Before and after (simulated) photos of the Alaskan Way Viaduct (photo credits, Google and Washington State DOT)
Why So Dangerous?
While the Cascadia Subduction zone is a scary prospect, the Seattle and Tacoma faults are likely the more serious earthquake threat to the populous Seattle–Tacoma area. A 2002 study (also by the Earthquake Engineering Resources Institute) estimated that a magnitude 7 earthquake on the Seattle Fault would damage approximately 80 bridges in the Seattle–Tacoma area and kill or injure thousands. There is concern that such an earthquake on the Seattle Fault would devastate unreinforced masonry buildings, of which the city has thousands. The fault runs under some of the oldest areas with the least-reinforced buildings- concentrated in Capitol Hill, Pioneer Square, and the International District.
The Perfect Storm
The damage from a Seattle fault earthquake would be massive, but the landslides that follow will be severe. "In Seattle, there's kind of a perfect storm of characteristics because the fault goes right through the city, it's wet, and there are steep slopes all around," according to USGS scientist Kate Allstadt. "If you look at Seattle, there's houses everywhere. They're built on slopes and on hills. We're looking at the possibility of having buildings falling down slopes into Lake Washington or the Puget Sound," she said.
Now half a million people live directly above the fault. Mansions are perched on steep hillsides. Entire neighborhoods are nestled in what are old landslide scars. Most buildings were built before building codes were updated to take into account the Seattle Fault in 2000. What is going to happen when tectonic forces push the fault over its threshold again?
Trying to Catch Up on Preparedness
The Seattle Fault was only first recognized as a significant seismic danger in 1992. Along with the Cascadia Subduction Zone, these faults have been identified as threats in just the last 2-3 decades. The region has moved slow, but it takes a generation for society to truly understand and prepare for a new disaster threat. While California has had hundreds of years to get prepared, it feels like we are just beginning.
This fault runs right under the city of Seattle, and we're still finding new things almost every year. Eric Holdeman, former director of the King County Office of Emergency Management, said we shouldn’t expect outsiders to swoop in and save us when a long-anticipated massive earthquake hits (and it will hit, we just don’t know when).
Holdeman said most individual Seattleites aren't ready for a quake. “People overestimate their capacity to survive a natural disaster,” he said. “Start thinking about urban camping. Think about being on your own for two weeks.”
Have a family communication plan – decide where you would meet them should disaster strike. You know you should have an earthquake bag in place, so stop putting it off and get it done. It’s important to have a smart, well-thought-out bag you can trust. If you don’t have time to track down the best tools and materials to do it right The Earthquake Bag makes it easy. It’s our mission to make sure everyone either buys one of ours or builds one of their own. Everyone is safer when we all are more prepared individually.