Three-dimensional crust structure beneath SE Tibetan plateau and its seismotectonic implications for the Ludian and Jinggu earthquakes

A detailed 3D crust S-wave velocity model is derived from joint analysis of Rayleigh wave group velocity and teleseismic P-wave receiver functions at permanent stations on the southeast margin of Tibet plateau and its surrounding area. Our new models show the velocity structure in the crust beneath SE Tibet is strongly heterogeneous. There are strong lateral variations in crustal thickness, which increases gradually from 30km in the south and east of Yunan to~65km in the SE Tibetan Plateau. Two obvious low velocity zones (LVZs) are revealed at various depths in the crust. The shallower LVZ in the middle crust (15~20 km depth) are limited in the Tengchong volcano and Sichuan-Yunnan (Chuan-Dian) rhombus block. Another LVZ in the middle-to-lower crust varies between 25 and 40 km and it shallows toward the east and southeast and is absent in the Sichuan Basin and the southern part of this study area. Our shear velocity model clearly shows an upper crustal high-velocity body and two LVZs in the middle crust and middle-to-lower crust (30~40 km depth) across the source area of the 2014 Ludian earthquake. Ludian earthquake sequences and the neighbouring Yongshan-Daguan seismic zone are distributed in the upper crustal high-velocity body. In contrast, no obvious intra-crustal low velocity zones (IC-LVZs) appear beneath the Jinggu earthquake and its adjacent areas. But low velocity anomalies are found in the upper crust beneath the Jinggu earthquake and its neighbouring Simao-Pu'er seismic zone, which may be due to a highly fractured and fluid-filled rock matrix that may have initiated the nucleation of the Jinggu earthquake. ©, 2014, State Seismology Administration. All right reserved.