Characteristics and geodynamic analysis of the focal fault for the Great 8.0 Ms Wenchuan Earthquake

Based on surface geological structure of the crust,researches on seismic geology and seismic sounding,and the result of magnetotelluric prospecting,the authors deal with the environment and characteristics of the deep structure and the result of geodynamic analysis of the Great 8.0 Ms Wenchuan earthquake.It is indicated that the concealed crust-mantle ductile shear zone under the Longmen mountain collisional orogenic belts is the focal fault,while Yingxiu fault,Beichuan fault and Pengxian-Guanxian fault formed at surface are earthquake faults in the main focal region of the Great 8.0 Ms Wenchuan Earthquake,which are distinct and connected.Studies show that Great 8.0 Ms Wenchuan Earthquake and surface ruptures might be attributed to the conflict of the Yangtze block with the Qinghai-Tibet plateau and the eastward obduction of the east edge of Qinghai-Tibet plateau and the eastward subduction of its deep part under the dynamic action of India Plate,Pacific Plate and Philippine Plate conflicting with Eurasia plate,which caused Longmen Mountain collisional orogenic belts to cut the Moho-crust-mantle ductile shear zone and expand to the middle-upper crust,thus resulting in high-degree stress concentration and rapid energy release.The study of the relationship between the focal fault and the earthquake fault is of great significance in the investigation of earthquake mechanism,dynamics of earthquake and earthquake disaster prevention and mitigation.