The Jinghenan Fault, located in the eastern segment of the Kusongmuqike Piedmont Fault, is an important thrust fault in the northern foothills of the Western Tianshan. Studying the active characteristics of thrust faults since the Late Quaternary is helpful for understanding the distribution of regional tectonic stress in a compressional environment and evaluating their seismic hazards risk. A detailed investigation including high-resolution satellite remote sensing image interpretation, trench excavation, optically stimulated luminescence dating were used to obtain the spatial geometry, fault kinematics, and activity chronology of the Jinghenan Fault. Based on fault scarps measurement using DGPS and OSL dating, We have gained the understanding of Jinghenan Fault as follows: (1) Fault scarps can generally be divided into two categories: NNE-trending positive scarps and SSW-trending reverse scarps. The maximum vertical displacement of the former reaches 17.1±0.2m, with a minimum vertical displacement of 4.6±1.1m and an average vertical displacement range of 9.4±0.3m. The maximum vertical displacement of the latter is 8.7±0.9m, with a minimum vertical displacement of 3.3±0.1m and an average displacement of 5.6±0.4m. (2) The trench excavation has revealed at least two thrust faults and identified two paleoearthquake events. Among them, the most recent earthquake event occurred between (51.1±3.3) ka and (29.0±1.7) ka, indicating that the fault has been active at least until the Late Pleistocene. In the trench, we observed a vertical displacement of up to 2.2 m along the Jinghenan Fault, but this value is significantly lower than the height of the topographic scarp formed on the surface. This difference is mainly due to the erosion of the landform surface on the footwall of the fault after the formation of the scarp, which has increased the relative height of the scarp beyond the actual vertical displacement of the fault. Through precise measurements of the fault's dip angle, we calculated that the total shortening of the Jinghenan Fault has reached 5.8 m. (3) We further analyzed the activity of the Jinghenan Fault since the Late Quaternary and found that its vertical activity rate is approximately 0.04 ~ 0.08 mm/a. At the same time, the horizontal shortening rate of the fault has also been measured at 0.1 ~ 0.2 mm/a. Although multiple earthquakes have occurred near the Jinghenan Fault, releasing some energy, the research results indicate that this fault still poses a potential high seismic risk to the nearby densely populated areas.
DownLoad: