Normal fault migration and basin evolution in complex rift settings: insights from the North Gulf of Evia, Central Greece

The North Gulf of Evia is a young, active continental rift system located in Central Greece. Extension of 2-4 mm/yr is accommodated by large normal fault systems, such as the onshore Coastal Faults near Kammena Vourla, but slip rates and timing of initiation of these structures and intrabasinal offshore faults are poorly constrained. Extension is also coupled with strong rotational and strike-slip influence from the westward-propagating North Anatolian Fault, providing contrast to the nearby, orthogonal rifting in the Gulf of Corinth. The geodynamic setting of the rift has resulted in a complex configuration of normal, oblique and strike-slip faults across the North Gulf of Evia rift system. Detailed, high resolution study of faulting processes (initiation, linkage and migration) and the temporal evolution of such systems requires a high-resolution age model of syn-kinematic sedimentation. To date, no pre-Holocene sedimentary correlation has been proposed for the North Gulf of Evia, restricting the temporal scope of evolutionary studies.

We aim to unlock the temporal evolution of late-Quaternary (0-~325 ka) sedimentation and faulting in the North Gulf of Evia through the development of a syn-tectonic depositional age model for the Western Basin of the Gulf. To do this, we exploit a high resolution, high density 2D seismic reflection dataset (WATER I and II) to identify three key mappable horizons across the semi-enclosed basin using seismic stratigraphic principles including reflection terminations and onlap relationships. Based on observed late-Pleistocene deltaic clinoform packages, ages of ~12 ka (MIS 2), ~130 ka (MIS 6) and ~325 ka (MIS 9) are attributed to these horizons within our sequence stratigraphic model. The age model is applied across the Western Basin alongside a new network of offshore faults to determine the major structural components, depocentres and evolutionary history of the rift system for the first time.

We resolve the major modern structural controls on the basin to be the Kalypso Fault at the southern margin of the rift and the axial Central Graben. Holocene throw on the extensional Kalypso Fault is ~3.75 mm/yr with faults of the Central Graben deforming at throw rates of ~0.9 - 1.7 mm/yr. We show that the Kalypso Fault is linked to the western part of the onshore Coastal Fault System, widely considered the most active fault zone of the North Gulf of Evia and uplifts the hanging wall of the active Arkitsa Fault, where a sequence of uplifted Pleistocene marine terraces is preserved. Initiation of the Kalypso Fault is temporally constrained to ~325 ka from thickening relationships of syn-kinematic sediment packages following a strain migration event from the Arkitsa Fault. This migration event occurs across non-parallel structures with evolving strike of >20°, likely reflecting the regional rotational influence of the North Anatolian Fault on Central Greece. The Kalypso Fault represents the most active resolved normal fault in the Western North Gulf of Evia and presents significant, previously unrecognised seismic hazard.