###### Abstract  
This study conducted water-induced fault slip experiments on saw-cut granite, sandstone, and limestone samples. Experimental results demonstrated that injecting 15 MPa pressurized water into the vicinity of a high-permeability sandstone fault could decrease the effective normal stress and induce fault slip but not significantly affect the stress of granite and limestone faults due to low permeability. When the pressurized water was injected into the fault plane, 1 MPa pressurized water could not significantly affect fault stress; however, the 15 MPa pressurized water caused a significant reduction in frictional strength and induced fault sliding. The actual pore pressure differed from the injection pressure and showed significant differences in three faults, resulting in the apparent difference in stress drop, slip duration, displacement, and sliding rate. Three faults showed velocity-strengthening properties at room temperature. The fault slip caused by 15 MPa pressurized water injection was a direct response of fault strength to the reduction in effective normal stress. The limestone fault was characterized by velocity-weakening behavior at 100 \({}^{\circ}\)C, and the sliding rate of the fault induced by the 15 MPa pressurized water injection was faster than that at room temperature. The experiment results suggest that high-pressure injection can dominate over velocity-dependent effects, inducing fault-unstable slips in velocity-strengthening faults, but is more likely to induce medium-strong earthquakes on the velocity-weakening fault. pressurized water injection; rock permeability; fault contact state; actual pore pressure; rate-and-state friction law +
Footnote †: journal: Applied  
stressed. As a result, the distribution of induced earthquakes is ultimately determined by the spatial distribution of the pre-existing faults [20], while the maximum magnitude of possible earthquakes is primarily defined by the fault scale, density, and maturity [14; 16; 19]. Lithology and rock permeability play essential roles in induced earthquakes, controlling their spatial and temporal migration characteristics [8], and even the depth position where seismicity is most prevalent [21]. Rock mechanics experiments performed in previous studies have provided many insights into the mechanism of injection-induced earthquakes. In a pioneering study, [PERSON] and [PERSON] [22] investigated the impact of fluid injection rate on sandstone failure and stated that shear fracture was induced by slow injection of pore fluid, whereas rapid injection caused a tensile fracture. At constant stress, [PERSON] and [PERSON] [23] found that acoustic emission (AE) events migrated as a cluster along the sample, following the migration of the waterfront closely. [PERSON] et al. [24] performed a similar injection experiment on dry granite and reported positive feedback between acoustic emission (AE) activity and pore pressure diffusion. The injection studies conducted over the last two decades provided substantial evidence that pore fluid diffusion was crucial to AE activity, altering its temporal and spatial distribution [25; 26]. For example, [PERSON] et al. [26] performed a series of rock fracture tests under different drainage conditions, demonstrating that drainage conditions played a governing role in rock deformation and fracture. Good drainage conditions are conducive to the fast diffusion of pore pressure, leading to a significant decrease in rock strength and stabilization of the dynamic rupture processes, which may enlarge the nucleation dimension and duration, thereby increasing the predictability of the final catastrophic failure. [PERSON] et al. [25] carried out injection tests on partly saturated (the middle part was dry) and fully saturated sandstone samples and compared their fracturing behaviors using acoustic emission (AE) monitoring. The results suggested that the local hydraulic condition controlled the geometry of the shear fracture zone, AE productivity, and mechanical properties.