9.0 Earthquake All But Certain to Devastate the Pacific Northwest

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The basic story here is that the Juan de Fuca Plate is being shoved beneath the North American Plate. Periodically, the two plates get stuck by friction, building up enormous strain over many hundreds of years until the rocks suddenly slip past each other, releasing that pent-up energy in seconds — and creating a staggeringly large earthquake.

When that happens, the land in the Pacific Northwest will suddenly drop several feet, while land to the west will rebound under the ocean, producing a large tidal wave heading for the West Coast. Terrible news.

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About 19 of those Cascadia earthquakes, however, were truly enormous events, running the full length of the fault — magnitude 9.0 or greater. (The magnitude scale is logarithmic, so a 9.0 earthquake releases about 31 times as much energy as an 8.0.) If one of these hit today, it could prove incredibly destructive. "It's the difference between a big event and a really big event," Roeloffs says.

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In Washington and Oregon, unfortunately, most buildings were constructed before anyone realized that massive subduction zone quakes were a possibility in Cascadia. Schulz cites a FEMA analysis suggesting that 1 million buildings in the Pacific Northwest could either collapse or be compromised in the event of a major earthquake.

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