Frictional Stability Transition during Olivine Serpentinization: Implications for Induced Seismicity in Natural Hydrogen Systems

Natural hydrogen produced via serpentinization is emerging as a critical carbon-free energy source, yet the potential for induced seismicity governed by the interplay of mineralogical transformations and thermal anomalies remains poorly understood. To constrain the seismic hazard of natural hydrogen systems, we investigated the frictional stability of simulated fault gouges composed of olivine, lizardite, and their mixtures using a triaxial shear apparatus under hydrothermal conditions relevant to deep reservoirs (125 MPa confining pressure and temperatures of 100–300 °C). Our results reveal a complex competition between mineralogical composition and thermal conditions in controlling fault stability; while the coefficient of friction systematically decreases with increasing serpentinization degree (from ~0.7 for olivine to ~0.4 for lizardite), the velocity dependence parameter (a-b) exhibits a critical transition towards instability at elevated temperatures. Specifically, pure olivine transitions from velocity-strengthening to velocity-weakening behavior as temperature increases, and unexpectedly, lizardite—typically considered a stable sliding mineral—exhibits a distinct window of velocity-weakening behavior at ~250 °C. Furthermore, in mixed gouges (e.g., 50% serpentinization), temperature dominates over mineralogy, shifting the fault from stable sliding at 150 °C to potentially unstable slip at 250 °C. These findings suggest that the exothermic nature of serpentinization could drive fault systems into a velocity-weakening regime before complete serpentinization stabilizes the fault, implying that natural hydrogen exploitation carries a specific, thermally driven seismic risk that necessitates rigorous monitoring.