Earth Planets Space, Vol. 56 (No. 12), pp. 1121-1133, 2004
A. Ord1, B. E. Hobbs1, and K. Regenauer-Lieb1,2
1Predictive Mineral Discovery Cooperative Research Centre, CSIRO Exploration and Mining, PO Box 1130, Bentley, WA 6102, Australia
2Johannes Gutenberg-Universitat Mainz, Geophysics and Geodynamics, 55099 Mainz, Germany
(Received June 15, 2004; Revised December 31, 2004; Accepted December 31, 2004)
The classical application of rate and state dependent frictional constitutive laws has involved the instabilities developed between two sliding surfaces. In such a situation, the behaviour and evolution of asperities is the controlling mechanism of velocity weakening. However, most faults have a substantial thickness and it would appear that it is the bulk behaviour of the fault gouge, at whatever scale, that is important. The purpose of this paper is to explore how bulk frictional sliding behaviour may be described. We explore here the consequences of applying the rate and state framework initially developed to describe the frictional behaviour at the interface between two interacting sliding blocks, to frictional behaviour within a layer of gouge that has bulk elasticplastic constitutive behaviour. The approach taken here is to replace the relative sliding velocity in the classical formulation with the maximum shear strain rate, D, and the characteristic length with a characteristic shear strain, gc. This means that the frictional behaviour of the bulk material now evolves with shear strain rate, D, over a characteristic shear strain, gc. This approach still does not address the problem of reproducing natural recurrence times between instabilities, but perhaps places the problem in a new framework.
Key words: Seismicity, constitutive model, rate and state dependant friction, bulk frictional elastic-plastic behaviour.