The San Andreas fault might be the sexier, more famous fault line predicted to destroy a sizeable portion of the West Coast, but another running through the Pacific Northwest, featured in an article in this week’s New Yorker, is scarier: not only will it cause more damage and kill or injure tens of thousands of people, it will likely do so within the next 100 years, with a one in three chance it will happen very, very soon.

According to the seismologists interviewed by The New Yorker, the fault line, known as the Cascadia subduction zone, runs hundreds of miles between Northern California and ends around Vancouver, and is the area where the continental plates are doing something they are not supposed to do. Whereas a tectonic plate will normally slide underneath another plate—remember eighth-grade geology?—these are jammed up against each other in the Cascades, explaining why no one’s felt an earthquake in the Pacific Northwest, whereas, say, Japan gets a ton of them.

“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,” the piece’s author, Kathryn Schulz, explains. “If, on that occasion, 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. 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.”

The less-scary earthquake will be the equivalent of the 2011 earthquake that devastated Japan, but the more-scary earthquake, which is about a hundred or so years overdue and has historical precedent . . . well, it’s going to look something like this:

“When the next very big earthquake hits, 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 thirty to a hundred feet to the west—losing, within minutes, all the elevation and compression it has gained over centuries. . . . The water will surge upward into a huge hill, then promptly collapse. One side will rush west, toward Japan. The other side will rush east, in a seven-hundred-mile liquid wall that will reach the Northwest coast, on average, fifteen minutes after the earthquake begins. 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.'”

Due to the lack of earthquakes in the region, no one is prepared for a potential earthquake, or even thought it could possibly happen. (The fault line was only discovered a few decades years ago.) Without the proper precautions, conservative projections estimate that 13,000 people will die, with an additional 27,000 injured, and millions of people will be displaced if nothing changes. And that’s if it hits during the low point of the tourist season: if the earthquake happens during the summer, when thousands of visitors are at the beach and have no ability to get to high ground, “those numbers could be off by a horrifying margin.”

Oh, and the region will collapse in every other way: “Crippled by a lack of basic services, businesses will fail or move away. Many residents will flee as well. OSSPAC predicts a mass-displacement event and a long-term population downturn.” It’s slightly terrifying.

The seismologists interviewed predict there’s a 1 in 3 chance of the less-scary earthquake, and a 1 in 10 chance of the really-scary earthquake, happening in the next 50 years.

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