Abstract - The thicknesses of fault rock and fault zones and the fault normal separations for breached and intact relay zones each show a positive correlation with fault displacement. The correlation for fault rocks is widely interpreted as a growth trend principally controlled by fault rock rheology, with new fault rock generated by wall rock wear or strain hardening of slip surfaces. Analysis of a large compilation of faults with a variety of fault and rock types, supports an alternative model in which faults localise as segmented arrays of irregular fault surfaces, with individual locations along a fault evolving across the thickness-displacement trend due to the progressive destruction of relay zones and fault surface irregularities. The final fault rock thicknesses are therefore strongly influenced by the original fault structure. Our model predicts and is supported by a progressive increase in the ratio of displacement to thickness, or shear strain, from a median value of 0.28 for intact relay zones to a median of 50 for fault rocks. The large scale range on which both fault segmentation and the irregularity of fault surfaces occurs, with the latter resulting from both propagation and from segment linkage, provides the basis for application of this model over a scale range of at least 8 orders of magnitude.
Abstract of talk given to:
Irish Geological Research Meeting, Coleraine, March 2007.