There is a large Subduction Zone just like the one that caused the big Tsunami in Thailand and Sumatra just a little ways off the Oregon coast.
There is historic evidence being dug up of previous Tsunami waves hitting the coastline every so many years on average. We are in the time Zone for another one. Most of Oregon and Washington's beach towns are full of houses for sale relatively cheaply at the moment.
There is an active Volcanic island in the Canary Islands that could (is starting) split in half and the side that will fall into the sea is facing the East Coast of the US. The resulting Tsunami would be BIG when it hit the US coast if it all fell in at once.
All of this shows up on the Discovery Channel for anyone who cares to watch.