Regional fluvial geomorphic index and terrace downcutting process in the southern section of lishi fault in Shanxi Province and their tectonic significance

Based on Digital Elevation Model (DEM), field river terrace survey and Optical Stimulated Luminescence dating (OSL) dating, the slope, topographic relief (RDLS), area elevation (HI) and channel steepness index (Ksn) of the southern section of the Lishi fault zone are extracted and analyzed. Monte Carlo simulation of the cutting rate of Zhongtuo River, a tributary of the Yellow River that passes through the fault is carried out. The results show that, according to the river geomorphic index, the river geomorphic index is low, the river geomorphic development is in the developing or mature stage overall, and the structural activity of the southern part of Lishi fault is weak. According to the faulting relationship between the river terrace and the fault in Zhongtuo River, combined with the terrace dating results, the fault zone is inactive at least since the late Pleistocene. Using the height and age data of terrace tug-of-war at all levels, the ages of T1-T4 of Zhongtuo River are 2.08±0.19 ka, 5.63±0.5 ka, 10.22±0.62 ka and 41.22± 2.33 a, respectively. The linear fitting result of the flow cutting rate of Zhongtuo River since 42ka is 0.78 mm/a. The downtangent rate of the Holocene is 1.89 mm/a, which is mainly influenced by climate change.