Geometries of extensional fault systems developed in model experiments

Abstract

The geometries of extensional fault systems have been studied by use of experimental sand analogues and are compared with examples in the literature. Extensional faulting above a uniformly extending basement produces a domino-style fault array involving both planar rotational faults and listric faults. The faults evolve with time and may change from listric geometries (concave upward) through planar fault segments to convex-upward geometries. At high extensional strains early faults are cut by later high-angle planar extensional faults. Hanging-wall deformation above a simple listric extensional detachment is characterized by faults that nucleate and propagate into the hanging wall and produce crestal collapse grabens. Listric extensional faults with a ramp/flat geometry also produce hanging-wall crestal collapse grabens and local reverse faults. The experiments show that hanging-wall blocks in listric extensional fault systems must undergo significant internal strains in order to accommodate progressive deformation over nonplanar fault surfaces.