Active Faulting in the Southern Bole Basin Within the Northern Tian Shan and Implications for Strong Earthquake Hazards and Tectonic Deformation, NW China.

In compressional active orogenic belts, crustal deformation is accommodated by strike‐slip faults and thrust faults. Studying the fault interactions of different types of active faults is important for understanding mountain building and seismogenic characteristics. This study uses field mapping, high‐resolution digital elevation models, and in situ cosmogenic nuclides to present data from active thrusts and thrust‐related folds on the southern margin of the Bole Basin, northern Tian Shan. These abandonment ages derived from in situ cosmogenic nuclides indicate that climate plays a significant role in controlling the alluvial surface incision. The crustal shortening rates of the eastern Jinghenan, central Jinghenan, and Yongji Faults are 0.21 ± 0.04, 0.37 ± 0.07, and 0.91 ± 0.08 mm/yr, respectively. Based on the fresh fault scarps, three paleo‐earthquakes are identified. The oldest paleo‐earthquake (16.6 ± 2.8 kyr) had a Mw of 6.5 ± 0.3. The penultimate event (3.0 ± 0.8–4.4 ± 0.8 kyr) had a Mw of 6.6 ± 0.3 or 6.8 ± 0.3, while the most recent one (1.1 ± 0.3 kyr) had a Mw of 7.0 ± 0.3 or 6.5 ± 0.3. Fault geometries and seismic activity indicate these thrusts and right‐lateral strike‐slip faults on both sides of Keguqin Range converge depth and form a positive half‐flower structure. Crustal thickening outpaces denudation, showing that the Bole Basin is in an unsteady state. Keguqin Range is experiencing lateral growth, and as a result, the intermountain basins are expected to gradually diminish. Plain Language Summary: In Northwest China, several active thrusts offset and fold late Pleistocene sediments on the southern margin of the Bole Basin, northern Tian Shan. Using unmanned aerial vehicles, we determine the fault and anticline scarp morphologies. Using late Quaternary dating methods, we can obtain the abandonment ages of different levels of alluvial surfaces. Combining the scarp morphology with the abandonment ages, the total crustal shortening rate of these thrusts in the southern Bole Basin is ∼1.5 mm/year. The morphology and morphological dating of the fresh scarp reveal three paleoseismological events in this region. The corresponding ages are 16.6 ± 2.8, 3.0 ± 0.8–4.4 ± 0.8, and 1.1 ± 0.3 kyr. Our results indicate that in active compressional orogenic belts, the lateral growth of mountain ranges and the subsidence of basins are jointly controlled by strike‐slip faults and thrust faults. Key Points: The crustal shortening rate in the southern Bole Basin is ∼1.5 mm/yrThree paleoearthquakes have been revealed by fault scarpsPositive half‐flower structures control mountain growth and basin consumption [ABSTRACT FROM AUTHOR]