A Stress Model for the Source Region of the 2011 off the Pacific Coast of Tohoku Earthquake

摘要

A model of tectonic stress state for the Source Region of the 2011 off the Pacific Coast of TohokurnEarthquake is derived from the seismicity modeling and analysis of focal mechanism before and afterrnthe mainshock from the NIED and JMA data. Stress state can be obtained by seismicity modeling andrnfocal mechanism, the former method can derive stress state parameters from the seismicity and sourcernmodel of the mainshock, representing the average stress state before mainshock, the latter can be usedrnas reference and further analysis of stress field change. The results show that the stress state remainsrnsteady in the place where distant from core of source region, which are representative by thernunchanged focal mechanism, stress changed a lot in central part of the source region, which are foundrnthat events before the mainshock were mainly reverse type all over the source region, however, therernare many normal fault type events distributed in the hanging wall after the mainshock, but the focalrnmechanisms in intermediate depth below the slab interface remains steady after the mainshock. Thernanalysis of stress change shows that the stress change pattern controls the seismicity pattern andrnfaulting type in the source region, the focal mechanisms are diverse in the place where stress changesrnare positive-negative transition/junction , and are consistent in the place where stress change arernpositive or negative. These results suggest that the stress field changed a lot in the core area of sourcernregion because of stress release and deformation, but kept steady in other places where seismicity arerntriggered because of stress transfer from mainshock’s dislocation. To certain extent, our resultsrnprovide a constrain on the spatial distribution of the stress release pattern spatially and temporally forrnthe source region of 2011 Tohoku earthquake.