Tsunamis can travel across open ocean at up to 500 mph. You could be on a cruise ship out in the middle of the sea and have one go under you and never notice it, because it would only be a foot or two high. It's only when they hit shallow water inshore that they slow down and pile up to great height.
Considering that this one caused devastation 1500 miles away from the earthquake's epicenter, there would've been at least a three-hour time lag before it hit some places. But, I guess that not all earthquakes, even powerful ones, create tsunamis this devastating...any seismologists have an idea?
}:-)4
If a quake of a given magnitude shears the land laterally apart, the tsunami produced is much less bad than if the land shears vertically, which would then require a whole bunch of water flow back downhill to equalize levels. This quake apparently resulted in a seafloor shift of 50 feet vertically.