河西走廊西端酒西盆地古地震研究进展

Research Progress on Paleoearthquake in Jiuxi Basin Located in the Western Hexi Corridor

摘要:

酒西盆地位于祁连山北缘、河西走廊西端，是一个被活动断裂围限的新生代压陷性盆地，盆地周缘及内部发育多条活动断裂。通过对前人古地震资料的总结分析和野外补充调查，发现酒西盆地断裂古地震大多符合特征地震模式，复发周期约为3~5 ka，根据经验公式推断，每次地震的震级约为6.8~7.2级。从区域古地震角度看，酒西盆地地震的发生具有丛集的特征。全新世以来存在3个丛集期，分别为10~8 ka、5.5~3.5 ka、2 ka以来，每个丛集期的长度约为2 ka。从复发特征和离逝时间上看，盆地内部的阴洼山断裂和白杨河断裂接近复发周期，具有较高的地震危险性。

Abstract:

Paleoearthquake refers to the prehistoric and historically unrecorded earthquake events according to the stratigraphic records. The advantage of the stratigraphic record is that it can make up for the transience and limitation of the historical and instrumental records and reduce the uncertainty in the seismic risk assessments (SRA). Only a few decades ago, recording of earthquakes by instruments started. Measuring historical earthquakes only reach the scale of thousands of years. The study of paleoearthquake can extend the seismic records to the scale of ten thousand years and span multiple occurrences of periods of earthquakes, which enables us to recognize the long-term activity habits of faults and helps us estimate the risk of future earthquakes over long periods of time. Paleoearthquake plays an important role in predicting the earthquake risk, and it becomes an indispensable branch of the earthquake disaster prevention information system. The Jiuxi Basin, located in the northern margin of the Qilian Shan and the western end of the Hexi Corridor, is a Cenozoic compressive basin surrounded by active faults. There are many active faults around and inside the Jiuxi Basin. There have been many medium to strong historically unrecorded earthquakes, which have caused the highly destructive earthquakes. Based on the summary of the previous paleoseismic data and supplementary investigation, it is found that most paleoearthquake along the active faults in the Jiuxi Basin conform to the earthquake model characteristics, with a recurrence interval of approximately 3-5 ka. According to the empirical formula, the magnitude of each earthquake is approximately 6.8-7.2. The occurrence of earthquakes in Jiuxi Basin is characterized by clustering from the perspective of regional paleoearthquake. There have been three cluster periods since Holocene, each of which lasts about 2 ka. The seismic risk for the Yinwashan and Baiyanghe faults is high in terms of recurrence characteristics and elapsed time.