Researchers examine impact of Cascadia disaster on coastal infrastructure

Aug. 15—Researchers have analyzed communities along the Oregon Coast to predict the resiliency of infrastructure and length of recovery following an earthquake and tsunami in the Cascadia Subduction Zone.

The study, done by researchers at Oregon State University, looked into 18 communities along the coast from Astoria to Brookings. The work explored the connectivity in developing a model that forecasts the impacts, primarily on transportation networks such as roads and bridges.

The Astoria and Warrenton region — grouped together for the study — yielded encouraging results, said Dan Cox, a professor of civil and construction engineering at Oregon State who was involved in the research.

"It came out to be one of the best in terms of having multiple avenues to go," Cox said. "That was the good news from Astoria's point of view — not saying it's not going to have a lot to do after the event, but relative to some of the other coastal cities, our studies show that Astoria is actually in better shape than some of the other neighboring cities."

The Cascadia Subduction Zone, extending offshore from British Columbia to Northern California, hasn't produced an earthquake since 1700 and is building up pressure where the Juan de Fuca plate is sliding underneath the North American plate.

According to a statement by Oregon State, some studies predict a 7% to 11% probability of a major earthquake — "a full-margin rupture" — in the Cascadia Subduction Zone in the next 50 years.

The research, led by engineering doctoral student Dylan Sanderson, examined factors such as the shaking ground from the earthquake, tsunami inundation depth and distances to airports and maintenance facilities.

Researchers identified disparities in recoveries for coastal communities and determined that additional work is needed to solve these issues.

Communities that had fast regional recoveries under the model had access to roads that were identified as higher priority for repair, while communities that recovered quickly on the local level had access to maintenance facilities.

Because Oregon Department of Transportation repair facilities are mostly located along the Willamette Valley and Interstate 5 corridor, researchers said an increase of available maintenance stations on the coast could benefit more rural communities in their recovery process.

Regional recovery must be considered alongside local recovery, the researchers also found. Without doing so, commonly used models may be severely underpredicting recovery time from a major disaster, Cox said.

In comparing results to other studies that only considered the local network, the recovery time for a single community was shown to be four times longer than previously estimated, Sanderson said in a statement.

"If we use these models, we have to use them carefully, so that we can plan accordingly," Cox said. "Our research is showing that we have to be really careful with using some of these other types of tools with their default values that were set up primarily for smaller events.

"Say for example, an earthquake in Knappa — that might just be a really isolated area that doesn't consider a huge swath the way that Cascadia really is going to affect our coastline."

But challenges for communities ultimately vary based on geography and connections, Cox said.

Cox and his team have held several listening sessions on the coast and hope to host more discussions in the future.

They have also held meetings with county leaders and emergency planners. Cox commended Tiffany Brown, Clatsop County's emergency manager, for her advocacy and preparation on the subject.

"The coast is vulnerable to the Cascadia threat in a way that inland partners aren't, which is to say that we will have a tsunami, where the bigger, more urban partners won't," Brown said. "What would add insult to injury with that is that we are then isolated and we will spend a greater amount of time also, in theory, than our inland partners waiting for assistance."

Brown emphasized the importance of understanding the threat and knowing how to respond.

The researchers hope to bring their results to communities soon.

"This is something (the communities) are really interested in knowing more about," Cox said.