In fact, the science is robust, and one of the chief scientists behind it is Chris Goldfinger. Thanks to work done by him and his colleagues, we now know that the odds of the big Cascadia earthquake [approximately 8.3 —Editor] happening in the next fifty years are roughly one in three. The odds of the very big one [approximately 9.0 —Editor] are roughly one in ten. Even those numbers do not fully reflect the danger—or, more to the point, how unprepared the Pacific Northwest is to face it. The truly worrisome figures in this story are these: Thirty years ago, no one knew that the Cascadia subduction zone had ever produced a major earthquake. Forty-five years ago, no one even knew it existed.
Via Jason Kottke [1], “The Earthquake That Will Devastate Seattle - The New Yorker [2]”
I knew about the San Adreas fault [3], and even the the New Madrid fault [4], but I did not know about the Cascadia subduction zone [5] and as the article above points out, it has a history of “blowing” every 250–300 years, with the previous one being in 1700. And from reading, it doesn't sound good when the earth finally does move in the Pacific Northwest.
[2] http://www.newyorker.com/magazine/2015/07/20/the-really-big-one
[3] https://en.wikipedia.org/wiki/San_Andreas_Fault
[4] https://en.wikipedia.org/wiki/New_Madrid_Seismic_Zone