Abstract: The Tianqiaogou Huangyangchuan Fault (called also Gulang Fault) lies to the east of Lenglongling,the highest peak on the eastern section of the Qilianshan Mountains. It is one of the important active faults in eastern Qilianshan. From west to east,the fault is about 86km long,initiating from Hongyaoxian,extending eastward along Tainqiaogou,Qianjin,Guanjiatai,and Huangyangchuan villages,and ending at Jiapigou. The western segment of the fault is NWW-trending,the middle is nearly E-W-trending and the eastern is NEE-trending. Among them,the middle segment is convex slightly to the south. The fault is basically continuous,except that a small step-over exists near Guanjiatai village,dividing the fault into two sub-segments:the Tianqiaogou sub-segment in the west and the Huangyangchuan sub-segment in the east. Field investigation revealed that offset landforms are well developed along the fault,such as offset gully,fault scarp,sag pond,offset terrace and alluvial fans. All the offset landforms indicate that the fault was dominated by left lateral strike-slip with a component of normal faulting. Tracing along the fault and trenching across 6 typical offset landforms revealed the evidence of Holocene activities and several palaeo earthquakes along the fault. By the use of progressive constraining method,7 Holocene palaeo-earthquakes and one historic earthquake are identified. The occurrence time of these events are determined to be 10,743±342a BP (Event Ⅰ),9038±39a BP (Event Ⅱ),6910±438a BP (Event Ⅲ),4847±185a BP (Event Ⅳ),3562±190a BP (Event Ⅴ),2476±194a BP (Event Ⅵ),1505±253a BP (Event Ⅶ) and 1927AD (Event Ⅷ,possibly the Gulang earthquake). The distribution and recurrence behavior of strong earthquakes along the fault show a distinct linearity and sub-periodical recurrence,for which the linear regression equation of event-time sequence is T_i=1516i-11734. Moreover,during field investigation we found new evidence indicating that surface rupture occurred along the Tianqiaogou-Huangyangchuan fault during the Gulang M_S8.0 in 1927.

Key words: active fault, palaeo-earthquake, activity, Gulang

摘要： 天桥沟-黄羊川断裂位于祁连山东段主峰冷龙岭以东,是祁连山东段的重要活动断裂之一。该断裂以关家台为界分为东西2段,全新世以来均有过明显的活动。沿断裂开挖了6个古地震探槽,通过综合对比得到了该断裂全新世以来的7次古地震事件和1次历史地震事件,其年代分别为事件Ⅰ(10743±343)aBP,事件Ⅱ(9038±39)aBP,事件Ⅲ(7050±577)aBP,事件Ⅳ(4847±185)aBP,事件Ⅴ(3562±190)aBP,事件Ⅵ(2476±194)aBP,事件Ⅶ(1505±253)aBP,事件Ⅷ为1927年古浪8级大地震。这表明该断裂可能也参与了1927年古浪8级地震的活动。各次古地震事件在时空分布上相对较均匀,大致具有准周期复发的特征。

关键词: 活动断裂, 古地震, 活动习性, 古浪