That doesn’t mean towering curls sixty feet high will slam the coast. As videos from Japan and Sumatra showed, tsunamis come ashore as massive surges. When scientists measure their size, what they’re talking about is run-up: how high the water reaches relative to sea level. A sixty-foot tsunami will flood coastal areas up to an elevation of sixty feet.
“In my mind Japan is a good proxy for what could happen here,” said Bernard, who almost single-handedly kept tsunami research alive in the United States at a time when few people took the threat seriously. When the tall Texan started graduate school in oceanography in 1969, tsunamis were of interest only because they occasionally snuck up on places like Hawaii, triggered by earthquakes far away. When he first heard Brian Atwater describe sand layers deposited on the Washington coast by ancient tsunamis, Bernard, by then the leader of NOAA’s Seattle lab, didn’t believe it. “I was one of Brian’s severest critics,” he recalled.
How could Atwater be sure the sand wasn’t washed in by storms, Bernard wanted to know. Maybe the shape of the coastline was different hundreds of years ago, making it more vulnerable to floods. At the time, NOAA’s small tsunami program was focused mainly on preventing false alarms. A needless evacuation after a 1986 Alaska quake cost the state of Hawaii $40 million, and it wasn’t the first. Officials there were fed up with rousting locals and tourists for piddling waves a foot or two high.
But a tsunami on the West Coast’s doorstep would be a much deadlier threat. Following in Atwater’s footsteps, geologists started digging in bays and marshes all along the coast. Almost everywhere they looked, including Seaside and Cannon Beach, they found similar layers of sand. Some of the ancient waves that roared up Ecola Creek left their tracks nearly a mile and a half inland. Other tsunamis seem to have been less ferocious. The surge kicked up by the 1700 megaquake—the one that flooded villages in Japan—left a sand layer so much smaller than some of the others that scientists called it “the wimp.” Muddy cores from one coastal lake in Oregon revealed a period when quake-triggered tsunamis were slapping the coast every three hundred years or so, lending credence to the argument that the southern portion of the subduction may rip more frequently.
What really launched tsunami science in the United States, though, was a 1992 earthquake in Northern California that might have been a dress rehearsal for a Cascadia megaquake. The main shock struck on April 25, when the artist colony of Ferndale was hosting a Wild West festival. The ground shook so hard that participants, many dressed in cowboy costumes, staggered and fell to the pavement. Elegantly restored Victorian homes collapsed.
In nearby Petrolia the post office, gas station, and general store caught fire and burned to the ground. Fissures a hundred feet long ripped through pastures where horses had been grazing minutes before. The ground motions were some of the strongest ever recorded, but the Church of Scientology’s underground vault in rural Humboldt County was reportedly unscathed. As the extent of the damage became clear, President George H. W. Bush issued a disaster declaration.
In the redwoods north of Eureka, Humboldt State University geology professor Lori Dengler and her family were getting ready for a picnic on the beach when their two-story house began to rock. After she caught her breath, Dengler started counting. When she ticked off seventy-five seconds, she knew it wasn’t a typical California temblor. “I could tell it was big,” she recalled. Her outing cancelled, Dengler sped to the office.
During the hubbub that followed, Dengler was pressed for one media interview after another. Good Morning America sent a prom limo to her doorstep to fetch her for a 3:00 AM spot. It was a few days before she and her colleagues were able to sort through the curious accounts trickling in from the coast. Some beachcombers described being chased out of the surf by violent churning. Others reported shellfish-covered rocks rising from the water.
When Dengler finally got down to the shore, she was floored. More than fifteen miles of coastline had been shoved up three feet or more. Mussels, periwinkles, and seaweed clung to the new shelf, rotting in the sun. “The stench was amazing.” Abalone beds normally too deep to reach were lifted so high that people were able to snag the prized shellfish by wading out up to their knees. The churning water on the day of the quake turned out to have been a tsunami, triggered when the seafloor jerked upward. Luckily for those on the beach, the three- to five-foot surge arrived at low tide.
Seismologists traced the magnitude 7.2 quake back to the southernmost tip of the Cascadia Subduction Zone. The stub of the Juan de Fuca Plate that lies off Northern California is sometimes called the Gorda Plate. It sits in the knotty, tectonic conflux where the San Andreas Fault ends and Cascadia begins. Riddled with cracks and under pressure from every direction, the area is a seismic hot spot, so it wasn’t immediately clear which fault was to blame. It was only after sorting through the data that scientists realized the region had just experienced a very close call. In a miniversion of a Cascadia megathrust, the very tip of the subduction zone had ripped. Blocks of seafloor and continent jerked past each other. Why the fault didn’t keep unzipping along its seven-hundred-mile length remains a mystery. “Mother Nature was kind to us,” Dengler said. “It could have easily been a 9.”
For the handful of experts and officials on the West Coast who paid attention to such things, the 1992 Cape Mendocino quake and tsunami was a shocker. If a tiny Cascadia rupture could trigger a five-foot tsunami, the prospect of scaling that up along the entire coast was hair-raising.
Tsunamis have always ranked among the most terrifying of natural disasters. They lure the curious by drawing back the sea, then rush in with deadly speed and a force that’s impossible to resist. The waves can travel halfway across the globe and still strike hard enough to kill. Although an earthquake lasts a few minutes at most, tsunami surges often pummel coastlines for twelve hours or more.
