Feeding system and magma storage beneath Mt. Etna as revealed by recent inflation/deflation cycles

Ground deformation at Mt. Etna detected by three GPS surveys carried out in 2004, 2005, and 2006 is analyzed. The data set encompasses the 2004 - 2005 eruptions and foreruns those of 2006. A wide deflation of the entire volcano was detected from 2004 to 2005, accompanying the 2004 - 2005 eruption; conversely an evident inflation phase, from 2005 to 2006, followed this eruption and preceded the 2006 one. In both cases, the deflation-inflation cycle was accompanied by a continuous seaward motion of the eastern flank. We inverted both data sets ( 2004 - 2005 deflation and 2005 - 2006 inflation) using an optimization algorithm based on the Genetic Algorithm ( GA) in order to detect the ground deformation sources. The wide contraction measured during the eruption reveals the drainage of a sill-shaped magma reservoir located by data inversions at a depth of about 4.5 km b.s.l. The pressurizing source modeled for the 2005 - 2006 time interval indicates a refilling of the shallower near-vertical plumbing system of the volcano. This could indicate a change in the geometry of the feeding system, active after the 2004 - 2005 eruption, with a new and shallower magma storage that could have enabled the resumption of volcanic activity that was observed at summit craters in 2006. These results improve the imaging of the plumbing system of Mt. Etna volcano.