Tomographic imaging of P and S wave velocity structure beneath northeastern Japan

Abstract

The seismic body wave tomography method has been improved and extended to adapt to a general velocity structure with a number of complexly shaped seismic velocity discontinuities (SVDs) and with three-dimensional variations in the velocities in the modeling space. The method is applied to 18 679 arrival times from 470 shallow and intermediate-depth earthquakes in order to study P and S wave tomographic images beneath northeastern Japan. High-resolution P and S wave tomographic images down to a depth of 200 km have been determined. Large velocity variations amounting to 6% for P wave and 10% for S wave are revealed in the crust and upper mantle. In the crust low-velocity (low-V) zones exist beneath active volcanoes. In the upper mantle the low-V zones dip toward the west from the volcanic front. A high-velocity (high-V) zone corresponding to the subducted Pacific plate is clearly delineated. -from Authors