Fluid pressure evolution during the earthquake cycle controlled by fluid flow and pressure solution crack sealing

Abstract

Recent studies of active Californian faults allow us to investigate the mechanisms of fluid flow and crack sealing along faults and to model fluid pressure evolution during earthquake cycles. The model is first based on the observation that fluids flow from depth along active faults (stables isotopes and traces elements analyses). The model is also based on the study of mechanisms of deformation of rocks near and within active faults at depth. Sampling was performed in faults that have been recently uplifted. Studies on thin sections of rocks produce evidence of the mechanisms of crack sealing and compaction of fractured zones as transient processes after each earthquake. We found that pressure solution creep and crack sealing are likely to control deformation and permeability change during inter-seismic period. Crack sealing and compaction processes are modeled to give the kinetics of these processes. Then numerical modeling of fluid pressure and transfer around active faults have been performed by integrating slow changes in permeability by crack sealing, gouge compaction and fluid flow from depth. This modeling shows that location and evolution of fluid overpressure varies during the inter-seismic period depending on the heterogeneity of the faults (nature of minerals and fluids, spacing between micro-fractures, thermodynamic and kinetics parameters).