Deep Earthquakes as a Precursor of the September- October 1989 Flank Eruption at Mt. Etna Volcano (italy)

The September-October 1989 flank eruption at Mt. Etna marked a change in the recent eruptive style of the volcano. Seismicity, at mid (order of months) and short (order of days) time, preceding the eruption onset has been analysed by means of D (time fractal dimension), and of materials science equation. The behaviour of the upper and lower crust volumes has been investigated, by considering shallow (h ≤ 7 km) and deep (h>7 km) events. Clear patterns of ‘deep’ events have been found to precede flank eruption onset, at the order of months, while the overall volcanic edifice is affected by seismic events at the order of days, prior the eruption onset.