摘要：The 2011 off the Pacific coast of Tohoku Earthquake occurred at the plate boundary between the Pacific plate and the landward plate on March 11, 2011, and had a magnitude of 9.Many aftershocks occurred following the mainshock.Obtaining a precise aftershock distribution is important for understanding the mechanism of earthquake generation.In order to study the aftershock activity of this event, we carried out extensive sea-floor aftershock observations using more than 100 ocean-bottom seismometers just after the mainshock.A precise aftershock distribution for approximately three months over the whole source area was obtained from the observations.The aftershocks form a plane dipping landward over the whole area, nevertheless the epicenter distribution is not uniform.Comparing seismic velocity structures, there is no aftershock along the plate boundary where a large slip during the mainshock is estimated.Activity of aftershocks in the landward plate in the source region was high and normal fault-type, and strike-slip-type, mechanisms are dominant.Within the subducting oceanic plate, most earthquakes have also a normal fault-type, or strike-slip-type, mechanism.The stress fields in and around the source region change as a result of the mainshock. Key words The 2011 off the Pacific coast of Tohoku Earthquake aftershock focal mechanism seismicity ocean-bottom seismometer (OBS).
关键词：The 2011 off the Pacific coast of Tohoku Earthquake ;aftershock ;focal mechanism ;seismicity ;ocean-bottom seismometer (OBS)
