Strong earthquake hazards in sparse earthquake segments of fault zones on the western Ordos margin: Insights from relocation and b-value analysis

To evaluate strong earthquake hazards of major active fault zones on the western margin of the Ordos Block, in this study we integrate multiple methods, including earthquake relocation, b-value analysis, identification of sparse earthquake segments of fault zones, and magnitude–rupture length scaling relations. With the aim of delineating the seismogenic potential of key tectonic belts and identifying potential asperities, we focus on the spatial correlation between sparse earthquake segments, low b-value anomalies, the crustal velocity structure, historical earthquakes (M ≥6), and modern earthquakes (M_L ≥5.0, 2009–2025).The results show that seismicity in the study area is spatially clustered along the strike of active faults, with focal depths mainly ranging from 0 to 30 km. Sparse earthquake segments are widely distributed in all major tectonic units, and their spatial overlap with low b-value zones (b < 0.7) reliably indicates high stress accumulation as well as locked fault segments and potential seismogenic asperities characterized by low V_p/V_s ratios. All modern M_L ≥5.0 earthquakes occurred within low b-value zones, consistent with the contemporary stress background, and some historical M ≥6 earthquakes were outside low b-value domains, which may be attributed to the mismatch between their occurrence times and the 2009–2025 earthquake catalog used for b-value calculation. Empirical magnitude–length scaling relations confirm that the geometric extent of sparse earthquake segments is consistent with the magnitude range of historical strong earthquakes in each tectonic belt. Localized high b-value zones (b > 1.1) with normal or low V_p/V_s ratios reveal friction-governed fault creep and correspond to seismic swarms, presenting a low short-term strong earthquake risk. Several core areas with elevated strong earthquake hazards are recognized, including parts of the Yinchuan Basin, the Tianjingshan–Yantongshan Fault, and the Haiyuan–Liupanshan Fault Zone. In conclusion, the integrated analysis of sparse earthquake segments and b-value anomalies provides a robust framework for identifying high-stress, seismogenically capable fault segments. This study improves the identification of potential asperities and their seismogenic potential in the western margin of the Ordos Block and provides critical scientific support for regional seismic hazard assessment.