Abstract - Faults are often simplified as planar structures but are, in reality, zones that contain variably deformed rock volumes, ranging from intact fault bound lenses to fault rock (breccia, gouge). The generation of fault bound lenses can often be explained by one of two processes: (i) Tip-line bifurcation in which a fault surface propagates through the rock volume and splits into two surfaces that enclose intact volume. (ii) Asperity bifurcation in which slip along a non-planar fault surface leads to the formation of a new fault strand that removes the fault plane irregularity. The newly formed fault bound lenses become progressively fractured with increasing fault displacement to become fault rock. Existing models for the formation of new fault strands, lenses and fault rock are, however, conceptual. We use the 3D Distinct Element Method (DEM) which represents rock as an assembly of cemented spheres, to model the propagation of normal faults through mechanically layered sequences. Although the numerical models are simple (e.g. effects of fluids and crystal plasticity are not included) they reproduce the two basic modes of generating fault bound lenses and the formation of fault rock, and provide unique insights into the 3D evolution of fault zone internal structure.
Abstract of talk presented at:
Tectonic Studies Group Annual Meeting, Birmingham, January 2010.