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216 G. LAVECCHIA ET ALII

Fig. 3 - Map and section view of the major Plio-Quaternary structural elements (thrusts and normal faults) in eastern central Italy (a) and in
north-eastern Sicily (b) compared with the surface and depth distribution of good quality instrumental data recorded from local networks
(see references within the figure). Cross sections AA’ is drawn along the trace of the DSS profile 1978 (after LAVECCHIA et alii, 2003). Cross-
section B-B’ has been interpreted considering data from the literature (see references in the caption of fig. 1c); the base of the crust and the
possible location at depth of the thrusts are mainly deduced from FINETTI (2005) and FINETTI et alii (2005b), also taking into account infor-
mation from CHIRONI et alii (2000). In both sections an inward deepening of the hypocentres of the events sited close to the outermost basal
thrust is evident.
– Geometria, in pianta ed in sezione, dei principali elementi strutturali attivi (sovrascorrimenti e faglie normali) in Italia centro-orientale (a) ed
in Sicilia nord-orientale (b), confrontati con la distribuzione in pianta ed in profondità di dati strumentali di buona qualità registrati da reti
locali (bibliografia in fig.). La sezione AA’ coincide con la traccia del profilo DSS 1978 ed è tratta da LAVECCHIA et alii (2003). La sezione B-B’ è
interpretata tenendo conto delle innumerevoli sezioni geologiche e geofisiche attraverso la Sicilia orientale le cui tracce sono riportate in fig. 1c;
l’andamento della base crosta è derivato principalmente da FINETTI, 2005; FINETTI et alii (2005b) e CHIRONI et alii (2000).

These events (striped epicentres in fig. 2), although lying and active deformation field, as well as the reconstructed
within the areas above the ABT and SBT, are not linked to three-dimensional geometry of the Adriatic and Sicilian
the compressional regime investigated here, but rather to basal thrust planes (figs. 2 and 3, tabs. 1, 2a and 2b), a
the extensional tectonics which is ongoing at upper crust seismogenic zoning of the two analysed areas can be pro-
levels in the areas which overlie the deepest ABT and SBT posed with a same interpretative clue (fig. 5). The consid-
segments (GHISETTI & VEZZANI, 1999 and 2002; LAVEC- ered seismicity is associated with the west-dipping ABT
CHIA et alii, 2003; BONCIO et alii, 2004; PACE et alii, 2006; and the north-dipping SBT and in both cases it occurs
NERI et alii, 2005; JENNY et alii, 2006). close to and along the thrust plane within two distinct
seismogenic layers: sited within the upper crust (<10 km)
and within the mid-to-lower crust (10-25 km) (LAVECCHIA
5. THE COMPRESSIONAL SEISMOGENIC PROVINCES et alii, 2003; LAVECCHIA et alii, 2006; PACE et alii, 2006).
We chose the depth threshold of 10 km on the basis of
Taking into account the surface and depth distribu- geological and geophysical investigations which allow the
tion of the historical and instrumental seismicity and the transition between the upper crust (cover) and the middle
available information on the kinematics of the geological crust (basement) to be located at about this depth