Activity Characteristics And Seismic Risk Assessment Of The Tuoli Fault In Late Quaternary

In the Cenozoic era,the collision and northward movement of the Indian-Eurasian continental plate caused deformation within the continent.The shortening of crustal deformation is not only manifested as crustal thickening,but also partially absorbed by the strike slip movement of faults.According to the GPS（Global Positioning System）velocity field,the crustal shortening rate absorbed by the area north of Tianshan is about 2mm/a.How these shortening rates are absorbed is a topic worth studying.Previous studies have shown that the Western Junggar region,located north of the Tianshan Mountains,is affected by the remote effects of the collision between the Indian-Eurasian plate and is an important area for absorbing crustal shortening.The region has developed a set of parallel and oblique strike slip fault systems,including the Tacheng East Fault,Tuoli Fault,and Daerbute Fault.The Tuoli Fault,as one of the important faults,has significant features of late Quaternary tectonic deformation for understanding the regional tectonic deformation and crustal shortening patterns in West Junggar.This article uses remote sensing image interpretation and field geological investigation to determine that the Tuoli Fault is a strike slip and thrust fault,which can be divided into two branches:east and west.The two branches converge at both ends,with the middle part extending in a northeast direction,nearly parallel,and resembling a"shuttle"shape.Typical geomorphic features such as fault scarps,fault troughs and pull apart basins are formed in the landform,and multiple geomorphic surfaces such as Kapusheke River terrace,Tiesibahan River terrace and alluvial fan in front of Shazi Lake are crossed by two faults,forming gullies and terraces of different magnitude.In this paper,Optically stimulated luminescence and ¹⁴C dating methods are used to determine the age of the landform,and unmanned aerial vehicle（UAV）photogrammetry technology is used to extract high-precision DEM（Digital Elevation Model）in the study area,and La Dicaoz＿v2.1 developed based on MATLAB is used.The software conducted dislocation recovery measurements and obtained four typical dislocations on the western branch fault:（3.6±0.2）m(T2c_min),（34.0±6.8）m（T2t）,（25.4±7.0）m(T2t_min),（37.5±4.1）m(T3k_min).Three typical dislocations were obtained on the eastern branch fault:（89±31）m（T3k）,（39±13）m（T2k）and（36±5）m(T2j_min).The activity rate of the Tuoli Fault since the Late Quaternary was calculated based on the obtained horizontal dislocations and geomorphological age,and the horizontal strike slip rate of the western branch fault was 1.8+0.5/-1.3mm/a,The horizontal strike slip rate of the east branch fault is 1.7±0.8mm/a.Through Monte Carlo simulation of1000 sliding history paths within the dislocation time error w Indianw,the average horizontal strike slip rates of both the west branch and east branch of the Tuoli Fault are 1.7mm/a,respectively,which effectively verifies the calculation results.Based on previous research on the Tacheng East Fault,it is believed that the parallel oblique sinistral strike slip fault system in the West Junggar region conforms to the characteristics of the bookshelf structure model and absorbs most of the compression shortfalls in the West Junggar region,playing a crucial role in controlling the shortening of the north-south crust in the region.At the same time,this article interprets the Tiesibahan ancient seismic exploration trough,combined with the analysis of the gully dislocation on the geomorphic surface,the Shazi Lake fault section,the Hujiertai fault section,and the Jamate fault section,and obtains three ancient earthquake events,with a time of 20.9-17.5ka,21ka,4.5-1.98ka,（1950±30）a,and（7.9±0.5）ka,respectively,According to analysis and calculation,the co seismic displacement of the west branch fault is 3.6～3.8m,with a surface rupture length of 47-70km and a recurrence period of（2.0+5.5/-0.6）ka.Calculate through two empirical formulas,indicating that the potential earthquake magnitude range is high possibility of a 7 magnitude earthquake.Therefore,the Tuoli Fault has a significant seismic risk in the future.