武威盆地南缘断裂晚第四纪活动地表形迹与活动速率

摘要

武威盆地南缘断裂位于河西走廊东端, 是祁连山北缘逆断裂系的重要组成部分, 是1927年古浪8级地震的发震断裂之一.基于遥感影像解译、 野外地质观测和{14C}年代学数据等方法对武威盆地南缘断裂进行了详细的几何学调查和运动学定量.依据平面上几何展布的不连续性和走向的变化, 该断裂可以分为5段: 康宁桥段(F1)、 南营河段(F2)、 上古城村-张流沟段(F3)、 他家庄段(F4)和严家庄段(F5).该断裂为晚更新世以来活动断裂, 地表活动形迹长约60km, 以逆冲为主, 局部兼具左旋走滑分量, 沿断层走向断错地貌发育.断裂全新世以来的垂直滑动速率(0.44±0.08)mm/a, 南营河段(F2)晚更新世以来左旋走滑速率(1.43±0.08)mm/a.%The fault along the southern margin of the Wuwei Basin, located in the eastern Hexi Corridor, NW China, plays an important role in the thrust fault system in the northern Qilian Mountains.The activities of this fault resulted in the generation of the Gulang earthquake(MS8.0) in 1927.Based on remote sensing image interpretation, geological and geomorphic observations in the field and {14C} geochronological dating results, we conducted a detailed research on the geometry and kinematics of the fault.According to the discontinuous geometric distribution and variable strike directions, we divide this fault into 5 segments: Kangningqiao Fault(F1), Nanyinghe Fault(F2), Shangguchengcun-Zhangliugou Fault(F3), Tajiazhuang Fault(F4)and Yanjiazhuang Fault(F5).Results indicate that this fault, with a total of 60km long trace at the surface, has been active since the late Pleistocene.It behaves predominantly as a thrust fault and is accompanied with a locally sinistral strike-slip component along the Nanyinghe Fault(F2).Intensive activities of this fault in Holocene have caused extensive occurrence of dislocated landforms along its strike.Some measured displacements of the dislocated geologic or geomorphic units, combined with the{14C} dating results, yield a vertical slip rate of (0.44±0.08)mm/a on this fault in Holocene, and a sinistral strike-slip rate of (1.43±0.08)mm/a on the Nanyinhhe Fault (F2) in late Pleistocene.