Pre‐Existing Structures and Stress Variations Jointly Control the Induced Seismicity in Enhanced Geothermal System of Gonghe Basin, China

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Abstract
Identifying the primary triggering factors that govern injection‐induced seismicity is essential for reliable seismic‐hazard assessment. Here, we present observations from 20 surface stations deployed at China's first enhanced geothermal system (EGS) project in the Gonghe Basin during hydraulic stimulation and circulation tests in 2021. Using a machine‐learning workflow, we compiled a high‐precision catalog of 7,346 events ( M L −2.0–2.18) that reveals a donut‐like seismicity distribution comprising four major clusters with variable faulting styles. Principal‐stress modeling indicates profoundly weak faults with a low friction coefficient ( μ ∼ 0.23 with 95% confidence interval of 0.19–0.48), consistent with chlorite‐rich gouges, and a subcritical stress state in which low‐to‐moderate fluid overpressure (∼0.8–34 MPa) is required to initiate seismic slip. We find that the seismicity distribution is controlled by scale‐dependent factors: at the site‐scale (i.e., within ∼1 km of the wellheads), events localize on mapped natural faults, indicating shear reactivation of subcritically stressed, pre‐existing structures rather than the creation of new tensile fractures; at the borehole‐scale (i.e., within ∼1–100 m of the borehole trajectories), the main seismogenic zone coincides with pronounced SHmax rotation, reflecting lithologic contrasts and localized fault‐damage zones. Overall, our integrated analysis underscores the necessity of explicitly incorporating the low‐friction mineral phases, and scale‐dependent controls, that is, heterogeneities of stress and structures, into seismic hazard assessments for EGS projects.
Funding Information
  • National Natural Science Foundation of China (42374068)
  • National Natural Science Foundation of China (42477213)

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