榆木山北缘断裂古地震特征研究

PALAEO-EARTHQUAKE STUDY ON THE NORTHERN YUMUSHAN ACTIVE FAULT

榆木山北缘断裂位于祁连山主体山系以北的榆木山北部边缘。断裂活动形成一系列沿山前发育的断层陡坎。通过探槽剖面对发生在该断裂带上的古地震事件进行了分析,大致可以确定全新世以来的2次古地震事件。事件Ⅰ的年代为距今(4.066±0.086)ka;事件Ⅱ为距今(6.852±0.102)ka至(6.107±0.082)ka之间。该断裂的最后一次古地震事件发生在距今(4.066±0.086)ka,并非公元180年表氏71/2级地震的发震断裂。

The northern Yumushan Fault located on the northern flank of Qilian fold system is an active fault in Holocene.The fault is about 60km long,trending NWW.It is a trust fault with left-lateral strike-slip component.The activity of the fault produced a series of scarps along the mountain front.The fault zone is divided into three segments,and the middle part is the most active.In this paper,palaeo-earthquake events on the fault are studied.With the study of trench profiles,two palaeo-earthquake events are determined.Event I occurred at 4.066±0.086kaBP,and event II is between 6.852±0.102kaBP and 6.107±0.082ka BP.The last palaeo-earthquake event on this fault occurred in 4.066±0.086kaBP.So,the northern Yumushan Fault is not the seismogenic fault of the M 71/2 Biaoshi earthquake of 180 AD.The elapse time from the latest event has been 4000yr,so the possibility of generating destructive earthquake in future should be recognized sufficiently.