P_n tomographic velocity and anisotropy beneath the Tibetan Plateau and the adjacent regions

摘要

We present a tomographic velocity and anisotropy model of the uppermost mantle beneath the Tibetan Plateau and the adjacent regions. The investigation analyzed 105,385 P_n phase readings from the International Seismological Centre (ISC) and the China Earthquake Data Center. The average P_n velocity under the study area is approximately 8.15 km/s, with velocity perturbations up to 3-4%. We find high P_n velocities under the Indian Plate and in the Tarim and Sichuan basins, low P_n velocities under the Hindu Kush and in Myanmar and the adjacent region, and especially low P_n velocities under the area north of the Indus-Yarlung Zangbo suture. The high P_n velocity anomalies of the Indian Plate are discontinuous at the collision region in the east-west direction, indicating that the Indian Plate probably subducts in a piecewise manner. Distributions of P_n velocities are used to validate mechanisms for the subduction of the Indian Plate presented in previous studies. In addition, P_n anisotropy is obtained simultaneously with P_n velocity. At plate collision zones, the fast P_n anisotropy direction is parallel to the direction of the collision edge. We validate the existence of P_n anisotropy under these regions and discuss the relationship of anisotropy with tectonic structure and plate movement