Earthquakes of magnitude 6 or above occurred in fault basins.
From 5 12 BC to 199 1 March, there were 69 earthquakes of magnitude 5 or above in Shanxi, including 4 earthquakes of magnitude 7-7.9, 6-6.9 10 and 53 earthquakes of magnitude 5-5.9. All earthquakes with M ≥ 6 occurred in a series of fault basins in the central part of the province.
As far as fault basins are concerned, there are also great differences in seismic activity. There have been two earthquakes of magnitude 8 and nine earthquakes of magnitude 5 in Linfen Basin. There are many series of high-intensity and low-frequency earthquakes in Ding Xin Basin. The earthquake intensity in Taiyuan Basin is moderate, but the frequency ranks first in the province. The intensity and frequency of earthquakes in Datong and Yuncheng basins are moderate.
According to the "Taiyuan Active Fault Detection and Risk Assessment Project" just passed by the Provincial Seismological Bureau, there are 18 hidden faults in Taiyuan, 7 of which have hidden dangers and need to be explored emphatically. After exploration, Fenhe West Fault, Fenhe East Fault and Xincheng-Qinxian Fault are "dead" faults, that is, these faults will not move and earthquakes will not occur. This conclusion will add a large number of planned land for the banks of Fenhe River in Taiyuan.
There is little possibility of a strong earthquake in Taiyuan in the next century.
Jiaocheng fault (including Chaicun section and Jinci section) is a fault with high earthquake risk in Taiyuan in the future, and the probability of earthquake in this section is high, and the earthquake disaster in Taiyuan also comes from the influence of this fault. However, the possibility of strong earthquakes in Taiyuan in the future 100 is very small (at the end of 2007, after the evaluation project was approved by the state, Shanxi Daily reported on the topic "The possibility of strong earthquakes in Taiyuan in the future is very small"). This is the result of the research on the new activity of each fault by the Seismological Bureau of Taiyuan City, and the conclusion obtained by using the probability evaluation method and seismic risk evaluation method suitable for the structural characteristics of Taiyuan City has been recognized by national experts.
Three strong earthquakes before Taiyuan ancient times
From May 24th to June 5th, 2005, Shanxi Earthquake Engineering Investigation and Research Institute excavated an extra-large trench with a length of 120m, a total width of 8m and a total depth of 9m in Zhang Cun, Chaicun Township, Taiyuan City. It is preliminarily confirmed that there are three faults in the trench, and the maximum fault distance is 2.8 meters. It is speculated that these three faults reflect three earthquakes of magnitude 7 or above that occurred in Holocene. Experts from the Institute of Geology, Seismological Bureau of China recently discovered an ancient earthquake site in China.
According to experts, the discovery of this site and a large number of physical evidences have overturned the conclusion that there has never been an earthquake of magnitude 7 or above in Taiyuan, which is of great significance to the study of crustal movement in Taiyuan and even Shanxi. The ancient earthquake site in West Zhang Cun shows that there have been at least three large-scale earthquakes in Taiyuan's history, with magnitude between 7 and 7.5 on the Richter scale. The time of three earthquakes occurred, the farthest one was about 6.5438+200,000 years ago, and the latest one was about 4,000 years ago.
Researcher He Yongnian, former deputy director of China Seismological Bureau, led many professionals from the Institute of Geology of China Seismological Bureau to Taiyuan for on-site investigation and sampling. He Yongnian pointed out that the discovery of Xizhang ancient earthquake site not only helps to study the history of Shanxi earthquake, but also provides a scientific basis for guiding the country's future earthquake prevention and disaster reduction work and avoiding active faults in urban planning and construction.
The earthquake with magnitude above 7 in Taiyuan only appeared before the emergence of human civilization, so there are only geological relics and no historical records.
In the mid-Northern Song Dynasty, strong earthquakes occurred frequently in Taiyuan.
Among the earthquakes recorded in historical books, the earthquake with the largest magnitude in Taiyuan's history was an earthquake with a magnitude of 6.5 on the Richter scale near Jiaocheng County in A.D. 1002. As one of the three wonders of Jinci, the painted statue of a lady in Song Dynasty was damaged in the earthquake. The earthquake has spread all the way to Datong and Yingxian, with a strong sense of shock.
During the Song Jingde period (A.D. 1004 ~ 1007), another earthquake occurred in Taiyuan.
As can be seen from the above, Taiyuan was a period of frequent strong earthquakes in the middle of the Northern Song Dynasty 1000 years ago, and there was no major earthquake in Taiyuan Basin since then. However, many earthquakes of magnitude 7 and 8 occurred in Ding Xin basin in the north and Linfen basin in the south of Taiyuan basin, which affected Taiyuan and caused earthquake damage.
Relatively speaking, the intensity and frequency of earthquakes in Datong basin in northern Shanxi are moderate. Less destructive and less frequent.
Four largest earthquakes in Linfen basin
Linfen basin used to be a high-risk place for major earthquakes in the Jin and Yuan Dynasties, and there were four major earthquakes in history.
1209 (the first year of Great An in Jin Shao), a strong earthquake occurred in Pingyang County (now Linfen City, Shanxi Province).
On the first day of August in A.D. 129 1 year (twenty-eight years from Yuan Shizu to Zheng Zheng), Pingyang County suffered another earthquake.
1303 (the seventh year of Yuan Chengzong Dade), earthquakes occurred all over the country, reaching Yunnan in the south, Inner Mongolia Autonomous Region in the north, Liaodong Peninsula in the east and Shaanxi-Gansu in the west, and earthquake disasters continued.
More than 300 years later, in May of 1695 (thirty-four years of Kangxi in Qing Dynasty), the fourth major earthquake occurred in Linfen, this time with a magnitude of 8.