ABSTRACT:

We conducted laboratory experiments that demonstrate how an increase in fluid pressure can induce “stick-slip” events along a preexisting fault. Our sample is a 760 x 356 x 76 mm poly(methyl methacrylate) (PMMA) plate with a saw cut simulated fault deformed in a biaxial loading apparatus. Water was injected directly into the simulated fault through a 3 mm diameter hole drilled in the sample. During experiments, normal stress was held constant, while shear stress and water pressure varied to generate dynamic slip events. Fluid-induced slip events were found to have similar slip rates, total slip time, and total displacement as events resulting solely from an increase in externally applied shear stress. Slip measurements reveal that shear-triggered events initiated close to the application of shear stress. Fluid-induced events often initiated in the center of the fault, near where the fluid was injected. We employed fluid pressure measurements from secondary monitoring wells to study the fluid behavior along the fault. These early experiments resulted in slip events induced within seconds of fluid injection, but further monitoring of the fluid on the fault suggests that delayed seismicity may be possible due to the time required for fluid pressure to diffuse along the fault.

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