Deformation band fault core : character, evolution and influence on bulk fluid flow

Abstract

Deformation band fault core has only recently been recognised as a distinct component of deformation band faults. Previously, deformation bands were divided into single deformation bands, zones of deformation bands and slip surfaces (Aydin, 1978). Shipton and Cowie (2001) recognised that, in outcrop, a unit of fine-grained material is always found in association with slip surfaces. Shipton and Cowie (2001) refer to this unit as fault core. Simple bulk fluid flow modelling by Shipton et al. (2002) shows that across-fault fluid flow is most sensitive to fault core thickness. However, the thickness of the fault core shows no increase with offset accumulation (Shipton et al., 2005). The principal aim of this thesis is to understand the evolution of deformation band fault core, in particular the character, geometry and fluid flow properties. In this dissertation, the fault core is divided into six components based on observations in a variety of different aeolian and fluvial sandstones. Four fault core components are found in all deformation band faults; zones of deformation bands, condensed deformation bands, cemented condensed bands, and slip surfaces. Two fault core components, shear fractures/breccia and gouge, are found in reactivated deformation band faults and heterogeneous host lithologies respectively. Occasionally, later joints are observed crosscutting deformation band fault core.