UPWARDS MIGRATION OF SEISMIC FOCII - A FORERUNNER OF THE 1989 ERUPTION OF MT-ETNA (ITALY)

Data from a portable array of three-component digital stations, run at Mt Etna from 1988 to early 1990, highlight the seismic behaviour of t he volcano before the 1989 eruption, one of the most significant in te rms of energy of the last two decades. After a two-year period of weak and discontinuous seismicity, the depth of the seismically active vol umes was observed to become shallower a few months before the volcanic event. The overall migration of the events, inferred by hypocentral l ocations and decreases of S-P time differences at two stations, agrees with other geophysical forerunners and allows further insights into t he changes in the stress field leading to the eruption.