19 years of tilt data on Mt. Vesuvius: state of the art and future perspectives

<p>Mt. Vesuvius, located along the SW border of the Campania Plane graben, is one of the most studied volcanoes worldwide, from both the volcanological and the geophysical, geochemical and geodetic point of view. In order to better understand its dynamics, the deformation of the volcano has been already studied since the early ’70s by setting up levelling lines and, since a few years later, through trilateration networks, whereas ground tilt monitoring started in 1993. Tilt variations were recorded by an automatic surface station set up at the Osservatorio Vesuviano (O.V.) bunker (OVO) and data recorded were transmitted to the O.V. Surveillance Centre in Naples. Afterwards, in 1996 two more identical stations were set up close to Torre del Greco (CMD), and close to Trecase (TRC). In 2002 the data acquisition system was replaced, while at the end of 2011 a Lily borehole sensor was set up at 26 m depth, replacing the old TRC tilt station. The paper describes in details the tilt network of Mt. Vesuvius, its development over time and the data processing procedure; moreover, the ground deformation pattern is discussed, as inferred from the study of 19 years of data and its change during the seismic crises of 1995-1996 and 1999-2000. From the information obtained from the tiltmetric monitoring, a complex deformation pattern can be deduced, strongly dependent on the position of the sites in which the sensors were set up with respect to the morphology of the volcanic edifice and its structural outlines. If we consider the signals as they were recorded, although previously corrected for the influences of the thermo-elastic strain on the sensors, the tilting occurs mainly in the SW direction with rates of about 11 µradians/year on both the western and eastern flanks and of about 13 µradians/year on the southern one. Because tilt vectors point in the long term outward from the summit and towards the subsiding area, this supports the hypothesis of a southern areas subsidence, according with a spreading effect of Vesuvius, taking into account geological, structural, geophysical and geodetical (optical levelling, InSAR) data. The SW tilting occurs therefore irregularly and shows some seasonalities, consistent with the solar thermal radiation whose removal by statistical procedure outlines a different but equally interesting deformation field as it shows interruptions with changes in both trend and amplitude during two periods of strong seismic activity that affected Mt. Vesuvius in the periods 1995-1996 and late 1999-2000, marked by an average rate of energy release of at least one order of magnitude greater than the previous and following periods. Another change in intensity and direction of the deformation detected by tiltmeters since 2000, connected with the variations of the phase shift between the tilt components and the temperature recorded, compared to previous years, occurs during a strong decrease of the energy released by Vesuvius earthquakes.</p>

X, Extract of a letter from Mr. Robert Mackinlay, to the Right Hon. the Earl of Morton, F. R. S. dated at Rome, the 9th January 1761. concerning the late eruption of mount vesuvius, and the discovery of an antient statue of Venus at Rome

There has been a most terrible eruption lately of mount vesuvius, about the latter end of last month, but the accounts hitherto arrived are not very distinct: however, they all agree, that there were nine new mouths, or openings, towards the Torre del Greco and Annonciada: that very considerable shocks of an earthquake were felt all over Naples: that neither fire nor smoke came, out of the old crater; that the lava had run into the sea: and that beyond Portici, upon the high-road, the lava was in height seventeen palms, and some of the sreams four hundred yards broad.