GNGTS 2015 - Atti del 34° Convegno Nazionale

62 GNGTS 2015 S essione 1.1 (i.e. the Calabrian and the Hellenic Arcs). It is one of the most seismically active regions in the Mediterranean Sea and has been struck repeatedly by destructive historical earthquakes, often associated with tsunamis. Slab tearing in a pre-collisional setting is reflected in dynamic topography with high uplift rates of the coastal mountain belts, accompanied with a great sediment discharge to the continental margins. This increases the susceptibility to mass failures implying a strong interplay between active tectonics, seismic shaking, mass flows and tsunami generation. We investigated the effects of historic earthquakes on abyssal marine sedimentation through the analysis of the turbidite record in tectonically controlled basins. Holocene resedimented units in the deep Ionian Sea represent more than 90% of the total thickness of the sedimentary record. We dated the most recent turbidite sequences using different radiometric methods and the results suggest that turbidite emplacement was triggered by major historic earthquakes and tsunamis recorded in the region (i.e. AD 365 Crete and AD 1169, 1693 and 1908 Italian earthquakes). Textural, micropaleontological, geochemical and mineralogical signatures reveal that turbidite beds are stacked sandy units, which have different compositions suggesting coeval multiple failures. They are characterized by organic-rich sandy layers, containing a mixture of lithic clasts, plant fragments and displaced benthic foraminifera derived from several sources and bathymetric ranges. Structure and composition of each turbidite unit, combined with geochemical and isotopic analysis on organic carbon, are being refined to unravel the relative contribution of seismic shaking and tsunami wave loading on mass flow processes generation. Average recurrence of seismoturbidites within sapropel S1, deduced considering chronology and number of turbidites, is about 500 yrs, and appears to be constant also before and after its deposition. This is in good agreement with the average frequency of major earthquakes in Calabria during historical time. However, age modelling performed on the entire sequence suggests that recurrence time is not constant, but rather it varies between 100 and 700 yrs. These findings enable us to extend back in time the paleoseismic catalogue of major seismic events in the CalabrianArc during a time span of about 10.000 yrs. Turbidites may be considered as the sedimentary earthquake code within the background pelagic sedimentation. Deciphering this code aims at reconstructing paleo-seismicity during several earthquake cycles, a time span long enough to perform reliable seismic and tsunami hazard assessment in tectonically active coastal regions. References Billi A., R. Funiciello, Minelli L., Faccenna C., Neri G., Orecchio B., and Presti D., 2009. Reply to comment by Andrea Argnani et al. on ‘‘On the cause of the 1908 Messina tsunami, southern Italy’’ . Geophysical Research Letters, 36, L13308. doi:10.1029/2009GL037499. Hieke W., 1984, Thick Holocene homogenite from the Ionian abyssal plain (Eastern Mediterranean) : Marine Geology, v. 55, p. 63–78. Kastens K.A., and Cita M.B., 1981, Tsunami-induced sediment transport in the abyssal Mediterranean Sea : Geological Society of America Bulletin, v. 92, p. 845–857. Favalli M., Boschi E., Mazzarini F., Pareschi M.T., 2009. Seismic and landslide source of the 1908 Straits of Messina tsunami (Sicily, Italy). Geophysical Research Letters 36 :. L16304. doi:10.1029/2009GL039135. GalliP.,BosiV.;2003. Catastrophic1638earthquakesinCalabria(southernItaly):newinsightsfrompaleoseismological investigation . Journal of Geophysical Research 108, B1. http://dx.doi.org/10.1029/2001JB001713. Galli P., Galadini F., Pantosti D.; 2008. Twenty years of paleoseismology in Italy , Earth Sciences Reviews, 88, 89-117, doi:10.1016/j.earscirev.2008.01.001. Galli P., Peronace E.; 2015. Low slip rates and multimillennial return times for Mw 7 earthquake faults in Southern Calabria (Italy) . ����������� �������� �������� ��� ���� ��������������������� Geophysical Research Letters, 42, doi: 10.1002/2015GL064062. Loperfido, A.: 1909. Livellazione geometrica di precisione eseguita dall’IGMI sulla costa orientale della Sicilia, da Messina a Catania, a Gesso ed a Faro Peloro e sulla costa occidentale della Calabria da Gioia Tauro a Melito di Porto Salvo . C.R. Accademia Naz. Lincei, 35, 131-155. Okal, E.A., Synolakis C.E., 2004. Source discriminants for near-field tsunamis . ����������� ������� ������������� Geophysical Journal International 158, 899–912.