河套断陷带主要活动断裂最新地表破裂事件与历史大地震

THE LATEST SURFACE RUPTURE EVENTS ON THE MAJOR ACTIVE FAULTS AND GREAT HISTORICAL EARTHQUAKES IN HETAO FAULT-DEPRESSION ZONE

对于历史记录的公元849年大地震的发震构造尚存在一定争议,公元前7年大地震是否发生在河套断陷带,也没有得到确认。通过影像解译、野外地质地貌调查和探槽开挖,结合14C和单颗粒OSL测年,利用构造地貌分析及古地震手段,对大青山山前断裂、乌拉山山前断裂及狼山山前断裂的最新破裂事件进行了对比研究。为了尽可能降低古地震定年的不确定性,采取了序列采样、重点层位多采样等措施。结合以往研究成果认为,大青山山前断裂应为公元849年大地震的发震构造,而狼山山前断裂最近1次地震破裂事件可能与公元前7年大地震有关。

Hetao fault-depression zone,the largest one of 4 fault-depression zones around the Ordos block,is characterized by intense tectonic activities. According to historical records,2 large earthquakes,occurring in 849 AD and 7BC respectively,were recognized to be located at this zone. However,there is still some dispute about the seismogenic structure of the 849 AD earthquake,and there is no tangible geological evidence to support the view that the 7BC event occurred in Hetao fault-depression. In this paper,based on the image interpretation（ from Google Earth）,field investigation,trench excavation,and14 C and single grain OSL dating,we analyzed the tectonic landform and paleoseismic events on the Daqingshan piedmont fault,Wulashan piedmont fault and Langshan piedmont fault in the Hetao faultdepression zone. Furthermore,a comparative study of the latest rupture events on the 3 active faults was carried out. In order to lower the uncertainty of paleoseismic event dating,several effective measures,such as sampling according to the stratigraphic sequence,collecting multi samples in important strata,were adopted. Combining the previous achievements, the seismogenic structures of the 849 AD earthquake and the 7BC earthquake were discussed. The results support that the Daqingshan piedmont fault is the seismogenic structure of the 849 AD earthquake,and the latest surface rupture event of the Langshan piedmont fault may be related to the 7BC earthquake.