Tectonic and Morphological Features of a Submarine Negative Flower Structure: In the Sinop Basin (Central Black Sea) and the Evaluation of Regional Seismic Hazard

The southern margin of the Eastern Black Sea is commonly regarded as a region of low seismicity, largely because onshore and offshore fault mapping remains limited. However, focal mechanism solutions from the last century indicate active normal and strike-slip faulting in addition to thrust earthquakes, with the reveal pronounced seismic clustering offshore of the Sinop Basin near Samsun. To investigate the origin of this seismotectonic complexity, approximately 1,300 km of high-resolution multichannel seismic reflection profiles were acquired, processed, and interpreted together with multibeam bathymetric data. This analysis addresses the long-standing debate on whether the basin represents a young foreland basin or a graben-type structure, and evaluates the present-day activity of basin-bounding faults. Fault geometries and their seafloor morphological expressions, particularly negative flower structures-provide key constraints on the regional seismotectonic framework. Four seismic units were identified and correlated with Upper Cretaceous–Paleocene, Eocene, Oligo–Miocene, and Plio–Quaternary successions. Faults that terminate above the Upper Cretaceous–Paleocene units are interpreted as inactive, whereas faults that cut all seismic units and reach the seafloor are considered active. Faults confined to the Plio–Quaternary unit are interpreted as syn-sedimentary. These results indicate that the Sinop Basin is not a passive depression but an actively deforming basin controlled by oblique to strike-slip faulting. The mapped active faults are capable of generating earthquakes with magnitudes of Mw ≈ 6.2–6.9, implying a significant seismic hazard for the central Black Sea region.