Three-dimensional magneto-seismic reconstruction of the Torre del Greco volcanic complex (Naples Bay, Southern Tyrrhenian sea, Italy): implications for the Somma-Vesuvius marine geophysics and volcanology

Three-dimensional magneto-seismic reconstruction of a large volcanic structure located offshore the Torre del Greco town (Naples Bay, Southern Tyrrhenian sea, Italy) and representing the seaward prolongation of the Vesuvius volcano has been carried out based on the integrated geological interpretation of densely-spaced high resolution seismic and magnetic profiles. This reconstruction has given new insights on the knowledge of marine geophysics and volcanology of the Vesuvius, one of most studied volcanoes in the world. Seismic stratigraphy of the volcanic structures shows acoustically-transparent seismic facies and high contrasts of acoustic impedance with respect to the overlying sediments. The structures have mounded-shaped external geometry and average dimensions in the order of kilometres. The base of the Torre del Greco volcanic structure is not acoustically evident, because it overlies the volcanic seismic unit correlated to the Campanian Ignimbrite pyroclastic flow deposits. Consequently, no contrast of acoustic impedance between the two volcanic units is clearly evident on the seismic profiles. The top of the structure is irregular and eroded and shows several culminations. The three-dimensional reconstruction of the Torre del Greco structure has been carried out using seismic constraints and correlations of volcanic structure to bathymetry. The sea floor topography is compared to the top of the Torre del Greco volcanic structure represented by contour depth of corresponding seismic horizons. Proceeding from south-east to north-west it exists a good correspondence between the sea floor topographic surface and the top of the volcanic structure, which doesn't crop out at the sea bottom. The rising of the volcanic structure in proximity to the sea bottom corresponds to the occurrence of topographic undulations in the order of ten meters. This evidence is confirmed by the interpretation of seismic profiles, showing three main vertical culminations of the volcanic structure, where the overlying sediment drape is significantly reduced. These culminations are linked to magnetic anomaly extremes, having values ranging between 250-350 nT. A striking coincidence between the long-shaped topographic high on the seafloor (towards the east) and the high in the top of volcanic structure underneath can be explained as a consequence of sea floor deformation due to the underlying volcanic culminations. Smaller volcanic mounds, buried and fossilised by marine sediments, are not related to any magnetic anomaly, probably due to their composition of volcanic tuffs.