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The spatiotemporal evolution of the M9.0 Tohoku earthquake sequence off the East Coast of Honshu in Japan on March 11,2011 and precursive seismic activity near the Japan Trench show that the earthquake sequence has foreshock-main shock-aftershock characteristics.Its foreshock sequence is characterized by a concentrated spatial distribution,low b value and the same focal mechanisms.Half an hour after the main shock,the two greatest aftershocks,with magnitudes of M7.9 and M7.7,occurred,followed by a rapid reduction in the strength of events.The aftershock activity was enhanced roughly two weeks and one month after the main event.This great earthquake ruptured bilaterally.Five hours after the main shock,the aftershock zone extended over a range that was 500 km in length and 300 km in width.A day later,the long axis of the aftershock area had expanded to about 600 km.Nine years prior to the 2011 earthquake,the seismicity in the location of the seismic source for this event enhanced significantly,with the extent of this area of enhanced seismicity being roughly equivalent to the aftershock zone.
The spatiotemporal evolution of the M9.0 Tohoku earthquake sequence off the East Coast of Honshu in Japan on March 11, 2011 and precursive seismic activity near the Japan Trench show that the earthquake sequence has foreshock-main shock-aftershock characteristics. Its foreshock sequence is characterized by a concentrated spatial distribution, low b value and the same focal mechanisms. Half an hour after the main shock, the two greatest aftershocks, with magnitudes of M7.9 and M7.7, occurred, followed by a rapid reduction in the strength of events. aftershock activity was enhanced roughly two weeks and one month after the main event. this great earthquake ruptured bilaterally. Five hours after the main shock, the aftershock zone extended over a range that was 500 km in length and 300 km in width .A day later, the long axis of the aftershock area had expanded to about 600 km. Neither years prior to the 2011 earthquake, the seismicity in the location of the seismic source for this event enhanced signifi cantly, with the extent of this area of enhanced seismicity being approximate equivalent to the aftershock zone.