Fine fault structure of a moderate earthquake in the 2007 earthquake sequence of Northern Mie, Japan

摘要

A moderate crustal earthquake (M-j = 5.4) occurred in the northern part of Mie Prefecture, Central Japan, 2007. In order to clarify the fault structure of the main shock and its relation to the active faults, we estimated the precise hypocenter locations and focal mechanisms. For the relocation of the hypocenters, we used the differential time obtained by both manual picking and waveform cross-correlation analysis. The estimated detailed fault structure suggests that the main shock ruptured the southwestward dipping fault plane. We found that the faults of the moderate earthquake possessed complex fault segments. Around the largest aftershock hypocenter, a subsidiary fault plane parallel to the main shock fault was identified. This result suggests that the fault structure around the deep part of the active fault is complicated. The hypocenters of the foreshock and main shock were located in the offset part of the aftershock alignment, implying that they did not occur on the same fault plane. The Chisato Fault and Yokkaichi Fault were located around the upward extension of the aftershock alignment. The main shock probably occurred in the deep parts of these faults.