There is (or should be) ample data mapping the continental rise and continental shelf off the eastern US. From what I've read, the shelf reaches out for a considerable distance from the shoreline. I remember reading about an Air Force radar site (Texas Tower #4) built in the 1950s on a converted oil platform. The site was over 100 miles from the shore and the water there was less than 200 feet deep. In several areas, it's less than 100 feet deep.

It wouldn't surprise me if someone has already modeled this, but I've never seen the results. If the rise is very gradual and extends for a long distance, then it seems reasonable to believe that an incoming tsunami wave might actually lose energy the longer it travels along the shallow slope. When a tsunami moves from deep water to shallow, the leading edge slows faster than the rear of the wave, causing it to rise in amplitude. What I'm wondering is what happens if the rise continues over a long distance. It's possible the wave just keeps getting bigger as the water gets shallower, but if there's significant friction with the ocean floor, wouldn't that cause the wave to lose some energy?