Active deformation in a sector of the Sicilian-Maghrebian Chain: new insights from integrated GNSS, structural high-resolution seismic reflection and seismological data

Abstract

We document active deformation in a sector of the Sicilian Maghrebian Chain exposed in north Sicily and in its offshore prolongation on the basis of the integrated analysis of 1) time series of data collected by GNSS acquisition representing the change in the positions (X and Y) of permanent stations located in Palermo, Partinico, Prizzi, and Termini compared to the IGS station of Noto, 2) high-resolution (Sparker) single-channel reflection seismic data, 3) structural data, and 4) seismological data. The average values for the velocity vectors obtained for the Palermo, Partinico, Prizzi, and Termini Imerese stations are 4.55, 2.97, 2.96, and 2.15 mm/yr, respectively. The direction of the velocity vectors for all stations is oriented towards the station IGS reference of Noto. The relative displacements of the Termini Imerese, Partinico and Prizzi stations respect to Palermo station are most equal to 0.5 mm; the directions of vectors are divided between them, with a clockwise rotation. In the area cropping out in the promontory of Capo Zafferano, Pleistocene conglomerates and grainstones are affected by recent tectonic deformation. Particularly, two sets of deformation bands striking: i) from N-S to NNW-SSE and ii) NE-SW are observed at two sites near the village of Porticello. Both sets have an almost vertical dip and show mutual cross-cutting relationships which suggest that they developed contemporaneously. The N-S/NNW-SSE striking set shows a left-lateral strike slip kinematic. At place, the deformation bands affect also Upper Pleistocene (Tyrrhenian) bio-calcarenites. A number of seismic units, which are bounded by unconformities, were identified on seismic lines based on the internal configuration and seismic-stratigraphic character of reflectors (amplitude, reflection continuity, external shape, and frequency). The shallowest seismic unit is limited at the bottom by an erosional unconformity which cuts the underlying units. This unconformity formed during the sea level lowstand of the Last Glacial Maximum (LGM), aged at~20 ka. The unit of inferred late Pleistocene age appears to be folded and faulted. Faults generally have an inclination of ca. 50°, small displacements up to 10 m and are sealed by the unit of inferred post LGM age. Only a limited number of these faults were observed moving ca. 3 km offshore towards the NE. The study area has been struck in the past by several significant earthquakes of I0≥6, and we jointly evaluated data and information available for these events with the results of analyses performed to define the spatial distribution and kinematics of the recent seismicity.