Velocity structure of the uppermost mantle beneath East Asia from Pn tomography and its dynamic implications

Abstract

AbstractEast Asia is one of the most tectonically active regions on Earth's surface due to the collision from the India plate and the suctions induced by the subduction of the Pacific and Philippine plates. To better understand the complicated deformation and active seismicity of the area, we conducted a Pn traveltime tomography to estimate the compressive wave speed of the uppermost mantle beneath East Asia. We collected a total of 296,334 Pn arrivals recorded by 1354 stations from 27,777 earthquakes in a rectangular area from 60°E to 145°E in longitude, 15°N to 60°N in latitude. The data set was carefully integrated from three different catalogs after examining potential systematic biases in the catalogs. The inversion results revealed a large‐scale velocity perturbation in the study area. Pn velocity in the region west to ~108°E is approximately 10% higher than that in the east. In each region, stable blocks tend to have high Pn velocity while the boundary regions, which show a high level of seismicity and surface deformation, appear to have low Pn velocity. We further computed the Benioff strain rate in the two regions and found it correlates negatively with the averaged Pn velocity. Our observations here suggest that Pn velocity, which is predominantly determined by Moho temperature, is a good indicator of lithosphere strength.