Slope stability along active and passive continental margins: a geotechnical approach

Submarine mass movements are widespread at submarine slopes and play an important role in transporting sediments across the continental slope to the deep basin, as well as potential danger to both offshore infrastructures (e.g., pipeline, cables and platforms) and coastal areas (e.g., slope failure-induced tsunamis). Sliding of the sediments on continental slope takes place when the shear stress within sediments exceeds the shear strength thereby causing slope failure. Slope failures are generally controlled by long-term preconditioning factors (e.g., high sedimentation rate, weak layer and oversteepening) and short-term triggering mechanisms (e.g., earthquake, anthropogenic activity). However, the exact causes for the different slope failure styles are still poorly understood. In summary, this thesis investigates preconditioning factors and triggering mechanisms governing slope instabilities of three distinct submarine landslides areas in passive and active continental margin settings. Geotechnical properties of sediments from undeformed, headwall and deposits present different stress histories and shear strengths (undrained and drained shear strength). Geotechnical results are used for infinite slope stability of undeformed sediments under various conditions (undrained and drained, each static and earthquake conditions) to identify the preconditioning factors and quantify the influence of earthquakes as a key factor in slope failing mechanisms. The three distinct case studies are located at: (1) the passive continental slope of Uruguay and north of Argentina, (2) the low seismic and tectonically active Gela foreland basin, central Mediterranean continental margin, and (3) the moderate seismic and tectonically active back-arc basin, deeper slope of the Ligurian margin, Southern France.