The propagation of deformation bands into compressive and extensional stepover geometries is investigated by integrating field observations with numerical model simulations of the effective stress state due to shear along the bands. Deformation bands are tabular discontinuities, with mm- to cm-scale thicknesses, of localized volumetric strain and shear. Deformation bands are precursors to frictional slip (i.e., faulting) in porous granular rocks and soils. Systematic rotations in near-tip principal stress orientation due to shear along the overlapping deformation bands are shown to predict band propagation paths that are consistent with characteristic stepover geometries as viewed in the mode II direction, the orientation in which the observation plane is parallel with the displacement direction. Therefore, propagation paths for deformation bands can be predicted from knowledge of the effective near-tip stress state. These results establish a mechanics-based framework for investigations of fault growth and fault-controlled fluid flow in porous granular rocks and soils.

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