Geometry and late Quaternary slip rate of the Tuolai Shan-Hala Hu segment of the Haiyuan fault, northeastern Tibetan Plateau

The location and long-term slip rate of active faults are key to elucidating regional deformation distribution and seismicity. The Haiyuan fault zone is an important left-lateral strike-slip fault zone on the northeastern margin of the Tibetan Plateau. However, the fault geometry and long-term slip rate of its western segment, especially in the Tuolai Shan–Hala Hu region, remain poorly constrained. To address this issue, this study utilizes high-resolution remote sensing images and regional geological maps, combined with unmanned aerial vehicle (UAV) surveys, to identify multiple left-lateral offset landforms and obtain a large number of left-lateral offset features and fault displacements. Based on these data, the fault location and geometric distribution of the Tuolai Shan–Hala Hu segment were preliminarily determined. Field investigations involved collecting radiocarbon ( 14 C) and optically stimulated luminescence (OSL) samples from an offset alluvial fan (F1), which yielded a displacement of 28.5 ± 0.5 m and abandonment ages between 10.92 ± 0.45 ka and 9221 ± 100 a. By correlating these data, we quantified the late Quaternary left-lateral slip rate of the Tuolai Shan segment to be 2.8 ± 0.3 mm/yr, which is slightly smaller than the latest geodetic research result of 3.7 ± 0.2 mm/yr. Our findings also show a westward decrease in the slip rate along the Haiyuan fault zone, a pattern that mirrors the slip rate decrease along the eastern segment of the Altyn Tagh fault. This suggests that the Qilian Shan orogenic belt may absorb the horizontal strike-slip deformation of the Haiyuan fault zone, implying a consistent structural deformation mechanism with Altyn Tagh fault.