Crustal 3-D S-Wave Velocity and Azimuthal Anisotropy in the Sanjiang Lateral Collision Zone in the SE Margin of the Tibetan Plateau

The eastward extrusion of the Tibetan Plateau materials has caused intricate tectonic deformations and frequent seismic activities in the Sanjiang lateral collision zone (SLCZ). To reveal crust structures and deformation mechanisms, we investigate high-resolution structural features of crustal depth (<= 40 km). A 3-D S-wave velocity and azimuthal anisotropy model is constructed by the direct tomography method with Rayleigh phase velocity at periods of 2-40 s from multiple temporary seismic arrays and regional permanent network. In the middle-to-lower crust, an obvious low-velocity zone is confined by the large-scale fault systems of Jinhe-Qinghe fault and Chenhai fault (CHF) to the northeast and east, Lancangjiang fault (LCJF) and Red River fault (RRF) to the west, with strong N-S-oriented anisotropy, which evident differs from the ENE-WSW-oriented weak anisotropy in the high-velocity zone on the northeastern side. We consider that the weak material may be obstructed by large faults and the high-velocity zone, resulting in complex crustal deformation and tectonic boundary. The crustal low-velocity materials beneath the Tengchong volcano (TCV) are probably separated with those from the Tibetan Plateau. The low-velocity beneath the Chuxiong basin (CXB) may be combinations of partial melts and fluid derived from shear deformation and deep material upwelling. The segmented anisotropy at the NW end of the RRF suggests complex deformation by crustal flow, emphasizing the important influence of faults on anisotropic pattern. The complex anisotropy in the fault intersection of the Lijiang-Xiaojinhe fault and RRF also highlights the important role of these faults in shaping crustal deformation. The Sanjiang lateral collision zone in the SE margin of the Tibetan Plateau has experienced a complex, multistage tectonic evolution and witnessed frequent seismic activity. A meticulous high-resolution 3-D S-wave velocity and azimuthal anisotropy is undeniably obtained due to adding up two elaborate temporary seismic arrays. Our model shows that the low-velocity with strong anisotropy in the middle-to-lower crust is probably related to the eastward extrusion of the Tibetan Plateau material blocked by large faults and high-velocity body, leading to complicated crustal deformation and distinct boundaries between tectonic blocks. Interestingly, the low-velocity from the Tibetan Plateau is seen to be well separated from the low-velocity under the Tengchong volcano. At the NW end of the Red River fault, the segmented anisotropic pattern, indicating that the complex deformation is caused by the southeastward movement of the crust and the nature of the fault itself. The complex anisotropy in the fault intersection also highlights the important role of these faults in shaping crustal deformation. An unprecedented high-resolution 3-D azimuthal anisotropy Vs model reveals the low-velocity from the Tibetan Plateau Middle-to-lower crustal low-velocity materials from Tibetan Plateau spreading southeast are confined by Jinhe-Qinghe fault Low-velocity materials under the Tengchong volcano seem to be separated with those from the Tibetan Plateau