An experimental study of the secondary deformation produced by oblique-slip normal faulting

Abstract

We have used scaled clay models to define the secondary deformation produced by oblique-slip normal faulting. In the models, the master fault beneath the clay layer dips 45 degrees and strikes at a 45 degrees angle relative to the heave direction (i.e., the horizontal component of the displacement direction). Thus, the master fault has both normal dip-slip and strike-slip components of displacement. The modeling results show the following. (1) The fault patterns produced by oblique-slip normal faulting vary significantly with depth. Secondary faults that strike obliquely to the master-fault trend are more abundant near the top of the clay layer, whereas secondary faults that are subparallel to the master-fault trend are more abundant at depth. (2) A single episode of oblique-slip normal faulting produces two populations of secondary faults that have different trends and ages. Secondary faults that strike obliquely to the master-fault trend are more abundant during the early stages of the experiments, whereas secondary faults that strike subparallel to the master-fault trend are more abundant during the later stages of the experiments. (3) Relay ramps between overlapping secondary synthetic normal faults are wide and temporally persistent in oblique-slip models. The ramps are cut by numerous small-scale normal faults that are subparallel to the ramp-bounding faults. Cross faults are uncommon and begin to develop only during the final stages of the experiments. (4) Both map and cross section data are necessary to distinguish among the deformation patterns produced by strike-slip, oblique-slip, and dip-slip faulting. The map views of oblique-slip models closely resemble those of strike-slip models; in both models, many of the secondary faults strike obliquely to the master-fault trend. These map views, however, differ considerably from those of dip-slip models, in which most of the secondary faults strike subparallel to the master-fault trend. Alternatively, the cross sectional views of oblique-slip models are similar to those of dip-slip models; in both models, a highly faulted extensional forced fold develops. These cross sectional views are dissimilar to those of strike-slip models, which show no appreciable folding and no change of regional level.