When Rob Witter’s phone beeped late the night of March 10 with a text message indicating there had been a magnitude 7.9 earthquake off the coast of Japan (later upgraded to 8.9), “That really caught my interest,” he says—and then he went to bed. He woke at 4:30 a.m. when the telephone rang: Due to the tsunami warning on the Oregon Coast, his daughter’s school in Newport would be closed for the day.
“That’s a first,” he recalls thinking. Still, he remained nonplussed.
This was not the tsunami Witter worries about.
Some day, probably in the next fifty to 100 years, part or all of an underwater fault stretching from Vancouver Island to Eureka, California, will rupture. The result will be an epic earthquake—roughly the size of the March 11 Japanese quake, or even higher, according to scientists’ projections—that will shake the Pacific Northwest like nothing has in 311 years. That rupture, the result of the Juan de Fuca tectonic plate’s inexorable, jerky slide under the North American plate, will displace a huge volume of ocean and send a series of massive waves speeding toward the Oregon shore.
That such massive quakes and tsunamis have happened here in the past and will happen again is virtually incontrovertible, according to geologists and others who have spent the past twenty or thirty years uncovering mounting evidence: ghost forests of standing dead trees drowned in one prehistoric fell swoop, patterns of underwater sediment deposits left by submarine avalanches, ocean sand and tidal mud layered like mille-feuille in estuaries, Edo-period samurai scribes’ jottings about flood damage from unexplained waves striking Japan’s east coast—just the way waves from Japan busted up boats in Brookings this spring. Exactly when the next Big One will hit is anyone’s guess. When it does, coastal residents and visitors will have just ten or twenty minutes to pick themselves up off the ground after the shaking stops and to run—not drive, as the roads will be a wreck—to high ground or risk being swept out to sea by the approaching tsunami.
How high will be high enough? That’s the question Rob Witter PhD ’99 has spent much of the past fifteen years or so investigating. It’s become a major focus of the Oregon Department of Geology and Mineral Industries (DOGAMI), a state agency that, until the past decade or two, was more concerned with regulating prospectors than mitigating natural hazards. Witter joined DOGAMI’s coastal field office in Newport in 2005 as a regional coastal geologist. He’s now managing the agency’s efforts to draw the projected worst-case-scenario high-water line for the state’s entire coastline and communicating it widely and clearly and accurately and compellingly to everyone who will listen, read, or look.
“It’s a really ambitious project. Our little agency is splitting its seams trying to get this project done, ’cause it’s so huge.”
No other U.S. state has attempted a tsunami hazard-mapping project this comprehensive. But excluding Alaska, Oregon faces the highest risk of any state to property and lives from tsunamis, because of its proximity to a quake-generating fault line—the Cascadia Subduction Zone—and the many low-lying coastal towns and accessible beaches. With detailed computer modeling of the inundation zone provided by Joseph Zhang of Oregon Health and Science University, Witter’s team is creating maps showing how high is high enough along every inch of the state’s more than 360-mile coastline. Printed maps are being prepared for the major cities and towns and updated maps of the entire coastline will be available online by 2013. (See Oregon.gov and search for “tsunami maps.”)
No one knows how big the next Big One will be, so Witter is drawing the limit of the evacuation zone at the height required for an extra-large tsunami (geologic records indicate that the last Big One, in 1700, was, relative to previous quakes, merely medium-sized). The project builds on earlier tsunami hazard assessment work completed by DOGAMI in the 1990s, but newer data suggest that that work underestimated the possible height of the inundation zone.
The new evacuation maps actually indicate two maximum tsunami inundation zones. The orange zone is the theoretical worst case inundation from a distant tsunami, such as the one generated by the quake from Japan on March 11—not a particularly emergent emergency. “When you hear a siren or see a warning about a tsunami coming from an earthquake far away, relax,” Witter says. “As long as you stay away from beaches, harbors, and marinas, there’s very little risk.”
It’s a local tsunami—whose much larger inundation zone is indicated in yellow on the new maps—that prompted the mapping project. In that case, warning sirens won’t even be necessary: the unmistakable shaking of a magnitude 8-plus earthquake will be all the warning you need. People just need to know where to go and how to get there. That’s why DOGAMI is doing more than handing out maps and posting them online. The project includes holding community meetings and hiring local organizers to begin and help sustain the consciousness-raising necessary to make a community truly tsunami-ready: today, and tomorrow, and long after DOGAMI has picked up its sediment corers and gone home.
It’s not exactly what Witter imagined he’d be doing when he grew up. He was a biology major at Whitman College, but by his senior year he’d lost his passion for the life sciences. Plate tectonics, though—continental and oceanic crusts colliding and pulling apart over eons and right this very minute—now that was interesting. He squeezed in a couple of geology classes toward the end of college, learning just enough to whet his interest and point him toward graduate school. At the UO, he fell in with a visiting geologist studying evidence of huge earthquakes and tsunamis on the southern Oregon coast. Such evidence had already been found elsewhere in the Pacific Northwest, but the mouths of the Coquille and Sixes rivers and adjacent coastal plain was virgin territory. Witter had intended to earn a master’s degree at Oregon, but after he and his supervising professor successfully applied for funding from the National Science Foundation, a doctoral dissertation was born. He spent several years with the leading geotechnical consulting firm William Lettis and Associates between grad school and the job with DOGAMI.
If the Japanese tsunami was a wake-up call, recent events in Chile—whose geologic history even more closely mirrors Oregon’s—are equally instructive. Witter made two trips there in 2010, once to deliver a paper at an academic conference and once following the magnitude 8.8 earthquake and tsunami of February 27. Two weeks later Witter was on site, taking sediment cores and documenting the disaster. It gave him a sobering firsthand view of what Oregon has to look forward to.
“It was unbelievable. Constitución was just flattened,” he recalls. Some 350 people were killed in that city alone—a number that might have been much higher had the town not held a tsunami-preparedness drill just two weeks earlier.
“Front-loaders were driving down the main city streets, clearing debris—still, when we got there, two weeks after the tsunami.” Constitución is a smallish seaside resort city spread out on the coastal plain at the mouth of a river.
“That’s Seaside, Oregon,” Witter adds. “Exactly.”
—By Bonnie Henderson ’79, MA ’85
Update: Witter was among a half-dozen geologists from around the world who spent early May doing field research on northern Japan’s Sendai Plain, site of the greatest tsunami devastation following the Tohoku earthquake. They tested a computer model designed to estimate the size and speed of tsunami waves from the thickness and grain size of sand deposited by a tsunami. From this work, scientists will be able to more closely estimate the magnitude of past tsunamis on the Pacific Northwest coast—and make projections about what’s ahead.