Engineers Australia

Landslide geomorphology along the Exmouth Plateau continental margin, North West Shelf, Australia

J.V. Hengesh, J.K. Dirstein and A.J. Stanley

Abstract

3D exploration seismic data were interpreted to investigate the locations and characteristics of submarine slope failures along the continental slope in the offshore Carnarvon Basin on Australia’s North West Shelf. Seisnetics™, a patented genetic algorithm was used to process the 3D seismic data to extract virtually all peak and trough surfaces in an unbiased and automated manner. The extracted surfaces were combined in a 3D visual database to develop a seafloor digital terrain model that extends from the continental slope to the Exmouth Plateau. The 3D data were used to map the subsurface extent and geometry of landslide failure planes, as well as to estimate the thickness and volumes of slide deposits. This paper describes the geomorphic characteristics of six of the survey areas.

Geomorphic mapping shows the presence of slope failures ranging from small (<3 km across) to moderate (<10 km across) scale debris flows, rotational block failures, translational slides and topple failures, as well as large scale (>20 km across) mass transport complexes (MTC). The features are associated with debris flow chutes, turbidity flow channels, and debris fields. Analysis of failure planes show prominent grooves or striations related to the mobilization of slide material down both the continental slope and Exmouth Plateau and into the Kangaroo Syncline.

Submarine slope failures can occur at the continental shelf break in approximately 200 m to 300 m of water and run out to the Exmouth Plateau surface in approximately 1,100 m to 1,400 m water depths. The largest individual slides in the survey areas have widths of >30 km and minimum run-out lengths of 75 km, though associated turbidity flow deposits likely extend much further. The subsurface expression of the large MTCs illustrates a history of sediment accumulation along the mid-slope followed by repeated slope failure and debris run-out.

Sediment accumulation and slope failure processes are actively occurring along the continental slope and submarine landslides thus are a major driver of hazard to subsea infrastructure development. Smaller slides seem to occur more frequently than large slides and thus may pose a greater hazard to subsea infrastructure than large infrequent MTCs.