Active tectonics around the northern terminus of the Shanxi Graben System, North China: Implications for regional tectonic deformation and seismic hazard assessment

The northeastern corner of the Ordos Block in North China represents a critical tectonic transition zone where the right-lateral transtensional Shanxi Graben System (SGS) intersects with the left-lateral strike-slip Zhangjiakou-Bohai fault zone (ZBFZ), yet kinematic interactions between these major structures remain poorly constrained. Through integrated analysis of high-resolution satellite imagery, uncrewed aerial vehicle (UAV)-derived topography, and field investigations, we characterize the late Quaternary activity of four ENE-striking faults at the northern termination of the SGS, including the Huai’an Basin fault (HBF), Huashan Basin fault (HSBF), Yanggao-Tianzhen fault (YTF), and South Xionger Shan fault (SXSF). Systematic geomorphic offsets reveal consistent left-lateral strike-slip components along these faults that were originally interpreted as normal faults. Chronological constraints from optically stimulated luminescence and 14C dating yield left-lateral slip rates of 0.47 +0.10/−0.07 mm/yr (HBF), 0.16 +0.03/− 0.04 mm/yr (YTF), and 0.86 +0.17/−0.12 mm/yr (SXSF). The most recent surface-rupturing faulting events (MRSEs) are constrained to post−3.5 ka for the HBF, post−4520 calibrated yr B.P. (cal BP) to post−4296 cal BP for the HSBF, and between 19.38 ka and 5.88 ka for the SXSF. We interpret these faults as synthetic horsetail fault splays that accommodate strain transfer at the northwestern tip of the ZBFZ. Furthermore, we propose that the coeval right-lateral shear along the SGS and left-lateral shear along the ZBFZ jointly control active deformation in this region. Middle-lower crustal flow beneath this region likely also contributes to the deformation of the upper crust in this region. According to elapsed time since the MRSEs, we suggest elevated earthquake potential in the Yangyuan and Yuguang basins in the south compared to the Huai’an, Huashan, and Yanggao-Tianzhen basins in the north. Our findings provide critical insights into deformation mechanisms at the SGS-ZBFZ intersection and contribute to improved regional seismic hazard assessment in this complex transfer zone.