Abstract: A fault scarp striking NW290° is identified through aerial photo examine and field survey. Differential GPS measure and DEM analysis show that the height of this scarp ranges from 3 to 13 m. This height difference is mainly related to different ages of geomorphology surfaces: the higher scarps can be found in the older alluvial fans and lower scarps in the younger ones. In addition, the fan-shaped fluvial deposition in the hanging wall also influences the scarp height on the alluvial fan of the same period, and the depositional effect goes weaker when farther away from the streams, hence higher the scarp is. Trench investigation suggests that at least two paleoseismic events occurred along this fault scarp in the southwest of Yuxiang County since the end of Late Pleistocene. The first event happened between 16720±70 and 7700±40 aBP, and close to 16720±70 aBP; the second event is between 7700±40 and 7020±40 aBP, with an over 2.2 m vertical displacement, suggesting that this is a Holocene fault scarp. The vertical rate of the fault activity is about 0.9 mm/a through comparative studies.

Key words: the northern Zhongtiaoshan fault, alluvial fan, fault scarps, Paleoearthquake, Holocene

摘要： 通过室内航片解译和野外调查, 发现中条山北麓中段虞乡镇西南山前洪积扇上发育走向NW290°的陡坎。野外差分GPS测量和DEM数据分析得到其最大高度为13 m, 最小高度只有3 m, 高度的差别主要与陡坎所在的地貌面的发育先后有关, 早期冲积扇上发育的陡坎高度较大, 晚期冲积扇上发育的陡坎高度较小。另外, 断层下降盘冲沟扇状堆积也影响同一期洪积扇面上陡坎的高度, 离开冲沟越远, 堆积作用越弱, 陡坎就高一些。探槽研究揭示, 虞乡镇西南洪积扇上断层陡坎晚更新世晚期以来至少发生过两次古地震事件, 断层第一次活动时间在16720±70 aBP以后, 7700±40 aBP之前, 接近16720±70 aBP; 断层第二次活动的时间在7700±40~7020±40 aBP之间, 垂直断距大于2.2 m, 说明该陡坎为全新世断层陡坎。对比研究估计, 该断层垂直活动速率约为0.9 mm/a。

关键词: 中条山北麓断裂, 洪积扇, 断层陡坎, 古地震, 全新世