Post-Injection Seismic Decay Dynamics at Geothermal Sites: Insights from Wellhead Pressure and Hydraulic Energy

Induced seismicity following fluid injection in geothermal reservoirs presents significant challenges for risk mitigation and hazard assessment. While numerous studies have focused on seismicity during active injection phases, less attention has been given to the critical post-injection period when seismic activity gradually subsides. In this study, we systematically analyze post-injection seismic decay at three prominent geothermal sites—Soultz-sous-Forêts (France), Cooper Basin (Australia), and Basel (Switzerland)—leveraging high-resolution industrial datasets. We thank the EPOS TCS-AH platform and CDGP for providing the data used in this study. This work was supported by the European Union’s Horizon 2020 research and innovation program (DT-Geo, grant agreement No. 101058129).

Using the Modified Omori Model, we characterize seismic event density decay rates and evaluate their dependence on operational and hydraulic parameters, such as wellhead pressure dynamics, injection duration, hydraulic energy, and reservoir diffusivity. Our results highlight the pivotal influence of sustained wellhead pressure and its dissipation rate (γ) on seismic decay, where faster pressure dissipation promotes fault stabilization and leads to reduced seismic activity. Secondary influences include cumulative injection volume and hydraulic energy, which moderate fault reactivation processes. The corner time parameter (c), marking the onset of seismic decay, shows limited correlation with operational metrics, suggesting the importance of site-specific geological properties.

By comparing the Modified Omori Model with alternative decay models (e.g., Cut-off Power Law, Gamma, and Stretched Exponential), we demonstrate its robustness in capturing the temporal evolution of seismicity across diverse geological settings. These findings highlight the critical role of wellhead pressure management in reducing trailing seismic risks and offer actionable insights for optimizing geothermal operations. This work contributes to a deeper understanding of post-injection seismicity, advancing risk management strategies for sustainable geothermal energy development.