PORTLAND, Ore. (CN) — It’s not a question of if, but when: A megathrust earthquake will someday occur along the subduction zone that lies beneath the Pacific Northwest.
In the last 10,000 years, the Cascadia Subduction Zone has experienced 43 earthquakes. The most recent one was in 1700, when the subduction zone unleashed an estimated 9.0-magnitude earthquake, collapsing the coastline by several feet and spurring a tsunami.
Current predictions estimate a 37% chance that a megathrust earthquake of over 7.1 magnitude will strike the subduction zone in the next 50 years. And all that raises another question: How prepared is the region for that dreaded day?
In late October, the Oregon Department of Emergency Management ran a weeklong scenario to test its readiness not only for the devastation but also disaster logistics afterwards. Preparing for an earthquake is a daunting task, not least because of their unpredictable nature. When a major Cascadia earthquake does eventually strike, officials expect no more than a few seconds’ notice.
As it happened, the exercise coincided with a 6.0-magnitude earthquake, with an epicenter around 170 miles off the central Oregon Coast. Though large, that earthquake was nothing compared to the size and scale the state is preparing for.
So, what is the worst that could happen? “It can't get much more than a 9.4,” Althea Rizzo,coordinator of the Geological Hazard Program coordinator at Oregon Emergency Management, said about the statewide exercise. In the test scenario, Oregon was projected to face as many as 25,000 deaths statewide — but it wouldn’t take a record-breaking quake to cause serious damage. Earthquakes’ intensity are measured on a logarithmic scale, “so even the small ones are really large.”
In the grim scenario of 25,000 deaths, only a fraction of those hypothetical casualties are from the earthquake itself. The rest are from the tsunami that would inevitably follow, inundating low-lying areas on the Oregon Coast.
“The tsunami is really going to be the killer when it comes to Cascadia,” Rizzo said, using the name for the Pacific Northwest’s fault line. Coastal Oregonians will need to flee to higher ground. They’ll also need to stick it out until rescue workers can get to them, as islanding — that is, the formation of temporary islands on what was once all land — will likely occur.
Even farther inland and on higher ground, Oregonians will need to be ready. Besides tsunamis, another major concern is liquefaction, in which shaking starts to essentially boil sand and force water to the surface. That’s one of the main drivers of earthquake damage, Rizzo said — and one that could turn older buildings into rubble.
Unlike weather-based natural disasters like hurricanes, which can be tracked and the subject of an early warning system, earthquakes are unpredictable. That makes preparing for them difficult, for both emergency officials and everyday residents.
In the event of an earthquake — a big earthquake — Oregonians will be lucky to have even a few seconds of warnings. What can Oregon residents do with those seconds to keep themselves safe?
For Chris Goldfinger, an earthquake geologist, paleoseismologist and professor emeritus at Oregon State University, the answer to that question is sometimes simple.
In certain cases, those seconds should be used to run outside, he said. If the building is a clear collapse hazard and there's an unobstructed path to get outside, fleeing may be the right choice.
That’s a departure from the traditional advice for earthquakes, which encourages people to drop, cover and hold on. But for an earthquake of the magnitude that Oregon’s facing, in which even seemingly solid buildings might crumble, that might not be enough to stay safe.
“It sounds like a conspiracy theory,” Goldfinger quipped, “but do your own research.”
