Improved landslide-tsunami prediction: Effects of block model parameters and slide model

Subaerial landslide-tsunamis and impulse waves are caused by mass movements impacting into a water body, and the hazards they pose have to be reliably assessed. Empirical equations developed with physical Froude model studies can be an efficient method for such predictions. The present study improves this methodology and addresses two significant shortcomings in detail for the first time: these are the effect of three commonly ignored block model parameters and whether the slide is represented by a rigid block or a deformable granular material. A total of 144 block slide tests were conducted in a wave flume under systematic variation of three important block model parameters, the slide Froude number, the relative slide thickness, and the relative slide mass. Empirical equations for the maximum wave amplitude, height, and period as well as their evolution with propagation distance are derived. For most wave parameters, remarkably small data scatter is achieved. The combined influence of the three block model parameters affects the wave amplitude and wave height by up to a factor of two. The newly derived equations for block slides are then related to published equations for granular slides. This comparison reveals that block slides do not necessarily generate larger waves than granular slides, as often argued in the technical literature. In fact, it is shown that they may also generate significant smaller waves. The new findings can readily be integrated in existing hazard assessment methodologies, and they explain a large part of the discrepancy between previously published data.