Pn anisotropic tomography and dynamics under eastern Tibetan plateau

Abstract

AbstractWe present a new anisotropic tomographic model of the uppermost mantle around eastern Tibet using Pn traveltime data from a newly deployed temporary seismic array and recent observation bulletins of Chinese provincial networks. Our results are generally consistent with previous results but provide new insights into the dynamics of Tibetan plateau. Prominent high‐velocity (high‐V) anomalies are visible under Alashan block and Qaidam and Sichuan basins, which clearly outline their tectonic margins. A distinct high‐V zone representing the double‐sided subduction of Indo‐Eurasian plates is imaged from Lhasa block to the south of Qaidam basin. A pronounced low‐velocity (low‐V) zone is observed from Songpan‐Ganzi block to southern Chuan‐Dian diamond block, suggesting the existence of hot material upwelling there. Crustal strong earthquakes frequently occurred around high‐V anomalies or transition zones from high‐V to low‐V anomalies, suggesting that these earthquakes could be related to lateral heterogeneities in the mantle. The Pn fast direction approximately rotates around Eastern Himalayan Syntaxis, and it is tangential to the margins of Sichuan basin, suggesting that the mantle material flow of Tibetan plateau may have affected east China. In the Yunnan region to the south of 26°N, the Pn fast direction is different from SKS splitting results, indicating that the mantle lithosphere could be mechanically decoupled at certain depth below the uppermost mantle, which might be attributable to the subduction of Indian (or Burma) slab. Although the correlation between anisotropy and velocity is complicated, anisotropy strength could be associated with the pattern of velocity anomalies in the region.