Jiaoyan Yang

The collision and compression between the Indian and Eurasian plates have resulted in intense crustal shortening and deformation in the Tian Shan since the Cenozoic, leading to its renewed uplift and making the Tian Shan one of the most intensely deformed intracontinental orogenic belts and seismically active regions in the world. Cenozoic deformation of the Tian Shan is characterized by north–south crustal shortening, which is mainly controlled by approximately E-W striking thrust faults, N-W striking dextral strike-slip faults, and N-E striking sinistral strike-slip faults. Concurrently, pronounced tectonic deformation occurred within the Tien Shan, forming a series of E-W trending intermontane basins, including the Turpan, Kumishi, Yanqi, and Yili basins. The Yanqi Basin, located in the southeastern Tian Shan, has experienced significant tectonic deformation due to the continuous uplift of the Tien Shan. Since the Late Quaternary, tectonic deformation has been mainly concentrated along the northern and southern margins of the basin. Two major active tectonic systems are developed along the northern margin, including the Yanqi Basin north-edge thrust fault and the piedmont thrust-fold belt. Along the southern margin, the Yanqi Basin south-edge thrust fault is developed, striking E-W and dipping southward, forming a complex thrust-fold belt. Within this fold belt on the southern margin of the basin, Quaternary geomorphic surfaces are well preserved and display fault scarps of variable heights. Multiple generations of alluvial fans are dissected along the fault scarps. In this study, high-resolution topographic data of faulted alluvial fan landforms along the southern margin thrust-fold belt were acquired using airborne LiDAR. Detailed geomorphic interpretation and quantitative analysis were conducted to identify multiple generations of landforms developed perpendicular to the fault strike. Based on comprehensive geomorphic interpretation and field investigations, deposits from different generations of alluvial fans were sampled for surface age determination. Furthermore, based on measurements of exposed strata and the construction of characteristic topographic profiles across the alluvial fans, we established the cross-sectional geometry and deformation model of the thrust fault-fold belt at the south-edge of the Yanqi Basin. By integrating the tri-shear fault-propagation fold model from fault-related fold theory, we constrain the shortening deformation characteristics of the thrust fault-fold belt. This allows us to estimate the shortening amount and shortening rate for the belt at the southern margin of the Yanqi Basin. Combined with analysis of surrounding fold deformation and fault slip rates, this work not only reveals the deep geometry and activity mechanism of the thrust fault at the south-edge of the Yanqi Basin but also provides constraints for understanding intracontinental deformation within the Southern Tian Shan.

As direct geomorphic evidence and records of earthquakes on the surface, coseismic surface ruptures have long been a key focus in earthquake research. However, compared with strike-slip and normal faults, studies on reverse-fault surface ruptures remain relatively scarce. In this study, surface rupture characteristics of the most recent earthquake on the Kumysh thrust fault in eastern Tianshan were investigated using high-resolution topographic data, including 0.5 m- and 5 cm-resolution Digital Elevation Models (DEMs) generated from the WorldView-2 satellite stereo image pairs and Unmanned Aerial Vehicle (UAV) images, respectively. We carefully mapped the spatial geometry of the surface rupture and measured 120 vertical displacements along the rupture strike. Using the moving-window method and statistical analysis, both moving-mean and moving-maximum coseismic displacement curves were obtained for the entire rupture zone. Results show that the most recent rupture on the Kumysh Fault extends ~25 km with an overall NWW strike, exhibits complex spatial geometry, and can be subdivided into five secondary segments, which are discontinuously distributed in arcuate shapes across both piedmont alluvial fans and mountain fronts. Reverse fault scarps dominate the rupture pattern. The along-strike coseismic displacements generally form three asymmetric triangles, with an average displacement of 0.9–1.1 m and a maximum displacement of 2.8–3.2 m, yielding an estimated earthquake magnitude of M_w 6.6–6.7. This study not only highlights the strong potential of high-resolution remote sensing data for investigating surface earthquake ruptures, but also provides an additional example to the relatively underexplored reverse-fault surface ruptures.