The Pacific Northwest is due for a continent-rending earthquake. Experts believe the odds of a Big One happening in the next half century are about one in three, the odds of a Very Big One roughly one in ten, and that, in either case, we are disastrously unprepared.
In the latest issue of The New Yorker, Kathryn Schulz writes extensively and captivatingly on the Pacific Northwest’s 700-mile-long Cascadia subduction zone, and the cataclysm that is projected to occur should it give way:
Take your hands and hold them palms down, middle fingertips touching. Your right hand represents the North American tectonic plate, which bears on its back, among other things, our entire continent, from One World Trade Center to the Space Needle, in Seattle. Your left hand represents an oceanic plate called Juan de Fuca, ninety thousand square miles in size. The place where they meet is the Cascadia subduction zone. Now slide your left hand under your right one. That is what the Juan de Fuca plate is doing: slipping steadily beneath North America. When you try it, your right hand will slide up your left arm, as if you were pushing up your sleeve. That is what North America is not doing. It is stuck, wedged tight against the surface of the other plate.
Without moving your hands, curl your right knuckles up, so that they point toward the ceiling. Under pressure from Juan de Fuca, the stuck edge of North America is bulging upward and compressing eastward, at the rate of, respectively, three to four millimetres and thirty to forty millimetres a year. It can do so for quite some time, because, as continent stuff goes, it is young, made of rock that is still relatively elastic. (Rocks, like us, get stiffer as they age.) But it cannot do so indefinitely. There is a backstop—the craton, that ancient unbudgeable mass at the center of the continent—and, sooner or later, North America will rebound like a spring. If, on that occasion, only the southern part of the Cascadia subduction zone gives way—your first two fingers, say—the magnitude of the resulting quake will be somewhere between 8.0 and 8.6.That’s the big one. If the entire zone gives way at once, an event that seismologists call a full-margin rupture, the magnitude will be somewhere between 8.7 and 9.2. That’s the very big one.
…By the time the shaking has ceased and the tsunami has receded, the region will be unrecognizable. Kenneth Murphy, who directs FEMA’s Region X, the division responsible for Oregon, Washington, Idaho, and Alaska, says, “Our operating assumption is that everything west of Interstate 5 will be toast.”
There is a 22 percent chance that by the time you finish reading this sentence, there will have been an earthquake somewhere on earth. This is a probability that is hard to grasp—it seems both obvious and diffuse. The world is a big place, and most earthquakes are relatively small.
But consider this: Geologists put the chance of a full rupture of the Cascadian Subduction Zone—that’s the fault line off the coast of California, Oregon, Washington, and British Columbia—at 7-15 percent over the next fifty years.1 This would result in a 8.7 to 9.3 Mw earthquake. The biggest quake in recorded history, the 1960 Valdivia quake in Chile, weighed in at 9.5 Mw; and the recent 2011 Tōhoku earthquake off the coast of Japan measured at 9.0 Mw. Relatively speaking, there is a significant chance the Pacific Northwest region will see an earthquake of historical magnitude in the not-so-distant future.
The chance of a slightly smaller (8.3 to 8.6 magnitude) earthquake is judged to beabout 37 percent over the same time frame.2 This is still a massive quake: the 1989 Loma Prieta quake that struck the Santa Cruz area during the World Series was “only” a 6.9 Mw, and the 1906 Great San Francisco quake is estimated to have been around 7.8 Mw. (See here for more on how we measure major earthquakes.) As a resident of Portland, Oregon, I had to take a pause after reading figures like that.
We shouldn’t merely be concerned about the earthquake, but about the uncertainty of probabilities. How can we bet for or against such a large-scale catastrophe? If there was a one-third chance I would be hit by a car if I stepped into the street without looking, would I do it? Being hit by a car would be a terrible way to settle the matter one way or the other.
There have been 41 of these giant quakes in the region in the last 10,000 years.3The last one hit in 1700 AD, coinciding with records of a massive tsunami that hit Japan and Pacific Northwest natives’ oral traditions depicting a massive battle between a thunderbird and a whale. This history is written in the local geology: cutaway river banks still show the line of debris and soil that was washed into new locations, and the continental shelf is banded by the flow of undersea landslides. Along the coast of Washington, dead forests still stand, where cedar groves were killed as they land they grew on was dropped more than six feet into salt water.
The Northwest has changed quite a bit in the last three hundred years. A battle between two mythical creatures across the contemporary I-5 corridor would probably involve not just massive floods and shaking, but a massive collapse of local infrastructure. It could destroy the means for sustaining everything we consider to be the bedrock of a normal modern life.
Because Portland has been my hometown for nearly nine years, I went looking for answers about this chance event, if and when it were to happen here. I found thousands of pages worth of studies and reports, written by hundreds of public employees who’ve long been working on this very question. The Federal Emergency Management Agency, the Oregon State Office of Geology and Mineral Industries, the Oregon Department of Transportation, the Oregon Office of Emergency Management, the Portland Bureau of Emergency Management, the city Bureau of Transportation and even the Parks Department—all of these agencies and more have taken a crack at telling parts of the story about what might happen during a Cascadia Subduction Zone event. The accounts, informed by geologists, seismologists, geographers, engineers, transit experts, and city officials, are detailed, compelling, and often exhaustive.
Some of it is quite alarming. One study declared the possibility that of 2,671 bridges in the “strong” shaking zone, 399 would be at least partially destroyed, and 621 heavily damaged.4 That means 38 percent of the region’s bridges, out of service, all at once.
There are systemic vulnerabilities affecting Oregon as well. Nearly all the petroleum products for the entire state are imported through one particular area of Northwest Portland.5 Despite being a modern state, Oregon is still cut off from the rest of the country by its terrain, and connected by only a limited number of roads, railroads, and sea lanes. I read hundreds, if not thousands of other facts, possibilities, probabilities, and potentialities like this, which remind me how amazing it is that our society holds together even in the best of times.
But these reports, too, are strictly in the language of estimates, in scenarios, in potential plans. And naturally so; there are no guarantees in engineering, let alone in emergencies. It is impossible for anyone to say exactly which bridges will collapse, which roads will be blocked, and which buildings will have electricity and sewer service. Similarly, there is no way to predict exactly how many people will die: either immediately, or in the long and difficult rebuilding process when water and electricity may be scarce. But there are estimates. There are scenarios.
The numbers began to slip through my fingers. To avoid the stress of gambling over the lifecycles of bridges and tunnels, I started to resign myself to fate. I took to telling myself, if it’s going to happen, it’s going to happen. But fate is a solipsistic wall erected between oneself and the world—a world which is always comprised of confounding, frustrating, and mysterious facts.
So, instead of trusting in luck or throwing up our hands to fate, let’s tell a story. This story routes around probability, by imagining a scenario in which the Cascadia Subduction zone finally shifts, and the earthquake memorably described as “The Really Big One” by the New Yorker’s Kathryn Schulz comes to pass. This is the story of what happens next.