Research Of The Seismogenic Mechanical Mechanism Of Wenchuan Earthquake

Wenchuan earthquake, occurring in 2008, is the most destructive earthquake in the north-central section of Longmenshan since the Tangshan earthquake in China, with more than 87 thousand compatriots killed in the earthquake. According to the post-earthquake survey, Wenchuan earthquake is a thrust and dextral strike-slip fault earthquake, which is generally considered to be the release of accumulating stress after the Songpan - Ganzi block migration eastward resisted by the stable Upper Yangtze block. However, according to published observations of GPS, the Sichuan Basin has western co-seismic displacement. It indicated that the seismogenic mechanism of Wenchuan earthquake may be more complicated than its showing. The ascertainment of the seismogenic mechanism of Wenchuan is the base to evaluate the risk of future Longmenshan earthquakes. This dissertation analyzes the seismogenic mechanism of Wenchuan earthquake from the co-seismic displacement of both sides of quaking-fault blocks. The thesis is divided into four chapters:The first chapter introduces the domestic research situation of the seismogenic mechanism of Wenchuan earthquake. The second chapter presents the distributions and characteristics of fractures of the Longmenshan belt. The third chapter introduces the co-seismic rupture of Wenchuan earthquake , the co-seismic displacement of quaking fault of the upper and lower plates and the analysis of the seismogenic mechanism based on it. The fourth chapter presents the prediction of the recurrence cycle of strong earthquakes based on the analysis of co-seismic strain energy.The analysis shows that the seismogenic mechanism of Wenchuan earthquake is the combined effect of the opposite compressive stress of the Songpan - Ganzi block and the Sichuan block and the dextral strike-slip shear stress of the central fault zone along Longmenshan.The results of the analysis and measurement show that the maximum horizontal displacement of the footwall which is Sichuan basin near the earthquake zone and vertical Longmenshan fault zone west is about 1.9m and that the maximum horizontal displacement of the hanging wall which is the Songpan - Ganzi block near the earthquake zone and vertical Longmenshan belt east is about 0.7m and that the NE maximum horizontal displacement of the hanging wall near the earthquake zone is about 1m and that the SW maximum horizontal displacement of the footwall near the earthquake zone is about 1.4m. Thus I believe that the seismogenic mechanism of Wenchuan earthquake is the combined effect of the opposite compressive stress of the Songpan - Ganzi block and the Sichuan block and the dextral strike-slip shear stress of the central fault zone along Longmenshan.The recurrence cycle of a Longmenshan Ms8.0 earthquake is 2,858-5,716 years calculated through the co-seismic strain energy.