SEATTLE– Today might bring back scary memories for you. It was just before 11am on this date back in 2001 that areas around Puget Sound got a 6.8 magnitude shaking centered in the South Sound. 16 years later, Washington state has come a long way in preparing for the next big quake. Still, there’s a long way to go.
Pine and Boren near Seattle’s downtown for many might seem like just another busy city intersection. But, the reality is, the both roads are suspended above Interstate 5. This is just one of hundreds of bridges, overpasses and elevated roadways that people could cross every day and not realize they could be compromised in a large quake.
"Because of topography, there's just a variety of bridges all over the Puget Sound area," says DeWayne Wilson is Bridge Asset Manager for Washington State Department of Transportation. He was on the job in 2001 when the Nisqually Quake hit, taking shelter under his desk, "it was definitely a wake up call." Wilson says the learning curve, though, wasn't that steep for Washington State DOT. He says lessons were learned from California earthquakes in the 1970s which he says made engineers along the whole west coast rethinking bridge design. Wilson says the process to fix, retro-fit or replace bridges got more attention post-Nisqually. To date, WSDOT has taken care of 435 bridges in the state. But, hundreds more still need work. If another major quake happened right now, it would cause major problems.
"It would definitely shut down I-5 through Seattle, for at least a day-- or even several days," says Wilson. Long bridges and the tallest buildings would have the biggest problems during a longer duration larger quake that would be centered off-shore in what's called the Cascadia Subduction Zone. The area under the Pacific Ocean floor is where the Juan de Fuca plate is diving under the North American plate. The stretch of fault which goes from Northern California up into British Columbia is where most of our deep earthquakes come from in the Pacific Northwest.
"Once the intensity [of a larger quake] ratchets up, that longer quake will find weak points in our infrastructure and find vulnerabilities. A bridge may be damaged, it may be closed, but our goal is to not have that bridge collapse." In the multi-state earthquake drill called Cascadia Rising, many lessons were learned. It's expected because of the kind of soil that Boeing Field and SeaTac Int'l Airport sit upon-- the only functional airport in the region will likely be the one at Joint Base Lewis-McChord. This gave some good marching orders for which crossings needed to be fixed first, says Wilson. "What we've done with the Dept. of Defense is to create a lifeline from JBLM up into the core of Seattle. And I-5 is the main route."
One crucial link I-5 link is over the Puyallup River near Tacoma. The current span is what's called a hollow core concrete pier bridge. There's 22 of these type of bridges that worry WSDOT engineers. Currently WSDOT contractors are in mid-construction for a completely new span over the Puyallup River. Another of similar construction technique is the Denny Way bridge in Seattle as it crosses from Capitol Hill over I-5 down to the South Lake Union area. Wilson says these hollow concrete supports could withstand the shaking of a Nisqually-sized quake-- but in a larger quake they could implode.
Another big concern for WSDOT engineers is the I-5 Ship Canal Bridge, which carries more than 200 thousand vehicles a day high above Seattle. While this crossing has seen several projects to improve seismic safety, there are several more slated for the next few years to make it even safer.
Due to the slow pace of infrastructure projects to replace and repair bridges, is why experts with the state are now recommending families in Western Washington be prepared with more than just the typical three days of food and water. They now recommend up to two weeks of supplies to make it through the major disruptions that could be possible when the 'big one' eventually does hit our region.