Seismic Attenuation Structure Beneath the Northeastern Japan

Detailed seismic attenuation mapping can provide critical constraints on the thermal evolution of the mantle dynamics. In this study, we investigate the seismic attenuation characteristics beneath northeastern Japan using the regional earthquakes recorded at 288 stations of three different seismic networks (S-net, Hi-net and F-net). Recent deployment of the S-net largely improves the structural resolvability near the trench, in particular at the junction between the Kuril Trench and the Japan Trench. Since the direction of S-net seismometers depends on the layout of marine cables, we correct the rotation angles by multiplying matrices calculated from tilt, rotation, and azimuth before measuring the spectra amplitudes of P and S waves in multiple frequencies using integrals over wavelet transforms. All measurements are referencing to the 1-D synthetics to eliminate the effects from the source and geometrical spreading. We invert the spectra amplitudes for a 1-D frequency-dependent attenuation model. The inverted station residuals, which account for unresolved lateral variations in attenuation structure, suggest stronger attenuation in the volcanic area and the collision region of the Kuril and Japan arcs. On the other hand, the raypaths passing through the subducting slab are characterized by low attenuation.