| Abstract: | Seismic and eruptive activities that occurred at Etna volcano during the decade 1978–1987 have been analyzed statistically. The seismic activity consists of about 7500 events. This catalog has been found complete above the magnitude threshold 2.8. On the basis of the complete catalog (1458 earthquakes), the clustering features of seismicity have been investigated. The hypothesis of a Simple Poisson process is rejected. Applying a Generalized Poisson process of the Shlien and Toksoz (1970) type, the “E” parameter of cluster size appears to be strongly dependent on the chosen time interval. The application of Gasperini and Mulargia (1989) algorithm for identifying the single earthquake sequences indicates that the whole period is composed of only three sequences. Etnean seismicity appears therefore characterized by a “diffuse” low-magnitude (less than about 3.0) earthquake occurrence. From the volcanological point of view, two time series of eruptions (flank and flank + summit) have been analyzed in order to identify different regimes in both magma output and inter-event time. No change-points are apparent in the magma output series, while both inter-event time series of flank and flank + summit eruptions are characterized by one change-point each. No evident relation between the series of eruptions and the identified earthquake sequences is apparent. |
