Abstract:Liupanshan is located at the border of the Ningxia Hui autonomous region, Gansu and Shanxi provinces.It belongs to the northern section of the north-south seismic structural zone, and according to its geological structures, it is located in the transitional region between the Ordos block of the western North China Plate and the Qilianshan orogenic belt of the northeastern Qinghai-Tibetan block.Its structures and landform development have their own specificity and sensitivity.Under the premise of the rapid uplift of the Tibetan Plateau and northeastern extension in the late Cenozoic, the Liupanshan area experienced strong deformational tectonic processes.These processes have controlled the development of regional landforms and evolution of rivers.The Liupanshan Fault zone includes the eastern and western Liupanshan piedmont faults, and based on the interpretation of aerial and satellite photos and data from field surveys, we undertook a detailed investigation of its activities.The total length of the eastern Liupanshan piedmont fault is ~90 km.The fault extends southward from Xiaokou to Majiaxinzhuang with an overall NW trend.The fault topography is very clearly defined along the fault.Analyses of its geomorphological features and of a typical fault section suggest that the eastern Liupanshan piedmont fault has characteristics of left-lateral thrust and that it moved in the late Holocene.According to the measurement of the offset terrace at Houmohe, the displacement of the T2 is about (25±3) m.The age of the T2 is about (9372±86) a based on 14C dating and therefore, we estimated the slip rate to be about (3.2±0.5) mm/a.This result was consistent with a previous study.The total length of the western Liupanshan piedmont fault is ~60 km.The fault extends southward from the Sanlidian Reservoir to the Taoshan Reservoir, then its trend changes from N-S to NNW-SSE.The fault topography is very clearly defined along the fault.Analyses of its geomorphological features and of a typical fault section suggest that the western Liupanshan piedmont fault is a high-angle reverse fault that moved in the early late-Pleistocene, but that has not dislocated since the middle late-Pleistocene.In this paper, we also discuss the geomorphologic response to the tectonic activity.Based on SRTM data, we established the Jinghe and Shuiluohe drainage basins and river systems that lie either side of Liupanshan, and we also obtained the hypsometric interval (HI) values of the drainage basins.In general, the HI values of bigger drainage basins reflect the influence of different regional neotectonic activity, while those of smaller basins reflect the influence of lithology and local tectonic activity.According to the map of HI values, there is a clear difference either side of Liupanshan;the two sides have similar lithologies, but the HI values to the east of Liupanshan are lower than those to the west.The reason for this might be connected to the different levels of activity between the eastern and western Liupanshan piedmont faults.Through the above research and geomorphological analysis, we provide basic data and interpretations to better understand the geomorphological evolution of the Liupanshan area.
