| Pore fluid pressurization is a potential fault-weakening mechanism. We develop a non-linear finite element method to model the pressurization of water due to frictional heating during earthquake slip. We test the importance of various processes involved, such as conduction and advection of heat. We use our model to investigate whether pore fluid pressurization would be an important factor during earthquakes, in the range of physical parameters that have been found or predicted on faults. We find that permeability, slip zone width, and slip rate are the most important factors that control pore fluid pressurization. The porosity only has a strong effect for intermediate permeability. When the permeability is sufficiently low, fluid pressures on the fault can approach the normal stress, though they can never exceed it due to feedback between pore pressure and frictional strength. However, if slip occurs at a boundary between rocks masses of different permeabilities, for example between fault gouge and a damage zone, a pore pressure peak develops off the fault, in the lower permeability material. The pressure increase off the fault can reach or exceed the normal stress given a large enough permeability contrast, because there is no direct feedback between the off-fault pressure and the frictional heating at the fault surface. We also model slip occurring within a low permeability gouge layer surrounded by a more permeable damage zone. If the slip is centered in the gouge zone, fluid flow is symmetric, and no off-fault pressure peak develops. For slip that is offset from the center, an off-fault pressure peak forms once the fluid diffusion reaches the boundary of the damage zone, and the pressure peak migrates toward the center of the gouge layer. |
