I have heard the suggestion that people in these areas might want to keep a hot air balloon stored in the garage. Probably even better than a high rise. Or you take your chances.
Plausible. There was a recent study which tried to debunk the threat, but I think the numbers are a fair estimate.
The Hawaiian islands have a geological history of volcanic flank collapse creating a tsunami. The Australian coastline has indications of debris deposited above 1100 foot above sea level attributed to such an episode.