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<p>Ancient basement faults within plate interiors may be reactivated by external forces, generating intraplate seismicity. However, the driving mechanisms remain unclear. The 2017 Changdao earthquake swarm in the Bohai Bay Basin, eastern China, provides an opportunity to investigate such processes. A high-resolution earthquake catalog, constructed using matched filter detection and waveform-based relocation, reveals that the swarm occurred at 7-13 km depth along an X-shaped fault network, with migration following sqrt(t) diffusion (D = 0.08 – 1.2 m² s<sup>-1</sup>). High b-values and external forcing rate, and substantial isotropic components (13-38%) in the moment tensors indicate fluid involvement. Combined with low <i>V</i><sub>P</sub>/<i>V</i><sub>S</sub> ratios and proximity to CO<sub>2</sub>-rich hydrocarbon fields, we propose a fault-valve model where highly compressible fluids episodically breach fault intersections, triggering transient crack opening and swarm migration. This study reveals how deep fluids reactivate ancient basement faults in intraplate regions, and provides new insights for seismic hazard assessment in hydrocarbon-bearing basins.</p>

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Reactivation of basement faults by deep fluids during the 2017 Changdao earthquake swarm, Eastern China

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年1月28日

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  • Peng Wang,
  • Baoshan Wang,
  • Zhigang Peng,
  • Xinglin Lei

摘要

Ancient basement faults within plate interiors may be reactivated by external forces, generating intraplate seismicity. However, the driving mechanisms remain unclear. The 2017 Changdao earthquake swarm in the Bohai Bay Basin, eastern China, provides an opportunity to investigate such processes. A high-resolution earthquake catalog, constructed using matched filter detection and waveform-based relocation, reveals that the swarm occurred at 7-13 km depth along an X-shaped fault network, with migration following sqrt(t) diffusion (D = 0.08 – 1.2 m² s-1). High b-values and external forcing rate, and substantial isotropic components (13-38%) in the moment tensors indicate fluid involvement. Combined with low VP/VS ratios and proximity to CO2-rich hydrocarbon fields, we propose a fault-valve model where highly compressible fluids episodically breach fault intersections, triggering transient crack opening and swarm migration. This study reveals how deep fluids reactivate ancient basement faults in intraplate regions, and provides new insights for seismic hazard assessment in hydrocarbon-bearing basins.