:38:49.061.22167.513320-5.7/ 35-5.5 Eastern Siberia, Russia
    200611162006-04-21 00:06:15.061.05167.453321-5.4/ 64.5 Eastern Siberia, Russia
    200611172006-04-21 00:28:57.061.53167.83321-5.0/ 63.5-4 Eastern Siberia, Russia
    200611182006-04-21 00:32:34.060.86166.385023-5.2/ 73-3.5 Eastern Siberia, Russia
    200611192006-04-21 00:51:11.061.11167.013330-5.7/ 65-5.5 Eastern Siberia, Russia
    200611302006-04-21 01:12:09.060.57165.793322-4.7/ 62.5-3 Eastern Siberia, Russia
    200611202006-04-21 01:30:06.060.87166.013324-5.2/ 64-4.5 Eastern Siberia, Russia
    200611212006-04-21 01:44:10.060.66166.153331-5.5/ 64.5-5 Eastern Siberia, Russia
    200611222006-04-21 01:53:36.060.82165.933318-4.9/ 63-3.5 Eastern Siberia, Russia
    200611232006-04-21 02:33:46.061.03167.13321-5.0/ 53.5-4 Eastern Siberia, Russia
    200611242006-04-21 03:05:14.061.07167.463321-4.9/ 63-3.5 Eastern Siberia, Russia
    200611252006-04-21 02:43:49.060.98166.723313-4.9/ 63-3.5 Eastern Siberia, Russia
    200611262006-04-21 03:41:54.060.71165.713326-5.1/ 73.5-4 Eastern Siberia, Russia
    200611272006-04-21 04:32:43.060.57165.8620496.2/ 186.4/ 177.5-8 Eastern Siberia, Russia
    200611282006-04-21 07:32:26.061.54167.724016-5.1/ 63.5 Eastern Siberia, Russia
    200611292006-04-21 07:40:06.060.93166.844027-5.3/ 84 Eastern Siberia, Russia
    200611312006-04-21 08:57:33.060.21165.983310-4.9/ 23-3.5 Eastern Siberia, Russia
    200611332006-04-21 11:14:17.061.37167.5640396.2/ 135.9/ 136.5-7 Eastern Siberia, Russia
    Macroseismic manifestations
         From RIA "News" this earthquake on April 21 has been felt in Olutorsk and Karagansk regian of Koriak autonomous region. It was felt in settlements Tilichiki, Ossora and Korf with intensity 4-5. In Tilichiki settlement, which is located 70 km from the epicenter, four people were injured. Cracks damaged airport field, one school and kindergarten were partially destroyed, some houses were damaged, cracks were observed on the walls of the buildings, chimneys of boiling stations have fallen down. Some parts of heating pipes and electricity supply lines were damaged. Diesel power stations were shut down. Electricity supply in settlements Korf and Tilichiki was terminated (fig.4). In accordance with Magadan branch of GS RAS this earthquake has been felt in Magadan with intensity 2. On OCP-97-C map epicenter of this earthquake was located within 9-MSK zone.

    Figure 4
    Historical records
         The earthquake on March 8, 1991 was the first one with such intensity, registered in Koriak mountains. (Koriak earthquake on March 8,1991 //Cat.earthquakes in the USSR in1991. M.1997 pp. 76-88). That earthquake was accompanied with long lasting series of aftershocks. Epicenter zone of that earthquake coincide with reported here earthquake and was located in the valley of Vivenka river to the north from Mallar mountain between two big ridges of Koriak mountains: Pilginsk and Vetveisk ridges (fig.3). From tectonics point Koriak mountains is reflection of formation processes in Komandor depression of Bering Sea (Zobin, 1997). Active tectonic of western frame of Komandor depression is proved by it’s rather high level of seismic activity (fig.5). At the same time unlike the seismic activity of Kurilo-Kamchatka island bow, which is in the North is continued directly by the ridges of Koriak mountains, the earthquakes near the western coast of Bering Sea do not demonstrate permanent high background activity. They happen in the form of seismic flashes during the long lasting calm periods, one can sea this on the map with epicenter of Kamchatka and Komondor islands regions which was created in accordance with Seismic Bulletin for the period between 1988 and 2006.(fig.5).

    Figure 5
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism of this earthquake has been calculated in GS RAS with initial signs of Р-wave arrivals at 59 stations, at 51 stations the waves of compression have been registered (symbols plus on the map), 8 stations registered the waves of expansion (symbols minus on the map). These stations are located in the epicenter distances of 7-97 degrees with rather uniform distribution along azimuths from 57 till 358 degrees. Focal mechanism solution of the origin is shown in stereographical projection on lower hemisphere in figure 6, elements of this mechanism are presented in table. 2. Fig. 7, 8 present focal mechanism solutions obtained from TMC method in National Earthquakes Information Center, USA (NEIC) and from CMT method in Harvard Center(USA) (HARVARD) for this event. As one can see these two solutions are almost identical. The motion in origin has happened under the action of expansion forces oriented to the South-East. Axis of compression and expansion are oriented to the cross of Kuril-Kamchatka bow, that is typical for the earthquakes of this zone. Focal mechanism represents reverse. Both nodal planes have North-Eastern direction of propagation coinciding with direction of Kuril-Kamchatka bow. Seismic moment Мо of this earthquake has been determined from spectra of Р-waves registered by IRIS digital equipment at three seismic stations: Arti (ARU), Obninsk (OBN), Kislovodsk (KIV), located at distances 50-66 degrees. Averaged value of Мо makes 2.4 Е 20 n*m. The value of moment magnitude Mw calculated with Kanamori formula is equal to Мw=7.5. The value of Мо from data of Harvard seismological center makes Мо =3.06 Е 20 n*m., Мw=7.6. As one can see, the values of Мо and Мw obtained with different methods are also close. Fig. 9 presents focal solutions for Koriak earthquake which happened on 8.03.1991 with М=7.0. Focal solution of that earthquake is close to focal solution of the reported earthquake on 20.04.2006. The motion in origin was characterized as взбросом, both nodal planes were oriented along Kuril-Kamchatka zone with the values of Мо=1.01 Е 19 n*m and Мw=6.6.
    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
    81390129 9219209467748 46103IPC GS RAS
    60619316 29221202605675 44134NEIC
    8026126 8217207407744 51101HARVARD
  • 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 6
    Figure 7

    Figure 8
    Figure 9


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