Faulting or shear fracturing refers to the deformation mechanisms that produce faults which have shear displacement predominantly parallel to the break or the material discontinuity. Faulting has been studied extensively during the past century. Several models, such as those of Anderson, Riedel, Dislocation, and Fracture Mechanics have been used and these are described under various categories in this Knowledgebase.

Here, it is appropriate to start this discussion with the premise that all rocks and regions are heterogeneous. In fine scale, these are due to crystal structures, grains, and pores and their various combinations. Recalling Griffith flaws and contacts between adjacent grains or crystals and how they amplify local stresses around them, it is natural that faulting in fine scale may be controlled by these microstructures. Therefore, faulting in rocks develops by shearing of pre-existing depositional and mechanical weaknesses such as crystal dislocation, grain boundaries, pores, microcracks, bedding planes, joints, and pressure solution seams. We will further discuss these topics under 'Faulting Based on Shearing of Initial Weaknesses.' Just briefly, shear bands are faults, which are localized shear strain into narrow bands with displacement predominantly across the bands. However, compactive and dilatation components of displacement components also occur across shear bands. Any plane of weakness subjected to shearing may result in faults in the form of sliding across the plane. Shale smearing is a faulting mechanism in which shale or other ductile materials get incorporated into a fault zone and are attenuated in an extensional fault relay. It owes its existence to alternating brittle and ductile layers or lamination. It is also possible that chemical transformation from one mineral form to another may result in faults similar in form to the shear bands. These are described in a bit more detail under the links listed below.

Shale smearing is listed separately below because its occurrence does not depend on the type of the pre-existing weakness, but the presence of alternating brittle and ductile layers.