Scientists estimate a 37 percent conditional probability that a Cascadia Subduction Zone earthquake will strike Oregon within the next 50 years. A large seismic event of this size will cause loss of life; destroy homes, businesses, and public buildings; and leave large areas of coastal and western Oregon isolated, perhaps for years.
The key to rescue efforts and to short- and long-term recovery of the state’s day-to-day services and its economy is a functioning transportation system—highways, bridges, waterways, aviation and marine facilities. All recovery efforts depend on the recovery of the transportation system.
The majority of bridges in western Oregon are susceptible to serious damage or destruction in a major seismic event because they were built before modern seismic codes were in place. Dozens of unstable slopes and pre-existing deep slides are expected to fail under the extended three or more minutes of shaking that will accompany a large Cascadia event. This means bridges and overpasses will fall or be unusable, landslides will come down on roads, and roads will wash into rivers, severely restricting rescue and evacuation work, and utility efforts to repair shattered systems.
A 2009 study by ODOT and Portland State found that U.S. 101 would have dozens of bridge failures and would be impassable. All the existing highways connecting U.S. 101 to Interstate 5 would be impassable due to bridge collapses, landslides, fallen trees and washouts. Various segments of I-5 would be unusable due to bridge damage or collapsed overpasses.
We can expect devastating impacts on coastal and Willamette Valley people and infrastructure. As many as 10,000-20,000 fatalities could be followed by 5,000 to 10,000 more because rescuers cannot get to the injured and medical facilities have been damaged or destroyed. The state’s economy would also suffer massive damage—an estimated loss in gross state product of $350 billion over 8-10 years. Many businesses will cease to exist or relocate and not come back.
In April 2011, the Oregon Legislature directed the Oregon Seismic Safety Policy Advisory Commission to lead the coordination of an Oregon Resilience Plan. Presented to the Oregon Legislature in March 2013, the Resilience Plan reviews policy options and makes recommendations on policy direction to protect lives and keep commerce flowing during and after a Cascadia earthquake and tsunami. ODOT participated in the preparation of that report, based on the research it has conducted over the past four years.
Complementing the Oregon Resilience Report is ODOT’s 2013 Seismic Options Report, which provides more focus on the effects of a major seismic event on Oregon’s surface transportation system. ODOT has identified critical “Lifeline Routes,” which will serve Oregonians as the backbone of the transportation system to speed the delivery of lifesaving resources and aid the delivery of recovery resources to reduce the time needed to restore essential services for the recovery of communities and businesses.
The Seismic Options Report discusses how to address bridges and unstable slopes on these Lifeline Routes with an investment in seismic upgrades. The report lays out three phases of work costing about $1.8 billion that can be completed by 2030. When complete, these routes would be resilient in the event of a major earthquake, allowing them to be reopened quickly so they can serve the initial response as well as contribute to long term economic recovery.
While the cost of strengthening the highways to withstand a massive earthquake is substantial, an economic analysis found that the rate of return on these investments is 46 to 1: the $1.8 billion investment in seismic resilience proposed in the Seismic Options Report can reduce the economic impacts of a major event by $84 billion, and also contribute to saving lives. By investing now, Oregon can reduce the long-term economic impact of a major seismic event by billions of dollars.