Multibend fault-bend folding

This paper shows how slightly complex but angular fault shapes with only a few bends lead to broadly curved and/or highly complex folds. A common perception exists that simple, angular fold geometries are a necessary consequence of the normal assumptions of fault-bend fold theory - namely angular fault-bends, straight faults and flexural slip. To the contrary, it is shown here that exact application of these low-level assumptions produces great complexity from simple fault shapes. This complexity is caused by the combination of (1) generation of new axial surfaces by displacement of hangingwall cut-offs past successive fault bends and (2) fragmentation of axial surfaces by mutual interference. The result is entwined arrays of fold axial surfaces that produce quasi-curved and/or complex folds from discrete angular fault bends. Fold complexity grows in a highly non-linear way. In the most extreme case the number of fold axial-surface segments grows as the fourth power of the number of fault bends. This paper presents examples of the immense variety of complex fold geometries that are thus generated. (C) 1997 Elsevier Science Ltd.