Information message about increase of seismic activity at the region of Baikal Lake in September 2003

     In September 2003 increase of seismic activity has been observed in the region of Baikal Lake. The earthqake with magnitude M=5.4 has happened on September 16, 2003 in it's northern part (area of Baikal Lake) which was felt in settlements Uoyan and Kumora with intensity up to 5 MSK; On September 17 - in the south-western part of border area with Mongolia the earthquake with magnitude М=4,2 has happened, which was felt in settlement Mondi with intensity up to 5 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 27 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).
     Preliminary summary processing for the earthquake on September 16, 2003 has been done with data from 22 stations, accurate - from 35 stations. It is this eaarthquake, for which Information message contains the results of most detailed analysis. For the weak earthqukes in the south-western part of this region, which happened in September 17-20 it was impossible to collect the data, however it is necessary to pay special attention to this area, because 53 years ago (on April 4, 1950) the strong 9-MSK Mondin earthquake has happened here with magnitude М=7.
     Fig. 1 presents fragments of records from digital stations Yakutsk (delta 11,1 degrees), Tiksi (delta 17,2 degrees), Magadan (delta 21,0 degrees), South-Sahalinsk (delta 21,4 degrees), Borovoe (delta 23,7 degrees), Petropavlovsk-Kamchatsky (delta 27,2 degrees).

Figure 1
 
     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 11-24-55.40 56 111  33  35  5.40/205.00/125.5-659 IPC GS RAS (accurate)
2 11-24-55.90 56 111  33  22  5.4/115.0/135.584 IPC GS RAS (preliminary)
3 11-24-52.42 56 111  10  108   5.1/68 39 NEIC
4 11-24-55.0 56 111    21  5.5/16   IS NAS KR
5 11-25-10.55 57 109  30    5.47/215.29/21  BRIPC (accurate)
6 11-25-10.55 57 109  30     5.29/21  BRIPC (preliminary)
  • IPC GS RAS - Informational Processing Center, Geophysical Survey, Russian Academy of Sciences
  • NEIC - National Earthquakes Information Center of US Geological Service
  • IS NAS KR - Institute of Seismology National Academy of sciences of the Kyrgyz Republic
  • BRIPC - Regional Informational Processing Center of Baikal Experimental-Methodical Seismological Expedition Geophysical Survey Siberian Branch Russian Academy of Sciences
    • Macroseismic manifestations
         The earthquake on 16.09.2003 (region of Baikal Lake) has been felt in the number of settlements located in Buriat and Irkutsk Regions: Kumora, Uayan, Davan with intensity of 5 MSK of MSK-64 scale, Nizhneangarsk, Severobaikalsk - 4 MSK, Magistralny, Taksimo, Bodaibo, Ulyunhan, Severomuisk - 3-4 MSK, Neliaty - 3 MSK, and in the cities: Chita - 3 MSK, Irkutsk -2 MSK. The earthquake on 17.09.2003 (Russia-Mongolia border area) was felt in: Mondi - 5 MSK, Arshan, Irkutsk - 3-4 MSK, Angarsk - 3 MSK, Orlik - 2 MSK. The earthquake on 18.09.2003 (Russia-Mongolia border area) was felt in Mondi with intensity 3 MSK. The earthquake on 20.09.2003 (Russia-Mongolia border area) was felt in Orlik with intensity 2 MSK.
    Historical records
         For the last 10 years the biggest increase of seismicity was observed in Baikal Lake region in 1999. Most significant earthquakes: Northern Baikal on March 21, 1999, MS=6.1 with 1800 aftershocks in 10 daysafter the earhquake, and Southern Baikal Lake on February 25, 1999 with MS=6.0 and 1032 minor earthquakes in its origin place, which happened within the whole year 1999 including 700 aftershocks within the first three days. Seismic activity on September 16 with magnitude М=5.4 increased the number of most significant earthquakes already known for this area and having the same levels of magnitudes: November 26, 1968, MS=5.3, November 02, 1976, MS=5.2 and June 04, 1977, mb=5.2. The earthquakes on September 17-20 with magnitudes М=3.7-4.2 have happened in origin place of the strongest 9 MSK Mondi earthquake, which happened on April 4, 1950 with magnitude 7.0 and it was felt on a vast territory. Interesting fact is that according to operative seismological bulletin there were no significant events in this region for the last 53 years, only negligible activity was observed here (with magnitudes mb=4.0-4.6) in 1999 (8 earthquakes per year) and in 2000 (6 earthquakes).

    Figure 2
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism solutions for origin place of the earthquake 16.09.2003 have been calculated with TMC method in different centers - National Earthquakes Information Center of Geological Service of the USA (NEIC) and in Harvard center HARVARD (USA), which are presented in table 2 and shown on figures 3-4. Solutions obtained in different centers are close to each other. Motion in origin place is characterized as trap down for both planes, it happened under the action transtensions oriented to the North-Western direction. Both nodal planes have nearly the same values of pitch angles (Dp=40-43 and 55 degrees) and almost the same North-Eastern spread direction. It is necessary to note, that focal mechanism solutions obtained for this event correspond well with directions of seismo tektonics deformations obtained from data on focal mechanisms of the earthquakes happened in this part of Baikal area, where expansion mode prevails (fig. 5 from "Report of BRC of GS RAS", 1997)). Average value of seismic moment Мо, determined in IPC GS RAS from Р-wave spectra at seismic stations "Arti" (delta 29 degrees) and "Kislovodsk" (delta 44 degrees), makes 5.6* 10** 17 n*m. The value of moment magnitude from these data is equal to Mw = 5.8. The value of seismic moment Мо from NEIC data makes 2.2* 10** 17 n*m, the value of moment magnitude - Mw = 5.5.
    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
    732872215 17614040-116253 55-69NEIC
    332577219 12554243-108245 5074HARVARD
  • NEIC - National Earthquakes Information Center of US Geological Service
  • HARVARD - Harvard Geophysical Center (USA)

    • Figure 3
    Figure 4

    Figure 5


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