What caused the Wenchuan earthquake in Sichuan?

Experts analyze the causes of Wenchuan earthquake. The concrete mechanism of this earthquake is mainly compression at first, and strike-slip energy may be released at the end of the earthquake. There has been no strong earthquake in Sichuan for a long time. In the words of the industry, it is called no earthquake, which means no strong earthquake. According to historical experience, the longer the absence, the greater the possibility of future (strong earthquake). Although it seems that the tectonic activity in Longmenshan area is not strong, it may be in the process of stress accumulation. To a certain extent, the earth's crust will break and earthquakes will occur. The public is generally concerned about why such a big earthquake happened in Wenchuan. Generally speaking, Wenchuan is located in the North-South seismic belt, a major seismic belt in China. Experts from the Seismological Bureau of China believe that due to the great differences in geological distribution, crustal thickness and crustal movement speed between the east and the west of China, the earthquake occurred in the zone with the greatest difference between the east and the west, that is, the North-South seismic zone, which includes from Ningxia to Yunnan via eastern Gansu and western Sichuan, which is an earthquake-intensive zone. The macro explanation is that "the Indian Ocean plate collided with the Eurasian plate from south to north, and the collision zone arched the Qinghai-Tibet Plateau." Professor Ni Sidao from the School of Earth and Space Sciences of China University of Science and Technology told Southern Weekend reporter, "The Qinghai-Tibet Plateau is rising, but it is also moving to the northeast, squeezing the Sichuan Basin to slide to the northeast. The Wenchuan earthquake occurred in the southeast of the Qinghai-Tibet Plateau." Ni Sidao said that the specific mechanism of the earthquake is squeezing. "At the beginning, it was mainly squeezing, and there may be a slip of energy release at the end of the earthquake." Ni Sidao said that the Wenchuan earthquake occurred on the southeast edge of the Qinghai-Tibet Plateau, in the center of Longmen Mountain in western Sichuan, and was located on the Wenchuan-Mao Wen fault zone. Erchie Wang, a researcher at the Institute of Geology and Geophysics of China Academy of Sciences, said that the Sichuan Basin is a relatively stable block. According to historical records, although there was no major earthquake in the main body of Longmen Mountain, there was a strong earthquake in Songpan in the north of the last century. Therefore, although the Longmenshan area seems to have weak tectonic activity, it may be in the process of stress accumulation. When the stress accumulates to a certain extent, the crust will break and an earthquake will occur. However, Erchie Wang also said that at present, we don't know the mechanism of this earthquake, and we don't know whether it was caused by the compression, extension or horizontal strike-slip of the earth's crust. To Xiaoli, Wenchuan is in the Longmenshan earthquake zone in Sichuan. Longmenshan is the intersection of the new Tibet uplift plate and the old Yunnan and Sichuan plates. Seen from this angle, this place is an earthquake-prone area. According to the Catalogue of Strong Earthquakes in China compiled by Forecast Management Office of Monitoring and Forecasting Department of Seismological Bureau of China 1999 in September, there were 8 earthquakes with magnitude above 7 1800 in Sichuan, among which 8 earthquakes with magnitude above 7 occurred since1800. An earthquake of magnitude 7.6 occurred in Luhuo, Sichuan in June of 5438+0973, and an earthquake of magnitude 7.2 occurred in Songpan-Pingwu, Sichuan three years later. In 2002, Chen Xuezhong, a researcher at the Institute of Geophysics, Seismological Bureau of China, analyzed the risk of earthquakes of magnitude 7 or above in Sichuan Province: "There has been no strong earthquake in Sichuan for a long time. In the words of the industry, it is called no earthquake, which means there is no strong earthquake. According to historical experience, the longer the absence, the more likely it will happen in the future. This is a qualitative estimate. " In this context, Chen Xuezhong studied the earthquake risk in Sichuan, and found that historically, there was a strong earthquake of about 8 years before a strong earthquake of magnitude 7 or above occurred in Sichuan. According to this phenomenon, an earthquake of magnitude 8. 1 occurred in Kunlun Mountain in 200 1 year. If this rule continues, this kind of earthquake will happen in Sichuan in a few years.