Abstract: In this paper, we studied seismicity and relocated earthquakes with M_L≥0.5 occurring in the Jinping reservoir and its surrounding area before and after the impoundment. Then we inversed the mechanism solutions of 71 M_L≥3.0 earthquakes occurred the stress field before and after impoundment. The initial response time of the earthquake Jinping Level Ⅰ Reservoir in the was relatively long, which should be related to the lack of coverage of the flooding area near the earthquake swarm. After expanding to Hulugou, seismicity increases sharply, the changes of seismicity in the following stages have good relationship with the impoundment process. After the impoundment, a large number of earthquakes concentrated near Hulugou in Tibetan Autonomous County of Muli, with focal depths ranging from 6 to 14 km, which became shallower compared to the focal depths before the impoundment. Except for the results of focal mechanism solutions in the Hulugou, P-axis and T-axis distribution, regional stress field except for Hulugou are consistent with previous research results. The focal mechanisms of the earthquake near Hulugou are mostly strike type, with the P-axis mainly in the NS and NNW-SSE directions, and the T-axis mainly in the EW and NEE-SWW directions. The maximum and minimum principal stress axes of the regional stress field are nearly horizontal, and the intermediate stress axis is nearly vertical, the R-value is 0.5, different from other regions. We infer that their mechanisms should be influenced by pore pressure diffusion and infiltration weakening.

Key words: Jinping Ⅰ reservoir, seismicity, Focal mechanism, Stress field inversion, R-value