Information message about the strong earthquake near the eastern coast of Honshu Island, Japan, June 22, 2011.

     The strong earthquake with M=7 has occurred near the eastern coast of Honshu Island, Japan on June 22, 2011 at 21:50 GMT (June 23, 2011 at 01:50 Moscow time).
     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 15 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).
     Preliminary processing has been done with data from 46 stations, accurate processing - with data 63 stations.
     Fig. 1 presents fragments of records obtained from digital stations Erimo (∆ 2.1º), Yuzhno-Kurilsk (∆ 4.7º), Matsushiro (∆ 4.8º), Kurilsk (∆ 6.6º), Kuldur (∆ 11.9º). Fig. 2 presents fragments of records obtained from digital stations Arti (∆ 54.7º), Lovozero (∆ 59.7º), Obninsk (∆ 66.2º), Nalchik (∆ 69.3º), Kislovodsk (∆ 69.6º).

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 21-50-50.5 40.02 142.42  33  63  7/306.6/338-8.5 82 IPC GS RAS (Accurate)
2 21-50-50.6 40.01 142.44  33  46  7/256.6/268-8.5 82 IPC GS RAS (Preliminary)
3 21-50-53.2 39.95 142.32  40  230  Mw 6.8   55 CSEM
4 21-50-48.3 39.98 142.25  5.7  461  6.7/156.2/408  NEIC (Preliminary)
5 21-50-48.3 39.98 142.25  32  515  Mw 6.7   25 NEIC (Accurate)
  • 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 red star epicenter of this earthquake which origin was located near the eastern coast of Honshu Island of Japan at the depth of 33 km, 165 km E-S-E off Aomori, 235 km N-E off Sendai and 530 km S-W off Yuzhno-Kurilsk.

    Figure 3
    Aftershock
         GS RS registered one foreshock with M>5.7 in 7 hours before 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
    201129472011-06-22 14:28:57.040.17142.793346-5.7/ 195-5.5 Near east coast of Honshu, Japan
    Macroseismic manifestations
         In accordance with TV Channel 1 the shocks were felt by residents of a few prefectures. The strongest of them were in Ivate region. High buildings were swinging there. Risk of tsunami was announced. This fear was in vain, but evacuation started from a few settlements located near the shore. On the territory of Russia this earthquake was felt in Yuzhno-Kurilsk and Malokurilsk with intensity 2. Fig. 4 obtained from WEB site of NEIC USA presents the map of intensities obtained with phone calls to 46 respondents living in 12 places.

    Figure 4
    Historical records
         This earthquake has occurred in 193 km N-N-W off destructive earthquake which happened on March 11, 2011 with intensity M=8.8 (Fig.5).

    Figure 5
    Focal mechanism and seismic moment of the earthquake
         Focal mechanism solution of the origin for this earthquake which occurred on June 22, 2011 at 21:50 GMT was calculated in IPC GS RAS with first signs of initial P-wave arrivals at 39 stations including 34 stations which registered the waves of compression (plus signs) and 5 stations which registered the waves of expansion (minus signs). These stations are located of epicentral distances of 2º-80º and are evenly dispersed along the azimuths, thus there is data lack for 2-nd segment. Focal mechanism solution in stereographic projection at lower hemisphere is shown at figure 6, elements of this solution are presented in table 2. Table. 2 and fig. 7 present also focal mechanism solutions of the origin which were calculated with CMT method in NEIC USA, USGS. All solutions are almost identical. The earthquake has occurred under the action of compression forces oriented to the east. Both nodal planes propagate nearly long meridian direction and in N-N-E direction, one of them was steeply falling (DP=70º-71º), another is flat (DP=4º-6º). Type of motion for steeply falling plane – uplift, for flat plane – overthrust. Seismic moment of this earthquake which occurred on June 22, 2011 was obtained in IPC GS RAS with spectra of Р waves at two stations: «Arti» (∆ 54.68º) and «Obninsk» (∆ 66.19º), it makes Мо=4.2*10**19 n*m. Averaged value of moment magnitude calculated with Kanamori formula makes Mw=7.0. Averaged value of seismic moment in accordance with USGS makes Мо=1.6*10**19 n*m, averaged value of moment magnitude makes Mw=6.7.
    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
    6125325106 149224241275 7175IPC GS RAS
    652792595 118518120866 7092NEIC
  • IPC GS RAS - Informational Processing Center, Geophysical Survey, Russian Academy of Sciences
  • NEIC - National Earthquakes Information Center of US Geological Service

    • Figure 6
    Figure 7


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