Has a major earthquake occurred in Taiyuan City, Shanxi Province before? Is it possible that it will happen in the future?

According to historical records, the largest earthquake in Taiyuan's history was an earthquake measuring 6.5 on the Richter scale near Jiaocheng County in 1002 AD. According to preliminary analysis by experts, the newly discovered ancient earthquake site in Xizhang Village shows that there have been at least three large-magnitude earthquakes in Taiyuan's history, with magnitudes ranging from about 7 to 7.5 on the Richter scale. The earthquake occurred about 12,000 years ago, and the most recent earthquake was about 4,000 years ago.

At the site of the ancient earthquake in Xizhang Village, people have excavated an exploration trench and straightened the earth walls to form an east-west line 120 meters long, eight meters wide at the top, four meters deep and wide at the bottom. A giant ladder-shaped exploration trench two meters deep and five meters deep. At a fault mark, an obvious misalignment line can be seen, with a clear distinction between soil and sand. The fault distance is 2.8 meters, indicating that the paleoseismic event was very large. At another mark, the break distance is 2.7 meters. There is another landmark that has not yet been excavated. This active fault runs northwest and is about 17 kilometers long. It crosses Yingze West Street in the center of Taiyuan City and is connected to the Jiaocheng Fault.

Taiyuan City is located in the Taiyuan Basin in the middle of the Shanxi seismic zone. The Shanxi seismic zone is an important seismic activity area in the country. It consists of a series of rift basins such as the Datong Basin, Xinding Basin, Taiyuan Basin, Linfen Basin, and Yuncheng Basin. It is distributed in an "S" shape from north to south. It has always been a key national monitoring One of the defense zones. According to predictions by national seismic experts, mainland my country is likely to enter a new period of active seismicity, and the increase in minor earthquake activity in Taiyuan is normal.

In terms of geological structure, Taiyuan City itself has several active faults, and Haozhuang is located at the intersection of the Dongshan Piedmont Fault and the Tianzhuang Fault. Since the energy of geological activities has been accumulated to a certain extent, a release point will be selected. Wherever the geological structure is weak, the release point will be selected. Therefore, Haozhuang has become a release point for energy accumulation in recent years. Experts said: "It is normal even if a strong earthquake occurs in Haozhuang," "It is just like the weather changes, people will catch a cold, and first feel a sore throat. There is no need to make a fuss." Moreover, except for the one in 2002 Except for magnitude 5 earthquakes, both history and statistical data since the 1970s show that Haozhuang has not had any strong earthquakes.

Sensitive Taiyuan

In fact, not only Haozhuang, but also Beige, Qingxu, Chaicun, Xiangyangdian, Xiaohuixiang and other places in our city are also geologically sensitive areas. At the Municipal Seismological Bureau, the reporter saw a schematic diagram of the faults in the Taiyuan Basin. Although this is only a speculative diagram, we can still have a general understanding of the fault layers underground in Taiyuan.

From the map, it is easy to find the Dongshan Piedmont Fault and Tianzhuang Fault where Haozhuang is located. In addition, there are Jinci Fault, Chaicun Fault, Qinxian Fault, etc. It is these faults that make Taiyuan an earthquake-prone area. According to data provided by the Municipal Seismological Bureau, from January 1, 1970 to December 31, 2004, 4,692 earthquakes of magnitude 1 or above occurred in the Taiyuan Basin, including 1,843 earthquakes of magnitude 2 or above, and 234 earthquakes of magnitude 3 or above. There were 23 earthquakes of magnitude 4 or above and 3 earthquakes of magnitude 5 or above. These earthquakes accounted for 37.7%, 40.9%, 34.0%, 25%, and 17.6% of the total number of earthquakes in Shanxi Province respectively. “The earthquake incidence rate in the Taiyuan Basin accounts for a considerable proportion in Shanxi Province. Therefore, it is not fair to say that Taiyuan is a sensitive city. Not too much.”

We also learned from experts that our city is currently using advanced equipment to accurately measure the active faults underground in Taiyuan. The measurement work will take about two years. By the end of 2006, We can clearly know which streets and buildings in Taiyuan City are located directly on the faults, whether these faults are active faults or solidified faults, the depth of the faults, etc. This will be of great significance to our urban construction and planning.

There have not been many major earthquakes in the history of Taiyuan

For us in Taiyuan, there are always five or six felt earthquakes with a magnitude of 3 or above on the Richter scale a year. As for those that do not feel There are more than a hundred earthquakes of the first and second level every year. It can be said that the Taiyuan Basin is one of the areas with the highest frequency of seismic activity in the Shanxi seismic zone and even North China, and the jurisdiction of Taiyuan City is one of the two areas with intensive seismic activity in the Taiyuan Basin.

Experts explained that several basins in the Shanxi seismic zone have experienced varying degrees of seismic activity and have a certain degree of alternating activity. The Taiyuan Basin was once active in the 1980s, and the Beige earthquake swarm showed a certain window effect. It began to become calm after 1995, and earthquakes became active again after 2001.

However, from a historical perspective, although the earthquakes that occurred in Taiyuan were frequent, their intensity was not high. In the 2,500-year history of Taiyuan City, there have been 11 earthquakes of magnitude 5 or above. The largest earthquake was a magnitude 6.5 earthquake that occurred in the Song Dynasty in 1102 AD. The 2002 Haozhuang earthquake was the largest earthquake Taiyuan had experienced in more than 20 years.

So, after integrating other monitoring data, experts initially speculated that it is unlikely that a devastating earthquake will occur in Taiyuan City in the near future.