Variations in topology and strain within strike-slip fault networks

Individual faults and fault populations are well understood, but their arrangement (topology) and the resulting distribution of deformation within networks is less clear. Two strike-slip fault networks from onshore and offshore, north Devon, UK, have been investigated with the objective of determining variations in geometry, kinematics, network topology and strain both spatially and at different scales. Both networks consist of NE-trending left-lateral faults and NW-trending right-lateral faults that cut steeply dipping (~60°) and folded strata. The fault networks were accurately mapped in the field with the use of aerial photography (onshore) and high resolution multibeam data (offshore). Displacements were measured from the lateral off-set of marker beds at various points along fault traces and used to determine displacement on fault segments. Spatially the strike-slip fault networks show much heterogeneity with varying fault patterns and strains. The relative proportion and dominance of each fault set can change with domino areas, with a dominance of one fault set, being separated by areas of conjugate faulting, in which both sets of faults are equally developed. Domino faults accommodate large strains, with up to 20° of rotation, and separate relatively weakly deformed blocks. The fault networks can be displayed at different scales, by clipping the fault segments at displacements ranging from 0.5-50 m. The distribution of different network attributes (trace-length, fault density, connectivity, fault set percentages, strain etc.) were then measured at each displacement. The results show that the majority of strain (>77%) is localized onto large-displacement fault segments with >10 m displacement. Small (<10 m) displacement fault segments infill fault blocks, bounded by large displacement (10-150 m) faults, and make up most of the trace-length. Furthermore, the fault networks appear less connected at lower resolutions as the connectivity of the fault network is very dependant on the presence of small fault segments and localization of deformation in damage zones. The fault networks also become better connected with increasing strain.