The South Apulia Fault System (SAFS) in the central Mediterranean Sea: a needle in a haystack?

The central Mediterranean is usually seen as a puzzle of microplates interwoven with a network of thrust belts, back-arc basins, and transfer zones. The Adria microplate lays in the middle of this puzzle, being surrounded by two opposite-verging chains and delimiting the northern margin of the ancient Tethys ocean. Almost all the Adria microplate is under the Adriatic and Ionian Seas, and therefore most of our knowledge relies on seafloor and subsurface mapping. The southernmost end of the Adria microplate is the foreland in between the Albanides-Hellenides and Apennines chains facing off against each other in the Otranto Channel (Apulia foreland). In its southern part, the preserved Mesozoic paleomargin shows the transition between the Apulian carbonatic platform and the Ionian oceanic crust that was subducted under the Calabrian Arc, to the west, and the Hellenic Arc, to the east. The instrumental seismicity in this area is scarce and the geodetic data reveal very slow strain rates, nonetheless, the historical catalogs report an Mw 6.7 earthquake occurred in 1743 that spread damages in southern Italy, Albania, and Greece, together with hints about a tsunami in the Brindisi harbor. The source of this earthquake is very uncertain and raises compelling questions on how to treat this type of seismic sources in hazard maps. In this study, we present the results of the analyses performed on a newly acquired high-resolution bathymetry and CHIRP data by R/V OGS Explora. These analyses allowed us to identify a 100-km-long, NW-SE trending, complex system of normal faults, here named South Apulia Fault System (SAFS), revealing the character of the internal deformation of the Apulia foreland. Both bathymetric analysis and previously acquired multichannel seismic profiles highlight the starting of the activity of this fault system during the Plio-Pleistocene and show clear evidence of very recent activity, probably in response to the loading of the surrounding chains. The quantitative analyses performed on the bathymetric data and on the seismic profile allow us to perform a 3D reconstruction of the SAFS and to calculate its activity rates. Our results have strong implications in the reconstruction of the arrangement of a key area in the Africa-Europe plate boundary and its evolution.