2009 年 61 巻 Supplement 号 p. 123-131
Change in regional seismic activity has been generally considered to be closely related to stress and fault strength or their spatio-temporal changes. To explain the causal relations between seismic activity and stress state, one must introduce some assumptions or hypotheses based on a physical scheme. In Shizuoka Prefecture, central Japan, small but distinct changes of seismic activity in the locked Tokai slab, which evidently divided the focal region into activated zones and quiescent ones, were observed almost simultaneously with the slow slip event beneath Lake Hamana from 2000 to 2005. Here, I propose the following hypothesis to associate the seismic activity change with the stress condition. The slow slip may have promoted a quasi-static sliding on the rim of the asperities, resulting in stress redistribution on the focal region. The zones possibly activated by stress concentration were then assigned to asperities. Based on this consideration, I specified several major asperities on the anticipated rupture area of the future Tokai earthquake. I thus conclude that monitoring seismic activity change together with an adequate mechanical hypothesis may help us understand the locking state along the plate interface with respect to the spatio-temporal changes in stress rate.