晚第四纪以来香山-天景山断裂左旋走滑量研究

THE STUDY OF THE LEFT-LATERAL DISPLACEMENT ON THE XIANGSHAN-TIANJINGSHAN FAULT IN LATE QUATERNARY

香山-天景山断裂是青藏高原东北缘弧形断裂带中一条重要的活动断裂,长期以来活动强烈,早期以挤压逆冲为主,可能在第四纪早期转变成以左旋走滑为主兼具逆冲性质的断裂。黄河在夜明山前缘穿过此断裂,在沙坡头大弯一带形成一个完美的"几"形拐弯。文中对沙坡头大弯一带黄河地貌、阶地特征、样品年龄进行了探查和分析测试,结果表明,距今170ka以来,香山-天景山断裂左旋位移量最大不超过880m,滑移速率<5.18mm/a。

Xiangshan-Tianjingshan Fault is one of the major active faults of the arc fault zone on the north- eastern margin of the Qinghai-Tibet Plateau. The Yellow River in the Shapotou area flows through the fault and forms a perfect ＂Ω-shape＂ bend. Shapotou not only is a tourist mecca,but also a hotspot for studying the geomorphology,neotectonics,the uplift of Qinghai-Tibet Plateau and other issues. Xiangs- han-Tianjingshan Fault is mainly a left-lateral strike-slip fault with a minor thrust component. So to study the fault＇s offsets is of vital importance. This paper, based on the characteristic of the distribu- tion of the Yellow River terraces in the Shapotou Big Bend area, analyzes the offsets of the Xiangshan- Tianjingshan Fault since the formation of the terraces. The results reveal that 3 river terraces are de- veloped on the right of the Yellow River in the Shapotou area,while there is no terrace developed on the left of the river. The maximum left-lateral displacement of Xiangshan-Tianjingshan Fault is less than 880m,and the slip rate is less than 5.18mm/a since 170ka BP.