| dc.description.abstract | Damage zone adjacent to slip zones commonly consist of fractures and fissures and can be either conduit or barrier for fluid flow. During fault movement, the various fluid drainage efficiency of the damage zone may affect the state of water saturation of the slipping zone and can result in different mechanisms operated for fault weakening, yet its effect on the fault strength (behavior) is still poorly understood. In this study, we conducted rotary shear rock friction experiments on water-saturated kaolinite gouge under undrained and drained conditions by using a newly designed pressure vessel. Under drained condition, we used two kinds of filter paper to simulate different efficiency of fluid drainage of the damage zone. All experiments were conducted at a velocity of 1 m/s, a normal stress of 10 MPa with total displacement of ~ 5–7 m. The results show that (1) under undrained condition, the friction coefficient (the ratio of shear stress/normal stress) achieves a peak value, then dramatically decreases to a steady-state associated with sample dilatancy. Under drained condition, the initial stage of frictional trend is similar to the one under undrained condition, but gradually restrengthens with slip accompanied with gouge compaction; (2) the slip-weakening distance D_c is varied from 2.43±0.71 m to 2.09±0.51 m under undrained and high-efficient-drainage conditions, respectively, and 1.14±0.51 m under less-efficient-drainage condition. After experiments, the color of kaolinite was changed from milky-white to grey-dark color, and slicken-side textures were observed on the slipping surface only under drained condition. Microstructural observations showed the similarity between the products from compaction and under undrained condition as randomly oriented clay fabrics. Under drained condition, the network of R-shear and Y-shear, sintering texture, and grain size reduction were observed. In particular, the occurrences of flow texture and vesicle under high-efficient-drainage condition imply the presence of thermal decomposition. We surmise that (1) thermal pressurization is the main weakening mechanism at our experimental conditions, and (2) various drainage conditions would result in various frictional evolution (as a result of frictional heat on different amounts of water within slip surface) and the associated processes (kaolinite fluidization or thermal decomposition). | en_US |