The mechanics of fault slip of M_S8.0 Wenchuan earthquake

The seismogenic structure of the M_S 8. 0 Wenchuan earthquake is the Longmenshan fault zone. Its surface rupture occurs mainly on the Beichuan-Yingxiu fault and the JiangyouGuanxian fault, especially the former, with a length of 240 km. By field investigation and observation, we got 311 data of active fault slickensides. And using the method of inversion of fault slip data, we can obtain the parameters of 8 tectonic stress tensors and the characteristics of recent tectonic stress field in the Wenchuan region. The result shows that the recent tectonic stress field in the region is characterized by horizontal components. The maximum compressional stress is nearly in EW direction, and the stress regime is of reverse-fault type. The direction of the maximum principal compressional stress (σ_1) is 76°-121°, and the average dip angle is 9°. Spatial distribution of the tectonic stress field and the geometrical characteristics of the Longmenshan fault zone show that the surface rupture has segmented characteristics. Up-thrust of the northwest wall is the main vertical slip on the Yingxiu-Beichuan segment. Both reverse faulting and strike slip occurred on the segment to the north of Beichuan, and strike slip offsets are greater than the vertical ones in some places.