Kilometer-scale heterogeneities inside volcanoes revealed by using a set of geophysical methods: variable stress field at Mount Etna, Sicily

Abstract A multidisciplinary study involving geological and geophysical techniques has been carried out on the lower southern slope of Mt. Etna, with the aim of discovering kilometer-scale heterogeneities, which are crucial in understanding how the volcano works. In this area, faults and ancient eruptive fractures outcrop, with a NNW–SSE trend, together with volcanic structures, such as elongated hills, also trending NNW–SSE or E–W, which had never been evidenced in the Etna literature. The old landscape has been revealed by considerable erosion. Gravimetry and seismic tomography prospecting, added to geoelectric and drilling surveys, show that the morphology of the sedimentary substratum forms a N–S trending horst, limited to the east and west by depressions, where erosion products and lava flows from the overlying volcanic pile have accumulated. There is also evidence at very shallow depth (≅1 km below sea level) of an elongated body with a NNW–SSE direction, which is interpreted as a small magma chamber that has now almost completely solidified. This shallow magma system is likely to have fed the 122 BC and ≅1150 AD eruptions, which historical accounts suggest are located very close to the city of Catania.