Tsunamis Triggered by Submarine Landslides in the NE Atlantic: Evidences of Mass Failures and Numerical Modeling

Abstract:

Tsunamis caused by submarine mass failures constitute a widely recognized source of natural hazard. However, in the NE Atlantic the tsunami hazard posed by landslides remains poorly studied.

In this study, we attempt to contribute to a better understanding of the tsunami hazard of landslides origin. We investigate the tsunami hazard posed by deepwater submarine landslide failures in the Gorringe Bank (GB) area, NE Atlantic. This investigation requires detailed marine geological data and a robust numerical model to simulate both the mass failure flow and the subsequent tsunami.

The analysis of both swath-bathymetric data and the multichannel seismic profiles revealed evidences of the presence of at least three large deepwater mass failures in the GB area of possible tsunamigenic potential. It also allows defining the geomorphologic characteristics of the identified submarine landslides, which include the erosional area (dimensions, scarps) and the depositional area (sediments extent, volume). Some depositional volumes reach ~80km³.

To simulate the flow of the mudslide failure and the wave induced by the seafloor motion we employ a multi-layers viscous shallow-water (VSW) model. The lower layer represents the slide assumed to be a viscous-incompressible fluid, and characterized by sediments density, and kinematic viscosity. It is bounded by the upper layer consisting of seawater assumed to be inviscid and incompressible. We solve the VSW equations in a finite-difference scheme considering a “two-way” coupling approach.

The results are presented in terms of: i) evidences of submarine mass failures in the area of GB; ii) simulations of seafloor motion due to the occurrence slides failures; ii) simulations of tsunami generation induced by the submarine landslide flow; and iii) simulations of tsunami propagation and coastal impact. Results show that, using the VSW model, we are able to reliably reproduce the sediment deposit induced by slide failures. In some cases, the resulting initial tsunami wave reaches ~10m. We find that deepwater mudslides in the GB area have a significant potential of tsunami generation in the NE Atlantic region with a possible impact along the near-coasts.

This work is supported by the FCT project CONDRIBER, Ref. PTDC/GEO-GEO/4430/2012.