On the active tectonics along the Messina Strait

The world's longest and tallest one-span bridge has been planned to connect peninsular Italy to Sicily across the Messina Strait. This is one of the most seismically active areas of the Mediterranean, located along the transfer zone between the faster SE ward retreating Calabria subduction zone and Sicily. Considering this historical background and the geological evidence of active deformation in the area, it should be discussed whether the bridge is compatible with our knowledge of the area. Since the regional tectonics is still unclear and the network of active faults not yet framed in a comprehensible structural model, we explored the area by a multichannel seismic reflection survey (TIR10, cruise report available at http://www.ismar.cnr.it). New regional cross sections allow to image the upper crust of the area, and to add information for the evaluation of the seismic risk. The following main features have been observed: i) the NW-trending Capo Peloro fault, running parallel to the coast of northeastern Sicily, offsetting the sea-floor, steeply southward dipping, and interpreted as a right-lateral transpressive system; ii) a 12 km wide, NE-trending crustal anticline deforming the sea-floor, en-échelon to the Capo Peloro fault, located at the eastern tip line of the fault itself in the southeastern Tyrrhenian Sea, just north of the Messina Strait; iii) a normal fault propagation-related actively growing syncline, buried in the ENE-trending segment of the Messina Strait, with a blind normal fault. Relative to fixed Eurasia, the GPS sites in Sicily move toward NNW, whereas those in Calabria are NE-trending, at slower rate. This implies a faster northward component of motion of Sicily with respect to Calabria, and E-W stretching between Sicily and Calabria. Therefore, the boundary between Sicily and Calabria is diffuse and is deforming by right-lateral transtension. Most of the right lateral motion and the extensional component appears to be concentrated onshore Sicily, along the northern prolongation of the Malta Escarpment in the central-western part of the Peloritani mountains (e.g., the Tindari fault). The strain rate indicates that the Messina Strait itself is presently not the most actively moving area, suggesting tectonic loading, i.e., the faults are locked and the elastic energy is accumulating more than elsewhere, making them more prone to rupture. Along the ENE-trend, the Messina Strait is expected to behave as a graben, possibly with a minor left-lateral transtensional component. Along the N-S trend of the strait, moving S-ward into the Ionian Sea, the Messina Strait is interpreted as a right-lateral transtensional fault system, merging into the Malta Escarpment. Therefore, the area represents the transfer zone between two geodynamic settings being characterized by the coexistence of extension and N-S dextral transtension in the southern Messina Strait, adjacent to an area of roughly E-W transpression along the Capo Peloro fault along the northern Sicilian offshore. Based on conservative estimates of the Capo Peloro fault length and vertical offset, and size of the upper crustal-scale anticline, a magnitude higher than the 1908 Messina earthquake (M 7.1) cannot be ruled out.