GNGTS 2022 - Atti del 40° Convegno Nazionale

424 GNGTS 2022 Sessione 3.2 displays discontinuously bedded high-amplitude seismic reflectors with acoustic blanking zones suggesting fluid migration in the sediments. The H echo-facies shows a high-amplitude bottom echo with irregular hyperbolae with variable elevation of their vertex and no sub- bottom seismic reflectors. We suppose it is related to landslide deposits. The T echo-facies comprises a high-amplitude bottom echo followed by sub-parallel sub-bottom echoes that contain transparent lenticular bodies we infer relate to debris flow deposits. Fig. 1 - Four acoustic facies were identified on sub-bottom profiles. The G facies (a), B (b), T (c) and H (d) and their distribution along the study area. Sub-bottom data allowed us to identify 4 relict pockmarks (on the continental shelf and slope), three main unconformities, polygonal faults, gas charged sediments and unstratified deposits. The unconformities mapped are low-angle and present on the continental shelf and slope. From the seabed down, the A1 unconformity is an erosive unconformity that correspond to the LGM episode and covers all the slide scarps. The U2 unconformity represents the glide plane for the inferred slope failures as aweak layer in the sedimentary column and extends from the headwall to the frontal ramp of the mapped slope failures (Fig. 2). The U3 unconformity is the basal glide plane of a failure that occurred before those interested by the U2 unconformity and mapped on the seabed, located on the lower part of the continental slope. Triggers for slope failure. Excess pore-pressure has been suggested as a triggering mechanism of the multiple slope failure as a response to climatic cyclicity. It is known that upwards migrating fluids increase pore pressures within marine clays (Bunz et al., 2005) which leads to a decrease in frictional resistance to sliding (Masson et al., 2006). According to the Videpi wells present in the study area, clays are the lithology that occur along the margin. The overpressure that acts oppositely to the lithostatic pressure makes sediments extremely weak (Bunz et al., 2005). Weak layers that correspond to the U2 and U3 unconformity, could also be