The last great earthquake to strike the Pacific Northwest occurred on January 26, 1700, at about 9 p.m. Parts of the coastline dropped three to six feet in an instant. It set off landslides throughout the Oregon Coast Range. Some of them are still moving. If you could hear soil, rocks and trees creep inch-by-inch downhill, some of those sounds would echo that massive jolt. At sea, it generated tsunamis that reshaped the Northwest coastline, traveled across the Pacific and swept through bays and coastal communities in Japan.
Scientists know that this scenario has happened repeatedly in the last 10,000 years and will do so again. Oregon State University geologist Chris Goldfinger calculates the chance of a major quake at 40 percent in the next 50 years off the southern Oregon coast. The frequency decreases as you move north, but the nearly 800-mile Cascadia subduction zone, where these quakes originate, could rupture anywhere. The last one wiped out villages. The next one will threaten cities and bring a regional economy to its knees.
Nevertheless, for most of us, the threat seems as likely as getting hit by lightning. We know it could happen, but we don’t take it seriously. It feels remote. “The paradigm shift among the citizens of the Northwest has not yet taken place,” says Bob Yeats, emeritus professor of geology at Oregon State and author of Living with Earthquakes in the Pacific Northwest.
As recently as 30 years ago, most scientists didn’t think a major quake could happen here. But, says Yeats in an upcoming book, evidence from coastal marshes, seafloor canyons, GPS monitoring stations and native traditions tell a compelling story: The western edge of North America is locked against another part of the Earth’s crust, the Juan de Fuca Plate, which is diving beneath us. Like wrestlers in mortal combat, they occasionally break their hold on each other and lurch into a new position. Geologists have given such events a name right out of Saturday night wrestling — “megathrust.” When it happens, the landscape vibrates like a bass drum. Seismic waves pulse through the crust for three minutes or more. Some types of soil liquefy and spread out. Bridge and building foundations get pushed out of alignment. Other soils could amplify the shaking from below, subjecting buildings, especially high-rises, to even more violent motion.
Scott Ashford has seen the consequences of these quakes in Chile, Japan and New Zealand: buildings and bridges tilted and broken like toys, beachfront tourist towns reduced to rubble, pipelines squeezed out of the ground like toothpaste out of a tube, businesses closed or forced to relocate.
“Many of Oregon’s lifeline providers have shared research needs, whether it’s to improve our ground motion predictions, to assess liquefaction potential of Oregon soils or to develop retrofit technologies for our legacy systems.”
— Matthew L. Garrett, Director, Oregon Department of Transportation
The Oregon State Kearney Professor of Engineering is determined to soften the blow when Oregon’s turn arrives. In 2010, after viewing damage from a megathrust quake in Chile, Ashford developed the idea for the Cascadia Lifelines Program, a consortium of Oregon businesses, government agencies and universities. The goal is to save lives and to shorten the time it will take for the state and the nation to recover.
“If you look at the effect on the people and at recovery, a key part of our resilience is lifelines,” Ashford says. “Electric power, natural gas, transportation systems, telecommunications, drinking water, sewer. And critical facilities like the Port of Portland and the Portland International Airport. All of these lifeline providers have common challenges to prepare for this next earthquake. None by itself has the financial ability to fund the research necessary. My vision is to pursue research of common interest to develop cost-effective solutions to mitigate the Cascadia earthquake.”
Members of the consortium already include the Oregon Department of Transportation, Portland General Electric, NW Natural (Northwest Natural Gas), the Port of Portland, the Portland Water Bureau and the Bonneville Power Administration. Ashford is lining up others as well. Among their concerns are building standards, landslides, communications and recovery strategies. But first up on their research agenda is an Oregon State study of soil liquefaction, the phenomenon that compounds the damage caused by seismic shaking.
Soils are often named for the places where they’re found. California’s state soil is called San Joaquin. In Washington, Tokul soil is named after a community in King County. Oregon’s state soil is Jory, named for a hill in Marion County where a family of that name settled in 1852. For geotechnical engineers, another local soil poses a potential risk in a megathrust earthquake: Willamette silt.
With a texture midway between sand and clay, this remnant of the ancient Missoula Floods underlies much of the Willamette Valley. From McMinnville nearly to Eugene, bridge piers, roads (I-5, U.S. Highway 99) and pipelines run through or on top of Willamette silt. It carries railroad tracks and electric transmission lines. Large parts of Salem sit on it, as do Albany, Corvallis and Sweet Home. It is up to 130 feet deep in some places.
“We don’t really know anything about how Willamette silt responds to earthquakes,” says Ben Mason, an assistant professor of civil engineering at Oregon State. What he does know is that, as soils go, it doesn’t take much water for it to change from being dry and crumbly to taking on the properties of a liquid. “It has a low plasticity index. What that means is that it can liquefy during an earthquake,” he says. At least theoretically.
