Ship Encounters Japan Tsunami at Sea
 

Fascinating footage of a Japanese Coast Guard vessel encountering the Honshu (Japan) tsunami in deep water on March 11. The vessel was said to be about 5 miles offshore, but I don't know what the depth of the water was at that point. The swells themselves seemed to have shorter wavelengths & periods than I'd expect them to have 5 miles offshore. (The periodicity looks to be about 2 minutes.)

Maybe this water wasn't very deep, & the tsunami was beginning to shoal (when a wave shoals, it frictions along the bottom, slows, & grows in height). Ordinarily, you wouldn't notice the tsunami pass in deep water, so this must be landward of the continental shelf.