Geotechnical profiling of deep-ocean sediments at the AFEN submarine slide complex

<p> The Atlantic Frontier Environmental Network (AFEN) submarine slide complex is located 95 km NW of the Shetland Islands, at a water depth of c. 1000 m. It is thought to have occurred some 2800 years ago. The slide complex is c. 4 km wide and 13 km in length, and lies on a shallow slope, between 0.7 and 2.5\textdegree. Previous sampling and laboratory testing of the very soft sediment has been limited, and did not penetrate the basal failure surface, nor the underlying sediments. This paper presents the first intensive geotechnical profiling of deep-sea sediments from the AFEN slide complex, carried out on core obtained during the July 2014 expedition of the R.V. Pelagia. Importantly, this core sampled through, and below, the failure surface of the AFEN slide, and was subjected to unusually closely spaced geotechnical testing using a range of index and classification testing techniques. These are shown to have great value, when taken together with standard sedimentological logging, in establishing ground profiles. From these data new mechanisms of triggering the long runout slope failure at AFEN are postulated, and explain how submarine slides here and elsewhere can have occurred on very shallow slopes, of the order of 1 \textendash 2\textdegree.</p>