Abstract: We use double difference location method to relocate 1569 small earthquakes recorded by 8 seismic stations of the Zipingpu reservoir network from August 16, 2004 to May 10, 2008. The results show that after relocation, the earthquake distribution is from spatial discretization and gridding to concentrated distribution, and the small earthquakes relocated are mainly concentrated in central Beichuan-Yingxiu fault, frontal Guanxian-Jiangyou fault and retral Wenchuan-Maowen fault of the Longmen Mountains. Most of the small earthquakes are located in the Beichuan-Yingxiu fault and converge to both ends of the Zipingpu reservoir, and occurred at the depth of 5~15 km,and a few at depth of 15~30 km, and the mean depth is 7.8 km. Seismic frequency of the Zipingpu Reservoir region has a correlation with the reservoir water level. The average root-mean-square of travel time residual after relocation is 0.048s, the horizontal average error is estimated to be 0.63 km, and the average vertical error had been controlled less than 0.51km. This paper also discussed the relation between location image and the geological structure.

Key words: Zipingpu reservoir, Wenchuan M_S8.0 earthquake, Double difference algorithm