Shear Wave Velocity Anomalies in the Lowermost Mantle beneath the Asia-Pacific Region

Lowermost mantle is a critical region for understanding Earth’s deep material circulation and thermal evolution. The Asia-Pacific region, characterized by a complex history of plate convergence involving the Tethyan, Paleo-Asian and Paleo-Pacific domains, serves as an ideal natural laboratory for studying deep mantle processes. However, the fine-scale shear wave velocity structure of this region remains poorly resolved. In this study, we invert a substantial dataset of over 57,000 ScS-S differential travel-time residuals to image shear wave velocity perturbations within the D’ layer beneath the Asia-Pacific region. We systematically evaluate 16 3-D global tomographic models, identifying TX2019slab as the optimal lowermost-mantle model in the Asia-Pacific region. Extensive high-velocity anomalies are widespread beneath the continental interior, which may be interpreted as remnants of the subducted Mongol-Okhotsk, Tethys and Izanagi plates. Another distinct high-velocity anomaly is newly detected in the southeast of Philippine Sea, representing a poorly constrained remnant of intra-oceanic subduction within Panthalassa. Segmented low-velocity anomalies are imaged beneath the South China Sea, being evidence for possible mantle plumes from the core-mantle boundary. Our study offers a comprehensive map of lower mantle velocity variations beneath the Asia-Pacific region, yielding specific and valuable constraints for geodynamic modeling and paleo-plate reconstruction in this complex region.