Information message about the strong earthquake off the south-eastern part of Honshu Island, Japan on August 9, 2009.

     The strong earthquake with М=6.8 has occured on August 9, 2009 at 10:55 GMT (14:55 Moscow time) in Pacific Ocean, S-E off Honshu Island, Japan.
     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 37 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).
     Preliminary processing has been done with data from 52 stations, accurate processing - with data 67 stations.
      Fig. 1 presents fragments of records obtained from digital stations Vladivostok (∆ 11.1º), Petropavlovsk (∆ 24.7º), Yakutsk (∆ 29.4º), Talaya (∆ 31.1º), Krasnoyarsk (∆ 38.6º). Fig. 2 presents fragments of records obtained from digital stations Tiksi (∆ 38.9º), Arti (∆ 57.6º), Obninsk (∆ 69.6º), Kislovodsk (∆ 71.4º), Garni (∆ 72º).

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 10-55-54.3 33.14 138.19  300  67   6.9/26 71 IPC GS RAS (Accurate)
2 10-55-54.7 33.19 138.18  300  52   6.8/16 71 IPC GS RAS (Preliminary)
3 10:55:55.9 33.136 138.042  300  397  6.9 Mw   29 CSEM
4 10:55:56.4 33.144 138.04  303.1  345  7.1 Mw 6.6/155 14 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
         Fig. 3 presents with yellow star epicenter of this earthquake, which was located in Pacific Ocean, S-E off Honshu Island, Japan, at the depth of 300 km., in 316 km. S-S-W off Tokyo, in 290 km. E-S-E off Osaka.

    Figure 3
    Aftershock
         GS RAS registered 1 aftershock with М=4.7, which occured in 5 hours after the main shock.
    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
    200925462009-08-09 16:01:24.033.08138.1730025-4.7/ 14-Southeast of Honshu, Japan
    Macroseismic manifestations
         In accordance with NEIC USA this earthquake was felt at Honshu Island with intensity up to 5 MSK . Fig. 4 was obtained from NEIC site, it presents the map with intensities registered from phone calls made by 408 respondents living in 84 places.

    Figure 4
    Historical records
         This earthquake has occurred on August 9, 2009 in seismic active region of Japan. Historically known and destructive earthquake has occurred in this region at Idzu Peninsula on November 25, 1930 at 19:02 GMT with М=7.1. It was felt on the most part of Honshu Island in the radius of nearly 500 km and was accompanied with crust ruptures. Pleistocene zone propagated 50 km. From the north to the south and 30 km. From the east to the west, capturing most narrow part of Idzu peninsula. During the earthquake itself "seismic light phenomena " were observed. 259 persons were killed, 2142 buildings destroyed [Dr. Richter "Elementary seismology", 1963].
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism solutions for this earthquake, which occurred on August 9, 2009 at10:55 GMT were obtained with TMC in NEIC USA and USGS, they are presented in table 2 and shown on fig.5. This earthquake has occurred under the action of almost equal compression and expansion forces oriented to the west and east respectively. Nodal plane NP1 has nearly latitudinal direction of propagation and lays flat, the type of motion along it – right side drift with thrust components. NP2 plane has nearly longitudinal direction of propagation with steeply falling angle (angle of falling DP=86º), type of motion – uplift with left side drift components. The value of seismic moment Мо of this earthquake, which occurred on August 9, 2009 at 10:55 GMT in accordance with USGS makes 4.5* 10** 19 n*m, moment magnitude makes Mw = 7.0.
    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
    468038291 161888217165187 8674NEIC
  • NEIC - National Earthquakes Information Center of US Geological Service

    • Figure 5


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