Emergency responders across the Pacific Northwest are holding an exercise to test their skills in a magnitude 9.0 earthquake. It's called Cascadia Rising.
And one of the challenges that responders would face after a real earthquake would be getting supplies through downtown Seattle.
Interstate 5 is our main route through downtown, but after a magnitude 9 earthquake, the state transportation department says that section is unlikely to be standing.
There is a workaround: State Route 99. It's part of what WSDOT calls its seismic lifeline – a route for responders to use after a major earthquake.
But even on SR 99 the challenges are obvious: Imagine picking up a load of food and water from Boeing Field south of downtown with the goal of delivering it to people in Fremont.
I asked professor Tom Heaton of the California Institute of Technology what responders might encounter. He studies the physics of earthquakes and the physics of buildings in earthquakes. Heaton has made a study of the Pacific Northwest’s prospects since 1982, when he saw the coastline from a rented airplane and first thought: “This could be really bad.”
The morning after a big quake in Seattle, Heaton said people would not be planning their commute to work.
“They’re trying to figure out how their lives work,” he said in an interview. “How they’re going to get food and water, how to repair things that have gone wrong in their homes.”
That leaves the roads to the emergency responders. One way to get supplies into Seattle could be by landing at Boeing Field and then using SR 99.
However, earthquake maps show that this section south of the city lies in a liquefaction zone.
“The soil turns into a mud slurry that just starts to ooze downhill,” overwhelming the asphalt before hardening into a different shape, Heaton said.
If responders were to try to drive over sections disturbed by liquefaction in a large SUV, they might be able to make it, or they might not.
The next big hurdle would be downtown’s southern doorstep. This is where responders would face either the Alaskan Way Viaduct, which is known to be unstable and is being replaced, or the tunnel that is doing the replacing.
Heaton said even the Alaskan Way tunnel isn't a sure thing. “Of course, there are cases where the ground liquefies and say a tunnel might have some failures in it. Just because something is new doesn’t mean that it will be fine in an earthquake.”
Still, the tunnel is a better bet than surface streets for getting supplies through downtown.
Heaton’s lab has modeled it. "If the earthquake gets close to Seattle, we saw ground motions that would potentially collapse relatively modern high-rise construction,” he said. “We expect them to more likely fall over sideways – just kind of folded over." Those collapses would potentially take out power, communications and other utility lines, such as sewers.
“It wouldn’t be nice," he said.
There are seismic lifeline routes that bypass downtown Seattle, using Interstate 405 on the Eastside, for example. And if the Seattle’s downtown is not reachable by road, then responders may explore water routes. Those too depend on the conditions at landing areas.
But say there is an Alaskan Way Tunnel, it’s working and it gets an emergency crew through the downtown. That would leave one final barrier: the Aurora bridge.
Built in the 1930s, it is infamously narrow and another seismic lifeline question mark. Heaton is not pessimistic. “Just because it’s old doesn’t mean it won’t do well in an earthquake.”
However, Heaton said a single supply run does not begin to solve the problems that await Seattle after a major earthquake.
“Let’s suppose you get your supplies through and you delivered them,” he said. “Now you’ve given everybody food and water for the next couple of days, but they still have to put everything back together again. And that’s going to take decades.”
Representatives from the Washington and Seattle transportation departments said they could not make themselves available to drive SR 99 with KUOW. They cited their preparations for the Cascadia Rising earthquake preparedness exercise and their reluctance to appear to be predicting exactly how the city’s infrastructure would respond in an earthquake.