Faulting and Ancient Earthquakes at Sybaris Archaeological Site, Ionian Calabria, Southern Italy

Abstract

The Sybaris archaeological site, founded by the Greeks in 720 B.C., is located within the Sibari Plain near the Crati River mouth (Ionian northern Calabria, southern Italy), in an almost flat and low-lying area (Fig. 1). The plain is bounded by the Pollino chain to the north and by the Sila massif and the northern Crati basin to the south and west. From a seismotectonic point of view, Sybaris is located inferences the northeastern Calabrian arc, the tectonic evolution of which is controlled by slow north-northwest/south-southeast convergence between the Eurasian and African–Adriatic continental plates (e.g., Gvirtzmann and Nur, 1999; Argnani, 2000; Jolivet and Faccenna, 2000). Throughout the Calabrian arc, complex dynamics associated with subduction and rollback have produced back-arc extension, widespread uplift, and relative subsidence in the major tectonic basins, including Sibari, where mainly normal seismogenic faults accommodate internal deformation. The interior of the Sibari Plain has a high seismogenic potential, and recently, on July 2010, theMt. Pollino chain area experienced a three-year seismic sequence with magnitudes up to 5.2 (Fig. 1), following 30 years of seismic quiescence. In contrast, low to moderate seismicity characterizes the eastern half of the plain closer to the Ionian Sea, where the archaeological site of Sybaris is located (Fig. 1). Although not well constrained, there is evidence for active compression in this portion of northern Calabria and the Ionian Sea, where mostly strike-slip faults aremapped (e.g., Frepoli and Amato, 2000; Galadini et al., 2001; Pondrelli et al., 2006; Scognamiglio et al., 2009; Comerci et al., 2013; Fig. 1), but significant uncertainty exists on locations, geometry, and age of these faults. The 2700-year long record of history stored in the archaeological site of Sybaris may have recorded the traces of earthquakes that occurred in the area by sealing their effects in the sediments and in the archaeological remains. An archaeoseismic study of the site constitutes a unique means to deepenour knowledge of the seismotectonic of the area. The recognition and characterization of the coseismic deformation affecting the structures of the Sybaris archaeological site is the objective of the present study. To identify past seismic deformation events at Sybaris, we proceeded with (1) a systematic survey of the deformed structures, (2) an analysis of the tectonic deformation, (3) the formulation of a hypothesis for tectonics and earthquakes inferences, and (4) constraints on the timing of the deformation based on archaeological stratigraphy and absolute dating.