On January 26, 1700, a magnitude 9.0 earthquake occurred along the Cascadia subduction zone off the coast of Oregon and Washington. It generated a tsunami that rolled across the Pacific an hit the Honshu region of Japan the next day, reaching 5 meters in height.
It was a mirror image of the 9.0 Japan quake and tsunami of two days ago.
And it is a geologic certainty that another Cascadia megaquake will strike the Pacific Northwest some time and we now have graphic evidence of what that means.
My colleagues in the Oregon and Washington geological surveys recognize this hazard and are heavily engaged in trying to understand the potential and mitigate the risks. But trying to prepare for an event that may not occur in the lifetimes of those who fund this work is often an uphill battle.
In Japan, they have a warning system that recognizes the P or primary waves of a major quake and sends out emergency warnings that the slower but much more damaging S (secondary) and later surface waves will be coming shortly. Many in Japan had a crucial 30-40 seconds warning. That can be enough time to shut down critical facilities or get to cover. The tsunami warning system gave residents 30-40 minutes in many areas to get to higher ground.
It's long past time to install similar warning systems in seismically vulnerable locations in the U.S.
Update: Geomika offers a review and comparison of West Coast quake hazards at http://www.geomika.com/blog/2011/03/12/tsunami-on-the-west-coast/