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

A three-dimensional reconstruction of a large volcanic structure located offshore the town of Torre del Greco (Naples Bay, Southern Tyrrhenian sea, Italy) and representing the seaward prolongation of the Vesuvius volcano has been carried out using integrated geological interpretation of existing densely-spaced high-resolution seismic and magnetic profiles. The reconstruction has provided new insights into the knowledge of marine geophysics and volcanology of Vesuvius, one of the 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 mound-shaped external geometry and average dimensions measurable in terms of kilometers. The base of the Torre del Greco volcanic structure 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 there is a good correspondence between the sea floor topographic surface and the top of the volcanic structure, which does not 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 up to ten metres. 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 sea floor (towards the east) and the high in the top of the volcanic structure underneath can be explained as a consequence of sea floor deformation due to underlying volcanic culminations. Smaller volcanic mounds, buried and fossilized by marine sediments, are not related to any magnetic anomaly, probably due to their composition of volcanic tuffs