Landslide tsunami vulnerability in the Ligurian Sea: case study of the 1979 October 16 Nice international airport submarine landslide and of identified geological mass failures

The Ligurian sea, at the France–Italy boarder of the Mediterranean Sea, has experienced in the past numerous submarine landslides within its very near continental slope, the continental shelf being very narrow. The most recent occurred on the 1979 October 16 near Nice international airport and generated tsunami waves of order 3 m of amplitude in some specific locations. More ancient landslides are also easily identified through bathymetric surveys of the seafloor. For the 1979 event we propose two distinct tsunamigenic landslides based on identified scars observable on the seafloor. The first one corresponds to the volume Vol1 that slid at the airport (in shallow water) while the second one corresponds to the more substantial volume Vol2 that has been localized at the slope. Former studies indicate that only the combination of the two slides may explain the event. We complement these studies by asserting that when the two slides are taken separately, they already explain a significant (although not a total) part of the event: Vol1 explains partly the tsunami observations in the vicinity of the airport while Vol2 contributes to explain the ones away from the area, in particular at Antibes where the highest wave has been observed. The modelling effort is then extended to evaluate the tsunamigenesis of selected (but representative) former landslides having a clear scar signature. The vulnerability of the area to landslide-triggered tsunami is then proposed to discussion along with possible mechanisms that can be responsible for local wave amplification.