A magnitude 9 Cascadia earthquake would leave Eugene-Springfield isolated and without essential services, UO professor Douglas Toomey told a crowd of some 500 people who attended the Aug. 6 forum on "The Really Big One."
"Focus on what we can do," was the message to area residents from Josh Bruce, director of the UO-based Oregon Partnership for Disaster Resilience, after asking "what would we do if tomorrow morning we wake up and Cascadia is shaking" and "what if it doesn't happen for 50 years."
The audience — those in Straub Hall and another 200-plus who tuned in to the live stream from the UO Channel — also learned how the Cascadia subduction zone was identified and how a fully functional earthquake early warning system could benefit cities from Eugene to Seattle.
Bruce provided practical guidance for residents to help their families and communities prepare for such an event both now and in the future to reduce the risks of personal injury, property damage and infrastructural interruptions.
A magnitude 9 quake offshore in the subduction zone would be felt for several minutes in the Eugene area but at a magnitude of about 6 to 7, Toomey said. The impact on critical services, Bruce said, could be a loss of electricity for one to three months and public drinking water for up to a year. In addition, damage to highways could lead to disruptions for up to 12 months and health services could be compromised for up to 18 months.
Area residents, Bruce said, should educate themselves about the potential disruptions and prepare disaster kits that include essentials such as food and water to cover up to three months. They also should pursue safety upgrades, if necessary, for their homes.
Toomey called the New Yorker stories that prompted the forum well written. While those articles spurred both conversation and fear, the public should understand the risks of the three forms of earthquakes that occur in the Pacific Northwest, he said.
Toomey and Chris Goldfinger, a professor of geology and geophysics at Oregon State University, estimated the risk of a Cascadia quake in the neighborhood of 10 to 20 percent in the next 50 years. The last full-length Cascadia subduction zone earthquake occurred about 300 years ago.
That risk is the result of a growing body of evidence that began in about 1984 with the work of Canadian geologist John Adams, said Goldfinger, who was quoted prominently in the first New Yorker article.
Goldfinger's research team has studied cores of sediment from under the ocean floor off the Pacific Northwest and from multiple lakebeds from northern California to northern Washington. Those core samples provide strong support to Adams' theoretical observations and a physical history of quakes in the subduction zone dating back 10,000 years. The zone stretches from Mendocino, California, to Vancouver, British Columbia.
Included in the core samples, Goldfinger said, is a region-wide layer of ash from the eruption of Mount Mazama that formed Crater Lake 7,700 years ago.
Based on Goldfinger's research, the Cascadia record shows the region's southern half is overdue and the northern half is in a geological time frame that provides the current probabilities for earthquakes in the next 50 years.
Toomey said it is vital to have continued federal and state support in the region to add seismometers, especially throughout Oregon, to tie the Pacific Northwest into a full West Coast earthquake early warning system.
U.S. Rep. Peter DeFazio, a leading proponent of a warning system, spoke briefly as the forum began about the potential to save lives and mitigate damage with advanced notification. "We need to continue to raise awareness among the populace so people will be educated on what to do," he said. "And we need to much more better educate our policymakers."
After the evening's presentations, numerous questions from the public were addressed. Additional questions submitted by the audience will be grouped and answered via the UO's "The Really Big One" forum website.
The UO Department of Geological Sciences organized the forum.
— By Jim Barlow, Public Affairs Communications