GNGTS 2022 - Atti del 40° Convegno Nazionale

52 GNGTS 2022 Sessione 1.1 HOLOCENE LARGE EARTHQUAKES RECORDED IN THE CALABRIA OFFSHORE SEDIMENTS A. Polonia 1 , E. Colizza 2 , P. Galli 3 , L. Gasperini 1 , D. Insinga 1 , R. Melis 2 1 CNR-ISMAR, Via Gobetti 101, I-40129 Bologna, Italy 2 Dip. di Matematica e Geoscienze, University of Trieste, Trieste, Italy 3 Dipartimento Protezione Civile Nazionale, Rome, Italy The Calabrian Arc (CA) is a subduction and rollback system related to the convergence between Africa and Eurasia plates, which produces uplifting coastal mountains, enhances discharge of sediments on the continental shelf and induces the frequent occurrence of earthquakes. It is populated by seismogenic structures capable of generating earthquakes exceeding Mw 6.7, as those occurred in 1638, 1783, 1905, and 1908. Active deformation is observed onshore and in the submarine accretionary wedge, even though no thrust type earthquake has been reported to date. This occurrence has been interpreted as possibly related to a locked subduction thrust. Despite the very slow present-day plate convergence rate, in fact, subduction may be locally still active in the CA as suggested by GPS measurements of Calabrian motion relative to Apulia that show systematic residuals directed towards the Ionian Sea (D’Agostino et al. , 2008). This suggests active crustal compression and shortening taken up in the accretionary wedge, eventually accommodated by long-term slip on the subduction interface (Polonia et al. , 2011; Bortoluzzi et al. , 2017). Results of multi-scale structural analysis in the CA suggest that the crustal extensional faults onshore, the thrust faults within the accretionary wedge and the lithospheric faults segmenting the plate boundary (Polonia et al. , 2016) are seismogenic features that might be responsible for past historical earthquakes and likely source regions for future events (Galli et al. , 2007; Polonia et al. , 2012). The seismicity of the Calabrian peninsula is one of the strongest of the Mediterranean region, both in terms of maximum magnitude and frequency (at least 25 M>6 earthquakes since 91 BCE between the Messina Strait and the Crati basin; Guidoboni et al. , 2019). Inland paleoseismic trenching permitted to discover some of the seismogenic sources responsible for themajor earthquakes of Calabria, such as those occurred on 5 and 7 February, 1783 (Mw 7 and Mw 6.7, respectively), or the 9 June 1638 (Mw 6.7) (Galli and Bosi, 2002; 2003; Galli and Scionti, 2006). However, beyond sparse and uncertain reports from the 16 th century, our knowledge of the regional seismicity starts with the onset of the 17 th century, when several 5.5 ≤ Mw ≤ 6.8 events struck central and southern Calabria (Scionti et al. , 2006). Paleoseismological studies suggest that the 95% of the seismic moment release in the past millennium occurred between the disruptive earthquakes of March 1638 and those of 1905 and 1908. Considering that the average time-recurrence for characteristic earthquakes on each fault is much longer than the period of completeness of the Calabrian catalogue (Galli, 2020), the seismic catalogues missed most of the ancient twins of the major events which struck Calabria. To reconstruct fault dynamics, it is essential to unravel past seismicity including the analysis of sedimentary events at sea, where high-energy sediment flows due to past earthquakes may have left their signature in the deep-sea environment. In this work, we analyze sediment samples collected in separate and disconnected sedimentary basins offshore Calabria to reconstruct resedimentation processes during the Holocene, and try to integrate inland and submarine information for a better assessment of tectonic activity and seismogenesis. This approach was already tested offshore eastern Sicily wheremajor historical earthquakes triggered the deposition of decimetric thick STs (Polonia et al. , 2013; 2017; 2022). Seismic shaking in the CA, in fact, is often associated with submarine slope failures, tsunamis and deposition of seismo-turbidites, which represent more than 90% of total sedimentation in the deep Mediterranean basins (Polonia et al. , 2017).