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Paleoseismic studies are critical for the assessment and prediction of large earthquakes (M ≥ 7). These studies involve excavating and analyzing evidence from surface–rupturing earthquakes. However, they often face limitations in spatiotemporal resolution. The Yuguang Graben, located in the northern Shanxi Grabens of North China, contains an abundance of Quaternary loess that can be utilized for extending paleoseismic records. Fine-grained deposits of loess contrast sharply with gravel deposits of the colluvial wedge, making the wedge shape apparent. To enhance our understanding of earthquake behavior in the Yuguang Graben, we excavated a trench on terrace T2 of the Songzhikou segment of the Yuguang Graben Fault (YGF). We used LiDAR to obtain a high–resolution orthophoto of the trench wall. Through OSL dating of colluvial wedges and loess, we identified at least four large paleoseismic events with a magnitude of M ≥ 7 that occurred along the YGF. These events took place at >77.6 ± 5.1, 63.9 ± 5.1, 51.0 ± 4.3, and 37.3 ± 0.3 kyr, respectively. Combined with previous paleoseismic studies, we identified seven paleoseismic events since the late Pleistocene. These findings reveal that earthquakes occurring on YGF follow a quasiperiodic pattern with an average recurrence interval of about 12 ± 3 kyr. The elapsed time of the most recent earthquake near the recurrence interval suggests an increased risk of a large earthquake along the YGF. We also analyzed earthquake clusters generated by neighboring faults in the active northeastern boundary of the Ordos block. Our analysis indicated that fault interactions can affect the recurrence interval of earthquakes along single faults, while regional seismic activity tends to concentrate in time during a seismically active period. These observations underscore the importance of expanding paleoseismic records and exploring regional seismic hazards to gain a more comprehensive understanding of earthquakes. • Colluvial wedges on normal fault reveal new paleoseismic events. • Establishment of the paleoseismic sequence of the Yuguang Graben Fault for 77,000 years. • Improve the understanding of fault behavior located at the boundary of the Ordos block. [ABSTRACT FROM AUTHOR]

The West Helanshan fault is situated at the junction of the northeastern Tibetan Plateau, Alxa, and Ordos blocks, providing an opportunity to investigate the deformation in the transitional zone between the contractional northeastern Tibetan Plateau and extensional North China. Using field investigations and satellite imagery interpretations, we determined detailed geometry and kinematics of the West Helanshan fault. The West Helanshan fault is divided into three segments, including the northern, middle, and southern segments, based on varying fault strike, slip sense, and geomorphic expression. The northern and middle segments are dominated by right-lateral strike-slip motion as indicated by linear fault traces, horizontally offset streams and terrace risers, relatively insignificant vertical offset, and frequently changing facing direction of fault scarps. The late Quaternary right-slip rate is estimated to be 0.2–0.4 mm/yr, which is relatively low comparing with other strike-slip faults in the northeastern Tibetan Plateau, based on 10Be-dated offset fluvial/alluvial surfaces. The southern segment shows conspicuous fault scarps with significant systematic vertical offset, which has a reverse component as revealed in the trench. The timing of the most recent earthquake revealed in the trench is constrained to be between 6.2 ± 0.7 ka and 5.9 ± 0.4 ka. Notably, the West Helanshan fault cuts through the city center of Azuoqi town, which is the capital of Azuoqi county and has about 100,000 residents, carrying high potential earthquake hazard in the future. Finally, combining the regional fault geometry and kinematics with GPS observations, we propose a limited north-northeastward extrusion model for the southern Alxa Block. • The West Helanshan fault is dominated by right-lateral strike-slip motion. • The most recent earthquake occurred between 6.2 ± 0.7 ka and 5.9 ± 0.4 ka. • A limited north-northeastward extrusion model is proposed to explain the geometry and kinematics of faults in the southern Alxa Block. [ABSTRACT FROM AUTHOR]