The BIG 1995 Submarine Landslide-Generated Tsunami: A Numerical Simulation

This article presents a reasonable present-day, sea-level highstand numerical simulation and scenario for a potential tsunami generated by a landslide with the characteristics of the BIG'95 debris flow, which occurred on the Ebro margin in the western Mediterranean Sea in prehistoric times (11,500 cal yr BP). The submarine landslide deposit covers an area of 2200 km2 of the slope and base of slope (200-1800-m water depth), involving a volume of 26 km3. A leapfrog finite difference model, COMCOT (Cornell multigrid coupled tsunami model), is used to simulate the propagation of the debris-flow-generated tsunami and its associated impact on the nearby Balearic Islands and Iberian coastlines. As a requisite of the model, reconstruction of the bathymetry before the landslide occurrence and seafloor variation during landsliding have been developed based on the conceptual and numerical model of Lastras et al. (2005). We have also taken into account all available multibeam bathymetry of the area and high-resolution seismic profiles of the debris flow deposit. The results of the numerical simulation are displayed using plots of snapshots at consecutive times, marigrams of synthetic stations, maximum amplitude plots, and spectral analyses. The obtained outputs show that the nearest shoreline, the Iberian coast, would not be the first one hit by the tsunami. The eastward, outgoing wave would arrive at Eivissa Island 18 min after the triggering of the slide and at Mallorca Island 9 min later, whereas the westward-spreading wave would hit the Iberian Peninsula 54 min after the slide was triggered. This noticeable delay in the arrival times at the peninsula is produced by the asymmetric bathymetry of the Catalano-Balearic Sea and the shoaling effect due to the presence of the wide Ebro continental shelf, which in addition significantly amplifies the tsunami wave (9 m). The wave amplitudes attain 8 m in Eivissa, and waves up to 3 m high would arrive to Palma Bay. Resonance effects produced in the narrow Santa Ponca Bay in Mallorca Island could produce waves up to 9 m high. A similar event occurring today would have catastrophic consequences, especially in summer when human use of these tourist coasts increases significantly.