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A catastrophic earthquake and tsunami are inevitable for the Pacific Northwest coast, scientists say. Planning for that means imagining a disaster unlike anything that has ever hit the modern United States.
“30 or 40 years ago, we didn’t even know that large earthquakes were possible in the Pacific Northwest,” said Diego Melgar, a seismologist at the University of Oregon.
Scientists now know that the 700-mile fault known as the Cascadia Subduction Zone, 100 miles off the coast of Northern California extending north to Vancouver Island, could trigger a magnitude 9.0 earthquake and tsunami, which is exactly what which happened in Japan 2011.
New in-depth images of the fault were recently reported in “Science Advances”. Scientists say it confirmed that the subduction zone is cut into 3 to 5 segments, each with its own unique geology. When the section of the fault ruptures off the Washington coast, it has the greatest potential to cause a devastating earthquake.
No one is ready for this.
Nothing built before 2005 was built to withstand the long, strong earthquake that Cascadia will produce, according to Corina Allen, chief hazard geologist at the Washington Geological Survey. And tsunami building codes only came into effect in 2016.
“We have bridges, buildings, hospitals, schools, all this infrastructure that is located in places where the tsunami could go,” Allen said. Can these facilities survive a subsequent earthquake and tsunami? “The answer is no.”
“What keeps me up at night is knowing that we’re not taking the steps we need to take, as quickly as we should be, to protect our people,” said Yumei Wang, senior infrastructure and risk consultant at Portland. State University.
Brick and masonry buildings are the most vulnerable to earthquakes. And Wang says timber frame buildings are particularly vulnerable to tsunami forces. “You can imagine water pushing over a typical house,” she says.
The geological record of the region shows that, on average, these mega earthquake and tsunami events occur every 500 years. There is no way to predict when the next one will happen, but it is expected to happen again within the next 200 years – or less.
Retrofitting existing communities will be a long process and cost billions of dollars, Allen said. Melgar believes the effort is well worth it. “My children may not see dividends, my grandchildren may not see dividends. We are playing a very long game if we are doing it right.”.
For those who live and vacation on the Pacific Northwest coast, tsunamis that last 15 to 30 minutes after an earthquake depend on how quickly they can reach higher ground. But maybe there is no safe place to go.
“In Washington, most people who live in the tsunami zone don’t have any high ground nearby,” Allen said.
In that case, vertical evacuation structures built within the tsunami zone are critical. These structures helped save thousands of lives in the 2011 tsunami in Japan.
Only three have been built in the Pacific Northwest, and four more are planned. But Allen estimates that 50 are needed in Washington alone. Each of the three existing structures could hold between 400 and 1,000 people, reach 76 feet in height and vary in cost. The Marine Sciences Center in Oregon is the most expensive, at $62 million, Wang said.
“The foundation is deeper than the tall building, like an iceberg. And the structure itself is a bit like a car bumper, so big, heavy debris can hit.”
“We know a lot about building codes. We know a lot about early warning. We know enough about tsunami evacuation zones that it’s not necessarily that bad,” says Melgar.
What is less clear is whether people are willing to invest billions of dollars to prepare for something that won’t happen for 200 years. “It’s an expensive problem to solve,” says Allen. “Perhaps we have more time and will be able to implement the systems we need to survive this event.”
The problem is, no one knows how much time is left.
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