GNGTS 2022 - Atti del 40° Convegno Nazionale

54 GNGTS 2022 Sessione 1.1 Turbidite beds are marked by sharp peaks in grain size and magnetic susceptibility and are characterized by varying geochemical composition and foraminifera association including benthic species displaced from diverse bathymetric environments. We identified a total of 20 turbidite beds (T1-T20) deposited during the last 10 kyrs whose thickness vary between few centimetres to 1.5 m. They are generally normally graded. Some of them present multiple textural pulses (sand pulses in the lower part of the turbidite) without hemipelagic sediment in between. The deposition time window of the thickest turbidite T5 is in good correlation with both the CE 365 Crete earthquake and tsunami and/or the twin of the 1783 event that occurred shortly before 374 CE (Galli and Bosi, 2002). Four turbidite beds were emplaced during the last millennia. T1 and T2 deposition time windows suggest a link with two seismic sequences happened in CE 1783 and CE 1638, respectively. The ages of turbidites T3 and T4 are very similar suggesting two events very close in time. They match the age, within the errors intimately related to radiometric dating, of the paleoearthquakes recognized along the Lakes fault dated in the 7 th century CE (Galli et al. , 2007) and the 951 CE earthquake sourced by the Rossano fault (Galli et al. , 2010). The emplacement time of older turbidites (T6-T20) is less constrained relative to the most recent events. However, T8 is compatible with an ancient twin of the 1783 earthquake sourced by the Cittanova fault around 2.9 ka (Galli and Peronace, 2015), while T10 matches the occurrence of the event recorded by the Cirò Marina fault around 3.5 ka (Galli and Piscitelli, 2014). T17, matches another paleo-earthquake generated by the Cittanova fault around 6.2 ka (Galli and Peronace, 2015). T20, likely deposited between 9960-9600 BP and matches the event sourced always by the Cittanova fault around 10 ka (Galli and Peronace, 2015). Within the uncertainties intimately related to the submarine paleoseismological method, the average recurrence time of re-sedimented deposits offshore Calabria is about 500 years but it is not constant in time showing periods of enhanced activity separated by more quiescent intervals. The same trend was found in other regions of the CA where the average recurrence of seismo turbidites is about 500 years but it varies between 100 and 700 years (Polonia et al. , 2015). If we compare the age of seismo-turbidites with trench studies onland it is clear that the number of turbidites is larger in the submarine environment. All sedimentary events deposited during historical times can be correlated with earthquakes onland. However when we go back in time, not all the turbidites are correlated with known events onland. This suggests that fault activity onland needs to be reconstructed in more detail and/or that some of the turbidites are related to the activity of submarine faults, including the subduction thrust. Seismo-turbidites that do not correlate with earthquakes onshore and for which we can suggest a link with subduction activity are major events that can be correlated in different disconnected basins and have large repeat time in the order of ~1 ka. Our results suggest that paleseismology onshore integrated with studies turbidite paleoseismology in confined submarine basins provides a more continuous and complete record of seismically triggered sedimentary events. Site selection plays a fundamental role and further work on gravity cores collected in proximal basins directly fed by single canyon systems and distal basins disconnected by canyons is fundamental to acquire more information on the link between seismo-turbidite generation, sediment source and causative faults. References Bortoluzzi, G. et al. ; 2017. Styles and rates of deformation in the frontal accretionary wedge of the Calabrian Arc (Ionian Sea): controls exerted by the structure of the lower African plate. Ital. J. Geosci. 136, 347–364. D’Agostino, N., Avallone, A., Cheloni, D., D’Anastasio, E., Mantenuto, S., Selvaggi, G.; 2008. Active tectonics of the Adriatic region from GPS and earthquake slip vectors. J. Geophys. Res. 113, B12413. doi:10.1029/2008JB005860.