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Identification of catastrophic events recorded as resedimented deep marine deposits can be challenging because of multiple possible triggering mechanisms. This study investigates seismo-turbidites (STs) deposited in the Ionian Sea as a consequence of major historical earthquakes related to the Calabrian Arc subduction system. Taking advantage of the available sedimentological reconstructions, we focused our analysis on high-resolution X-ray fluorescence core scanner (XRF-CS), organic carbon and isotopic data to define geochemical signatures characterizing the ST units. The relationships between geochemical and sedimentological proxies were statistically tested using Pearson correlation and principal component analysis (PCA). Up to ∼78% of the total variance in the data set can be reduced to three principal components which identified four elemental ratio groups associated to the degree of terrestrial/coastal influence in each major depositional unit (i.e., pelagic, ST sandy stacked units, homogenites, tsunamite-seiche laminites, and tsunamite backwash). The sample score results were evaluated together with organic carbon data in order to assess geochemical variability throughout the composite turbidite structure in different basins settings. The basal parts of the ST contain coarse-grained sediment stacks whose sources can be traced back and sedimentary processes (surficial sediment erosion/massive slope failures) can be defined using geochemical data. The topmost parts of the STs exhibit a mixed compositional character suggesting basin-wide processes such as seiche oscillations and tsunami wave erosion/backwashing. The application of selected XRF-CS based elemental ratios as proxies in paleoseismological studies can help reconstruct the seismic history of a continental margin.

The Calabrian Arc is a narrow subduction-rollback system resulting from Africa/Eurasia plate convergence. While crustal shortening is taken up in the accretionary wedge, transtensive deformation accounts for margin segmentation along transverse lithospheric faults. One of these structures is the NNW-SSE transtensive fault system connecting the Alfeo seamount and the Etna volcano (Alfeo-Etna Fault, AEF). A second, NW-SE crustal discontinuity, the Ionian Fault (IF), separates two lobes of the CA subduction complex (Western and Eastern Lobes) and impinges on the Sicilian coasts south of the Messina Straits.Analysis of multichannel seismic reflection profiles shows that: 1) the IF and the AEF are transfer crustal tectonic features bounding a complex deformation zone, which produces the downthrown of the Western lobe along a set of transtensive fault strands; 2) during Pleistocene times, transtensive faulting reactivated structural boundaries inherited from the Mesozoic Tethyan domain which acted as thrust faults during the Messinian and Pliocene; and 3) the IF and the AEF, and locally the Malta escarpment, accommodate a recent tectonic event coeval and possibly linked to the Mt. Etna formation.Regional geodynamic models show that, whereas AEF and IF are neighboring fault systems, their individual roles are different. Faulting primarily resulting from the ESE retreat of the Ionian slab is expressed in the northwestern part of the IF. The AEF, on the other hand, is part of the overall dextral shear deformation, resulting from differences in Africa-Eurasia motion between the western and eastern sectors of the Tyrrhenian margin of northern Sicily, and accommodating diverging motions in the adjacent compartments, which results in rifting processes within the Western Lobe of the Calabrian Arc accretionary wedge. As such, it is primarily associated with Africa-Eurasia relative motion.

Probabilistic seismic hazard analysis (PSHA) are performed for routine applications using source models and ground motion prediction equations (GMPEs) recommended by a government agency (e.g., US Geological Survey) or an expert panel (e.g., SHARE project). For important projects, site-specific PSHA involves critical analysis of GMPEs and sources for the application region. We adopt the latter approach for a dam site in Calabria (southern Italy), a high seismic hazard region. Following SHARE convention, we consider faults sources, background zones, and area sources. We identify several problems with assigned maximum magnitudes in the SHARE model for fault and in-slab subduction sources. We add two sources not present in some prior inventories – the crustal Lakes fault and the Calabrian arc subduction interface. Following procedures developed for the Global Earthquake Model, we select GMPEs that are much better constrained in the hazard-controlling range of magnitudes and distances than those typically used in prior Italian applications. Short-period spectral accelerations at the 2475 year return period exceed those from prior SHARE studies by about 10-15%. Despite the site being located in a region with finite faults capable of generating large events, the 2475-year hazard is dominated by source zones that allow for earthquakes directly beneath the site.

Probabilistic seismic hazard analysis (PSHA) are performed for routine applications using source models and ground motion prediction equations (GMPEs) recommended by a government agency (e.g., US Geological Survey) or an expert panel (e.g., SHARE project). For important projects, site-specific PSHA involves critical analysis of GMPEs and sources for the application region. We adopt the latter approach for a dam site in Calabria (southern Italy), a high seismic hazard region. Following SHARE convention, we consider faults sources, background zones, and area sources. We identify several problems with assigned maximum magnitudes in the SHARE model for fault and in-slab subduction sources. We add two sources not present in some prior inventories – the crustal Lakes fault and the Calabrian arc subduction interface. Following procedures developed for the Global Earthquake Model, we select GMPEs that are much better constrained in the hazard-controlling range of magnitudes and distances than those typically used in prior Italian applications. Short-period spectral accelerations at the 2475 year return period exceed those from prior SHARE studies by about 10-15%. Despite the site being located in a region with finite faults capable of generating large events, the 2475-year hazard is dominated by source zones that allow for earthquakes directly beneath the site.