Dynamic inversion of ground deformation data for modelling volcanic sources (Etna 1991-93)

The 1991-93 Etna eruption, that represented the most important recent eruptive event both in terms of duration (472 days) and total volume of erupted lava (ca. 250(.)10(6) m(3)), caused marked ground deformation measured by using different geodetic techniques such as EDM, GPS, levelling, and tiltmetry. An inversion, termed ''dynamic'' because it took into account the sequence of events considering both the separate and cumulative effects of two sources, (a shallow tensile crack and a deeper ellipsoidal deflating source), was performed. It was based on 163 data collected by the different techniques plus 2 geometrical conditions for constraining the geometry of the crack on the surface. The final solution furnished a good fit for all measurements, defining a shallow tensile crack located inside the volcanic edifice, which represents the effect of the intrusion, and a depressuring body with centre at ca. 3000 m b.s.l., which could represent the centre of a generalized and more complex deflation of the volcanic edifice during the course of the eruption.