Co-seismic Faults and Geological Hazards and Incidence of Active Fault of Wenchuan Ms 8.0 Earthquake, Sichuan, China

: There are two co-seismic faults which developed when the Wenchuan earthquake happened. One occurred along the active fault zone in the central Longmen Mts. and the other in the front of Longmen Mts. The length of which is more than 270 km and about 80 km respectively. The co-seismic fault shows a reverse flexure belt with strike of N45°–60°E in the ground, which caused uplift at its northwest side and subsidence at the southeast. The fault face dips to the northwest with a dip angle ranging from 50° to 60°. The vertical offset of the co-seismic fault ranges 2.5–3.0 m along the Yingxiu-Beichuan co-seismic fault, and 1.5–1.1 m along the Doujiangyan-Hanwang fault. Movement of the coseismic fault presents obvious segmented features along the active fault zone in central Longmen Mts. For instance, in the section from Yingxiu to Leigu town, thrust without evident slip occurred; while from Beichuan to Qingchuan, thrust and dextral strike-slip take place. Main movement along the front Longmen Mts. shows thrust without slip and segmented features. The area of earthquake intensity more than IX degree and the distribution of secondary geological hazards occurred along the hanging wall of co-seismic faults, and were consistent with the area of aftershock, and its width is less than 40 km from co-seismic faults in the hanging wall. The secondary geological hazards, collapses, landslides, debris flows et al., concentrated in the hanging wall of co-seismic fault within 0–20 km from co-seismic fault.