The hydrogeological structure of fault zones in poorly lithified sediment, Gulf of Corinth rift

Often, the structure of fault zones cutting poorly lithified sediment examined in outcrop indicate such fault zones should behave as hydraulic barriers, but hydrological observations indicate they behave as conduit-barriers. This thesis investigates the hydrogeological structure of fault zones cutting poorly lithified sediment to better understand the observed conduit-barrier behaviour. The macro- and micro-structure of fault zones was investigated at outcrops of five fault arrays cutting syn-rift sediment of the rapidly extending Gulf of Corinth rift, Central Greece. Fault zone evolution was interpreted from these observations and changes to sediment hydraulic characteristics in fault zones estimated. Based upon the field data, characteristic fault zone hydrogeological structure was represented in two-dimensional numerical fluid-flow models in order to assess likely hydraulic impacts. Fault zone structure is found to be dominated by a mixed zone and differs to those previously reported. Two models of fault zone evolution are proposed for faults cutting: 1. Only poorly lithified sediment, in which beds are rotated and smeared in the mixed zone, where these can mix at the grain-scale through distributed, controlled particulate flow. 2. Sediment of contrasting competency, with mixed zones comprising blocks and lenses, and fine-grained smears in which strain localisation and fault-tip bifurcation are central to their evolution. Both models apply to fault zones that juxtapose fine and coarse-grained sediment. Numerical models show that the majority of these fault zones will behave as barriers to fluid-flow due to a reduction in hydraulic conductivity. Fault zones of all sizes influence fluid-flow, but hydraulic impact increases with fault throw. Conduit-barrier behaviour can be explained by anisotropies, particularly from slip-surface cataclasites, in fault zones cutting poorly lithified sediment only. Fault hydraulic behaviour is strongly dependent on structural hetereogeneities and their geometry in the fault zone. The cumulative effects of these faults will be significant for subsurface fluid-flow.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2013

Author dc:creator

• Loveless, Sian

Language dc:language

en