The Really Big One

This post was published more than a few years ago (on 2015-07-14) and may contain inaccurate technical information, outmoded thoughts, or cringe takes. Proceed at your own risk.

When we moved out to Seattle two years ago, we knew that earthquakes might be a thing we’d have to worry about, but it hadn’t really sunk in how real of a danger that might be. A recent New Yorker article got my office buzzing about the possibility of a Really Big One occurring on the Cascadia fault, which runs right under Seattle. So, for my own edification, here are some facts, and what we can do to prepare:

The original New Yorker piece

  • The Really Big One” by Kathryn Schulz — a dramatic look at what could happen, if (apparently) a bit hyperbolic

Some facts

  • We are earthquake experts. Ask us anything about The Really Big One coming for the Pacific Northwest. (AMA) — with questions answered by John Vidale, director of the Pacific Northwest Seismic Network, Debbie Goetz of Seattle’s Emergency Management Office, and Sandi Doughton, science writer at The Seattle Times and author of Full Rip 9.0: The Next Big Earthquake in the Pacific Northwest
  • Cascadia’s recurrence interval — the average time between subduction-zone earthquakes — is 243 years. We are currently 315 years since the last major Cascadia earthquake (M9.0) at 9pm, January 26, 1700.1
  • “Overdue” seems a bit of a fear-mongering word to use here. The pressure in the fault is still slowly building, but thanks to how complex the probabilities are, that could mean any number of things. The current thinking is, “For the M9 [earthquake] along the coast, the best estimate is 10 to 15% chance per 50 years, or 1 in 300 each year.2
  • There is also a chance that when “the big one” happens, only part of the fault will slip at first, increasing chances that there will be another major earthquake soon after to relieve pressure on the rest of the fault,3 in addition to expected aftershocks.
  • The shaking will be much more devastating to Seattle than any risk of tsunami related to this event. “The tsunami won't really be a factor in Seattle or Puget Sound. By the time the swell gets here, it will be pretty small.4” In my neighborhood specifically, “You might see a little coastal swell in Ballard, but the tsunami will not be a major factor there.5
  • There is an early warning system in testing, and John Vidale (and a neighbor of mine that works for him) said testers have it on their phones right now.6 However, it needs more work to be tuned to our region’s specific seismic activity so it doesn’t give false alarms to the public.7
  • Sandi Doughton says, “I live here, and I personally wouldn't advise anyone to stay away from this beautiful region because of earthquake risks. Some things you might consider […], make emergency kits for home, work and car, and a plan for contacting family members (designate an out of state contact everyone can check in with). My philosophy is be prepared, not paranoid - and enjoy the spectacular landscape provided to us by tectonic forces.8
  • The Seattle Times has an article with more links, and the first chapter excerpted from the Full Rip 9.0 book


  • Make It Through (local) and (national) have information on making an evacuation plan, a communications plan, and lists for what should be in your disaster kit.
  • While preparing a kit with 3 days of food/water/etc. is the usual recommendation, Debbie Goetz said in the AMA, “We recommend people prepare themselves for 7 to 10 days vs. three. For a major quake, life won’t be back to ‘normal’ after just three days. I’ve got enough at home to make it through a week, and also keep a stash of stuff in my car as well as at work. Beyond supplies, I always encourage people to talk about their plans — especially around communication, which we know will be affected. Where will they be? How can they get back together? Where could they meet if not at home?9
  • Seattle Disaster Readiness and Response Plans
  • The Great Washington ShakeOut — a state-wide drill to learn how to drop, cover, and hold on, instead of heading for a doorway

  1. The Really Big One” by Kathryn Schulz, in The New Yorker July 20, 2015 Issue (retrieved from web 2015-07-13) 
  2. John Vidale, 2015-07-14, Reddit AMA 
  3. Sandi Daughton, 2015-07-14 Reddit AMA 
  4. Sandi Daughton, 2015-07-14 Reddit AMA 
  5. Sandi Daughton, 2015-07-14 Reddit AMA 
  6. John Vidale, 2015-07-14, Reddit AMA 
  7. John Vidale, 2015-07-14, Reddit AMA 
  8. Sandi Daughton, 2015-07-14 Reddit AMA 
  9. Debbie Goetz, 2015-07-14, Reddit AMA