HIGH-FREQUENCY WAVE GENERATION OF THE INTERMEDIATE-DEPTH EARTHQUAKES IN AND AROUND TOHOKU DISTRICT FROM STRONG MOTION RECORDS

Abstract

Acceleration source spectra of the intermediate-depth earthquakes in and around Tohoku district are estimated. And then, stress parameter ACT is estimated from the constant level higher than corner frequency of the acceleration source spectra. It is concluded that (1) averageΔσof down dip extension and down dip compression type earthquakes are 26MPa and 22MPa respectively; (2) average Δσ of the intra-slab earthquakes in and around Tohoku district (M_0<1×10^<19>Nm) is 24MPa and nearly equal to 25MPa obtained from earthquakes in Hokkaido; (3) Δσ of the large intra-slab earthquakes is higher than that of small earthquakes; (4) Δσ of small intra-slab earthquakes (M_0<5×10^<17>Nm) shows focal depth dependency, but Δσ of large earthquakes (M_0>5×10^<17>Nm) is independent to their focal depth.