Analysis of deformation structures in Pliocene and Quaternary deposits of the Hyblean Plateaux (south-eastern Sicily)

A singular association of deformation structures that have disturbed terrains up to Quaternary age, has been detected along the rocky coast of Vendicari (south-eastern Sicily). These structures are soft sediment deformations consisting of autoclastic breccias, diapyr-like injections and thixotropic wedges, as well as fractures, generally opened and filled by sediments. Both soft and brittle deformations can be due either to trigger mechanisms internal to the sedimentary environment or to external causes. In order to define the deformation mechanisms affecting the deposits, the local paleo-environmental reconstruction and detailed deformation structure investigations have been performed. Moreover, fractures have been analysed by a mesostructural study and the examination of the microscopic features of the filling materials, to highlight possible relationships with the stress field induced by regional tectonics. The multi-theme analysis allowed us to discard internal trigger mechanisms as responsible of the deformations and to reasonably infer these deformation structures as being seismically induced. This interpretation is also supported by similarities with structures studied in other areas worldwide and commonly interpreted as seismites. The link between these records of seismic activity and the eastern Sicily seismicity is set into evidence by the analysis of the historical accounts which report the occurrence of structures similar to those detected at Vendicari, in several sites close to the study area. A major result of the present study is to improve the catalogue of deformation features, recorded in sedimentary units, attributed to earthquakes.

Research Highlights
► A case study of both brittle and soft-sedimentary deformations was performed.
► Analyses allowed to discard internal causes as responsible of the deformations.
► Investigations showed that the deformation structures are seismically induced.
► Seismites are triggered by earthquakes with M greater than 5 and I greater than IX.