EVALUATING THE SHEAR-STRESS RESPONSE OF INCLINED FAULTS TO NORMAL STRESS OSCILLATIONS - A RATE- STATE FRICTION MODEL

Recent observations from major fault systems, including the Main Himalayan Thrust (MHT) and New Madrid Seismic Zone (NMSZ), demonstrate strong correlations between seasonal hydrological loading and seismicity patterns. However, existing fault resonance theory, developed by Perfettini et al. (2001) for horizontal faults, inadequately addresses the mechanics of inclined fault systems that characterize many critical seismic zones.This study extends the theoretical framework of fault resonance to inclined faults using rate-state friction theory. Linear perturbation analysis was applied to an inclined spring-block slider system subjected to oscillatory normal stress variations, examining the complex harmonic response of shear stress and slip rate perturbations. Our numerical simulations demonstrate that when oscillation periods match the resonant time period, both shear traction and slip rate perturbations can be amplified by orders of magnitude—up to 10,000 times for shear stress and 1,000 times for slip rate. This framework explains the variable phase lags observed in field data and provides a physics-based approach for earthquake timing prediction based on hydrological loading cycles, representing a significant advance in seismic hazard assessment for inclined fault systems.