Competing Controls of Effective Stress Variation and Chloritization on Friction and Stability of Faults in Granite: Implications for Seismicity Triggered by Fluid Injection

Fluids injection for hydraulic stimulation and fracturing, typical in the development of enhanced geothermal systems (EGS) granites, can reactivate deep faults induce seismicity. Such typically contain chlorite coatings as an alteration product that may impact styles deformation—aseismic through seismic. We performed low velocity shear experiments on simulated granite fault gouges under conditions typifying a reservoir at ?4-km depth with confining pressure 110 MPa, temperature 150°C, fluid pressures 21–80 contents 0–100%, to investigate influence variation effective stress mineral composition strength stability. Our results show transition from velocity-strengthening velocity-weakening behavior gouge when was reduced 89 30 characterized by compaction dilation—as revealed microstructural observations—with implications enabling unstable failure. Conversely, increasing content stabilizes slip but reduces frictional strength. The microstructures these mixed exhibit localized chlorite-enriched planes promoting sliding. These suggest earthquake ruptures occurring during be facilitated variations both controlling overpressures (effective stresses) being aware presence minerals are important controls mitigating such injection-induced seismic risks.