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154 G. Lavecchia et al. / Tectonophysics 445 (2007) 145–167

N170°E trending average shortening axis. In general,
the deep Etna active stress tensor computed by inversion
of focal mechanism is characterized by a nearly N–S

Fig. 7. Depth distribution and energy release versus depth of the
instrumental seismicity projected in the map of Fig. 6. The arrows
indicate the percentage values relative to the cumulative curve of the
total number of events and of the total energy release.

seismicity datasets in Castellano et al. (1997) and Neri
et al. (2005a). In section view, a northward deepening of
the seismogenic source is clearly evident, as already
pointed out by Castellano et al. (1997), who analyzed
four seismic sequences, with magnitudes up to 3.7,
recorded at Mt. Etna during the period 1988 to 1991. In
Fig. 8c, we have projected the hypocenters of Fig. 8b
above an independently reconstructed crustal section
across the Etna edifice and we observe a striking cor-
respondence between the deep Etna seismogenic
volume and the SBT shape, as defined in this paper.
The intriguing hypothesis of a kinematic link between
these two is reinforced when considering the fault plane
solutions of the Castellano et al. (1997) and Neri et al.
(2005a) events. These solutions, shown within the in-
set of Fig. 6, have an evident prevailing compression-
al kinematics, compatible with a sub-horizontal, about

Fig. 8. Seismogenic interpretation of the deep Etna seismicity. a) —
Major Plio-Quaternary structural elements and epicenters of earth-
quakes with MlN2.5 (gapb100°, phase readingsN10, RMSb0.5s)
within an half-width of 35 km from the trace of the section (key: 1 —
Plio-Quaternary normal, normal–oblique faults; 2 — Sicilian Basal
Thrust and splays; 3 — Quaternary anticline fold axes. b) — Section
view distribution of the seismic events projected within the map
(vertical error b 3 km; horizontal error b 2 km). c) — Overposition of
the hypocentral distributions above the interpretative crustal section
A–A', which correspond to crustal section E in Fig. 5.