Spacing and linkage of confined normal faults: Importance of mechanical thickness

Abstract

In this paper we present the results of the analysis of fault spacing from a population of faults confined to a 4.5 m thick mechanical layer. We demonstrate the control of a discrete layer on the specific geometry of a so‐called “domino‐style” or “bookshelf” fault population. The fault population shows a logarithmic‐normal frequency distribution of fault spacing, with a minimum value of spacing S* (∼0.25 layer thickness), revealing a nearly regular spacing distribution between the “long faults” (i.e., length greater than height), which are confined within the layer. We also observe an upper limit of fault linkage at relay ramp close to the minimum value of spacing S*, after which free overlapping between faults having the same dip direction is allowed. On the basis of field observations, we simulate the quasi‐static displacement‐related Coulomb shear stress perturbation of faults of various aspect ratios (length/height). The models show that on faults that increase in aspect ratio with a constant height (as expected for the confined faults), the horizontal extent of the local stress reduction tends to localize at a constant distance from the fault surface close to S*. For the studied case, the correspondence between the models and the field data suggests that the limited extent of the stress reduction around the confined faults controls fault spacing and fault ability to link at relay ramps. Both field data collection from different scales and modeling suggest that fault spacing in confined fault populations is linearly related to the mechanical layer thickness. We therefore highlight the importance of the thickness of layers confining faults in the evaluation of interaction, linkage and propagation of active fault segments over a broad range of scales.