東北-中部-西南日本の広域応力場

Abstract

I constructed the regional stress fields of northern-central-southwest Japan on the basis of the forearc differential stress determined by ridge push and slab pull forces of the subducting oceanic plate, differential stress variation across the arc due to crust/plate structural variation, and the along-arc differential stress level. Assuming a simple geometry of northern-central-southwest Japan and a high stress level in the north-south direction in central-northern Japan due to collision of the Izu-Bonin arc and the south Kuril forearc, I constructed the principal stress profiles in these regions, which are consistent with the observed E-W σHmax stress fields (i. e. strike and sense of motion of the reverse fauling in northern Japan and strike-slip faulting in southwest-central Japan). On the basis of this reconstruction, I concluded that the E-W compression which caused the 1995 South Hyogo earthquake resulted from the ridge push of the Pacific plate. This force, however, cannot be distinguished from the force at Fossa Magna due to the collision between the Amurian and Okhotsk plates. Higher seismicity in southwest Japan and in the foothills of central Japan than in the high mountain areas in central Japan is due to the larger horizontal differential stress in the former areas.