Crustal structure of southeastern Tibetan Plateau inferred from double-difference tomography

We applied the double-difference tomography to relocate seismic events and deter-mined the crustal structure of the southeastern Tibetan Plateau from the inversion of the local seismic data recorded by regional networks of Yunnan and its surrounding regions from 2010 to 2016. Our results demonstrate that the accuracy of events relocation is significantly improved, and the events are mainly distributed in upper-mid crust at the depths shallower than 20 km. The locations of events are closely related to the velocity structure of upper-mid crust. Most of the earthquakes occurred in some regions with low-velocity anomaly or in the regions between low-velocity and high-velocity anomalies. Tomography results also show that the velocity structure of upper crust exhibits apparent horizontal heterogeneities, which is largely consistent with surface geological and topographic features. In the mid-lower crust, there are two main NS-trending low-velocity zones, one is located in the east of Sichuan-Yunnan diamond block along the trace of Anninghe and Xiaojiang faults, and the other is mainly located in the northwestern Sichuan sub-block and extends to the south across the Lijiang fault. These low-velocity zones are deduced to be the two crustal channels for the southward escape of crustal matter in the middle and lower crust of Tibetan Plateau.