Abstract

The rise of fluid pressure along a fault plane can trigger an earthquake as shear strength decreases. Recent models have thus suggested that the rate of interseismic fluid-pressure increase may control earthquake recurrence. In electric-analog model simulations incorporating new experimental data on rock properties within the lower seismogenic zone, resultant fluid-pressure fluctuations are restricted to the fault plane, and are strongly attenuated during their slow propagation into the country rock. Fluid-pressure drops, triggered by coseismic fault dilation, require days to hundreds of years to propagate over distances ≥1 m into low-permeability country rock (≤10−17 m2). The equilibration of fluid pressure between the faulted and the intact country rock requires tens to hundreds of years. If the fault seals prior to this equilibration, the fluid pressure recovers instantaneously to near the prefailure value. These results may imply that if elevated fluid pressure weakens transcrustal fault zones, they are likely to remain weak after earthquakes.

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