Axi‐symmetric deformation of a thermo‐poro‐elastic half‐space: inflation of a magma chamber

Abstract

The deformation observed at Phlegraean Fields (Italy) during the recent 1982–1984 crisis is interpreted in terms of overpressure in a shallow magma chamber and migration of hot pressurized fluids. Elastic effects are studied first, and previous results, obtained from Maruyama's strain nuclei, are corrected. Poro‐elastic and thermo‐elastic effects are found to be as important as the elastic ones: in a semi‐pervious medium, the three terms are typically of the same magnitude. Results are applied to interpreting the bradyseismic crisis of 1982–84 at Phlegraean Fields (PF), near Naples, Italy. The concave shape of the first phase of the deformation history at PF can be reproduced by linearly increasing fluid pressure and/or temperature at the boundary of a spherical cavity. The convex shape of the second phase is interpreted in terms of a gradual return to normal conditions. The late phase of slow subsidence is interpreted as the effect of diffusional dissipation of temperature and pressure excess. The deconvolution of the real source time history at PF is largely non‐unique, but in any case the importance of fluids in the deformation history is assessed; furthermore, the inclusion of fluid migration in the deformation model allows simple explanations of several geochemical and geophysical observations made during the bradyseismic crisis. Copyright © 1990, Wiley Blackwell. All rights reserved