Eruptive and seismic activity at Etna Volcano (Italy) betwen 1977 and 1991

A review of volcanic and seismic activity at Etna (Sicily, Italy) between 1977–1991 is presented with the purpose of looking for possible relations between the main phases of seismic energy release and the principal eruptive episodes. Flank eruptions are normally preceded by both deep and shallow seismic swarms (0 <h<20km) which accompany the opening of fracture systems some hours before the eruption onset. Conversely, summit eruptions usually take place without any immediate change in the seismic patterns, even if moderate seismic activity some months before the onset suggests that magma uprises gradually and might rest within shallow reservoirs during ascent. It is worth noting that in some cases (1981, 1983, 1984 and 1986) significant episodes of seismic energy release occurred during the late phases of the eruptions. The analysis of the temporal evolution of the coefficient b of the magnitude-frequency relation suggests that the shallow seismicity of the eastern flank reflects the existence of a high level of geodynamic activity, probably associated with both regional tectonic forces and seaward sliding of this unbuttressed sector of the volcano.