If it is a tsunami & not a giant tidal wave wouldn't the worst occur at the shore & then depending on how much water is displaced, the land inward? If this were the case airports could be put on emergency basis to evacuate. Evacuees would have to abandon luggage (for security/weight concerns). Seaworthy boats could take evacuees several miles out to sea beyond the continental shelf & ride above the surge of water.

I would be uncertain of how far a tsunami of that size would travel inland. There is is a book 'Lucifer's Hammer' by Larry Niven that describes a fictional event like this caused by a meteor fragment which strikes mostly in the ocean. The scenario speculates on the actions taken by various people under the stress of such a catastrophy. It's an entertaining read at the very least.

Tim