A high-resolution Holocene fault activity history of the Aigion Shelf, Gulf of Corinth, Greece

Abstract

The Gulf of Corinth is a continental rift in the western Aegean, Greece. It is the most active rift basin in Europe, with maximum N-S extension rates across the rift of ~15 mm yr-1. The data presented in this thesis reveal the behaviour of the Aigion Shelf Fault, part of one of the active normal fault systems in the Gulf of Corinth, over the past ~12 kyr, using high-resolution seismic reflection and multibeam bathymetry datasets.
The Aigion Shelf Fault is part of an en echelon system comprising four basin bounding faults that control the southern margin of the Gulf of Corinth. It is a segmented, N-dipping normal fault, which overlaps and is active concurrently with the older Western Eliki Fault. It forms the southern boundary to a graben structure that narrows eastwards, which is bounded to the north by a S-dipping segmented fault. Approximately 500 m west of the shelf edge the graben geometry changes, with the Aigion Shelf Fault stepping north, and the S-dipping fault switching polarity to become N-dipping.
Sequence stratigraphic markers relating to the post-lowstand transgression and more recent progradational beach deltaics form the boundaries between three distinct seismic packages, enabling quantification of fault slip rates and changes in sediment deposition. Isopachs from five specific time periods show that the development of depocentres is predominantly controlled by faulting.
Displacement on the Aigion Shelf is distributed over a complex fault population. This is interpreted as a damage zone associated with the eastern tip of the Aigion Shelf Fault, formed through upward bifurcation of fault splays from a single structure at depth. The combined spatially averaged total slip rate for all the splays identified is 2.6 0.4 mm yr ± -1. The average vertical displacement rate on the Aigion Shelf Fault is ~0.6 0.1 mm yr ± -1. Significant short-term spatial and temporal variability within the 12 kyr time period suggests the influence of segment boundaries, and periods of enhanced activity over 1 kyr timescales representing multiple earthquake cycles. Observation periods of >4 kyr are found to represent the longer-term displacement behaviour on the Aigion Shelf Fault.
The displacement profile of the Aigion Shelf Fault indicates that it is extends onshore. There is no apparent structural link between the main Aigion and Aigion Shelf Faults. However, a similarity in displacement rates and profiles suggest that both are immature structures that form part of the larger Aigion-Neos Erineos Fault system. Fault structure plots indicate that there has been no lateral fault growth over the Holocene, with burial and mortality of minor faults. Formation of growth wedges against both the Aigion Shelf Fault and S-dipping graben bounding fault indicate that the relative dominance of both faults has varied spatially and temporally.

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