To find out for sure, Mason has collected Willamette silt from the Oregon State campus. Last winter, he and a colleague, Li Zheng from the Nanjing Hydraulic Research Institute in China (Li wants to know how earthen dams will perform during an earthquake), placed soil samples the size of hockey pucks in a device that simulates conditions deep underground. They subjected the samples to repeated, precisely controlled cycles of shaking. As a piston shook the sample, simulating seismic waves, sensors measured changes in volume and in water pressure inside the soil.
As the shaking continued, “the water pressure builds up, builds up and builds up and eventually the soil will act like a liquid,” says Mason. “And that’s when we say liquefaction happens.” In effect, he explains, soil structure breaks down, water oozes from pores where it had been bound and the soil turns into a mass with the consistency of pea soup.
We can see liquefaction in action when we walk on a beach, Mason adds. “If you run, you cause these minor liquefaction events. It’s a very dynamic load hitting the sand.” Water is forced out from between the grains and pools briefly on the surface. In contrast, water underground has nowhere to go. As Mason’s experiments show, pressure rises. The question is: Will it get high enough to trigger liquefaction? If it does and the soil happens to be on a slope, it can spread out, jeopardizing any structure that is in the way, such as a bridge pier, building foundation or pipeline.
Mason’s experiments are the first to be supported by Cascadia Lifelines Program funding. His lab is one of the few on the West Coast with the ability to subject soils to a wide range of precisely controlled earthquakes. His “cyclic simple shear” device can be programmed to mimic seismic waves with varying duration and strength. With accurate information about Willamette silt, engineers will be able to design structures that can minimize the damage from the possibility of soil movement caused by liquefaction. Engineering firms are already contacting him to test soil samples for project design purposes.
Buildings and Bridges
Most schools, city halls, bridges, commercial buildings and other structures in Oregon were built before the possibility of big earthquakes was taken seriously. “We don’t know how these buildings will perform (in an earthquake),” says Andre Barbosa, an Oregon State structural engineer. “We have a very rough idea. We know by year and type of construction, whether this or that building may behave well or not so well. But we don’t really know.”
As an epidemiologist, Jeff Bethel understands the vital role of public health in saving lives after a natural disaster. Most at risk, he says, are vulnerable populations — migrant laborers and people who live alone or have chronic illnesses.
Because seismic stresses were not even recognized in the state’s building codes until 1974, our infrastructure and architectural heritage are highly vulnerable. According to the Oregon Resilience Plan, a report produced by the Oregon Seismic Safety Policy Advisory Commission (OSSPAC) in 2013, nearly half of 2,193 schools assessed in the state have a high to very high potential for collapse. More than a third of the 2,567 bridges in the state highway system were built with no seismic considerations. All nine of Portland’s bridges over the Willamette were built before seismic codes were in force, although some have been strengthened.
But estimating vulnerability is only the start, says Barbosa, who specializes in structural performance in earthquakes. Engineers also need to evaluate strategies for retrofitting old structures and improving standards for new construction. Toward that end, Barbosa conducts experiments on building and bridge components in the Oregon State structures lab, which boasts the second-largest “strong floor” on the West Coast. It allows researchers to simulate earthquake forces up to 1 million pounds on frames up to two stories high. In a project for the Oregon Department of Transportation, Barbosa is evaluating the performance of high-strength reinforcing steel (aka “rebar”) to resist long-duration shaking.
That fills an important need in the Northwest where subduction zone earthquakes are likely to last three to five minutes or more. In contrast, crustal earthquakes, such as those along the famed San Andreas Fault in California, typically last 30 seconds or less. The difference adds up to higher demands on buildings, especially where the frequency of the seismic waves matches a structure’s internal characteristics.
“The main objective of our modern building codes is life safety,” Barbosa adds. “We design structures so that people can evacuate in case of strong shaking. The structure can vibrate back and forth, but it is designed not to collapse. That’s the life safety design approach.”
In addition to living in earthquake country, Barbosa has a personal connection to such events. He grew up in Lisbon, Portugal, which suffered a cataclysmic earthquake and tsunami in 1755. Geologists now estimate that it approached the strength of the 1700 megathrust earthquake in the Pacific Northwest. Since then, Portugal and the Northwest have experienced thousands of smaller quakes centered in local faults, but there have been no large events of the kind seen recently in Chile and Japan. “The problems we have in Portugal are the same as we have here in Oregon,” he says. “The return period for large earthquakes is very long. People just don’t remember.”
Nevertheless, Oregon is taking a leadership role in planning. Elsewhere, agencies and regions (the San Francisco Bay Area) have developed a holistic approach to resilience, but Oregon is the first to do so at the state level. “Through OSSPAC,” says Barbosa, “Oregon is doing something that is amazing.”
