GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 3.2 423 QUATERNARY SLOPE INSTABILITY OFFSHORE SOUTHERN CALABRIA: INSIGHTS ON POSSIBLE TRIGGERING MECHANISMS N. Markezic¹, S. Ceramicola¹, L. Baradello¹, G. Brancatelli¹, D. Morelli², E. Colizza³ 1 Istituto Nazionale di Oceanografia e di Geofisica Sperimentale – OGS, Trieste, Italy 2 Università degli Studi di Genova – DISTAV, Genova, Italy 3 Università degli Studi di Trieste – DISGAM, Trieste, Italy Introduction. Submarine landslides are considered one of the most damaging geohazards to coastal population and infrastructures, and they frequently interest areas where submarine canyons incise continental margins. With the increased requirement of coastal geohazard assessment, seabed mapping and near seabed investigation become important prerequisite to reconstruct submarine failure and triggering mechanisms. The seabed morphology of the Ionian Margin of Calabria, a tectonically active margin, has been a matter of interest in the frame of the Italian projects MaGIC (Marine Geohazards along the Italian Coasts) and RITMARE (La Ricerca Italiana per il Mare). Numerous slide scars indicative of slope failures have been revealed by means of seabed mapping integrated with sub-bottom profile interpretation (Ceramicola et al., 2014; Ceramicola et al., 2014b; Morelli et al., 2011). We here present an analysis of the possible triggering mechanism of slope failure that acted and influenced the stability of the seafloor, during the Quaternary evolution of the Assi slide in southern Calabria. Geological setting. The Assi slide lies on the seabed of a forearc basin generated during the SE migration of the Calabrian arc since the Middle Miocene (Van Dijk, 1992; Roda et al., 1964). The SE migration has slowed during the last 10 Ma (Mattei et al., 2007) when a rapid uplift of onshore areas initiated (Westaway, 1993; Van Dijk 1992) steepening the slope offshore southern Calabria. This area is highly affected by canyon incisions remarkably close to the coastline, which are crucial in sediment transport from coastal areas into deep-water. In fact, the continental slope is eroded by several scarps that indicate recurrent and retrogressive slope failures. The Assi slide is located between the Siderno canyon system and the Assi canyon (Fig. 2). Data. The geophysical datasets were acquired during three research campaigns: MESC (funded by the OGS and organized in collaboration with the University of Trieste, in 2005), MAGIC (funded by the Italian Civil Protection with the OGS, from 2005 to 2009) and GSGT15 (funded by MIUR in the framework of the project RITMARE, in 2015). Swath bathymetric data were acquired with Reason Seabat 8111 (100 kHz) and 8150 (12 kHz) for the creation of DTMs with a 10x10, 20x20 and 50x50 grid size. The sub-bottom profiler used is the Benthos Chirp II. Among these data, the ViDepi wells LUCIANA_001 e LUISA_001 were used to calibrate where possible the sub-bottom data. Seabed mapping and acoustic facies mapping. Morphobathymetric data revealed numerous scarps on the continental slope in a depth range that goes from – 200 m to -950 m, as well as concave upwards and convex downwards morphological profiles indicating deposits and voids created by the failures. The slide scarps follow the slope dip orientation which is approximately 2°. The scarps located on the upper part of the continental slope are smaller but more arcuate, while those situated on the lower portion of the continental slope exhibit a larger lateral extension and height (Fig. 1). Four acoustic facies were identified on the sub-bottom profiles: B, G, H and T (Fig. 1). The B echo-facies identifies a distinct bottom echo and an alternation of high-amplitude seismic reflectors and acoustic blanking levels in sub-bottom echoes. We infer these facies is related to hemipelagic or low-turbidite sedimentation with high-energetic processes. The G echo-facies