Repeated instability of the NW African margin related to buried landslide scarps

The Sahara Slide occurred approximately at 50-59 Ka offshore Western Sahara in a mid-slope setting (1900 m water-depth). The existence of several buried and stacked slide events, seen on high resolution seismic profiles, provide new insights into slide location and triggering mechanisms. Buried slide scarps coincide remarkably with scarps and boundaries of the Sahara Slide, presently exposed on the seafloor. The objectives of this work are to examine the long-term stability of this part of the margin and investigate the triggering mechanism(s) that led to these massive events. Buried slide scarps occur in sediments of Miocene-Pliocene age. Multiple scarps becoming more closely spaced towards a larger scarp that may be the main headwall suggest that most of the buried slides developed as retrogressive slides. The seismic record shows that differential compaction across an area of depression bound by scarps generates compaction hinges (anticlines) leading to oversteepening and possible excess pore pressure. We propose that alignment of ancient and present scarps and vertically stacked slide deposits points towards differential compaction as being a key factor in landslide triggering.