[Yume-sama]

It would surely be disastrous but we are lucky that the infrastructure in Tokyo has been designed with a major earthquake in mind, as "the big one" has and will always be a major threat.

Many older buildings would likely be destructed, but I would think most modern skyscrapers would be fine.

However, no matter how prepared, and Japan is very prepared, you can never be prepared for something like a tsunami hitting within 10 minutes.

Tsunami has always been more worrisome than an earthquake, for obvious reasons now.