Structural properties of rift-related normal faults: the case study of the Gulf of Corinth, Greece

Abstract

In the frame of the Corinth Rift Laboratory project, which aims to understand the relation between stress, strain and fluid flow in an extensional context, three normal faults have been studied and sampled in the south-western sector of the Gulf of Corinth. Two of these faults (the Pirgaki and Helike faults) juxtapose carbonate pre-rift sediments and syn-rift conglomerates at outcrop, and the third (the Aigion fault) has been drilled and cored at 760 m depth. The distance between the faults is around 4 km, and the offsets are approximately 1000, 700 and 170 m, respectively. The fault damage zones and cores of the analysed faults exhibit different geometry, size and textural characteristics. In general, it has been assessed that fault cores behave as near-impermeable barriers to transverse fluid flow, whereas highly fractured damage zones act mostly as conduits for nearly along-strike flow. Different types of fault rocks are exposed along the main faults; these include cataclasite, ultra-cataclasite, fault breccia and gouge, with random or foliated fabrics. Along the Pirgaki fault zone only, fault rock micro-fabrics have been related to multiple tectonic episodes. The results of our work also emphasise that the current conditions of deformation, in this sector of the Gulf of Corinth, are responsible for the development of a system of extension fractures that is only partially sealed. These fractures mainly control the permeability structure of the analysed fault zones and furnish information on the stress field acting in the area. Furthermore, their orientation and distribution indicate that they are consistent with a deformation pattern resulting from active extension.