The experts say it's inevitable that the Seattle area will be hit with another tsunami similar to the one from 1,000 years ago. Here's a computer-generated video of what a tsunami hitting Seattle would look like:
(video courtesy of NOAA's Center for Tsunami Research)
The animation assumes a magnitude 7.3 quake on the Seattle Fault.
Here are similar projections, based on a 9.1 quake, for Long Beach, Ocean Shores, and Bellingham, all modeled on a quake similar in size to what Japan experienced last week. (These are very big files; give them plenty of time to load. Smaller, less-detailed versions are at the NOAA link above.)