Gravity changes due to overpressure sources in 3D heterogeneous media: application to Campi Flegrei caldera, Italy

E. Trasatti, M. Bonafede


Employing a 3D finite element method, we develop an algorithm to calculate gravity changes due to pressurized
sources of any shape in elastic and inelastic heterogeneous media. We consider 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 to reproduce the gravity changes and the surface deformation observed at Campi
Flegrei caldera (Italy), during the 1982-1984 unrest episode. The source shape and the characteristics of the
medium have great influence on the calculated gravity changes, leading to very different values for the source
densities. Indeed, the gravity residual strongly depends upon the shape of the source. Non negligible contributions
also come from density and rigidity heterogeneities within the medium. Furthermore, if the caldera is elasto-
plastic, the resulting gravity changes exhibit a 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
the source ranges from ?400 kg/m3 (super critical water) to ?3300 kg/m3 (higher than trachytic basalts), with
drastically different implications for risk assessment.


Campi Flegrei;deformation;gravity;finite element method;heterogeneous medium

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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X