Information Report on appreciable earthquake in the southwest part of Sakhalin island on August, 17, 2006.

     The appreciable earthquake with magnitude М=5.6 has taken place on August 17, 2006 at 15:22 GMT in the south of the coastal part of Sakhalin island from the side of Tatar Strait. It was felt in the settlements Shebunino and Gornozavodsk of Nevelsk Region with intensity of up to 6 MSK. This is the strongest event in the southern part of Sakhalin Island after the earthquake on May 30, 2004 (see. Information Report).
     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 55 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).
     Preliminary processing has been done with data from 22 stations, accurate processing - with data 47 stations.
     Figure 1 presents fragments of records of this earthquake obtained from digital stations Yuzhno-Sakhalinsk (∆ 0.7º), Petropavlovsk (∆ 12.6º), Magadan (∆ 14.1º), Yakutsk (∆ 17º), Bilibino (∆ 25º). Figure 2 presents fragments of records obtained from digital stations Tiksi (∆ 26º), Ala-Archa (∆ 47º), Arti (∆ 50º), Obninsk (∆ 61º), Kislovodsk (∆ 65º).

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 15-20-35.7 46.53 141.96  33  47  5.6/236.3/15696 IPC GS RAS (Accurate)
2 15 20 36.1 46.56 141.89  33  22  5.4/106.1/95.5-697 IPC GS RAS (Preliminary)
3 15 20 36.7 46.53 141.88  40  512   5.9  38 CSEM
4 15 20 38.0 46.58 141.86  32  225  5.6Mw 5.9/69 40 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 this earthquake was in a southwest part of Sakhalin Island. Tectonic zone this earthquake belongs to the Southern Sakhalin, namely to the West- Sakhalin system of deep breaks, the most powerful and stretching under the bottom of Tatar Strait along the western coast of the Island up to the Poyasok neck (48º latitude), joining further with Middle Sakhalin breaks.

    Figure 3
    Macroseismic manifestations
         In accordance with information from ITAR TASS: according to the seismic station "Yuzhno-Sakhalinsk" epicentre of this earthquake was in 20 kms to the east from settlement Gornozavodsk. The earthquake has destroyed systems of water supply in the south of Sakhalin Island in settlements Shebunino and Gornozavodsk of Nevelsk Region, it caused numerous cracks in the buildings, 40 percents of chimneys have fallen down in private houses. Underground shock has disturbed population, nearly 25 thousand people have run away from their houses and within three hours they were in the street. From the words of Vladimir Paka - the mayor of Nevelsk Region “many buildings have through cracks. Glass-ware , TV sets and household devices are broken in apartments. The bowls were moved away from their places and water heaters fallen down in 48 room building in Gornozavodsk because of deep sinking of the basement. Vladimir Pak informed that there are no victims of this earthquake in Nevelsk Region. This earthquake was felt in the settlements Shebunino and Gornozavodsk with intensity up to 6 MSK, in Holmsk, Korsakov, Krilone, Ogonki – with intensity of 4 MSK.
    Historical records
         The area of the reported earthquake belongs to the seismically active region. The strongest earthquake (Moneron earthquake) of this region for the last hundred years with M = 7.5 and the depth H = 18 km has happened near Moneron Island on September 5, 1971. Location of epicenter of Moneron earthquake can be found on fig. 3. The reported earthquake is located to the east no more than 100 km from the origin zone of this strongest earthquake. Besides that, three strong earthquakes have happened in the south of Sakhalin for the last hundred years: Anivsk 2.02.1951 (M = 5.5; Н =10 km) and Takoisk 1.09.2001 (M = 5.6; Н = 10 km) and the Kostroma earthquake on May 30, 2004 (M = 4.6; Н = 10 km). Takoisk earthquake has happened in Dolinsky region and was the strongest in force of numerous shocks in the strip zone from Kluchi settlement to Uglezavodsk settlement. Similar bunches of shocks were observed here earlier on a regular basis within last 13 years. These earthquakes also are shown on the map (fig. 3)
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism solution of the reported earthquake has been obtained by GS RAS from the first arrivals of Р-waves at 22 stations, 19 stations registered the waves of compression (signs plus) and 3 stations - the waves of expansion (signs minus). These stations are located in the interval of epicentral distances 0.76-70 degrees with rather uniform distribution along azimuths. Focal mechanism solutions of the origin are shown on figure 4 in stereographic projection on the bottom hemisphere, elements of the mechanism are presented in tab. 2. Figures 5,6 present focal mechanism solutions of this event’s origin obtained from TMC method in the National Earthquakes Information Center of Geological Service, USA (NEIC) and from CMT method obtained in Harvard Center (USA) (HARVARD). Apparently, the decisions obtained by different methods, are close. Movement in the origin has occurred under the action of the compressing pressure focused in nearly latitudinal direction. The mechanism of the origin is characterized as the thrust. Both nodal planes have nearly longitudinal direction of propagation coinciding with direction of Sakhalin Island. Seismic moment Мо of this earthquake is determined from Р-waves spectra registered by IRIS digital equipment installed at seismic station Obninsk (OBN), located at 62 degrees of the distance. Average value of Мо makes 6.7 Е 17 n*m. The value of moment magnitude Mw, determined from Kanamori formula is equal to Мw=5.8. The value Мо from NEIC data makes 2.5 Е 17 n*m., Мw=5.5; according to the data of Harward seismological center these values are - Мо =3.43 Е 17 n*m., Мw=5.6. Apparently, the values of parameters Мо and Мw, obtained by different techniques are also close and within the limits of admissible error.
    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
    772701390 018005890180 3290IPC GS RAS
    8452252 61623484398157 4782NEIC
    81719255 11653463691164 5489HARVARD
  • 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 4
    Figure 5

    Figure 6


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