3D Gravity Inversion by Growing Bodies and Shaping Layers at Mt. Vesuvius (Southern Italy)

Abstract

To improve our knowledge of the structural pattern of Mt. Vesuvius and its magmatic system, which represents one of the three volcanoes located in the Neapolitan area (together with Campi Flegrei and Ischia; southern Italy), we analyze here the Bouguer gravity map that is already available through its interpretation by means of 2.5-dimensional modelling. We have carried out a three-dimensional interpretation using a new and original algorithm, known as 'Layers', that has been especially processed for this purpose. Layers works in an automatic and non-subjective way, and allows the definition of the structural settings in terms of several layers, each representing a specific geological formation. The same data are also interpreted in terms of isolated and shallow anomalous density bodies using a well tested algorithm known as 'Growth'. We focus our inversions on the Mt. Vesuvius volcano, while globally analyzing the entire Neapolitan area, in order to investigate the deep structures, and in particular the deep extended 'sill' that has been revealed by seismic tomography.The final models generally confirm the global setting of the area as outlined by previous investigations, mainly for the shape and depth of the carbonate basement below Mt. Vesuvius. The presence of lateral density contrasts inside the volcano edifice is also shown, which was only hypothesized in the 2.5-dimensional inversion. Moreover, the models allow us to note a high density body that rises from the top of the carbonate basement and further elongates above sea level. This probably represents an uprising of the same basement, which is just below the volcano and which coincides with the V P and V P /V S anomalies detected under the crater. The three-dimensional results also reveal that the two inversion methods provide very similar models, where the high density isolated body in the Growth model can be associated with the rising high density anomaly in the Layers model. Taking into account the density of these modelled bodies, we would also suggest that they represent solidified magma bodies, as suggested by other studies. Finally, we did not clearly detect any deep anomalous body that can be associated with the sill that was suggested by seismic tomography.

The 3-D structure of the Somma-Vesuvius volcanic complex (Italy) inferred from new and historic gravimetric data

“…Nevertheless, the highest resolution 3-D gravimetric inversion study to date 20 largely dismisses the seismic findings based on a density model that features a low-density body below the Vesuvius crater. This result contrasts with another 3-D density model 21 that indicates a central high-density body, but the sparse station distribution used in the latter study yields a poor model resolution. It is important to better constrain and understand the origin of this central anomalous body as most of the present-day seismicity is confounded along its boundaries 27 , 28 .…”

“…10 26 ). Its presence is also suggested by certain 3D gravity inversion results (published figures: Figs 6 21 and 7 21 ). A 3-D rendering of the dense regions (Fig.…”

“…Figure 2a presents the distribution of the historic data in a square of size 20 km × 20 km that is centered on the Vesuvius crater. These data (and additional data outside this region) have been used in previous 3-D inversions 21 . Our new data set was acquired within the central 10 km × 10 km square region shown in Fig.…”

A new petrological and geophysical investigation of the present‐day plumbing system of Mount Vesuvius

“…Should this result be confirmed by less noisy field data, it would contrast with the interpretation of several seismic experiments [Zollo et al, 1996[Zollo et al, , 1998Auger et al, 2001;Nunziata et al, 2006 [Cassano and La Torre, 1987]) is significantly lower than that of the surrounding carbonates (2,600-2,800 kg/m 3 [Berrino et al, 1998]). The deep anomalies detected by gravimetric studies were interpreted as solidified magma bodies [De Natale et al, 2004;Berrino and Camacho, 2008]. More generally, we note that the unlikely presence of an extended hot magma reservoir also represents a case against a potential interconnection of Mt.…”

“…Vesuvius corresponds to a superficial brine layer rather than to the presence of a deep conductive magma body. This is consistent with the gravimetric observations from Berrino and Camacho [2008] that could not detect the deep anomalous layer interpreted by seismic tomography as an extended sill but attributed the different deep anomalies to solidified magma bodies. [5] In the present paper, we propose a new approach for an improved characterization of the present-day plumbing system of Mt.…”