Geophysical Exploration of the Campi Flegrei (Southern Italy) Caldera' Interiors: Data, Methods and Results. Edited by Aldo Zollo, Paolo Capuano, Margherita Corciulo, 2006
A. Zollo, D. Dello Iacono, S. Judenherc
The volcanic areas of Vesuvius and Campi Flegrei in the Naples volcanic region occupy the central part of the Campania Plain. The plain itself lies to the east of the Tyrrhenian Sea between a latitude of 40° and 41° North. It represents a large semi-graben from the Superior Pliocene (5.3 My) that was subjected to a pronounced sinking during the Quaternary (on average, over 1,000 m/My). The geological evolution of the Campania continental edge was marked by two orthogonal extension phases: the first was more ancient and was connected to the NW-SE-oriented faults, producing structures that have extended parallel to the Apennines; the second is connected to the NE-SWoriented faults and has led to the formation within the plain of asymmetric horsts and grabens (Milia et al. 2003). The first volcanic products were disgorged around 400 ky BP at the end of the main extension phases, when the thinning of the crust of the continental edge resulted in the lower crust being more susceptible to fusion and to a rise in the magma. As a result of this Campi Flegrei activity, there were explosive eruptions throughout the entire Campania Plain and in the Bays of Naples and Pozzuoli at 315 ky, 205 ky, 184 ky, 157 ky, 39 ky, 18 ky, 12 ky BP (and more recently) (De Vivo et al., 2001, Milia et al., 2003). The Gulf of Naples was instead explored in a seismic reflection study in the 1970s, conducted by the Experimental Geophysics Observatory (Osservatorio Geofisico Sperimentale), that identified a strong reflector dipping towards the WNW that has been interpreted as being the top of the Mesozoic carbonatic base (Finetti & Morelli 1974). More recently, Bruno et al. (1998) mapped the depth of the reflector around Vesuvius using the reflection data of AGIP. The large urban centres that are inhabited by more than 2 million people, which will be immediately reachable by the volcanic products should there be an eruption, and the still-active magma systems of Vesuvius and Campi Flegrei represent a great risk to the population, as testified by the historic eruptions, the seismic- volcanic activity, the fumarolic activity, and the hot springs. A definition of the structures that characterise the area and knowledge of their relationships to the volcanic activity represent key elements for an understanding of the system and an evaluation of the risk. For this reason, Vesuvius and Campi Flegrei have been subjected to intensive active-seismic studies over the past ten years, with the main aim of obtaining high resolution images of their internal structure for the identification and depth localisation of their magma-supply systems.