Scientists were baffled at how the world’s most organized and earthquake-ready nation could have been taken so much by surprise by the mega quake and tsunami that struck the island of Japan in March of 2011. They were hit by an earthquake roughly 25 times more powerful than experts thought possible in that part of the country. How could the forecast have been so wrong? The short answer is, they didn’t look far enough BACK in geologic time to see that quakes and tsunamis just this big had indeed occurred there before. Had they prepared themselves for a much larger quake and wave, the outcome may have been entirely different.
Exactly the same is true of the Cascadia subduction zone—an almost identical threat off the west coast of North America. When it was first discovered, many scientists thought Cascadia’s fault was incapable of generating giant earthquakes. Now they know they were wrong. They, too, just hadn’t looked far enough into the past.
People living in the United States and Canada, when they think about earthquake disasters, probably conjure up the San Andreas fault in the worst-case scenario. As Californians wait for the “Big One,” people wonder which city the San Andreas will wreck next—San Francisco or Los Angeles? But guess what? If by the “Big One” they mean the earthquake that will wreak havoc over the widest geographic area, that could destroy the most critical infrastructure, and that could send a train of tsunamis across the Pacific, then the San Andreas could not possibly be the culprit. It would have to be Cascadia’s fault. The one smack dab in our own front yard.
The Cascadia subduction zone is a crack in the Earth’s crust, roughly 60 miles offshore and running 800 miles from northern Vancouver Island to Northern California. This fault is part of the infamous Pacific Ring of Fire, the impact zone where several massive tectonic plates collide. Here, a slab of the Pacific Ocean floor called the Juan de Fuca plate, slides eastward and downward, “subducting” underneath the continental plate of North America.
Based on historical averages, the southern end of the fault–from Cape Mendocino, California, to Newport, Oregon—has a large earthquake every 240 years. For the northern end—from mid-Oregon to mid-Vancouver Island—the average “recurrence interval” is 480 years, according to a recent Canadian study. And while the north may have only half as many jolts, they tend to be full-size disasters in which the entire fault breaks from end to end.
With a time-line of 41 events, the science team at OSU has now calculated that the California-Oregon end of Cascadia’s fault has a 37 percent chance of producing a major earthquake in the next 50 years. The odds are at 10 percent that an even larger quake will strike the upper end, in a full-margin rupture, within 15 years. Given that the last big quake was 312 years ago, one might argue that a major event on the Cascadia Subduction Zone is ominously overdue.
Two years after witnessing the devastation in Japan, what have you done to prepare for your family’s safety should this mega quake strike along the Cascadia? Is your home anchored to its foundation? Do you have earthquake insurance in place? Have you put together your emergency supply kit to last your family at least 3 days without local services? Do you have a plan of action to follow if the quake hits during the day when family members are separated? Being prepared is our best hope of survival. Please, start talking and making plans, and then carry out those plans. There just won’t be time enough to throw things together when the shaking starts.
(Portions excerpted from an article by Jerry Thompson, Discover Magazine, 2012)