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Experimental and Numerical Modelling of Deformation and Fluid Flow |
Department of Geological Sciences, University of Durham, Durham DH1 3LE, UK
A numerical simulation of coupled fluid flow and failure in a fault zone is presented, that shows the impact of the dynamics of fault growth on the relationship between seismic and sub-seismic fault scaling. A tabular fault zone is modelled which undergoes non-uniform compaction, leading to development of pressure gradients in the fault zone. Increased pore fluid pressures result in a reduction of the fault-normal stresses, and hence frictional failure. The model suggests a possible physical mechanism for the development of non-power-law scaling of fault displacements, implying that observations of such behaviour are real, rather than the result of poor sampling. The fault displacement scaling law appears to result from the dynamics of the fault evolution, which depend upon the relative rates of compaction of fault material and fluid flow within the fault zone. When fault compaction is slow, event sizes show a power-law scaling relationship. When compaction is fast, pressure gradients are unable to dissipate and the distribution of these event sizes is non-power-law. It is suggested that the dynamics of fault evolution may be inferred from geological evidence, with the relics of repeated small events (e.g. aligned calcite fibres) implying a relatively high compaction rate, whereas cataclasites would suggest relatively low compaction rates.
