Abstract: Because of recent activity of the fault zone of northern piedment of Nanhua Mountain,21 gullies along the fault zone within 16 kilometers from Caiyuan to Luanduizi were obviously offsetted,showing well oriented sinistral displacements.This paper studies geological and geomorphological features,precoss and offsets of the gullies,and determines for the fault zone the average slip rate (4.3mm/yr,since Late Pleistocene),on the basis of ¹⁴C dating of deposits and data on the rate of head-ward erosion.Moreover,according to observations in the field,the maximum displacement for the seismic fault in the epicentral area of Haiyuan M 8.5 Earthquake of 1920 is about 6.9m.On the basis of above data,the recurrence time of 8.5 strong earthquake along the fault zone has been estimated as about 1600 years.

摘要： 由于南华山北麓断裂带的新活动,使得南华山北麓菜园—乱堆子16公里范围内的21条冲沟发生明显断错,显示出左旋位移指向。本文研究了这些断错冲沟的地质地貌表征、断错冲沟的发育过程和断错量,并根据晚更新世以来沉积物的¹⁴C年龄和区域冲沟的溯源侵蚀速率,计算出晚更新世以来南华山北麓断裂带的平均滑动速率为4.3毫米/年;同时,量测出1920年海原8.5级地震震中区地震断层的最位移量为6.9米。根据以上资料,估算出南华山北麓断裂带8.5级强震的重复率约为1600年。