It may come like it did the last time, in the middle of a cold and blustery January night. Suddenly the ground will begin to shake, windows will shatter, bridges collapse, the electricity will go out and parents will frantically try to find a flashlight and dig sleepy kids out of bed, ignore everything else and run – because they know they only have minutes before the water arrives.
Even worse, it may come on a warm and breezy summer afternoon in July, when tens of thousands of visitors fly kites, build sand castles and play fetch with their dogs on one of the most beautiful stretches of coastline in the world. The rumble and shaking on the crowded beaches will quickly be replaced by a receding shoreline as the water eerily slides away, and people will start to run, anywhere they can, to get to higher ground – because they know the water will soon be coming back.
It will be scary, it will be destructive, and it’s going to happen, reasonably soon. People will talk for generations to come about the great subduction zone earthquake and tsunami of ____. Fill in the blank with a date; science can provide some guidance, but no one knows for certain when it will be.
Pat Corcoran, a coastal hazards outreach specialist with Oregon Sea Grant, is mindful of these risks and calls the disaster that’s waiting to happen “arguably the greatest recurring natural hazard in the lowest 48 states.” That’s about right. Subduction zones – like the Cascadia Subduction Zone that lurks just off the coast of the Pacific Northwest – produce the most massive earthquakes in the world. And their “up and down” ground motion triggers tsunamis, one of the most deadly ocean wave events in the world.
The problem is, at least in the United States, these events don’t happen very often. In fact, until the mid-1980s, scientists didn’t think great earthquakes and tsunamis were caused by Pacific Northwest fault zones. Then some pioneering research by the U.S. Geological Survey, Oregon State University and others began to unravel some ancient mysteries. Scientists found that not only do they happen here, they occur pretty regularly, about every 300 to 500 years on one part or all of the Cascadia Subduction Zone, which runs 700 miles from Cape Mendocino in California to Vancouver Island in Canada. The last event was pinpointed because the enormous tsunami it created raced all the way across the Pacific Ocean to Japan, where written records were kept. It occurred here about 9 p.m. on Jan. 26, 1700.
“The Native Americans at the time of the last subduction zone earthquake in 1700 had a rich oral history surrounding earthquakes and tsunamis,” Corcoran says. “One tradition encouraged people to weave long ropes. That way, the saying went, following the earthquake a person could tie one end of the long rope around a tree and the other onto their canoe in order to ride out the tsunami waves.”
It’s now 2010, more than three centuries later. The newest studies produced by Chris Goldfinger, an OSU marine geologist and one of the world’s leading experts on the Cascadia Subduction Zone, indicate that there’s a 37 percent chance of a partial rupture of the zone within the next 50 years, an event that could be similar in magnitude to the earthquake just experienced in Chile.
“Perhaps more striking than the probability numbers is that we have already gone longer without an earthquake than 75 percent of the known times between earthquakes in the last 10,000 years,” Goldfinger says. “And 50 years from now, that number will rise to 85 percent.”
So it’s coming soon, possibly tomorrow. Possibly in 10 years. A better than one in three chance within the next 50 years. But no one knows for sure, and that isn’t going to change. With existing science, earthquakes cannot be predicted with precision; we can only prepare.
But Are We Prepared?
A few years ago, local residents in Cannon Beach, Oregon, were pondering that question, as they followed the developing science on subduction zone earthquakes and worked with officials from the Oregon Department of Geology and Mineral Industries on evacuation maps for the anticipated tsunami.
Preparation for a tsunami, in this context, would be defined as people knowing what to do, where to go, getting to high ground and having the time to do it. Jay Raskin, a longtime resident, community leader and local architect, didn’t like what he was hearing.
“Around then, the scientists were describing and updating the potential risks for an earthquake and tsunami caused by the Cascadia Subduction Zone,” Raskin says. “We talked about the distances we needed to go, how high the water might get, where high enough ground was, the bridges that probably would be destroyed.
“And then we’re thinking, oh darn, this strategy of getting to high ground might not work for everyone,” he says. “For some people there just might not be enough time. We needed another option.”
Then Hurricane Katrina struck, and another lesson was offered to the Cannon Beach residents. In the aftermath of the storm, not only had the devastation of coastal communities been enormous, but there was no functioning city government, no working facility to help rebuild.
A Sunny Day at the Beach
Cannon Beach is a small coastal community a little south of Seaside, Oregon. It’s butted up against coastal headlands and stretches for several lovely miles along the Pacific Ocean coast. Most of its 1,700 residents live within a few blocks of the beach, and about half of them, and 75 percent of the businesses, reside within a tsunami inundation zone. But it could be much worse. On a peak summer day, up to 12,000 people may crowd the beaches around Cannon Beach. The city presents a microcosm of an issue that affects a vulnerable shoreline about 900 miles long.
Read more on this story at Terra Magazine
Photo by Frank Miller