Five years of continuous gravity observations in the Neapolitan volcanic area

Campania (southern Italy) is a region characterized by a high volcanic risk because of its active volcanoes. Five years of continuous gravity observations obtained in the Neapolitan volcanic area have been analysed. The tidal analysis of the gravity records over more than 5 years has provided amplitudes and phases of the main waves of the gravity tide. The availability of such a tidal model is necessary to extract, from the gravity records, the signal possibly associated to volcanic sources. The gravity contribution of the Ocean Tide Load has been computed and removed from the recorded changes in order to obtain the amplitudes, the amplification factors δ and the phase shifts of the main waves of the tidal field. The DDW99/NH Earth\'s model well fits the obtained results. Small values of the tidal residual vectors have been obtained, indicating that no significant tidal anomaly is affecting the Neapolitan area despite the presence of two very close active volcanoes. The obtained results are compared with those already obtained in the Vesuvius and Phlegraean Fields areas. Moreover a clear seasonal contribution of the rainfall is observed in the recorded gravity changes.