No moderate and strong earthquake occurred for many years in Wenxian since the M8.0 great earthquake occurring in 1879 A.D. The June 21,2006 Wenxian earthquake with M5.0 occurred in an area where the tectonic setting is complex. Seismic activity level in Wenxian would enhance after the occurrence of this earthquake(M5.0). Since the earthquake did not produce surface rupture zone,it is very difficulty to study the seismogenic fault. However,we can still study the seismogenic fault based on geological map(1∶200 000),remote sensing interpretation,inversion of focal mechanism and seismic sequence precise location method. In order to determine the future seismic risk of the region,the paper intends to analyze the earthquake causative structure by jointly using the remote sensing interpretation,various methods of inversion of focal mechanism,and double-difference earthquake location algorithm. The geological map(1:200 000)shows there are many faults in this area,and the interpretation of remote sensing reveals that only one fault named Shifang-Linjing Fault is active. Focal mechanisms derived from the two methods show that the earthquake is of left-lateral strike-slip and thrust,and the principal compressive stress is in the direction of N60°E. The results of double-difference earthquake locations also support this result. The distribution of aftershocks is related to the thrust faulting. Results of combined analyses show that the Shifang-Linjiang Fault is the seismogenic fault of this earthquake,and the direction of the principal compressive stress is N60°E.

The East Kunlun active fault zone, which lies in the valley of the Kunlun Mountains above the elevation of 4,000 meters, is an important active fault in the Northeast Tibetan Plateau. The Tuosuohu Lake earthquake of magnitude 7.5 in 1937 occurred in the eastern segment of the East Kunlun active fault zone. Four field investigations have been launched on this seism in 1963,1971 and between 1986 and 1990 respectively, and four different conclusions have been gained. From the length aspect of the surface deformation zone of this earthquake, it is commonly recognized that its east end lies in the west side of the main Ridge of Animaqing Mountains; the opinion about the west end and the location of the macro-epicenter is different. Based on our investigation and comprehensive study, a series scientific problems like geometric and kinetic characteristics, the length of the rupture zone, the maximum sinistrally horizontal displacement and the macro-epicenter were reestimated. It is considered that the total length of this zone should be at least 240km; the maximum sinistrally horizontal displacement is 8m, the maximum vertical displacement is 3.5m; the macro-epicenter is in Sanchakou.