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, relief degree of land surface (RDLS), hypsometric integral (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 Zhongduo 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 section of Lishi fault is weak. According to the faulting relationship between the river terrace and the fault in Zhongduo 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 Zhongduo River are (2.08 ± 0.19) ka, (5.63 ± 0.5) ka, (10.22 ± 0.62) ka and (41.22 ± 2.33) ka, respectively. The linear fitting result of the river cutting rate of Zhongduo River since 42 ka is 0.78 mm/a. The river cutting rate since Holocene is 1.89 mm/a, which is mainly influenced by climate change.