The influence of initial damage on microcrack healing at hydrothermal conditions

Abstract:

Off-fault coseismic fracture damage at depth can be inferred from reductions of crustal seismic velocity following large earthquakes. A growing body of geophysical evidence exists for ‘healing’ processes occurring in the bulk following such earthquakes, inferred from time-dependent increases in seismic velocity lasting from days to years. Surprisingly, little is known about the controls on co-seismic microfracture damage healing rates. Here, we present experimental and microstructural observations on the rates of microfracture healing in terms of post-seismic recovery of seismic velocity, porosity and permeability, as a function of varying initial damage. Preliminary results indicate that highly damaged samples show up to three orders of magnitude reduction in permeability over several days at temperatures and pressures commensurate with just 4km depth, combined with significant decreases in porosity and increases in seismic velocity.