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10 Terrifying Facts About the Cascadia Zone, The Pacific Northwest’s Sleeping Earthquake Giant

July 16, 2015 Leave a comment dridrive

Earthquake warning sign45 years ago, practically nothing was known about the Cascadia subduction zone that sits under the U.S. Pacific Northwest. Now, scientists have a lot more data – and all of it is terrifying. Is there any way the region can recover when – not if – an earthquake hits?

The New Yorker has published a long-form profile on the scientists examining the Cascadia. 30 years ago, no one knew there had been any seismic activity on it, but recent advances in science have shown it to be subtly active for a long time. The Pacific Northwest has experienced 41 subduction-zone earthquakes in the past ten thousand years. Counting from the recently recognized earthquake of 1700, we are now 315 years into a 243-year cycle, meaning a major catastrophic event is almost certainly building.

10 alarming takeaways:

  1. If only the southern part of the Cascadia subduction zone gives way, the magnitude of the resulting quake will be somewhere between 8.0 and 8.6. But if the entire zone gives way, the magnitude will be somewhere between 8.7 and 9.2.
  2. The northwest edge of the continent, from California to Canada and the continental shelf to the Cascades, will drop by as much as six feet and rebound 30 to 100 feet to the west. Some of that shift will take place beneath the ocean, displacing massive amounts of seawater.
  3. “Everything west of Interstate 5 is toast,” as one FEMA representative put it. This includes Seattle, Tacoma, Portland, Eugene, Salem, Olympia, and some seven million people. It would be the worst natural disaster in the history of North America.
  4. FEMA projects that nearly 13,000 people will die in the Cascadia earthquake and the resulting tsunami. With another twenty-seven thousand will be injured, and a million more displaced people in need of shelter.
  5. The odds of the big Cascadia earthquake (8-8.6 magnitude) happening in the next 50 years are roughly one in three. The odds of an 8.7-9 magnitude: roughly one in ten.
  6. Until 1974, the state of Oregon had no seismic code, and few places in the Pacific Northwest had one appropriate to a magnitude-9.0 earthquake until 1994. The vast majority of buildings in the region were constructed before then. An estimated 75% of all structures in the state are not designed to withstand a major Cascadia quake.
  7. FEMA calculates that approximately a million buildings – including more than 3,000 schools – will collapse or be compromised in the earthquake.
  8. The shaking from the Cascadia quake will set off landslides throughout the region—up to 30,000 in Seattle alone. It will also induce a process called liquefaction, whereby seemingly solid ground starts behaving like a liquid, to the detriment of anything on top of it.
  9. The resulting tsunami will be moving more than 13 miles per hour when it arrives. Its height will vary with the contours of the coast, from twenty feet to more than a hundred feet. And once it reaches the shore, it will be a five-story deluge packed with trucks, debris, and the remains of coastal towns across the Pacific Northwest.
  10. The economy of the Pacific Northwest will collapse. Crippled by a lack of basic services, businesses will fail or move away, along with many residents, for years to come.

What can organizations in the region do? Start prepping now, and encourage innovation, such as last year’s cargo bike disaster drill in Portland.