When Michael Olsen pulls up a map of the Oregon Coast Range on his computer, he sees wide swaths of red dots. Each one represents landslide-prone areas identified through the highly accurate lens of a remote sensing technology known as LIDAR (“light detection and ranging”). The Oregon State civil engineer and Hoffman Faculty Scholar specializes in the emerging field of geomatics, which is land surveying on steroids. Geomatics practitioners analyze landscapes by combining remote sensing data (from the ground, the air or planetary orbit) and large spatial datasets for soils, vegetation, precipitation, streams and other features.
In the Coast Range, Olsen and his graduate students are assembling LIDAR data and layering it with what engineers know about the terrain. Working with the Oregon Department of Transportation, their goal is to estimate the likelihood of earthquake-triggered landslides near highways that link the I-5 corridor with coastal communities.
These mountains might be beautiful, but Olsen’s picture isn’t pretty. “The Coast Range consists of very loose soils that are of very poor quality. They don’t have a lot of strength to them,” he says. In an emergency, “barriers along these lifeline corridors would be a big problem. Even a small landslide can close down a road for a day or two.”
And it doesn’t take much to start Coast Range soils moving. Based on the locations of previous slides and knowledge of soil types, it appears that slopes as low as 10 to 15 percent are vulnerable to sliding. “That isn’t that much. It’s pretty scary that it’s that low,” Olsen says.
Landslides are hardly a new phenomenon in Oregon, but they are more common in some years than in others. The winter storms of 1996-97 generated an estimated 9,500 landslides, mostly in western Oregon. Scientists at the Oregon Department of Geology and Mineral Industries (DOGAMI) have calculated that, while economic losses exceed $10 million in a typical year, they exceeded $100 million that winter.
Although all Coast Range roads pass through slide-prone terrain, some may be less vulnerable and easier to re-open than others. Such information, says Olsen, will help ODOT prioritize roads for earthquake recovery purposes.
A Statewide Effort
By coordinating these and other research investments, Cascadia Lifelines meets an important need for state agencies and utility companies and fills a critical niche in statewide preparedness efforts. Spurred by the state Legislature, scientists, utility companies and agencies are evaluating risks and identifying solutions to mitigate the most significant impacts of the next megathrust earthquake. Schools and other public buildings have been assessed, and retrofits have begun. Roadways are being ranked for vulnerability to landslides and bridge failures. On the coast, evacuation routes are being marked to help coastal residents and visitors escape the tsunami zone.
“Given the nature and wide-ranging impact of seismic activity, it is appropriate that a consortium of organizations engaged in building, operating and maintaining critical infrastructure in Oregon could work together to identify and address concerns about improving seismic resilience.”
— Grant Yoshihara, Vice President, NW Natural
In 2011, Oregon’s Earthquake Commission (aka the Oregon Seismic Safety Policy Advisory Commission or OSSPAC) assembled experts to lay out the risks and recommend a series of steps for the next 50 years. It released a final report — The Oregon Resilience Plan — last February. “The broad picture of what needs to be done is pretty straightforward,” says Ian Madin, chief scientist for DOGAMI and an Oregon State alum who helped to lead the planning. “We need to strengthen our infrastructure so that it physically resists the effects of the earthquake, so that it is either undamaged or easily repairable.”
Engineers know how to design earthquake-resilient structures, say Madin and Ashford. They can “harden” foundation soils to resist liquefaction and construct bridges and buildings that can survive shaking. Such measures carry a stiff price tag, but the return on investment can be positive. For example, says Ashford, after the earthquake in Christchurch, New Zealand, earthquake preparedness steps saved $10 for $1 spent.
Power to Recover
Ultimately, recovery is about more than engineering. It is about assistance for a traumatized citizenry, strategies for keeping small businesses afloat, security to prevent looting, radio systems that will work after cell-phone towers and land lines go down and policies that allow restoration projects to be fast-tracked. In Chile, Ashford adds, electricity was crucial for recovery efforts. Water pumps in rural areas, for example, couldn’t even be tested until power was restored.
In New Zealand, homeowners insure against earthquakes as well as fire. The government helped businesses get back on their feet by creating a temporary mall out of shipping containers. Grants kept paychecks flowing to employees who otherwise would have qualified for unemployment. Some businesses provided food and fuel to employees’ families so that workers could focus on the job of rebuilding without worrying if their loved-ones were safe.
Individuals need to prepare as well. “I’m a big believer in personal responsibility,” says Ashford. He has installed an electrical generator port on his home, keeps extra medication on hand and fills his truck’s fuel tank when it hits half empty. “Every family needs to be prepared to be on their own for a few days. Every community needs to be prepared to be on its own. If you are expecting the government to come in immediately with assistance, it may take many days or weeks for that help to arrive.”