Deformation on Mount Etna interpreted by inversion of 3D finite element solutions

The interpretation of geodetic data in volcanic areas is usually based on simple deformation models of pressure sources embedded in an elastic and homogeneous half-space. These models are characterized by assumptions which cannot be appropriate and that can potentially bias the estimate of source parameters such as location and shape. Our purpose is to develop a general tool to perform inversions of geodetic data taking into account lateral variations of mechanical properties and effects due to the topographic relief. To this end we use as forward model an array of point sources computed by a 3D finite element numerical technique. A direct search is performed in the parameters space using the neighbourhood algorithm followed by an appraisal of the sampled solutions. This procedure is applied to study the inflation process on Mount Etna from 1993 to 1997, documented by data recorded by GPS stations, EDM measurements and analysis of interferometric synthetic aperture radar images. We consider four different forward models including the following characteristics: homogeneous/heterogeneous medium and flat/topographic free surface. Our results suggest that while the effect of topography can be negligible, elastic heterogeneities in the medium can significantly alter the position of the inferred source. Furthermore, since the data show a significant signal in the SE sector due to flank instability, we also include in our study some simple sliding mechanisms.