Yes, but I think makmanalp point was that earthquakes of up to 8.9 are not unknown in Japan, and there's also been a 9.5 in the world. Thus it would be reasonable to expect 9+ earthquakes and tsunamis in Japan.
Now, can you make anything withstand that? I am not sure, but I think it is possible. It would make electrical power more expensive but how much would more expensive electricity shave of Japan's GDP? Enough to justify not doing it?
It is also a logarithmic scale.
Furthermore, as with Richter,
> This means that a Richter magnitude of 9 has a 10 time bigger shaking amplitude than Richter magnitude 8
Yes, and a bit above 30 times the energy released (2 magnitudes indicate a thousandfold increase in energy)