FAULTING CHARACTERISTICS OF WENCHUAN EARTHQUAKE AND EVALUATION THEORY OF REGIONAL CRUSTAL STABILITY FOR ENGINEERING

The Wenchuan earthquake of May 12th, 2008 on the tectonic margin between the Longmenshan orogenic belt and Sichuan basin had a magnitude of 8.0 Ms, on the Yingxiu-Beichuan fault. A 350-km-long surface rupture zone exhibits right-lateral and left-step features. It is related to the west-dip Wenchuan-Maowen-Qingchuan fault, Yingxiu-Beichuan fault and the Jiangyou-Dujiangyan fault which show dextral strike-slip and thrust. The brittle seismogenic faults in the upper crust，which controlled surface rupture zones and landslides, were produced by slowly ductile flow of lower crust with the stress and strain accumulation at the ductile-brittle shear zone of the middle crust. Seismic source locates at the connection spot between the ductile-brittle shear zone in middle crust and brittle active faults in upper crust. This paper examines the Wenchuan Earthquake in association with the basic characters of intra-plate earthquake. It is believed that it is necessary to develop the theory of regional stability for engineering by continental dynamic theory. The evaluating system must be established together by plate theory, geological mechanics and continental dynamic theory. Some opinions about active faults and earthquake prediction are discussed. It is stressed that earthquake prediction only by active fault is insufficient or improper. The causative structure in lower crust, ductile-brittle transition zone in middle crust and brittle seismogenic faults in upper crust must be considered as a whole in the study. At last, an evaluation index system of regional crustal stability for engineering projects is put forward and the key index for safety island is pointed out.