[seanflyon]

> the tsunami it experienced was accepted by the best engineering data at the time to be impossible.

I find that hard to believe. It was the 4th largest earthquake in the last century and doesn't make the Wikipedia list of "Megatsunamis". It was more a question of how long between such extreme events than if such an extreme event could occur.

[abduhl]

Megatsunamis are caused by large volumetric displacements of water resulting from massive amounts of earth entering the water. The tsunami that caused the Fukushima disaster was not a megatsunami - it was caused by thrust faulting resulting in underwater displacement rather than the megatsunami mechanism discussed above.

The analogy here is splashing your hand into water (megatsunami) versus moving your hand underwater.