Absolute gravimetry and gradiometry on active volcanoes of Southern Italy.

The aim of the paper is to outline the role played by absolute and gradiometric gravimetry in the investigation of volcano dynamics. High precision gravity networks operate on the active volcanoes of Southern Italy to detect changes in the gravity field indicating mass variations correlated with the volcanic activity. A combination of absolute and relative gravimetry is needed; absolute gravity measurements cheek the base stations and may reveal long term variations or confirm stable zones. Moreover, they permit continuous calibration checks and a comparison for relative gravimeters. Therefore in 1986 a program of measurement of the absolute value of g, and its vertical gradient, was started in the active volcanic, areas of Southern Italy. In addition, the Free Air Gradient (FAG) is directly measured in the investigated areas to better define gravity changes produced by sources at shallow depth. The results obtained so far are presented and discussed.