The quantification of the geometry and kinematics of the boundary faults of an active orogenic belt is key to exploring its deformation pattern. The Kashihe fault (KSHF), which bounds the northern margin of the Ili Basin and is more than 400 km long, is a WNW-striking fault in the northern Tian Shan. Although the KSHF displays active faulting and is the seismogenic fault of the 1812 Ms 8 Nilka earthquake, the quantitative slip rate and its role in regional strain accommodation have not been reported. Here, we quantify the late Quaternary activity of the KSHF based on high-resolution remote sensing image interpretations and detailed field investigations. Six field observation sites along a~270 km active fault in the Chinese Tian Shan indicate that the KSHF is characterized by dextral strike-slip faulting and N-S thrusting. Based on the surveying of offset geomorphic surfaces with an unmanned drone and the dating of late Quaternary sediments using optically stimulated luminescence (OSL) and radiocarbon methods, we estimated a late Quaternary right-lateral strike-slip rate across the fault of 2.39 ± 0.55 mm/yr and a shortening rate of 0.62 ± 0.30 mm/yr. Analysis of field investigations and fault section exposing indicated that a young paleoearthquake event occurred on the western segment of the KSHF. Active tectonics around the Ili Basin imply that the rigid Ili block extrudes westward along its boundary strike-slip faults and rotates counterclockwise. We propose that this block rotation driven by dextral faulting accommodates regional N-S convergence and sinistral shearing.

Summary The Kepingtag (Kalpin) fold-and-thrust belt of the southern Chinese Tian Shan is characterized by active shortening and intense seismic activity. Geological cross-sections and seismic reflection profiles suggest thin-skinned, northward-dipping thrust sheets detached in an Upper Cambrian décollement. The January 19 2020 Mw 6.0 Jiashi earthquake provides an opportunity to investigate how coseismic deformation is accommodated in this structural setting. Coseismic surface deformation resolved with Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) is centered on the back limb of the frontal Kepingtag anticline. Elastic dislocation modelling suggests that the causative fault is located at ∼7 km depth and dips ∼7○ northward, consistent with the inferred position of the décollement. Our calibrated relocation of the mainshock hypocenter is consistent with eastward, unilateral rupture of this fault. The narrow slip pattern (length ∼37 km but width only ∼9 km) implies that there is a strong structural or lithological control on the rupture extent, with up-dip slip propagation possibly halted by an abrupt change in dip angle where the Kepingtag thrust is inferred to branch off the décollement. A depth discrepancy between mainshock slip constrained by InSAR and teleseismic waveform modelling (∼7 km) and well-relocated aftershocks (∼10–20 km) may suggest that faults within sediments above the décollement exhibit velocity-strengthening friction.

Faulting and folding on the margins of intermontane basins play important roles in accommodating the Cenozoic deformation of the Tian Shan, an intracontinental orogen in central Asia. In the eastern Tian Shan, the southern margin of the elongated Kumysh Basin is bounded by a NE dipping thrust fault, the Kumysh Fault. We report the first investigation of the slip rate of this fault, which is constrained at two sites by profiling the faulted topography and dating the abandoned alluvial fan surfaces. We obtained the topographic data using the satellite stereo imagery and dated geomorphic units using cosmogenic nuclide (10Be) exposure ages and optically stimulated luminescence methods. The results from Monte Carlo simulations of the data suggest an average dip‐slip rate of ~0.35 mm/yr on the Kumysh Fault since 50–60 ka. The “best fit” models indicate an increase after ~5 ka, which may be apparent or caused by the most recent earthquakes. Structural analysis of the displaced strata on a trench wall suggest at least 2.8 m dip offset caused by the late Holocene earthquakes, which is similar to the heights of fault scarps (1.8–2.9 m) on the second youngest alluvial fans (5.6–5.2 ka). Using the dip angle of ~25–40°, we estimate ~0.31 mm/yr shortening rate across the Kumysh Fault during the late Quaternary. By comparing our results with other estimates published in the easternmost Tian Shan, we suggest that deformation within intermontane basins may accommodate up to 50% of the total late Quaternary shortening rate between the Junggar and Tarim blocks, with only the remaining half accommodated by the main, range‐bounding thrusts.

Investigation on the kinematics and deformation rates about active fault interior of the Tian Shan can provide significant information for strengthening our understanding on the present tectonic evolution of this range. The Baoertu Fault (BETF) is a major E-W striking active structure within the eastern Tian Shan and separates the south and central Tian Shan. But its kinematics and slip rates in the late Quaternary have never been systematically reported before. Based on interpretations of remote sensing images, drone photography, and detailed field investigations, we propose that the BETF is characterized by left-lateral strike-slip faulting with a thrust component and provides the first late Pleistocene slip rate for this fault. At the northern margin of the Kumishi Basin, combining offset reconstructions of displaced alluvial fan surfaces with the terrestrial cosmogenic nuclide (TCN) exposure age dating, we calculate an average sinistral slip rate of 0.65±0.16 mm/yr and average vertical slip rate of 0.07±0.01 mm/yr for the BETF since 95-106 ka. The differential movement eastward between the central Tian Shan block and Yanqi-Kumishi Basin block is likely the dominant driver of the left-lateral slip of the BETF. Synthesizing other quantitative data in eastern Tian Shan, we suggest that the hinterland active faults or folds, including the BEFT, roughly accommodate ~28-45% of the total N-S convergence across the eastern Tian Shan.