Understanding Extreme Geohazards: The Science of the Disaster Risk Management Cycle European Science Foundation Conference November 28 to December 1, 2011, Sant Feliu de Guixols, Spain

Tsunamis Caused by Submarine Landslides

Carl B. Harbitz
Norwegian Geotechnical Institute/International Centre for Geohazards, Oslo, Norway

It is now generally accepted that submarine landslides may represent the source of large tsunamis, while the earthquakes play an indirect role as the landslide triggering mechanism. Risk assessment of tsunamis generated by submarine landslides includes both geotechnical and geological considerations for the probability and the tsunamigenic power of the landslide, as well as tsunami inundation and vulnerability evaluations for determination of the consequences.

As most deepwater petroleum resources are located in continental slope settings, seafloor instability is a major concern (despite the fact that other geohazards, such as shallow gas, gas hydrates, and mud volcanism also must be assessed). As the slope angles of continental margins in general are small, the most important factors controlling slope stability (excluding the triggering mechanisms) are sediment types (including weak layers) and the presence of excess pore pressure. Both are functions of the geological setting and the depositional regime and history. High and variable sedimentation rate is probably the most important factor generating excess pore pressures. The sediment type controls also the rheology and thus the dynamics (transport mechanisms and flow regime) of the landslide.

Landslide parameters such as volume, acceleration, maximum velocity, and possible retrogressive behaviour are of key importance for the tsunami characteristics and may in addition be applied in the probability assessment for hazard and risk analyses. Also the landslide location (i.e. sea depth, distance from shore, and travelling direction) influences upon the wave field. Landslide tsunami characteristics are further illustrated by comparisons to tsunamis from other sources.m Examples of landslide tsunami sources and landslide tsunami hazard assessments for various regions will be presented.

Challenges in numerical modelling are related to range and validity of models for the huge dimensions and the long run-out distances of the landslides. Also the optimal coupling and the application of a diversity of hydrodynamic models for landslide dynamics, tsunami generation by landslide/water interaction, propagation, and run-up of tsunamis in huge and complex domains must be aspired to.