Information message about the earthquake in the North-West of Russia near Kaliningrad on September 21.

     On September 21, 2004 a few series of the earthquakes have been registered in the North-West of Russia near Kaliningrad with the maximum magnitude (Ms=4.3) at 13:32 GMT (16:32 Moscow time). This strongest event has been preceded by the earthquake with magnitude Ms=4.0 at 11:05 GMT (13:05 Moscow time). The weak strike has been registered later at 13:36 GMT (16:36 Moscow time). From EMERCOM and mass media messages the first two events have been felt on the territory of Kaliningrad region and in adjacent regions of Byelorussia and Baltic states, as well as in Northern regions of Poland and in the South of Finland.
     Alert message about the first earthquake has been sent to EMERCOM Russia in 25 minutes after it happened. Alert message about the second earthquake has been sent in 10 minutes.
     Preliminary processing has been done with data from 14 stations, accurate processing - with data 24 stations.
      Fig. 1 presents fragments of records for the first earthquake at 11:05 obtained by 4 digital stations nearest to the epicenter and located in Vasula - VSU, Estonia (delta 5 degrees), Kasperske Hory - KHC, Czech Republic (delta 7 degreesов), Pulkovo - PUL (delta 7.4 degrees), Obninsk - OBN (delta 9.3 degrees), Fig. 2 presents fragments of records from the same digital stations for the second earthquake at 13:32. The earthquake has been registered by all stations of Institute of Geophysics of Poland’s Academy of Sciences. The nearest to the epicenter station of this network - Suvalki (SUW), records from this station along with others are available in Internet and have been used at getting accurate parameters of the epicenter. Besides that, these earthquakes have been registered by the station of Petrozavodsk Institute of Geology in Karelia scientific center of RAN, records from this station have been sent to Obninsk and used in getting accurate parameters of hypocenter.

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]- for the first earthquake[2]- 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 13-32-29.30 54.77 20.29  15  24  4.30/45.40/45-698 IPC GS RAS (accurate [2])
2 11-05-03.30 54.78 20.29  15  24  4.10/25.70/34-598 IPC GS RAS (accurate [1])
3 11-05-04.40 54.76 20.37  20  14  4.10/25.70/34-598 IPC GS RAS (preliminary [1])
4 13-32-29.80 54.59 20.48  15  14  4.3/45.4/45-698 IPC GS RAS (preliminary [2])
5 13-32-29.20 54.77 19.94  10  97   5.0  78 CSEM ([2])
6 11-05-04.20 54.69 20.23  10  73   4.4  85 CSEM ([1])
7 13-32-30.61 54.787 20.026  10  46   5.0/24 38 NEIC ([2])
8 11-05-03.86 54.914 20.172  10  23   4.8/11 63 NEIC ([1])
9 11-05-08.70 54.8 19.7  100     4.8   ORFEUS ([1])
10 13-32-29.2 54.8 19.9  10     5.0   ORFEUS ([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
  • ORFEUS - Observatories and Research Facilities for EUropean Seismology
    • Epicenter
         From the tectonics point (fig. 3) these earthquakes have happened on the territory of East-European Platform which is part of Baltic syncline (Yudahin, Shukin, Makarov, 2003 – “Deep structure and modern geodynamical processes in lithosphere of East-European Platform”) Forecasts of potential danger and investigations of scientists from Belorussia and Baltic states classify this area as Kaliningrad-Lithuanian potentially seismogenous zone. Complex seismo tectonics analysis (Reisner, Iohanson, 1980) estimates the potential seismic danger of this area as 7 MSK and corresponds to M max = 4.0 (at the minimum depths of hypocenters equal to 5 km.).

    Figure 3
    Aftershock
         Alert Service of GS RAS has identified that in 4 minutes after the second most strongest earthquake at 13:36 it was accompanied with aftershock having magnitude Ms=3.
    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
    200416212004-09-21 13:36:49.054.7220.711543.0/ 1-3-3.5 Baltic-Belarus-NW Russia reg.
    Macroseismic manifestations
         The earthquakes on September 21 have been felt on a vast territory of Kaliningrad region, Baltic States including Lithuania, Latvia, Estonia and Finland, as well as in Byelorussia and Poland. Information on these earthquakes have been published on many seismological WEB sights (ORFEUS, CSEM, NEIC, Institute of Geophysics of Poland’s Academy of Sciences ) and in mass media. Regional EMERCOM center claims that epicenter was located near Lublino settlement in 20 km. From Kaliningrad. In Kaliningrad and resorts Svetlogorsk and Peonersky the earthquakes were felt with intensity 4-5MSK of 12MSK scale. During these earthquakes furniture and household appliances were falling down in the houses. From the latest information (ORT) on September 22 by 4pm. 20 injured people visited hospitals for aid, minor damage of buildings was observed and pump hole with depth of 20 meters has occurred in Svetlogorsk. From Poland’s agency these earthquakes have been felt in many towns of Poland and they are considered now as the strongest from known earthquakes for the territory of Poland. Preliminary estimations of collected information and calculated strength in epicenter the first earthquake at 11:05 may be considered as 5 MSK event, while the second earthquake at 13:32 may be considered as 5-6 MSK event. In accordance with data from Geophysical Monitoring Center of Belorussia the earthquake at 13:32 has been felt on a vast territory of Belorussia: in Minsk, Grodno, Pleshinica, Narochi – with intensity 3-4MSK. This earthquake has been felt in St.Petersburg with intensity 2 MSK. From ITAR-TASS information nearly 1146 buildings in Kaliningrad have obtained different damages. These buildings included 1061 living buildings, 46 cultural objects, 39 communal structures. Preliminary calculations estimated the damage as 98 million rubles. At the same time no serious destructions are noticed in Kaliningrad.
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism solution of the earthquake 21.09.2004 at 13:32 has been obtained in Harvard center (США) HARVARD with TMC method. Table 3 presents elements of this mechanism from HARVARD data. Figure 4 gives graphical representation of stereographical projection for lower hemisphere of focal mechanism. The solution obtained in Harvard demonstrates shift nature of focal mechanism. Investigated earthquake has happened in conditions of both compression strengths oriented in South-South-East-North-North-West direction and expansion strengths oriented to the North-East-East-South-West-West. Both nodal planes have rather steep falling angle with prevailing shift component in motion along both planes. The value of seismic moment Мо from Harvard makes 1.41* 10** 16 n*m, the value of moment magnitude - Mw = 4.7.
    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
    17116161 7433820578-11297 80-168HARVARD
  • HARVARD - Harvard Geophysical Center (USA)

    • Figure 4


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