Interface News Reporter | Zhao Meng
Interface News Editor | Zhai Ruimin
At 23:59 on December 18, 2023, a 6.2-magnitude earthquake occurred in Jishishan County, Linxia Prefecture, Gansu Province, with a focal depth of 10 kilometers. According to Xinhua News Agency, so far, the earthquake has killed 100 people in Gansu and 11 people in Qinghai, and damaged some water, electricity, transportation, communications and other infrastructure.
Why were the casualties in this earthquake so serious? Earthquake expert Chen Huizhong analyzed to Jiemian News that the first reason is that the magnitude of the earthquake is relatively large, with 6.2 magnitude being considered a strong earthquake; second, the focal depth of this earthquake is relatively shallow, and earthquakes with shallow focal points can easily cause considerable damage to the ground; third Third, the earthquake occurred late at night, almost 12 o'clock in the middle of the night, when people were sleeping or asleep, which was also one of the reasons for the heavy casualties.
It is understood that the epicenter of the earthquake is 8 kilometers away from Jishishan Baoan Dongxiang Salar Autonomous County, 32 kilometers away from Qinghai Xunhua Salar Autonomous County, 34 kilometers away from Linxia County, 53 kilometers away from Yongjing County, and 40 kilometers away from Linxia Hui Autonomous Prefecture. , 102 kilometers away from Lanzhou City.
In addition, Chen Huizhong explained that this earthquake occurred in a relatively densely populated area. Although the population here is not as dense as in the eastern region, the epicenter and nearby areas have a relatively large population and high residential density. In addition, the local economy is relatively backward, and the seismic strength of the buildings is weak, not as strong as the buildings in the eastern region. These reasons are all important reasons for the heavy casualties in this earthquake.
Previously, CCTV News reported that the China Seismological Network Center organized experts to conduct research and analysis on seismic activity near Jishi Mountain in Gansu Province. The earthquake was located in southeastern Gansu, about 3 kilometers away from the northern edge of the nearest fault, Laji Mountain. Preliminary focal mechanism analysis results show that this earthquake was a thrust rupture.
China Seismological Network data shows that within 200 kilometers of the epicenter of this earthquake, a total of three earthquakes with magnitude 6 or above have occurred since 1900, all of which were isolated or mainshock-aftershock type earthquakes.
Chen Huizhong introduced that this earthquake occurred in the Lajishan fault zone and was an earthquake caused by a thrust fault.
He said that the structure where this earthquake occurred is the northern edge fault zone of Laji Mountain. Laji Mountain is located on the northeastern edge of the Qinghai-Tibet Plateau and is the dividing line between the hinterland of the Qinghai-Tibet Plateau and the Loess Plateau. The Lajishan fault is an ancient fault zone formed in the Caledonian period. It has experienced multiple periods of intense tectonic changes. It is a structural window that reflects multi-stage tectonic uplift. It has been resurrected since the late Cenozoic to form a regenerative orogenic belt.
The Lajishan fault zone is composed of two arc-shaped compression thrust fault zones protruding toward the NE, namely the northern margin fault of Lajishan and the southern fault of Lajishan. They form the Xining-Minhe basin in the north and the Xunhua-Minhe basin in the south. It is the boundary of several late Cenozoic rift basins such as the Hualong Basin and the Linxia Basin to the east. The area around Laji Mountain is also a densely populated and relatively economically developed area in eastern Qinghai Province. In history, more than 20 moderately destructive earthquakes of around magnitude 5 have occurred along the south and north sides of Laji Mountain.
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