The Shape and Seismic Characteristics of the Philippine Sea Plate around the Iyo-nada, Shikoku, Japan, Judging from the Hypocenter Distribution

Abstract

Using hypocentral data of JMA from 1997 to 2000, we determined upper surface shape of the Philippine Sea plate around Iyo-nada.
The contour lines indicate that the Philippine Sea plate is spreading northward from Iyo-nada to Aki-nada in west Setonai-kai area. From 3-D bird's eye view, slight dent of the plate-upper surface, possibly due to buckling, can be seen at bound of the plate subducting around Iyo-nada area.
It is considered that in addition to the plate bending, change of local tectonics from buckling to spreading may contribute to seismicity of the Iyo-nada area events. As well as this change may contribute to the source mechanism of small events and cyclic Geiyo earthquake.