Along- and across-strike variation of damage zone parameters in the Kornos-Aghios Ioannis normal fault, Lemnos Island, Greece

Abstract

The Kornos-Aghios Ioannis Fault (KAIF) is an extensional fault system that deformed Lower Miocene volcanic rocks and Middle Eocene to Lower Miocene turbidite sandstones at shallow depth (<1 km). The fault system is exposed for about 10 km and consists of two major NW-SE-striking segments connected by an E-W-striking one. This structural architecture provides the opportunity to study the variation of damage zone parameters (i.e., damage zone width, fracture density, attitude of deformation structures, and fracture connectivity) in wall, tip and intersecting damage zones. The >122 m wide tip damage zone has a width greater than the wall and intersecting damage zones (72.6 and 50.9m, respectively) and exhibits the highest average fracture density recognized along the entire KAIF. In tip and intersecting damage zones, damage structures exhibit a larger azimuthal variability and hence a greater fracture connectivity (average number of connections per branch (CB) 1.60 and 1.53, respectively) compared to wall damage zones (average CB value 0.88). Accordingly, significant along-strike variations of damage zone parameters occur in the absence of a clear dependence on fault displacement. Particularly, fault intersections and tip regions represent areas of enhanced secondary permeability potentially controlling fluid circulation in the subsurface.