青海乌兰盆地东缘断裂带的新活动特征

Study of the Recent Features of Eastern Margin Active Fault of Wulan Basin in Qinghai Province

在青海乌兰盆地东缘山前冲洪积扇上新发现了一条长约 2 2km的逆冲断裂带 ,该断裂带是NNW向的鄂拉山右旋走滑断裂带北段西侧的次级挤压构造。其新活动受主断裂带的制约和影响 ,地貌上表现为明显的正向断层陡坎。晚更新世以来其垂直滑动速率为 0 11～ 0 17mm/a ,全新世晚期的垂直滑动速率为 0 35mm/a。综合探槽剖面及断层陡坎年代可以确定四次古地震事件 ,其年代分别为距今 2 4 6 5 0± 85 0a、 14 2 0 0± 70 0a、 5 2 0 0±5 2 0a和 2 2 5 0± 380a ,古地震活动具有不均匀性。

In the alluvial and pluvial fan of the margin of Wulan basin in Qinghai Province,a thrust fault zone which runs 22km long has been found.This fault is the secondary compressional structure in north segment of the NNW oriented,right-lateral,strike-slip fault zone in Mt.Elashan.So its new activity is controlled and influenced by the main fault zone.It is characterized by obvious fault scarps in geomorphology.The vertical slip rate of eastern margin active fault zone of Wulan basin is about 0.11～0.17mm/a.On the basis of comprehensive research about the trench profiles and fault scarp ages calculated by diffusion equation,four palaeo-earthquake events can be decided and their ages are about 24650±850a.B.P,14200±700a.B.P,5200±520a.B.P and 2250±380a.B.P.So a conclusion is made that there exists an inhomogeneity in time and space for the activities of palaeo-earthquake.