SUMMARY
Employing 3D finite element method, we develop an algorithm to calculate gravity changesdue to pressurized sources of any shape in elastic and inelastic heterogeneous media. Weconsider different source models, such as sphere, spheroid and sill, dilating in elastic media(homogeneous and heterogeneous) and in elasto-plastic media. The models are oriented toreproduce the gravity changes and the surface deformation observed at Campi Flegrei caldera(Italy), during the 1982-84 unrest episode. The source shape and the characteristics of themedium have great influence in the calculated gravity changes, leading to very different valuesfor the source densities. Indeed, the gravity residual strongly depends upon the shape of thesource. Non negligible contributions also come from density and rigidity heterogeneities withinthe medium. Furthermore, if the caldera is elasto-plastic, the resulting gravity changes exhibita pattern similar to that provided by a low effective rigidity. Even if the variation of the source volumes is quite similar for most of the models considered, the density inferred for thesource ranges from ? 400 kg/m3 (supercritical water) to ? 3300 kg/m3 (higher than trachyticbasalts), with drastically different implications for risk assessment.