Fault-zone fluids control effective normal stress and fault strength. While most earthquake models assume a fixed pore fluid pressure distribution, geologists have documented fault valving behavior, that is, cyclic changes in pressure and unsteady fluid migration along faults. Here we quantify fault valving through 2-D antiplane shear simulations of earthquake sequences on a strike-slip fault with rate-and-state friction, upward Darcy flow along a permeable fault zone, and permeability evolution. Fluid overpressure develops during the interseismic period, when healing/sealing reduces fault permeability, and is released after earthquakes enhance permeability. Coupling between fluid flow, permeability and pressure evolution, and slip produces fluid-driven aseismic slip near the base of the seismogenic zone and earthquake swarms within the seismogenic zone, as ascending fluids pressurize and weaken the fault. This model might explain observations of late interseismic fault unlocking, slow slip and creep transients, swarm seismicity, and rapid pressure/stress transmission in induced seismicity sequences.

Fluid injection has been associated with the triggering of seismic events in geologically stable regions that previously had minimal detected seismicity (McGarr et al., 2015). Injection is done in the context of wastewater disposal and hydraulic fracturing in oil and gas operations, carbon sequestration, and geothermal energy production (

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Inversions of InSAR ground deformation in the Delaware Basin have revealed an aseismic slip on semi‐optimally oriented normal faults located close to disposal wells. The slip, occurring over 3–5 years, extends approximately 1 km down‐dip, over 10 km along strike, and reaches 25 cm. We develop and calibrate 2D and pseudo‐3D coupled pore pressure diffusion and rate‐state models with velocity‐strengthening friction tailored to this unique height‐bounded fault geometry. Pressure diffusion is limited to a high‐permeability fault damage zone, and the net influx of fluid is adjusted to match the observed slip. A 1–2 MPa pressure increase initiates slip, with ∼5 MPa additional pressure increase required to produce ∼20 cm slip. Most slip occurs at approximately constant friction. Fault zone permeability must exceed ∼10−13 m2 to match the along‐strike extent of slip. Models of the type developed here can be used to operationally manage injection‐induced aseismic slip.