Viscoelastic modeling of deformation and gravity changes induced by pressurized magmatic sources

Abstract

Gravity and height changes, which reflectmagma accumulation in subsurface chambers, are evaluated using analytical and numericalmodels in order to investigate their relationships and temporal evolutions. The analysis focuses mainly on the exploration of the time-dependent response of gravity and height changes to the pressurization of ellipsoidalmagmatic chambers in viscoelasticmedia. Firstly, the validation of the numerical Finite Element results is performed by comparison with analytical solutions,which are devised for a simple spherical source embedded in a homogeneous viscoelastic half-space medium. Then, the effect of several model parameters on time-dependent height and gravity changes is investigated thanks to the flexibility of the numerical method in handling complex configurations. Both homogeneous and viscoelastic shell models reveal significantly different amplitudes in the ratio between gravity and height changes depending on geometry factors and mediumrheology. The results showthat these factors also influence the relaxation characteristic times of the investigated geophysical changes. Overall, these temporal patterns are compatible with time-dependent height and gravity changes observed on Etna volcano during the 1994–1997 inflation period. By modeling the viscoelastic response of a pressurized prolate magmatic source, a general agreement between computed and observed geophysical variations is achieved.