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Growth of Faults based on Shear Banding

Shear band based faults grow by forming a zone of deformation bands and later slip surfaces. Following the formation of single shear bands, zones of shear bands form to accommodate larger displacement. In contrast to sheared joints and sheared pressure solution seams, splays accompanying shear bands are not common. One possible reason is that deformation bands occur in high porosity rocks or loose sediments that do not have a rigid enough matrix to concentrate stress at the ends of the shear bands. The other possible reason is that shear bands have no sharp discrete tip regions to produce a splay. The width of blunt tips of a band dilutes the stress concentration.

As accumulated displacement across the zone grows larger, say greater than 30 to 50 cm, slip-surfaces may form at the edge of shear band zones, which may favor formation of splays in opening mode. These splays establish bridges and result in the extension of through-going slip surfaces which accommodate significant displacements.

As displacement increases, fault core and damage zone develop. The width of the damage zone increases approximately with displacement with irregularities along strike.

Reference:

Aydin, A., Johnson, A.M., 1978. Development of faults as zones of deformation bands and as slip surfaces in sandstone. Pure and Applied Geophysics 116: 931–942.

Shipton, Z.K., Cowie, P.A., 2003. A conceptual model for the origin of fault damage zone structures in high-porosity sandstone. Journal of Structural Geolgy 25: 333-345.



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