新Mカタログによる東海地域における地震活動の変化

抄録

We investigate changes in seismicity and the b-value in the Tokai region, Central Japan, based on the new magnitude catalog of JMA. We show seismicity in the subducted slab increased remarkably in October 2000 and decreased in October 2001. In contrast, seismicity in the crust decreased in October 2000 and increased in October 2001. We propose that these changes in seismicity in the slab and crust in the Tokai region were caused by the changes of the coupling state. The change of the displacement rate at locations of GPS stations indicates that the interplate coupling was weakened in late 2000 and it resumed partly in late 2001. Correlation is noted between change in seismicity and that in the b-value; the low seismicity corresponds to the high b-value. We consider the quiescence that appeared in August 1999 in the slab beneath the western coast of Suruga Bay might have been a precursor for the seismic activity including two M5-class earthquakes in April and June of 2001. Increase of seismic activities was observed in the slab and crust as well as in the Zenisu region in the beginning of 2003. We suggest that the increase might have been generatedby the acceleration of the subduction of the Izu micro-plate on the Suruga-Nankai Trough.