Relocation of aftershocks of the Wenchuan M_S8.0 earthquake and its implication to seismotectonics

From 14:28 (GMT+8) on May 12th, 2008, the origin time of M_S 8.0 Wenchuan earthquake, to December 31th, 2008, more than 10 000 aftershocks (M≥2.0) had been recorded by the seismic networks in Sichuan and surrounding areas. Using double difference algorithm, the main shock and more than 7 000 aftershocks were relocated. The aftershocks distribute about 350 km long. The depths of aftershocks are mainly between 10 km and 20 km. The average depth of aftershocks is about 13 km after relocation. In the southwest, the distribution of aftershocks is along the back-range fault, the central-range fault and the front-range fault of Longmenshan faults. In the middle, the distribution of aftershocks is along the central-range fault. In the north, aftershocks are relocated along the Qingchuan-Pingwu fault. Relocations suggest that the back-range fault mainly induced and controlled the aftershock occurrence in the northern section of aftershocks sequence. The M_S 8.0 main shock is between central-range and front-range of Longmenshan faults and is near the shear plane of the fault bottom. From the depth distribution of aftershock sequence, it suggests that these three faults show imbricate thrust structure.