The Jinsha River flows through the tectonically active Sichuan and Yunnan regions, which have frequent strong earthquake activities. Four large-scale hydropower dams have been built in the lower reaches of the river and had begun impounding water successively since October 2012, with the Baihetan (BHT) and Xiluodu (XLD) being the second and fourth largest hydropower stations in the world. Using the seismic data recorded by dense seismic stations in the lower reaches of the Jinsha River from January 2010 to December 2019, we obtain the 3D crustal VP, VS, and VP/VS models and seismic relocations by applying the VP/VS model consistency-constrained double-difference tomography method (tomoDDMC). After Xiangjiaba (XJB) and XLD started to store water, earthquakes were mainly clustered in two areas where the seismicity was weak before the impoundment, that is, (1) the western segment of the Mabian-Yanjin fault (MBYJF) zone on the west side of the river and the tail section of XJB, and (2) the southwest part of Leibo-Yongshan basin near the middle section of XLD reservoir. We find that the areas where earthquakes are concentrated have characteristics of high-velocity and low-VP/VS. These particular features may provide important information for predicting the potential earthquake risk areas. In addition, we found a well-resolved high-velocity and low-VP/VS zone sandwiched between two layers of low velocity and high VP/VS at depths ranging from 3 to 10 km beneath the Qiaojia area along the Xiaojiang fault (XJF), which suggests that the seismic activity in this area may increase with the storage of the BHT dam in April 2021.

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In this study, through the seismic phase observation report obtained by a river reservoir seismic network from September 2012 to July 2015, the joint inversion method of source and velocity structure is employed, combined with the regional seismic geological environment data. Such method gives the P-wave velocity structure of different sections in the reservoir area and tries to find out the impact range of the reservoir water depth. And the impact of reservoir water infiltration on crustal medium is discussed. The obtained location results show that the earthquake activity is mainly concentrated in the first reservoir tail and the second reservoir head. As such, the spatial distribution characteristics of the recorded earthquakes are given, and the resolution results of detection board at different depths are speculated and discussed.