How fast does a tidal wave travel?
It depends on the depth. On deep oceans it can hit 500 mph. Near
the land it slows down to 20 or 30 mph.
It is important to note that the 500 mph is simply a theory,
there is no method to truly measure the speed of the wave. Also, if
you follow the above link it explains that when the tsunami
approaches any land it slows to 20-30 mph. This would even further
refute the 500 mph.