Structural development and seismogenesis in the Messina Straits revealed by stress/strain pattern above the edge of the Calabrian slab (Central Mediterranean)

The Messina Straits is a narrow marine basin shaped by regional-scale uplift and localized subsidence driven by crustal faulting along the diffuse Africa-Eurasia convergent plate boundary. Catastrophic earthquakes have struck the region, most notably the 1908 Mw 7.1 Messina event. However, the causative fault(s) and the geodynamic drivers of this deformation remain unclear. In this study, we use seismological and marine geophysical data to investigate neotectonic activity within the broader central Mediterranean geodynamic framework. By analysing relocated hypocentres, principal stress conditions and deformation patterns, we explore the link between seismicity and tectonic features identified in seismic reflection profiles and morphobathymetric maps. Our findings reveal a significant variation in seismogenic thickness and earthquake distribution across the Messina Straits suggesting spatially variable tectonic processes. Stress tensors show a composite deformation pattern, from predominantly extensional deformation between 6 and 20 km, to more heterogeneous deeper deformation (40-80 km) that includes compressional mechanisms. We interpret our fault structure data in the Messina Straits as reflecting the shallow crustal response to active tectonics occurring within a large deformation zone oriented along and above the Calabrian slab edge. This zone is characterized by several strike slip faults, including the Ionian fault in the Ionian Sea and the Capo Peloro fault in the southern Tyrrhenian Sea, which together bound the extensional domain of the Messina Straits. Based on our analysis, we propose that present-day subsidence and seismogenesis in the Messina Straits are strongly influenced by deformation along these strike-slip segments, primarily driven by the relative motion between Africa and Eurasia, in combination with tensile forces deriving from lateral variations in gravitational potential energy. Plain language summary: The Strait of Messina is a narrow stretch of sea between the island of Sicily and Calabria, in southern Italy. This region of the central Mediterranean is located along the African and Eurasian plate boundary, west of the Calabrian subduction zone where African lithosphere subducts underneath Calabria. Many earthquakes strike the area, including a moment magnitude 7.1 event in 1908. In this study, we examine seismological and marine geophysical data to better understand the processes that cause movement of the Earth's surface and deformation at depth, the direction of stresses in the Earth's crust, and the links between faults and earthquakes. Our analysis shows that the thickness of the crust capable of producing earthquakes varies significantly across the Strait of Messina. Seismic activity is mainly concentrated in two seismogenic layers; one layer is located at shallow depth (6 to 20 km below the sea floor) while the other is deeper (40-80 km). We find evidence of tectonic activity across a broad zone. The Strait of Messina lies within this zone, which is located above, but not constrained to, the southwestern edge of the subducting plate. The zone includes two main faults that directly surround the Strait of Messina, the Ionian fault in the Ionian Sea and the Capo Peloro fault in the southern Tyrrhenian Sea. Together, these faults form a step-like structure that seems to be responsible for the vertical and horizontal movements in the Strait of Messina.