Tectonic geomorphological evidence of Late Quaternary segmental activity of North Lajishan Fault

Lajishan-Jishishan is an important arc-shaped tectonic belt that extends to NE in the northeastern margin of the Tibetan Plateau, which is controlled by two extrusion thrust fault zones, the North Lajishan Fault and the South Lajishan Fault. Since the Late Cenozoic, the Lajishan area has strong tectonic activity, forming a significant basin-mountain coupling tectonic landform pattern, which is an ideal area to study the development and evolution of geomorphology and tectonic activities by using tectonic geomorphological methods. In this paper, using DEM data with a resolution of 30m, based on ArcGIS and MatLab platforms, plug-in tools and open-source code packages, the river steepness index (Ksn) values of 105 small and micro channels located above the fault at the outfall of the northern margin of Lajishan, and the HI values of 54 small and micro channels located in the bedrock area at the head of the river along the fault were extracted, and the area-elevation integral value (HI) interpolation value of the Lajishan-Jishishan area was calculated. According to the distribution of Ksn values, the uplift rate of the northern margin of the Lajishan showed an overall upward trend from west to east, but there was a local low value in the NE turning part of the fault on the northern margin of the Lajishan, which was speculated to be related to the weakening of the influence of the eastward thrust of the Dextel strike-slip fault in the Riyueshan from west to east, which also revealed the complexity, difference and segmentation of tectonic activities in this area. According to the results of Ksn value statistics, the Jishishan section has the fastest uplift rate and the strongest activity, which is likely to be an important reason for the occurrence of the 6.2 magnitude earthquake in Jishishan in 2023. Combined with the results of the geological survey of the route and the comprehensive interpretation of the oil exploration profile, the HI value shows that the Late Quaternary tectonic activity in the fault zone on the northern margin of the Lajishan has extended to the NE in addition to its own continuous activity, showing the characteristics of reverse fault and folding, resulting in more than ten moderate and strong earthquakes in the basin, and the migration characteristics and seismic activity of this tectonic activity are worthy of attention.
　　Kaywords: Lajishan;Jishishan;Channel Steepness Index;Hypsometric Integral;Tectonic-geomorphology