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1 Dipartimento di Scienze della
Terra
Università di Messina
Salita Sperone 31
98166 Messina,
Italy
A review of the seismic, geologic, and geodynamic information available for
the Calabro-Sicilian region of southern Italy leads us to suggest a unifying
view of the larger (M 
7) earthquakes that have occurred there in
the last millennium coincidentally concentrated in the last 3.7 centuries. The
seismicity coincides with a narrow curvilinear extensional belt that passes
through western Calabria and eastern Sicily (WCES belt) and which
includes a nearly continuous north–south succession of primarily
east-dipping normal faults. In our reconstruction of the seismotectonic process
the faulting is activated by west-northwest–east-southeast extension
induced by residual rollback of the Ionian subduction slab. Our analysis of the
space-time distribution of strong earthquakes indicates a zone of conspicuous
aseismicity (M > 4.5 since 1700, M 7 since 1000) along
the belt, corresponding to the 30-km-long Scaletta-Fiumefreddo segment of the
Messina–Fiumefreddo fault in eastern Sicily. Moreover, because estimated
recurrence times are on the order of a millennium for M 7 earthquakes
along different parts of the WCES belt, and because historical data
for destructive earthquakes in the first millennium A.D. are not
detailed enough to allow reliable identification of the source zones, we cannot
definitely state whether or not there is a late-stage seismic gap for a large
earthquake in eastern Sicily. By applying standard relationships, the potential
for a magnitude 7 earthquake can be estimated for the Scaletta–Fiumefreddo
30-km-long normal fault segment. The level of seismic activity has been low in
the possible gap area in the past two decades when the upgraded local network
has detected tens of events above magnitude 2.5 with values up to 3.7.
Hypocenter locations of these events seem to delineate the deep geometry of two
faults reported in the surface geologic maps, one of which is the
Scaletta–Fiumefreddo silent fault. Coulomb stress changes not larger than
+0.6 bar produced on the silent fault by the most recent M 7
regional earthquake (1908), and the substantially nil Coulomb stress change on
the same fault by M 7 earthquakes of 1693 and 1783, imply relatively
small perturbation by previous earthquakes to the silent fault compared with the
Coulomb stress perturbation of 2–2.5 bars estimated by other investigators
on the 1908 earthquake source caused by major earthquakes of the previous
centuries.
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