Seismotectonics of the active thrust front in southwestern Sicily: hints on the Beliceand Selinunte seismogenic sources

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We present a seismotectonic model of the active thrust front in western Sicily, which includes the area hit by the1968 Belice earthquake sequence. The ~40 km long South-WEstern Sicilian Thrust (SWEST) is formed by two alignedalbeit 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 longand composed of two segments, with the northern, ~12 km long one showing geodetic and geologic evidence of activedeformation (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° steepscarp, which is the fore-limb of a broad fold involving Lower Pleistocene shore calcarenites, and cm-scale reversedisplacement of an ancient road dated as early Bronze-Hellenistic age. Inversion of fault slip-lineation data fromstructures displacing the archaeological remains yields a ~N110°E shortening axis, consistent with the geodeticshortening direction estimated from GPS differential velocities.The ~ENE-WSW trending PPTS stretches from Partanna to the macro-seismic area of the 1968 earthquake sequenceand is composed of two ~10 km long segments limited by relay ramps. Although geologic and geodetic evidence ofdeformation are less clear than for the GCTS, we nonetheless observe a gradient in interferometry data for the westernsegment, 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 uppermostexpression 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 partlyactivated during the 1968 sequence, and that rupture stopped at the junction with the GCTS. The current geodetic strainaccumulation on the GCTS, on the other hand, suggests that the fault array has been significantly loaded, and that itslast important co-seismic event could have been caused the 4th–5th century A.D. destruction of Selinunte (Bottari et al.,2009).
Lingua originaleEnglish
Numero di pagine1
Stato di pubblicazionePublished - 2014

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