Experimental modeling of extensional fault systems by use of plaster

Plane-strain extension experiments with plaster as the deforming medium produce faults and related structures that closely resemble natural examples. The faults with the largest displacement are normally developed at about 25% overall extension (beta = 1.25). Major faults develop as composite structures, and although the main movement map be accommodated by a relatively simple slip surface, the fault zones commonly develop internal, lense-shaped geometries. Small, synthetic faults dipping more steeply than the main zone are typical components of the fault zones, particularly on the hanging wall side. Fault displacements develop over 2 orders of magnitude, and the distribution of fault displacements closely follows a power-law relationship, similar to data from seismic and field mapping. The main, through-cutting faults accommodate about 60-70% of the total deformation, while smaller, visible faults typically account for co 10-20%. Only 20-30% extension is due to faults and ductile deformation that occur below the resolution of the models, which roughly corresponds to seismic resolution a hen scaled up to natural size. The internal fault-block formation may include zones of normal faults accommodating significant internal shear deformation associated with collapse of fault blocks. Collapse has been recorded in the upper part of footwalls, resulting in a flattening of the upper part of the main faults. Although internal block deformation by simple shear or other deformations can be shown to play a significant role in the deformation, a component of rigid-block rotation is demonstrated, for example by the rotation of steep normal faults into orientations where they appear as reverse faults. Copyright (C) 1996 Elsevier Science Ltd