Interseismic re-strengthening and stabilization of carbonate faults by "non-Dieterich" healing under hydrothermal conditions

Abstract

Friction experiments, consisting of a "velocity stepping" stage, a "slide-hold-slide" (SHS) stage and a second "velocity stepping" stage, have been performed to study the frictional healing behavior of carbonate fault gouge, and the effects of healing on the velocity dependence of friction, at 20-140°C and at 50 MPa effective normal stress. Dry experiments show classical Dieterich healing characterized by a transient peak in friction after each hold period, with no effects of SHS testing on steady-state friction or velocity dependence. By contrast, the wet tests show 1) an increase in apparent steady-state friction upon re-sliding after a hold period, and 2) a pronounced increase in the velocity dependence parameter, (a- b), after the SHS stage. While the first of these "non-Dieterich-type" healing effects has been observed in previous hydrothermal experiments on simulated quartz gouges, it has not been reported previously for carbonate gouges. The observed effect of SHS-testing on (a- b) has never been reported. Our findings suggest that, under in-situ hydrothermal conditions, interseismic fluid-assisted deformation processes, such as pressure solution, can significantly promote fault re-strengthening in carbonates and can cause slip stabilization. If the results are applicable to active faults in carbonate terrains, they have important implications for understanding how the extent of the seismogenic zone, and how earthquake magnitude and aftershock distributions, may evolve with repeated cycles of natural seismicity and interseismic healing.