As we wait for any possible tsunami fallout on the Oregon Coast from the distant and devastating earthquake that has rocked Japan, we're reminded of a cover story WW's Aaron Mesh did last year called "Quake Up Call."
That January 2010 piece was about the prospect of the ocean floor splitting 75 miles off the Oregon Coast and sending shock waves that would rumble in to Portland. The last such destructive Cascadia subduction zone quake happened in 1700, and experts estimate the chances of it happening again here in the next 50 years at about one in eight.
As Aaron wrote then:
About 75 miles off the Pacific coastline, two plates in the earth’s crust meet on a sloping fault line stretching from midway up Vancouver Island down to Humboldt County, Calif. Along the length of this 600-mile-plus fault, the Juan de Fuca Plate is slowly scraping under the North American Plate, building up pressure—much like slipping your foot under the edge of a Persian rug, which curls up until it pops free.
But instead of causing a muffled thump that wouldn’t frighten a housecat, the Cascadia subduction zone would thrust the two plates apart vertically, “unzipping” the length of the fault at a rate of a mile a second. Shock waves would register as high as 9.0 on the moment magnitude scale, the seismic measurement that has replaced the Richter scale. These ruptures cause the most severe quakes on earth.
The latest studies of undersea landslide debris, released last spring by Oregon State University geologist Chris Goldfinger, suggest a Cascadia subduction zone quake happens every 300 to 350 years.
If you want to read the rest of that piece and the massive impact such a quake would have on Portland, it's right here.