Influence of fault mechanism, depth, and region on stress drops of small and moderate earthquakes in Japan

Abstract

Stress drops of 168 earthquakes (focal depth ≦ 60 km, 4.4≦M W≦6.9) are estimated by a generalized-inverse method using strong motion records in Japan. Stress drops of crustal earthquakes are dependent of focal depths. Stress drops of reverse-faulting earthquakes are two times greater than those of strike-slip faulting earthquakes and stress drops of strike-slip faulting earthquakes are two times greater than those of normal-faulting earthquakes. These results are consistent with the crustal strength expected from a frictional law. Stress drops of intraplate earthquakes have more variation than those of interplate earthquakes, but are two times greater than those of interplate earthquakes on average.