Focal Mechanism Solutions of Micro- and Small Earthquakes Occurred in the Western Kanagawa Area Situated in the Izu Collision Zone

Abstract

Focal mechanism solutions of earthquakes in the western Kanagawa area are compiled and characteristics of fault types in the Izu collision zone are discussed. Reverse, strike-slip, and oblique fault mechanisms are seen in the Izu collision zone. Although only about 10 per cent of micro- and small earthquakes, are associated with strike-slip fault mechanisms, the largest and the second largest earthquakes (M 6.0 and M 5.6) are of that type. It was found that the direction of the P axis is somewhat different in the western and eastern Tanzawa areas : in western Tanzawa the average direction of the P axis is NW-SE, while it is NNW-SSE in eastern Tanzawa. We think this difference in the P axis direction reflects differences in tectonic conditions in those areas. In the Ashigara plain area, mechanism solutions are mostly reverse and oblique faults with the P axis direction between E-W and NNW-SSE