Morphology of the distorted subducted Pacific slab beneath the Hokkaido corner, Japan

Abstract

The intersection of the Japan and Kurile arcs is expressed as a cuspate feature at the trench, a bend in the Japanese islands, and a complex lithospheric structure and is known as the Hokkaido corner. The Pacific plate is subducting beneath the two arcs in the northwest Pacific at different velocities, which has resulted in an arc-arc collision and distortion of the subducting oceanic lithosphere. Using P and S wave tomographic images and seismicity the distorted shape of the subducted Pacific plate beneath the Hokkaido corner can be interpreted in three dimensions. The Pacific plate is imaged as continuous along the Japan-Kurile arc with dip angle increasing from south to north, but at the arc-arc junction the geometry is complex and appears crumpled. Beneath the Hokkaido corner there are two features in the tomography that are clearly imaged: a region of low velocity at approximately 50-150 km depth between 142.5-145°E and 41-43°N and a distorted, buckled lower slab boundary. These two unusual characteristics in the slab morphology are likely to be related to deformation of the subducted Pacific plate at the arc-arc junction.