Review of seismological studies at Mount Etna.

This paper reports the present state of seismological research at Mt. Etna. A schematic classification of the earthquakes that occur on the volcano is proposed, based on both seismogram and spectrum features. We have made both focal solutions and estimates of earthquake source parameters (stress drop values between 2 and 20 bars and small source dimensions). The crust of Etna thus appears as an extremely heterogeneous medium that does not permit great stress accumulation. The coexistence of an extensional regime with an older and deeper compressive one seems confirmed at depths greater than about 7 km. Eruptive and seismic phenomena occur mainly along the principal structural trends of the volcano, but often the directions of the eruptive fractures and the earthquake concentration during the same eruption do not coincide. Tectonics seem to play an important role in controlling seismo-volcanic behaviour. [ABSTRACT FROM AUTHOR]