Experiments on the frictional properties of quartz gouge under hydrothermal conditions have revealed a new fault healing mechanism that operates only at elevated temperature in the presence of liquid-phase water. This distinguishes it from the well-known "Dieterich-type'' healing that also operates at room temperature and depends only on the chemical activity of water and not on its phase. The requirement for liquid water to be present is diagnostic of some form of solution transfer being the underlying process. Furthermore, the new healing mechanism operates when the aqueous pore fluid is in chemical equilibrium with silica, indicating solution transfer with only local mass redistribution, such as pressure solution. This new solution transfer healing mechanism has the same logarithmic form, Delta(mu)=b ln (t(h)/t(c)+1), as Dieterich-type healing. Its b value was 0.010-0.014, with no clear temperature dependence in the range 100-200degreesC, and its magnitude is not very different from that of Dieterich-type healing. It is distinguished by a cutoff time, t(c), many orders of magnitude greater than the Dieterich-type mechanism. This parameter decreases exponentially with temperature, indicating an apparent activation energy of 54 kJ/mol. This mechanism also has a critical slip distance similar to500 mum, much greater than the 10 mum typical of Dieterich-type healing. Comparison of the manifestations of this solution transfer healing in velocity step and slide-hold-slide tests indicates that this mechanism is compatible with the rate-state friction law, but its different parameter values may have new implications for earthquake physics.
837SSTimes Cited:7Cited References Count:75