Pn Anisotropic Tomography of Northeast Asia: New Insight Into Subduction Dynamics and Volcanism

We present a new high-resolution model of P-wave anisotropic tomography of the uppermost mantle beneath NE Asia obtained by inverting 88,303 high-quality manually picked Pn arrival times. Our model reveals strong lateral heterogeneities in both isotropic velocity and azimuthal anisotropy. Distinct high Pn velocities are visible under the basins in NE China, and eastern and western Japan basins. Very high Pn velocities with trench-normal fast Pn anisotropy are revealed near the Kurile-Japan trench, representing the incoming Pacific plate. Prominent low Pn velocity anomalies are revealed under active intraplate volcanoes in NE China and arc volcanoes on the Japan Islands. Very low Pn velocities with trench-parallel fast Pn anisotropy are observed along the volcanic front in Japan, reflecting compressed mantle flows. An NW-SE oriented low-velocity (low-V) zone from the Wudalianchi volcano to the Changbaishan volcano meets the E-W oriented low-V zone around the Changbaishan volcano and the N-S low-V zone east of the Sanjiang basin, which converge to a broad N-S low-V zone. This zone passes through the central Japan basin to the junction of the Japan and Izu-Bonin trenches, where it meets the nearly E-W low-V zone from the Changle volcano. These low-V anomalies exhibit zone-parallel fast Pn anisotropy and may indicate channels for material and energy exchanges among the volcanoes, driven by mantle flows in the big mantle wedge. These results provide new insights into interplate and intraplate volcanism and subduction dynamics in the study region.