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Detailed marine geological-geophysical survey of the submarine groundwater discharge (SGD) system at Stoupa, Messinia (Greece) was conducted as part of an offshore study aiming at the evaluation of the discharge rate, the quality of the water and the investigation of potential ways for exploitation. Systematic mapping of the seafloor included swath bathymetry, seismic profiling and side-scan sonar imaging in order to reveal the precise morphology of the submarine discharge site, to better understand the structure of the SGD system and the nature and thickness of the sedimentary cover, and finally to provide the necessary data for a potential exploitation design. The SGD system is located in an E-W trending ellipsoidal depression characterized by two depth maxima at 27 and 29 m. This depression has been developed on the hanging wall of a N-S trending fault, whilst the groundwater discharges occur at the base of a 10-m-high steep and faulted rocky slope developed on conglomerates or limestone formations, also occurring in the coast. Recent sand deposits cover the seabed around the depression. The complex morphology of the discharge site, the steep slopes, and the rapid changes (due to erosion with subsequent slope collapse) during enhanced water flow periods, do not favor submarine constructions for the exploitation of the SGD system. [ABSTRACT FROM AUTHOR]

Highlights • New bathymetric and seismic data in Skyros Basin, North Aegean Sea • Oblique opening of the Skyros Basin similar to the North Aegean Basin • 19 major active faults that can generate M > 6.0 have been mapped for the first time. • Seismic hazard underestimated, only 3 active faults within the seismic catalogues • Subsidence of the North Aegean Sea is accelerated since Middle Pleistocene. [ABSTRACT FROM AUTHOR]