Twelve Years of Ground Deformation Studies on Mt. Etna Volcano Based on Gps Surveys

GPS (Global Positioning System) monitoring has been performed on Etna volcano since 1988, making this volcano one of those with the longest records of GPS data. The first order network, measured at least once every year in accurate static mode, was progressively augmented from 9 benchmarks in 1988 to ∼70 benchmarks. The whole network is subdivided into seven sub-networks that are surveyed in static, quick-static or kinematic mode, according to the accuracy and density needed, with respect to the volcanic activity. This network provides key constraints to locate the deformation sources inside the volcano (reservoirs, dykes, faults) and track their evolution. Etna has proved an optimum testing ground of new surveying approaches in order to optimize geodetic fieldwork. Several methodological developments related to kinematic surveys and to the correction of tropospheric delays were made on Etna. Here, we discuss the overall picture of the entire data set up to 1999. The results show large scale displacements related to the activity of the volcano during the last twelve years. They are used to infer the location of magma reservoirs acting in this period, identifying a pressure zone beneath the western flank at a depth ranging from 2 to 9 km, several shallow intrusion following the regional NNW-SSE trend, and to quantify the eastward movement of the eastern flank of Mt. Etna, modeling two detachment surfaces beneath the eastern and southern flanks. At a local scale (e.g. in the summit areas and across the Pernicana fault), displacements are also identified and discussed.