Submarine Landslides and Gas Hydrates: Using a Rate and State Friction Model to Describe Incipient Motion Triggered by the Dissociation of High Saturation Hydrate Anomalies

Abstract:

The dissociation of gas hydrates along the continental shelf can potentially trigger submarine landslides. The hazard produced by such landslides can generate tsunamis, damage or destroy infrastructure, and result in a catastrophic release of methane to the ocean and atmosphere. Here we develop a 1D numerical model to identify the conditions under which the dissociation of gas hydrates can trigger submarine landslides. In particular we focus on high saturation hydrate anomalies (e.g., lenses and nodules) that unload the sediment particle contacts and prevent normal consolidation. These areas are of interest because upon dissociation they can generate excess pore pressure from rapid consolidation and from fluid flow due to changes in the averaged density of pore constituents. Our model tracks the evolution of pore pressure and effective stress as the hydrate anomalies decay using lab derived constitutive relationships from consolidation experiments. To quantify the potential for slope failure, we use a rate- and state-dependent frictional model adapted from standard fault mechanics treatments to assess the stability of finite slip patches subjected to these excess pore pressures. We find that submarine landslides will occur if the size of the slip patch exceeds a critical nucleation length. Thus, excess pore pressures generated by hydrate dissociation have the potential to trigger submarine landslides, if not significantly weaken the sediment such that external forces (e.g., nearby earthquakes) can trigger failure. Our results illustrate the fundamental mechanisms through which the dissociation of gas hydrates can pose a significant geohazard. Further tests using this model will help to better assess the risks of hydrate-triggered slope failure in a changing environment