Characteristics of P wave velocity structure changes before and after impoundment in Nuozhadu reservoir，Pu’er，Yunnan

Using both absolute arrival time, relative arrival time and waveform correlation data of Nuozhadu reservoir earthquake events, we obtained seismic relocation and 3D P wave velocity structure of three periods by double-difference seismic tomography method. The results show that after the reservoir impoundment, a large number of earthquakes occurred at the reservoir area, and the aftershocks after relocation is mostly located at the depth within 10 km, especially in the range of less than 5 km, which is basically consistent with the previous result that the depth of reservoir-induced earthquake is less than 10 km. With the increase of water storage, the reservoir water penetrates along the fault, the pore pressure changes, which causes earthquakes-increased-area to extend to the Heihe river and the middle part of the Lancangjiang river, and further to the Weiyuanjiang and the Xiaoheijiang rivers. The P wave velocity in these regions is reduced. The maximum depth of the overall reservoir seepage is less than 7 km.