Abstract
We investigated the seismic activity around the northern neighbor of the 2011 off the Pacific coast of Tohoku Earthquake (MW 9.0) with special attention to a potential large aftershock in the area. We obtained a combined data set by adding our manually-picked locations to the catalog locations by the Japan Meteorological Agency. The hypocenter distribution delineates active and inactive bands of seismicity. The band of low seismicity corresponds to a zone of a large seismic slip, indicating that aftershocks occurred in peripheral neighbors of the mainshock asperity. The broad band of active seismicity along the coast corresponds to the zone of a large postseismic slip, suggesting the enhancement of the aftershock activity by the slip. Although the northern neighbor of the mainshock fault is a favored region of increased seismicity, as shown from a Coulomb stress calculation, no significant seismic activity is observed within the potential source area except along the Japan Trench and the SW corner. This implies that the zone of interplate moment release by previous large earthquakes and the subsequent slow slip acted as a barrier to the migration of both the mainshock rupture and aftershock activity. However, an aftershock area in the zone may reflect inhomogeneous moment release by past seismic and aseismic sequences.
Highlights
The 2011 off the Pacific coast of Tohoku Earthquake (MW 9.0) is the largest earthquake recorded in Japan, and it caused indescribably severe damage mainly by a huge tsunami along the coast from the Tohoku to the Kanto district in Honshu Island
Kawasaki et al (1998, 2001) argued that the accumulated seismic moment in a region from 39.0◦N to 40.6◦N along the Japan Trench was considerably released by the seismic and aseismic sequences in the period between 1989 and 1995. This zone possibly acted as a barrier to both the rupture of the 2011 Tohoku Earthquake and the aftershock migration
The monitoring of postseismic slip together with seismicity change around the potential source area is important in the prediction of future large earthquakes
Summary
The 2011 off the Pacific coast of Tohoku Earthquake (MW 9.0) is the largest earthquake recorded in Japan, and it caused indescribably severe damage mainly by a huge tsunami along the coast from the Tohoku to the Kanto district in Honshu Island. The aftershock distribution of large earthquakes is essential for estimating the extent of a source fault This information is of particular importance when assessing the location of future large aftershocks that may be hazardous to areas severely damaged by a mainshock. We will investigate the activity using a precise hypocenter distribution from a combined data set of the local seismic network of Hirosaki University and the catalog location of the Japan Meteorological Agency (JMA). Because our catalog does not cover the period before March 15, 2011, we combined the JMA data during this period with our data of up to April 01, 2011 We think this combined data provides the best manually-located hypocenters for the northern part of the aftershock zone
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