There's no doubt that tsunamis will wreak havoc on waterfront property and I guess this is a generational awareness issue that will come up every 75 to a 100 years. You can check
here for the latest earthquake info in Japan and see that earthquakes strike several times a day. Fortunately, they are mostly small and not capable of producing tsunamis. There may be some great deals coming up on water-front property near Tokyo! They may be safe enough for your lifetime, depending on age of course. The window of opportunity may be coming soon!