Abstract
Ubiquitous wet cracks in fault damage zones alter the mechanical behavior of fault rocks. Quantifying the effects of crack damage and water on stress evolution is fundamental for earthquake rupture model establishment. We conducted increasing-amplitude cyclic loading experiments on dry and wet sandstones to investigate the effects of crack damage, confining pressure and water on the stress rotation and fault weakening. The energy dissipated in each loading-unloading cycle was quantified for inference of the evolution of crack damage within the fault zone. A multi-layer elastic model was used to investigate the effects of crack damage and water on stress rotation in the fault damage zone. The results show that the observed decrease of elastic modulus in both dry and wet rocks greatly increased the maximum principal stress in the fault core as deformation progressed, but reduced the differential stress and the angle between the maximum principal stress and the orientation of the fault damage zone. However, water within fault rocks results in a lower reduction in differential stress within the fault damage zone when compared to the dry condition. The observed decrease of differential stress implies that the stress state evolves away from failure, and we infer water affects the proximity to fault instability both by affecting the stress rotation and by reducing in local strength, where these two effects are in competition. These results and inferences indicate that the stress rotation amplitude of fault damage zone increased with the crack damage, demonstrating that the stress rotation is greater near the damage zone-core interface than that near the fault damage zone/host rock boundary. We also found that the changes in the elastic modulus of the deformed rocks remains almost the same under different confining pressures, indicating that stress rotation of fault damage zone is not affected by confining pressure.
NSTL
Elsevier