There was a show on PBS in Seattle about a month ago talking about the Cascadia subduction zone. It was fascinating, some really good detective work.
Turns out the zone (which stretches from north Vancouver Island almost all the way to Sacramento) is capable of great quakes, we're talking Indonesia size tsunami events.
The last GREAT quake was a 9.0+, and it was recorded in 1698? or thereabouts in the records in Japan (tsunami).
The biggest question has been whether it is the "minute of terror" or the "decade of terror" scenario, in other words, does it give a little here, the a while later give a little there, etc. Or does it just simply give a whole lot all at once.
Studies of core samples of the sediments on the sea floor off of BC, Washington, Oregon, and Northern California have answered that question.
When it goes, it does it all at once. A 9.0+ that stretches from North of Vancouver all the way to Redding or so...
And we're overdue.
"overdue" = those Cascadia subduction zone quakes were recorded on AN AVERAGE of 300 years. That's what they mean by overdue. So it could happen tomorrow, or 200 years from now.