Interaction between normal faults and fractures and fault scarp morphology

Fault slip and geomorphic surface processes create and modify bedrock norma l fault scarps. Our field studies and numerical models show that mechanical interaction between near-surface fractures and active faults may diminish scarp slopes and broaden deformation near the surface. In our models, incre asing fracture density and depth reduces and complicates the scarp's topogr aphic expression. Fracture depth and density, and orientation of the struct ures control the location and magnitude of zones of positive and negative s hear displacements along the fractures. Our field studies of the interactio n of active graben bounding normal faults and fractures in Northern Arizona illustrate the mechanical analysis. Reduction in scarp slopes and broadeni ng of the deformation field may cause incorrect interpretations of shallow bedrock scarp morphologies as old, rather than as the result of slip along fractures around the fault.