ACTIVE THRUSTING IN SW SICILY (ITALY): HUNTING FOR SEISMOGENIC SOURCES USING A MULTIDISCIPLINARY APPROACH

SW Sicily hosts the active outer front of the Maghrebian chain, and has been repeatedly hit by destructive earthquakes as the Mw-max 5.5 1968 Belice sequence and as shown by archaeological evidence from the old Greek town of Selinunte. For several reasons this area remains among the most enigmatic in Italy as regards the identification of the seismogenic sources.

We present a multidisciplinary study of a stretch of the SE-verging active thrust belt of SW Sicily formed by two aligned albeit non-parallel fault arrays, which may be associated with the local seismicity.

The southern 18 km-long, NE-SW trending fault array (GCTS) straddles across the coastline and it is composed of two segments showing geodetic and geologic evidence of active deformation. The northern, on-land segment corresponds with an up to 60 m high morphological scarp, which is the fore-limb of a broad fold involving Lower Pleistocene sediments and cm-scale reverse displacement of an early Bronze-Hellenistic road. It is marked by a sharp gradient in Differential SAR interferometry and GPS velocity fields. 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 offshore southern segment shows on Sparker seismic profiles folding of Late Pleistocene-Holocene deposits and out-of-syncline thrust splays cutting the sea-floor.

The northern ENE-WSW trending fault array (PPTS) is composed of two 10 km long segments connected by relay ramps. Although the deformation pattern is less clear, a gradient in SAR data and slow deformation (creep?) in historical to recent man-made structures are possible evidence of activity.

Integration of previous datasets with deep seismic lines suggests that the two active fault arrays are the shallow expression of a steep crustal ramp which up-thrust platform limestone at depth.

Based on macroseismic and seismological evidence, we suggest that the PPTS may be associated with the 1968 sequence. On the other hand, the current geodetic strain accumulation on the GCTS suggests that the fault array has been significantly loaded since its last important seismic event, tentatively correlated to the 4th–5th century A.D. destruction of Selinunte temples.