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<p>This study integrates dense short-period seismic array observations, ambient noise tomography, machine learning-based earthquake detection and double-difference tomography to investigate the shallow crustal structure and seismogenic fault system associated with the 1976 <i>M</i>6.2 Horinger earthquake in Inner Mongolia, China. Using 31-day continuous records from a dense array, we extracted Rayleigh wave dispersion curves in the 2–4 s period band from noise cross-correlations. A direct surface-wave inversion approach was applied to obtain a high-resolution 3-D S-wave velocity model for the upper 3 km. Concurrently, the PhaseNet deep learning model was employed for automatic P- and S-wave phase picking, and the GaMMA algorithm was used to establish a high-precision microseismic catalog. The double-difference relocation method was subsequently applied to refine hypocentral locations. Our results reveal pronounced lateral heterogeneity in shallow S-wave velocities, with major faults exhibiting distinct high-to-low velocity transition zones. The mainshock of this <i>M</i>6.2 event is situated near the intersection of the Jiucaizhuang–Haolaigou fault and a NW-trending subsidiary fault, within a strong velocity gradient at the edge of a high-velocity anomaly interpreted as a fault-plane asperity. Relocated microseismicity exhibits linear clustering along the NE-striking fault, delineating its SE-dipping geometry. When integrated with regional stress field analysis, we propose that under NW–SE extensional stress along the northern Ordos Block margin, the pre-existing Jiucaizhuang–Haolaigou fault underwent right-lateral strike-slip reactivation. Local stress concentration near the high-velocity asperity ultimately triggered the <i>M</i>6.2 event. This study elucidates the coupling between shallow velocity structure and deep seismogenic processes, providing detailed evidence for understanding the nucleation of moderate-to-strong intracontinental earthquakes.</p>

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Study on S-wave Velocity Structure and Seismogenic Structure in the Source Region of the 1976 M6.2 Horinger Earthquake

  • 期刊论文

  • 发表日期：

    2026年4月23日

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  • Dong-yang Pei,
  • Xiao-ming Han,
  • Juan Li,
  • Fan Zhang,
  • Li-feng Chen,
  • Shu-bo Wang,
  • Wei Guo,
  • Xin Wang,
  • Tie-suo Zhao,
  • Xing Zhao,
  • Jin-zhe Bao

摘要

This study integrates dense short-period seismic array observations, ambient noise tomography, machine learning-based earthquake detection and double-difference tomography to investigate the shallow crustal structure and seismogenic fault system associated with the 1976 M6.2 Horinger earthquake in Inner Mongolia, China. Using 31-day continuous records from a dense array, we extracted Rayleigh wave dispersion curves in the 2–4 s period band from noise cross-correlations. A direct surface-wave inversion approach was applied to obtain a high-resolution 3-D S-wave velocity model for the upper 3 km. Concurrently, the PhaseNet deep learning model was employed for automatic P- and S-wave phase picking, and the GaMMA algorithm was used to establish a high-precision microseismic catalog. The double-difference relocation method was subsequently applied to refine hypocentral locations. Our results reveal pronounced lateral heterogeneity in shallow S-wave velocities, with major faults exhibiting distinct high-to-low velocity transition zones. The mainshock of this M6.2 event is situated near the intersection of the Jiucaizhuang–Haolaigou fault and a NW-trending subsidiary fault, within a strong velocity gradient at the edge of a high-velocity anomaly interpreted as a fault-plane asperity. Relocated microseismicity exhibits linear clustering along the NE-striking fault, delineating its SE-dipping geometry. When integrated with regional stress field analysis, we propose that under NW–SE extensional stress along the northern Ordos Block margin, the pre-existing Jiucaizhuang–Haolaigou fault underwent right-lateral strike-slip reactivation. Local stress concentration near the high-velocity asperity ultimately triggered the M6.2 event. This study elucidates the coupling between shallow velocity structure and deep seismogenic processes, providing detailed evidence for understanding the nucleation of moderate-to-strong intracontinental earthquakes.