Japanese scientist, going over the damage from 11 March tsunami, say buildings made of the toughest concrete, and several stories tall, were totally destroyed by the tsunami.  That included building that were thought to be safe for use as emergency shelters, of course most people in those shelters died.

The scientist say the most damage was not caused by the in rushing tsunami, but by the tsunami rushing back out to sea. They point out that anything that rushes uphill, will go faster when it rolls back downhill.  They say the same is true with tsunami, and of course, the bigger the tsunami the more dangerous its backwash is.

The strongest buildings, that were wiped out, show evidence that they were destroyed by the tsunami backwash.