QUANTITATIVE MODELING OF FAULT-FLUID-DISCHARGE AND FAULT-DILATION-INDUCED FLUID-PRESSURE VARIATIONS IN THE SEISMOGENIC ZONE

The rise of fluid pressure along a fault plane can trigger an earthqua ke as shear strength decreases, Recent models have thus suggested that the rate of interseismic fluid-pressure increase may control earthqua ke 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 pl ane, and are strongly attenuated during their slow propagation into th e country rock Fluid-pressure drops, triggered by coseismic fault dila tion, require days to hundreds of years to propagate over distances gr eater than or equal to 1 m into low-permeability country rock (less th an or equal to 10(-17) m(2)), The equilibration of fluid pressure betw een the faulted and the intact country rock requires tens to hundreds of years, If the fault seals prior to this equilibration, the fluid pr essure recovers instantaneously to near the prefailure value, These re sults may imply that if elevated fluid pressure weakens transcrustal f ault zones, they are likely to remain weak after earthquakes.