Massive landslides can generate large tsunamis and endanger human lives and properties. While a number of laboratory experiments on either subaerial or submarine landslide-tsunamis have been conducted, few studies have focused on partially submerged events. The present study aimed to investigate the characteristics of partially submerged landslide-tsunamis and to develop a predictive equation that can estimate their heights through three-dimensional laboratory experiments that used 114 different conditions. The experimental results showed that, while waves generated in the landslide sliding direction had around 1.7 times higher amplitude than those propagating laterally in the near-field region, the wave period, celerity, and wavelength did not alter significantly according to the propagation angles. The effects of wave dispersion were also shown to be significant during the propagation process. Such wave characteristics were consistent with those reported in existing subaerial landslide tsunami experiments conducted by other researchers. Based on the data set obtained, the authors also derived a predictive equation which was confirmed to be able to estimate the results of other experimental studies on partially submerged landslide-tsunamis with an error of around ±30%, and thus can be helpful for a rapid tsunami hazard assessment. The developed equation indicated that the volume of a landslide could have more than twice the impact on the height of a partially submerged landslide-tsunami than other parameters. The effects of the landslide size were also shown to be more significant than in the case of a subaerial landslide-tsunami, though the wave attenuation process was similar in both types.
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