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Abstract

The central body of the Sanjiang lateral collision zone is located in western Yunnan, China, in the southeast margin of the Tibetan Plateau. The long evolutionary history resulted in numerous changes in crustal thickness, and complex deep tectonics in the study area, which also makes it an important metallogenic belt in China. With the seismic data recorded by a temporary array (SJ-Array) and permanent stations (Nov. 2018 ~ Dec. 2020), we build a high-precision earthquake catalog using a workflow of deep learning-based phase automatic picking, correlation, and location. We automatically detect and locate more than six times as many microseismic events as in the regular catalog, and the minimum magnitude of completeness MC was reduced from ML1.1 to ML0.1. Our high-precision earthquake catalog clearly reveals the characteristics of faults, and also provides more abundant effective records for S-wave splitting analysis. Using the S-wave splitting analysis technique and microseismic events, we obtain the spatial variation characteristics of upper crustal anisotropy of the Sanjiang lateral collision zone, with finer distribution and accuracy. In the interested area, it is shown that the dominant polarization of the fast S wave is NNW. In addition, the study area can be divided into three subzones from the west to the east according to the various mean polarizations. Our study demonstrates the local tectonic differences in the Sanjiang lateral collision zone and indicates that the crustal structure may be strongly controlled by the fault and block boundary strike.