Abstract: The Wenchuan M8 earthquake occurred on the Longmenshan fault zone. Based on field investigation of the surface rupture and focal mechanism study of the aftershocks, we studied the geological relationship of main rupture, secondary rupture and trigged rupture. The main rupture is about 200 km long which can be divided into the south part and north part. The south part consists of two parallel fault zones mainly reverse, with several parallel secondary ruptures on the hanging wall of the main fault, and the north part is a single main fault zone characterized with lateral strike slip and reverse faulting. Comparing with 300 km long aftershock distribution, the surface rupture only occupy 200 km of them, and the left 100km on the northeast of the main rupture were triggered earthquakes. The Earthquake geology results of this paper may be useful for studying the earthquake risk evolution on the Longmenshan fault system.

Key words: Wenchuan M8.0 earthquake, Longmenshan fault, Surface rupture, Focal mechanism, Aftershocks