关键词: 山西高原, 六棱山北麓断裂, 地貌面, 滑动速率

Abstract: The northern piedmont fault of the Liuleng Mountain in the extentional region of the north-ern end of Shanxi graben system lies along the southern edge of Yangyuan basin and controls theorigin and development of the basin, It is a dip-slip normal fault, NEE-trending and N-dipping.Two moderate and large earthquake swarms (Ms=6.1, Ms=5.8) successively occurried alongthe fault in 1989 and 1991.The fault consists of a marginal faul of the basin (F₁)and a newly formed fault(F₂) cuttingthe late Pleistocene to Holocene alluvial deposits within the basin. The F₁ and F₂ faults form astepped fault zone along the northern piedmont and joint together into the western segment. Thefault activity is characterized by inheritant displacements. It cuts stream terraces of different agesand piedmont loess terraces, causing two basalt eruptions (K-Ar age of the basalt and TL age ofits underlying baked bed is 1.71±0.41Ma, 18.29±1.39～19.7±1.54×10⁴a B.P. respectively). Later activity along the fault offset the basalt to form a 30～50m high scarp. At the middlesegment of the fault, F₁ has been inactive since late Pleistocene,whereas newly formed fault F₂ at 2～3km north of the edge of the basin has offset alluvial fan surface and stream terraces of different ages since late Quaternary. The eastern segment of the fault cuts the third terrace at thejunction of Sanggan and Huliu rivers and formed a 50～60m high scarp.Several topographic profiles across the scarps on different segments and un-coeval geomorphic surface were mapped to obtain vertical offset by using auto-level. Ages of the different geomorphic surfaces were determined by TL and ¹⁴C. Average vertical slip rate is 0.43～0.75mm/aduring the late Pleistocene to the Holocene. The age of the youngest layer cut by the fault is 0.76～0.86×10⁴a B.P..

Key words: Shanxi plateau, Northern Liulengshan piedmont fault, Geomorphic surface, Slip rate