Anomalies of seismic wave propagation at Mt. Etna Volcano, Italy

Macroseismic and instrumental data concerning earthquakes that occurred in the Etnean area during 1978–1987 have been used to reveal the possible anomalies in the propagation of seismic waves in the shallowest part of the volcanic edifice. of 134 shocks located in different sectors of the volcano and having a depth not exceeding 5–8 km was used. The availability of instrumental records and accurate macroseismic information made it possible to compare the epicentres derived from these two data sets. esiduals, obtained after fixing the macroseismic epicentre as the reference one, were mapped for each permanent station of the local seismic network. Maps of residuals pointed out the existence of wide anomalies in the eastern sector of the volcano at a depth not greater than 4–5 km. These anomalies strongly influence the seismic wave propagation, so that the shallow part of the crustal model generally adopted should take them into account. Moreover, a very shallow anomaly was detected in the upper parts of the southern sector of the volcano. Although based on a qualitative approach, such findings strongly support the hypothesis that shallow volcanic structures and heterogeneity significantly influence the seismic energy propagation and they can be used to improve a three-dimensional velocity model for the Etnean area.