[Godzilla]

I had no idea that tsumani waves could last that long.

First, tsumani waves are long period, not short period like normal waves. The wave just keeps rising after the front part of the wave crashes in. Longer warning periods deal with reflections of the wave from across the basin.

[Velveeta]

Thanks, Zilla. Growing up in Chicago, I never gave tsunamis much thought. Love the things I learn here at FR. ;-)