[SSS05-P03] Megathrust-inducing azimuthal seismic anisotropy in local and regional crusts
キーワード：megathrust earthquake, crustal deformation, induced seismicity
Megathrust earthquakes produce large coseismic and postseismic lithospheric displacements. The 2011 M9.0 Tohoku-Oki megathrust earthquakes produced large displacements up to regional distances. The lithospheric displacements directing to the epicenter on the convergent plate boundary developed transient uniaxial tension field over the backarc lithospheres. The Vp/Vs changes display characteristic 2 theta azimuthal variations in the upper crust of the Japanese islands, ranging between -0.0458 and 0.0422. Large lateral variations in Vp/Vs changes suggest medium-dependent perturbation. The lower crust of the Korean Peninsula in distances of ~1300 km displayed coseismic velocity changes of 3 % after the megathrust earthquake. The Vp/Vsratios and seismic velocities recovered gradually over time. Peak Vp/Vs and seismic velocity changes were observed along paths subparallel or subperpendicular to the directions toward the megathrust earthquake. The azimuthal seismic anisotropy may have developed from preferential crack orientation and azimuthal lithostatic stress changes. It appears that recovery of the medium properties may take decades. A series of moderate-sized earthquakes occurred as a consequence of medium response to the temporal evolution of stress field in the Korean Peninsula.