Sparse earthquake segments and b‑values identify potential seismogenic asperities along western Ordos margin faults

This study led by Yingcai Xu (Earthquake Agency of Ningxia Hui Autonomous Region, China) focuses on identifying potential asperities for major active faults on the western Ordos margin. The study integrates multiple seismological approaches including earthquake relocation, b‑value calculation, sparse earthquake segment identification, and magnitude‑rupture length relationships. The work primarily explores spatial correlations among sparse earthquake segments, low b‑value anomalies, crustal velocity structures, historical earthquakes of M≥6, and modern ML≥5.0 events for the period 2009~2025.

Relocated earthquakes are mainly distributed along the strike of active faults, with focal depths mostly between 0~30 km. Sparse earthquake segments are widely distributed within tectonic units of major fault zones. Regions where sparse earthquake segments overlap with low b‑value areas (b < 0.7) indicate highly‑stressed locked fault sections with low Vp/Vs ratios, which are interpreted as potential seismogenic asperities.

All modern ML≥5.0 earthquakes occur within low b‑value zones, consistent with present‑day tectonic stress. Some historical M≥6 earthquakes lie outside low b‑value regions,and this discrepancy may stem from the mismatch between the 2009~2025 catalogue used for b‑value computation and the occurrence times of historical M≥6 earthquakes.

As revealed by the magnitude‑rupture length relationship, theoretical magnitudes derived from the spatial scales of sparse earthquake segments are basically consistent with the magnitude ranges of historical strong earthquakes on each fault zone.

Local high b‑value zones (b > 1.1) show normal or relatively low Vp/Vs ratios, mostly representing friction‑controlled fault creep and swarm‑type seismicity with relatively low short‑term strong earthquake risk.

The work presents several strong earthquake hazard areas, including parts of the Yinchuan Basin, the Tianjingshan‑Yantongshan fault zone, and the Haiyuan‑Liupanshan fault zone.

Combined analysis of sparse earthquake segments, b-value anomalies, and multiple seismological approaches helps recognize strong earthquake hazard segments. This research improves the identification and seismogenic‑capacity evaluation of potential asperities on the western Ordos block and offers important scientific support for regional seismic hazard assessment.

See the article:

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

https://doi.org/10.26464/epp2026071