MECHANISM OF MANTLE EARTHQUAKES NEAR THE JUNCTION OF THE KURILE AND THE NORTHERN HONSHU ARCS

Abstract

The geometry of the slab as well as the stress inside the slab near the junction of the Kurile and the northern Honshu arcs, that is, the Hokkaido corner, are studied based on the seismicity and the focal mechanism solutions of mantle earthquakes. Focal mechanism solutions vary depending on the focal depth and the local strike of the slab. The distribution of mantle earthquakes and the variation of the mechanism solutions reveal slab contortion on the Kurile side of the Hokkaido corner. The relative motion on the fault plane is estimated based on the analysis of source processes of mantle earthquakes. The sense of the earthquake slip motion is consistent with the sense of the slab contortion. This may indicate that the slab contortion, suggesting a plastic deformation, results partly from the earthquake slip motion.