Detailed analysis of a submarine landslide (SAR-27) in the deep basin offshore Algiers (Western Mediterranean)

Abstract

On May 21, 2003 an earthquake with a magnitude of 6.8 (Mw) struck the city of Boumerdes, located on the coast near Algiers, and generated significant gravity flows recognized by numerous submarine cable breaks. In order to investigate a possible offshore imprint of past earthquakes in terms of sediment instabilities, we analyzed one of the numerous escarpments of tectonic origin existing on the Algerian margin. This escarpment, located about 50 km NE offshore Algiers is within water depths between 2, 600-2, 900 m and has an average slope of 4°. A variety of geotechnical (piezocone), geophysical (swath bathymetry, Chirp echo-sounder and high-resolution deep-towed side scan sonar) and sedimentological (sediment cores) techniques were used to realize this work. Our study focuses on a well-defined submarine landslide scar (called SAR27) revealed by side-scan sonar images. The SAR 27 slide is small in size (0.5 × 1.7 km), but exhibits a complex morphology including a 10-m high headwall scar, tilted blocks, an area of reworked sediment and a distal deposit. Correlations between in-situ measurements, sampling and CHIRP profile provided a comprehensive understanding of the slide geometry and emphasized the role of thin silty sand beds in the slide initiation. These silty sand beds are probably acting as liquefied slip surfaces, implying a translational displacement mode which correlates the slide morphology. © Springer Science + Business Media B.V. 2010.