Experts analyze the causes of the Wenchuan earthquake

The specific mechanism of this earthquake was mainly compression at the beginning, and there may be a release of strike-slip energy towards the end of the earthquake.< /p>

There has not been a strong earthquake in Sichuan for a long time. In industry terms, it is called missing earthquake, which means the absence of strong earthquakes. According to historical experience, the longer the lack of time, the greater the possibility of a (strong earthquake) occurring in the future. The greater the sex.

Although the Longmen Mountain area does not appear to have strong tectonic activity, it may be in the process of accumulating stress. When the accumulation reaches a certain level, the crust will rupture, resulting in an earthquake.

The public is generally concerned about why such a large earthquake occurred in Wenchuan.

From a large perspective, Wenchuan is located in a major earthquake zone in China - the North and South Earthquake Zone.

Experts from the China Earthquake Administration believe that because the geological distribution, crustal thickness, and crustal movement speed are very different between eastern and western China, and this earthquake occurred in the zone where the changes are most different between the eastern and western parts of China, That is, the north and south seismic zones - including from Ningxia through eastern Gansu, western Sichuan and Yunnan, are all earthquake-intensive zones.

The macro explanation is that "the Indian Ocean Plate collides with the Eurasian Plate from south to north, and the collision area arches the Tibetan Plateau." Professor Ni Sidao from the School of Earth and Space Sciences at the University of Science and Technology of China told a Southern Weekend reporter, " While the Qinghai-Tibet Plateau was uplifting, it also moved northeastward, squeezing the Sichuan Basin to strike northeast, and the Wenchuan earthquake occurred in the southeast of the Tibetan Plateau. "

Ni Sidao said this earthquake. The specific mechanism is extrusion. "It was mainly extrusion at the beginning, and there may be a release of strike-slip energy towards the end of the earthquake." Ni Sidao said that the Wenchuan earthquake occurred on the southeastern edge of the Qinghai-Tibet Plateau and in the Longmen Mountains of western Sichuan. The center is located on the Wenchuan-Maowen fault zone.

Wang Erqi, a researcher at the Institute of Geology and Geophysics, Chinese Academy of Sciences, said that the Sichuan Basin is a relatively stable land mass. Judging from historical records, although there have been no major earthquakes in the main body of Longmen Mountain, there was a strong earthquake in Songpan to the north of it at the beginning of the last century. Therefore, although the Longmen Mountain area does not appear to have strong tectonic activity, it may be in the process of accumulating stress. When the accumulation reaches a certain level, the crust will rupture and earthquakes will occur.

However, Wang Erqi also said that at present, we still don’t know the mechanism of this earthquake. We don’t know whether it is caused by the extrusion and extension of the earth’s crust or horizontal strike-slip.

From a small perspective, Wenchuan is in the Longmen Mountain seismic zone of Sichuan. Longmen Mountain is where the new Tibet uplift plate intersects with the old Yunnan and Sichuan plates. From this perspective, this place is an earthquake-prone area.

According to the "Catalogue of Strong Earthquakes in China" compiled by the Forecast Management Office of the Monitoring and Forecasting Department of the China Earthquake Administration in September 1999, there have been 18 earthquakes of magnitude 7 or above in Sichuan, of which 8 have occurred since 1800. earthquake of magnitude 7 or above. In 1973, a magnitude 7.6 earthquake occurred in Luhuo, Sichuan, and three years later, a magnitude 7.2 earthquake occurred in Songpan-Pingwu, Sichuan.

Researcher Chen Xuezhong from the Institute of Geophysics of the China Earthquake Administration once analyzed the risk of earthquakes with magnitude 7 or above in Sichuan Province in 2002: "There has been no strong earthquake in Sichuan for a long time. In the words of the industry, It is called missing earthquake, which means the lack of strong earthquakes. According to historical experience, the longer the missing time, the greater the possibility of (strong earthquakes) occurring in the future. This is a qualitative estimate."

In this context, Chen Xuezhong studied the earthquake risk in Sichuan and found that from a historical experience, in the past few years before strong earthquakes with a magnitude of 7 or above occurred in Sichuan, there were nearby earthquakes with a magnitude close to 8. Large earthquakes occur around the world. According to this phenomenon, and then pushed back, an 8.1-magnitude earthquake occurred in Kunlun Mountain in 2001. If this pattern continues, this kind of earthquake will occur in Sichuan in a few years.