PALAEO-EARTHQUAKE STUDY ON THE NORTHERN YUMUSHAN ACTIVE FAULT

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.