The distribution of seismic anisotropy in the mantle wedge beneath northeast Japan is inferred from deformation mechanisms: a lattice-preferred orientation and seismic anisotropy are generated by deformation via dislocation creep in the upper mantle, but not by diffusion creep or frictional sliding. Based on the thermal structure and stress field of the upper mantle beneath northeast Japan, deformation throughout most of the mantle wedge is inferred to be controlled by diffusion creep, and the region of dislocation creep is limited to a thin layer of 10–20 km thickness within a region of relatively high stress and low temperature located above the subducting slab and beneath the island arc crust. The relatively short delay time recorded in northeast Japan is consistent with the occurrence of a thin anisotropic layer within the mantle wedge.

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