Stanford Geothermal WorkshopFebruary 9-11, 2026

Reservoirs in Enhanced Geothermal Systems (EGS) are often embedded within faulted rock masses where stimulation can trigger slip reactivation and rupture propagation across geometrically complex fault networks. Understanding how fault geometry governs rupture dynamics, slip stability, and seismic behavior is essential for predicting induced seismicity and ensuring safe reservoir operation. While prior research has largely focused on failure prediction in isolated faults, this study explores complex fault networks to capture the broader mechanical and seismic evolution. To this end, the mechanical and microstructural evolution of fault activation is investigated under three representative geometries, single fault, two subparallel faults, and two faults connected by an oblique cross-fault. Cylindrical faulted rock cores are subjected to triaxial shear testing to reproduce stress conditions characteristic of deep EGS environments. Mechanical response is characterized through complete stress–strain curves, while acoustic emission (AE) monitoring captures high-resolution signatures of slip nucleation and evolution. The temporal evolution of the b-value provides quantitative insight into progressive instability and the transition toward dynamic rupture. Post-failure analyses using optical and scanning electron microscopy document both on-fault and off-fault damage. Three-dimensional surface scanning quantifies roughness evolution, linking asperity degradation to macroscopic weakening. By integrating mechanical, acoustic, and microstructural observations across distinct fault configurations, this research elucidates how geometric complexity controls rupture dynamics and slip stability in EGS fault systems. The findings establish a physics-based framework for improving fault stability assessment and seismic risk mitigation in engineered geothermal reservoirs.

Topic: Enhanced Geothermal Systems