We used a newly developed Pn tomography method to obtain high-resolution uppermost mantle velocity and anisotropy structures beneath the Northwest Pacific region. The observed Pn velocities are consistent with the local tectonic background, where high Pn velocities are observed beneath the Japan Trench area and Songliao Basin, and low Pn velocities beneath the Kuril Islands, Japan Archipelago-Izu Islands, Kyushu Island, Changbaishan-Jingpohu volcanoes, Korea Peninsula, and Japan Basin. The new Pn velocity image outlines the subducting slabs along the trenches and the young seafloor within the Japan Basin. Our results also support the existence of hot upwelling feeding the Changbaishan, Jingpohu, and Chuga-Ryong volcanoes, where small-scale mantle convection may exist below the Northeast China region. Further east, both trench-parallel anisotropy below arcs and trench-perpendicular anisotropy within the back-arc region suggest subduction-dominant mantle flow, where anisotropy may be attributable to the lattice-preferred orientation of olivine induced by flow-related strain. The highly accurate uppermost mantle velocity and anisotropy structures provide crucial information outlining the complex dynamic processes near convergent plate boundaries.

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The continuous convergence between the Indian and Eurasian plates caused massive lithospheric deformation in the Tibetan Plateau and led to excessive crustal material escaping through its southeastern margin. However, the mechanisms that accommodate the escaping materials and whether they intrude into the Indochina Peninsula are continually under debate. Seismic Lg waves mostly propagate within the crust waveguide with an amplitude decay that is sensitive to crustal material properties, such as temperature, partial melting, and fracture. Therefore, Lg attenuation can be a useful indicator of potential crustal material escape. In this study, we developed a high‐resolution broadband Lg attenuation model in this region between 0.05 and 10.0 Hz, with the resolution reaching 1° in regions with dense raypath coverage. Prominent low‐Q anomalies beneath the southeastern margin of the Tibetan Plateau, correlating with previously observed low velocity, high conductivity and high Poisson’s ratio, may indicate possible high temperature and/or partial melting within a relatively weak crust, and suggest a north‐south interconnected corridor for gravity‐driven material flow. Through our results and other geological and geophysical observations, a dynamic model is suggested here by combining shallow rigid block extrusion and deep viscous crustal flow to explain crustal material escape in the southeastern margin of the Tibetan Plateau. Additionally, neither shallow extrusion nor deep material flow enter the Indochina Peninsula based on the relatively high Q values, which indicate a stronger crust there.