We present a seismotectonic model of the active thrust front in western Sicily, which includes the area hit by the
1968 Belice earthquake sequence. The ~40 km long South-WEstern Sicilian Thrust (SWEST) is formed by two aligned
albeit non-parallel fault arrays, the Granitola-Castelevetrano Thrust System (GCTS) in the west and the Partanna-
Poggioreale Thrust System (PPTS) in the east.
The ~NE-SW trending, NW-dipping GCTS straddles from the Pelagian coastline to Castelvetrano, is ~18 km long
and composed of two segments, with the northern, ~12 km long one showing geodetic and geologic evidence of active
deformation (Barreca et al., 2014). The segment is marked by a sharp gradient in Differential SAR interferometry
(DinSAR and STAMPs) and GPS velocity fields. Geologic evidence include an up to 60 m high, and up to 15° steep
scarp, which is the fore-limb of a broad fold involving Lower Pleistocene shore calcarenites, and cm-scale reverse
displacement of an ancient road dated as early Bronze-Hellenistic age. Inversion of fault slip-lineation data from
structures displacing the archaeological remains yields a ~N110°E shortening axis, consistent with the geodetic
shortening direction estimated from GPS differential velocities.
The ~ENE-WSW trending PPTS stretches from Partanna to the macro-seismic area of the 1968 earthquake sequence
and is composed of two ~10 km long segments limited by relay ramps. Although geologic and geodetic evidence of
deformation are less clear than for the GCTS, we nonetheless observe a gradient in interferometry data for the western
segment, and evidence of slow deformation (creep?) in historical to recent (last ~400 yr?) man-made structures.
Integration of geologic, geodetic and seismology data suggests the active folds and thrusts are the uppermost
expression of steep (45°) crustal ramps (Monaco et al., 1996) which upthrust the Saccense platform at depth.
Based on macroseismic and seismological evidence (Monaco et al., 1996), we contend that the PPTS was partly
activated during the 1968 sequence, and that rupture stopped at the junction with the GCTS. The current geodetic strain
accumulation on the GCTS, on the other hand, suggests that the fault array has been significantly loaded, and that its
last important co-seismic event could have been caused the 4th–5th century A.D. destruction of Selinunte (Bottari et al.,
2009)
