According to the revised data of Seismological Bureau of China, the magnitude of surface wave of Wenchuan earthquake on 5. 12 was 8.0. According to the data of Japan Meteorological Agency, the seismic wave of Wenchuan earthquake on May 12 confirmed that * * * circled the earth 6 times.
The earthquake affected most parts of China and many countries and regions in Asia. The earthquake was felt in Inner Mongolia in the north of China, Shanghai in the east, Tibet in the west, Hong Kong in China and Taiwan Province Province in China in the south, and Thailand, Viet Nam, the Philippines and Japan outside China.
Cause of earthquake
5. 12 Wenchuan earthquake occurred in Longmenshan thrust nappe structural belt, Sichuan. This tectonic belt is the boundary tectonic belt between Bayankala block in Qinghai-Tibet Plateau and South China block in eastern China. It has experienced a long history of geological evolution and has a very complex structure and structure.
Late Cenozoic structural deformation mainly concentrated in guanxian-Jiangyou fault (Qianshan fault), Yingxiu-Beichuan fault (central fault), Wenchuan-Maoxian fault (Houshan fault) and their related folds. 5. 12 Wenchuan earthquake occurred on Yingxiu-Beichuan fault, which was the result of clockwise shear and southeast nappe of Longmenshan thrust.
The Yingxiu-Beichuan fault has been active since Holocene (10000), and the long-term geological slip rate is less than 1mm/ year. GPS observation shows that the present structural deformation of Longmenshan structural belt also has the characteristics of thrust and right-lateral shear, but the deformation speed is not large. Therefore, Longmenshan structural belt and its internal faults belong to special faults with low seismic activity frequency but potential danger of super strong earthquakes.
5. 12 Wenchuan earthquake and southeast thrust of Longmen Mountain were driven by the collision between India plate and Eurasia and its northward thrust. The relative movement between these plates leads to large-scale structural deformation within the Asian continent, which leads to the shortening of the crust, the uplift of the landform and the eastward compression of the Qinghai-Tibet Plateau.
Because the Qinghai-Tibet Plateau was strongly blocked by the active block in South China of Sichuan Basin during the northeast movement, the stress was highly accumulated in Longmenshan nappe structure belt, so that it suddenly dislocated along Yingxiu-Beichuan fault and a strong earthquake of magnitude 8.0 occurred.