Model constraints on infiltration of surface-derived fluid deep into the brittle crust: numerical results

Numerical simulations were performed to investigate the downward infiltration of surface derived water along faults with imposed transient variations in permeability arising from fracturing and healing over earthquakes cycles. Fluid is driven downward along a fault either due to gradients in hydraulic head arising from topography or due to dilation on the fault during earthquakes (seismic pumping).   Results show that both forcing scenarios are equally capable of driving surface-derived fluid to the base of faults at 10 km depth in several tens of thousands of years. Downward flow of cold fluid occurs almost exclusively during and shortly after earthquakes, while during the remaining portion of the seismic cycle fluids remain relatively stationary while they undergo thermal relaxation (i.e., heating). Rapid downward flow is favoured by a large coseismic permeability, long permeability healing time scale, and large coseismic dilatancy or high topographic relief above the fault at the surface. However, downward fluid flow may be completely inhibited if the fluid pressure exceeds the hydrostatic gradient, even by modest amounts, which suggests that deep fluid infiltration is unlikely to occur in every region.Results of the models are presented and discussed in a paper submitted to Geophysical Journal International by Guy Simpson in 2024.