Tectonic stresses and volcanism: in-situ stress measurements and neotectonic investigations in the Etna area (Italy)

Abstract

Mt. Etna has been building up for about 500,000 years on the eastern margin of Sicily, at the external border of the Apenninic—Maghrebian mountain chain and at the crossing of several important regional fault systems. The tholeiitic and alkaline magmatism of Mt. Etna represents the northernmost manifestation of present-day volcanism which was continuous in space and time from the Upper Miocene to the Lower Pleistocene in central eastern Sicily. In-situ stress measurements and neotectonic investigations have been carried out on Mt. Etna, on its periphery and on the Hyblean Mountains to obtain a better understanding of the stress field, which is connected to the present-day activity of the volcano, and a clearer picture of the regional geodynamical evolution. The investigations allow a comparison of the present stress field with that acting during the Quaternary. The neotectonic analysis has given evidence of strong compressional stresses exerted on the Pleistocene sediments overlying the substratum of the volcano and its immediate surroundings in addition to evidencing the already known extensional deformation. The compressional forces were oriented approximately N-S at the beginning of the volcanic activity. The in-situ stress measurements show now that this N-S compression is today active only in the northernmost part of the Etna area, whereas in the remaining area extensional stresses oriented approximately WNW-ESE prevail. It is concluded that the compressional stresses near the surface, today limited to the northernmost part of the Etna area, had a much more widespread distribution at the beginning of the volcanic activity. This conclusion is important for understanding the deep-seated magmatic process. Focal mechanisms of earthquakes indicate a complex tectonic situation with normal faulting down to a depth of 5 km and reverse faulting at deeper levels.