DEFORMAZIONI DEL SUOLO MEDIANTE ANALISI DEI DATI MAREOGRAFICI NELL’AREA VULCANICA NAPOLETANA NEL PERIODO 1999-2006

Abstract

Osservatorio Vesuviano, department of Istituto Nazionale di Geofisica e Vulcanologia, is in charge of the surveillance monitoring of the Campanian volcanic areas, to promptly recognize any variation of the physical-chemical parameters helpful as precursors of eruption. The ground deformations in the Vesuvius and Phlegrean area are monitored by means of classical technique (like optical leveling and tiltmetry) and satellite technique (like global positioning system). Moreover, due to the vicinity of a coastline for both the volcanic system, the ground deformations are also monitored by the continuous recording of the sea level, using suitable tide gauge stations. Tide gauge data are also used to analyze the local characteristics of the sea wave even in presence of extreme phenomena. The Vesuvius Observatory tide gauge network, used in this paper, is operating since 1970 and reached, in the eighties, the consistency of 6 stations, Napoli, Nisida, Pozzuoli, Miseno,Castellamare di Stabia and Torre del Greco. Data since 1999 are retrieved and a database have been organized, corrected and validated up today, spanning over 8 years, using were necessary statistical gap filling technique. Data have been analyzed in the frequency domain and the local astronomical components have been defined by harmonic analysis, inferring amplitude and phase for the main diurnal and semi-diurnal components The obtained residual respect to the astronomical tide contains information about meteorological component, eustatic variation, ground deformation and noise. The residual sea level variation, for each site, can be represented by two terms: sea level background and local sea level variations due to noise, site effects and ground deformation. Removing, by deconvolution, the differential behavior of the sea-level respect to a reference station, provide an estimation of the ground level variation. This analysis shows no significant level variation at Vesuvius, while in the Campi Flegrei caldera, tide gauge data, put in evidence the presence of the so-called mini-uplift during last 7 years.