"When that earthquake hits, it's going to shake for a long time," says Corcoran. "Three to five minutes or more. You're going to feel lucky to survive. Then guess what. You rode out the quake? Congratulations. Now you have 15 minutes to get above 50 feet of elevation. Fifteen minutes. [...]"
This startling evidence made seismologists sit up and take notice. Clearly, the Cascadia subduction zone had ruptured in a megaquake in 1700, down-dropping the Northwest coast several feet in elevation and unleashing a killer tsunami.
Of course, the magic number could be 500 years, or (gulp) 244. For the past decade, Chris Goldfinger has been pulling samples from landslide zones off the Oregon coast. By interpreting the cross-sections, he found a record of 19 full-rip nines in the past 10,000 years -- a rate of about one every 500 years. He also discovered 22 CSZ quakes measuring 8.0 to 8.5. That means the CSZ has caused 41 major quakes in the past 10,000 years, or one every 244 years.
So what we have now is a 740-mile section of the world's most seismically active zone, the Ring of Fire, that has been building up elastic strain for 311 years. The North American plate, by some estimates, is now springloaded to leap more than 57 feet west and drop three to six feet in elevation at the coast.
Here's an almost-gleeful, Lucifer's Hammer-esque fictionalized narrative of what kind of quake is likely to be caused when the Cascadia Subduction Zone next slips.
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