Modeling of Tsunamis Induced by Landslides: Application in the Bay of Biscay.

Abstract:

Tsunami hazard in metropolitan France is poorly known. The TANDEM (Tsunamis in northern AtlaNtic : Definition of Effects by Modeling) project is a French initiative to draw lessons from the 2011 catastrophic tsunami in Japan on French coastlines, in order to provide guidance for risk assessment on the nuclear facilities in the area.

This project is aimed at adapting numerical methods of tsunami hazard assessment against the outstanding observation database of the 2011 tsunami, in order to apply these validated methods to the definition of the tsunami hazard for the French Atlantic and Channel coastlines.

As part of the TANDEM project, this work focuses on tsunami induced by landslides, and uses the CEA's model named AVALANCHE that can model simultaneously model a landslide and the resulting tsunami. AVALANCHE assumes that the landslide has a fluid-like behavior and applies shallow water/thin layer approximations to both aspect. The similarity of the resulting equations of momentum and mass conservation enables to use a single numerical scheme for both parts of the model.

The model is being submitted to several benchmarks to compare its response to analytical or experimental results. The first case compares the simulation result to the analytical result obtain by a fixed slide movement in one dimension and introduces the importance of the shallow water assumption in our results. The second case consists in the modeling of a wedge going down a slope and is compared to experimental results.

The last part of this work focuses on the continental slope of the Bay of Biscay off the South of France (NE Atlantic ocean). The slope presents scars left by large scale landslides. Investigation is carried out to identify the scenarios that could have caused paleo-tsunamis, with a special interest on the large scar of the Cap Breton (~100 millions m3). Several scenarios in this area are tested using the AVANLANCHE method in order to determine the potential threat.