Analysis of submarine slumping in the Gabon continental slope

Abstract

The Gabon continental slope is selected as a case study for slope-stability analysis because of evidence of previous slide activities. Different types of data were collected from the continental slope in the Gulf of Guinea off west Africa during Guiness and ZaiAngo surveys. The offshore investigation was carried out using swath bathymetry and associated imagery, deep-towed high-resolution subbottom profiles, side-scan sonar images, observation from remotely operated vehicle Victor, and Kullenberg cores. These data reveal different examples of seafloor instabilities commonly related to fluid-escape features. These slides occur on the continental slope at low declivities, showing that slope gradient has a secondary role on the marine slope instability with respect to external triggering mechanisms such as fluid flow, earthquake, shallow gas, and gas hydrates. One case of mass slide with small downslope displacement was studied on the Gabon slope.In this work, a pseudothree-dimensional slope-stability analysis (Sultan et al., 2001) was undertaken. Three scenarios of instability were tested to identify the possible trigger mechanism of the observed slide instability: (1) under static gravity loading, (2) under earthquakes, and (3) under upward fluid flow. Simulation results show that static stability of the area is satisfactory. However, the stability is very sensitive to fluid escape. These results agree with sonar images showing seepage features aligned along the upslope limit of the observed slide.