东昆仑断裂带西大滩段晚第四纪古地震历史

对东昆仑断裂带西大滩段进行了断错地貌填图和古地震探槽揭露,共揭露出9次古地震事件,它们的年龄分别为39090±2348aB.P.,27780±2360aB.P.,24100±1451aB.P.,19850±1690aB.P.,12670±714aB.P.,8980±544aB.P.,6380±388aB.P.,4425±265aB.P.和3030±182aB.P.。古地震重复间隔分别为11310±2880a,3680±2211a,4250±1879a,7180±1392a,3690±897a,2600±668a,1955±470a,1395±321a和3030±182a。结果表明,西大滩段晚第四纪古地震活动具有准周期性,其中7次古地震事件发生时间与东昆仑断裂带库赛湖段古地震事件的发生时间非常接近,这意味着东昆仑断裂带库赛湖段和西大滩段既可以独立破裂形成中强地震,也可以同时发生破裂形成强震。东昆仑断裂带的古地震活动历史对于认识该断裂的破裂特征和强震复发规律具有重要的意义。

LATE QUATERNARY SEISMIC HISTORY ON THE XIDATAN SEGMENT OF EAST KUNLUN FAULT ZONE IN NORTHERN TIBET

The East Kunlun fault zone in Northern Tibetan Plateau is a typical active fault zone,characterized by sinistral strike-slip faults.The field investigation indicates that there are a lot of relics along the fault traces of the Xidatan segment,Kunlun fault.The relics include push-up,pull-apart basins,sag pond,and earthquake fault scarps.This implies that the Xidatan segment of Kunlun fault is a seismogenic fault on which surface-rupturing earthquakes often occurred in regular or irregular intervals.To determine the chronology of Late Quaternary surface ruptures of this part of Kunlun fault,three trenches were excavated across the Xidatan segment at Xizangdagou.All sediment samples collected from the trenches were dated by using thermoluminescence（TL）method.Paleoseismic evidence,combined with the thermoluminescence（TL）dating for sediment units from the trenches,show that the Xidatan segment of Kunlun fault has generated at least 9 paleoearthquakes since Late Quaternary,whose ages are 39090±2348aB.P.,27780±2360aB.P.,24100±1451aB.P.,19850±1690aB.P.,12670±714aB.P.,8980±544aB.P.,6380±388aB.P.,4425±265aB.P.,and 3030±182aB.P.,respectively.The recurrence interval between two adjacent events is 11310±2880a,3680±2211a,4250±1879a,7180±1392a,3690±897a,2600±668a,1955±470a,1395±321a,and 3030±182a,respectively.It shows that the rupture behavior and recurrence of great earthquakes along Xidatan segment is similar to those on the Kusai Lake segment of the fault.These results have significant implications for seismic hazard assessment in the East Kunlun fault zone.Although only 9 paleoearthquake events are able to be dated,together with the 9 paleoearthquake events on the Kusai Lake segment of the East Kunlun fault,they can provide more information on major paleoearthquakes occurring along the fault during the Late Quaternary.Combined with the paleoearthquake history on Kusai Lake segment,it is clear that the paleoearthquake rupture on Xidatan segment coexisted with most of those on Kusai Lake segment of the fault.