Episodic movement of a submarine landslide complex driven by dynamic loading during earthquakes

Although subaqueous slopes on active continental margins are subject to a variety of failure styles, their movement mechanisms during earthquakes remain poorly constrained. A primary explanation is that few submarine landslides have been directly sampled for detailed investigation. We have conducted a series of dynamic shear experiments on samples recovered from the base of the Tuaheni Landslide Complex, located off the east coast of the North Island of New Zealand, to explore its behaviour during earthquakes. Our experiments suggest that whilst the basal landslide sediments can be prone to liquefaction in certain conditions, this is not a likely failure mechanism at the stress states operating in the low angled shear zone at the base of this landslide system. Instead, episodic landslide movement can occur through basal sliding when pore water pressures increase sufficiently to lower the shear zone effective stress to the material failure envelope. These low effective stress conditions are most likely to be reached during earthquakes that produce large amplitude, long duration ground shaking. The observed behaviour provides a credible mechanism through which subaqueous landslides moving on low angled shear zones in similar materials may be subject to episodic movement during earthquakes without undergoing catastrophic failure.