Submarine landslides of the upper east Australian continental margin

Abstract

Stable continental margins experience submarine landslides relatively frequently and some of the largest slides on record have been shed from these relatively passive terrains. Despite this, and the obvious accompanying tsunami hazard, slides from passive margins such as Australia are poorly understood when compared to other settings, such as the flanks of volcanic islands, active subduction-zone margins and submarine fans. This work presents an investigation into the submarine landslides occurring along east Australia’s (EA) continental margin, with a focus on investigating the causes, timing, and mechanisms responsible for these features. It has focused on analysing gravity core samples and interpreting of high-resolution multibeam and subbottom profiles. The age, morphology, composition, and origin of particular submarine landslides on the EA continental margin offshore New South Wales/Queensland has been described and the mechanical characteristics of sediments from the EA continental slope has been presented. The hazard posed by these submarine landslides has also been evaluated by investigating their potential to generate tsunamis along this margin. The widespread occurrence of slides across the EA margin indicates that submarine sliding should be considered to be a common characteristic of this margin. Engineering properties imply that the sediment forming the margin is reasonably strong and inherently stable and classical limit-equilibrium modeling indicates that submarine landslides should not be a common occurrence. This indicates that a pre-conditioning trigger, or some other mechanism, is required to destabilise the slope and enable failure. The most likely suspected processes include: 1) dramatic reduction of the shear strength of the sediments to extremely low values; 2) long-term modification of the slope-geometry; and/or 3) seismic events large enough to trigger sediment liquefaction or a sudden increase of pore-fluid pressure.