GNGTS 2015 - Atti del 34° Convegno Nazionale

60 GNGTS 2015 S essione 1.1 in the Western Ionian Sea offshore the Messina Straits region (Fig. 1). Sedimentological and micropaleontological findings together with radiometric dating below and/or above key-layers outlined that turbidite emplacement may be related with the occurrence of major earthquakes in the area, such as the AD 1169, 1693 and 1908 events (Fig. 2). Sediment composition deduced by mineralogical analysis and SEM observations unravel the source region of the different turbidite beds and identify the links between sedimentary or tectonic preconditioning factors and the occurrence of the catastrophic event (Polonia et al. , 2013a). The surveying techniques and approaches used in this study have therefore the potential of documenting earthquake ruptures of fault segments, extending the earthquake record far before the known history. Moreover, the regional analysis of sediment samples is useful to understand if the recurrence time of major catastrophic events is constant and which portions of the Calabrian Arc have experienced great earthquakes in the past thus improving hazard evaluations and the fundamental understanding of earthquake process in this highly populated region of the central Mediterranean. The recurrence of mass-flow units within sapropel S1, an organic carbon-rich lower Holocene marker bed in the Eastern Mediterranean Sea, was used to reconstruct seismicity back in time (6000-10000 yrs BP) in the Calabria offshore (Fig. 1). Nine turbidite beds interrupt anoxic conditions during the deposition of sapropel S1 (Fig. 3). Turbidite structure and composition, as well as comparison with historical seismoturbidites, suggest a seismic triggering for such mass flows events. The pelagic units bracketing turbidite beds were radiometrically dated and age modelling provided the emplacement age of each turbidite. In this way, we compiled a catalogue of mass flow events during sapropel S1 deposition, a time span long enough to include several earthquake cycles and allow reliable seismic and tsunami hazard assessment in this area. Our results are in good agreement with paleoseismological studies onland (Galli et Fig. 3 – Age model for core CALA 21 in the eastern Ionian Sea offshore Calabria. Left side: photograph and stratigraphic log from the base of sapropel S1 to the core top. Right side: age of turbidite beds within sapropel S1 calculated using: thickness of sapropel sub-units and average sedimentation rate (column 1); OxCal age modelling (column 2) [modified from Polonia et al. (2015)].