FAULT DAMAGE ZONES

Abstract

Damage zones showvery similar geometries across awide range of scales and fault types, including strike-slip, normal and thrust faults.We use a geometric classification of damage zones into tip-, wall-,and linking-damage zones, based on their location around faults. These classes can be subdivided in terms of fault and fracture patterns within the damage zone. A variety of damage zone structures can occur at mode II tips of strike-slip faults, including wing cracks, horsetail fractures, antithetic faults, and synthetic branch faults. Wall damage zones result from the propagation of mode II andmode III fault tips through a rock, or fromdamage associatedwith the increase in slip on a fault.Wall damage zone structures include extension fractures, antithetic faults, synthetic faults, and rotated blockswith associated triangular openings.The damage formed at themode III tips of strike-slip faults (e.g. observed in cliff sections) are classified as wall damage zones, because the damage zone structures are distributed along a fault trace inmap view.Mixed-mode tips are likely to showcharacteristics of bothmode II andmode III tips.Linking damage zones are developed at steps between two sub-parallel faults, and the structures developed depend on whether the step is extensional or contractional. Extension fractures and pull-aparts typically develop in extensional steps,whilst solution seams, antithetic faults and synthetic faults commonly develop in contractional steps. Rotated blocks, isolated lenses or strike-slip duplexes may occur in both extensional and contractional steps.