Underwater landslides and volcanic eruptions can trigger tsunamis, but most of the giant waves are born in subduction zone quakes. As tectonic forces overcome the friction that locks oceanic and continental crust in a tight embrace, masses of rock lurch violently. The continental margin, which is dragged downward by the subducting seafloor, breaks free and springs up. Parts of the seafloor also drop. It’s the combination of that upward flick and downward drop that initiates the tsunami by displacing tons of seawater. Strike-slip earthquakes, caused when blocks of rock jerk past each other side by side, don’t usually trigger tsunamis because they don’t raise or lower the ocean floor.
Japan’s 2011 tsunami was so enormous because the underwater upheaval was beyond what anyone had considered possible. In some places plates slid past each other by a staggering 160 feet—more than half the length of a football field. Expanses of rock thrust up 35 feet—taller than a three-story building. A robot submarine filmed the seafloor soon after the quake and found towering new cliffs and fissures so deep they appeared bottomless.
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At its origin a tsunami seems innocuous. The sea surface might bob a few feet as water bulges upward then ripples out in concentric rings. But unlike ordinary waves, which merely ruffle the surface, tsunamis shift a water column that can be two miles deep. Multiply that across the thousands of square miles of seafloor warped by a giant quake and it starts to explain the unstoppable momentum behind the waves that ripped through Japan and Indonesia.
Tsunamis traverse the open ocean as fast as a jetliner flies. As they speed out in either direction, underwater ridges and canyons can steer the waves. Crescent City, on the Northern California coast, is a tsunami magnet largely because it sits in the crosshairs of a 1,200-mile-long submarine hogback called the Mendocino Escarpment. The ridge steers tsunamis toward the small harbor, which is also the perfect size and shape to amplify the sloshing.
Until a tsunami nears shore, it’s barely noticeable among the surface waves that roil the sea. The surge starts to build only when its leading edge scrapes across the shallow continental shelf. As the water at the front of the wave slows
, the steamroller behind it keeps coming. The sea piles up, building into a churning mass that grows like an out-of-control tide. Many victims venture back to the water’s edge after the initial surge retreats, only to be caught up by subsequent waves.
A year after California’s 1992 warning shot, an earthquake and tsunami wreaked havoc on a small island off Japan’s west coast, killing nearly two hundred people. Eddie Bernard was part of the scientific team that documented the devastation. He came home more convinced than ever that this was something the United States needed to pay attention to. Propelled by Bernard’s enthusiasm and backed by powerful senators from the Northwest, Alaska, and Hawaii, the National Tsunami Hazard Mitigation Program was launched. “It was a hard sell,” Bernard recalled. Congressional earmarks were the only thing that kept the program alive in its early days. Then the Indian Ocean tsunami hit and everything soared off the scale.
In 2004 Vasily Titov, the lead tsunami modeler at Bernard’s lab, was spending a lonely Christmas in Seattle. He’d planned to join his wife and her family in Chicago, but his flight was cancelled. When he got an automated phone message on Christmas Day alerting him to an earthquake near Sumatra, Titov figured he might as well check it out. The initial magnitude report wasn’t very big. Titov tracked aftershocks on his home computer. Following major quakes, the fault segment that just ruptured keeps twitching and slipping and popping. The pattern of aftershocks offers a rough measure of the rupture length. Titov could barely believe what he was seeing on his screen. Aftershocks were flaring up over an area nearly seven hundred miles long. “I knew then that this was a much bigger event and that it was going to be a sizable tsunami.”
Titov dashed to his car and sped to the NOAA complex on Lake Washington. It was around 7:00 PM. The building was dark and deserted as Titov switched on his office lights and fired up his computer. He started setting up a numerical grid and feeding in bathymetric data from the Indian Ocean. The tsunami model he’d been working on for nearly a decade was one of the most advanced in the world, but it was still experimental. It had never been tested against an actual tsunami, unfolding in real time.
But that had always been Titov’s goal. He wanted a model that was useful, not theoretical. Ideally, he would someday be able to predict within minutes of an earthquake when the tsunami surges would hit shore and how big they would be.
Titov, a Russian native, started studying the giant waves in the world’s most unlikely spot: Novosibirsk, a Siberian science city at the geographical center of the Asian continent. “If you want to get as far as possible from the sea, that’s where you go,” Titov said.
In the 1980s tsunami research was exotic. Except for grainy black-and-white pictures, few of those working in the field had ever seen one of the giant waves. Titov expected to spend a few years tinkering with the model, then move on to something with better career prospects. But when Bernard offered him a job in Seattle with top-notch computing facilities and an opportunity to help figure out a way to forecast tsunami flooding, Titov couldn’t resist.
On that Christmas in 2004, he worked through the night. Procedures that now take minutes ate up hours. Titov switched on CNN, but news reports were sparse. It was nearing 3:00 AM when he was finally ready to start running his model. The tsunami had already spread death and destruction along the coasts of Indonesia, Thailand, and India, and was racing toward the coast of Africa where more than three hundred people would be swept away. But there was nothing Titov could do to warn those in the tsunami’s path. His model wasn’t fast enough yet to get in front of the speeding waves. During the days that followed, however, Titov’s map of the tsunami’s intensity became the go- to source for search-and-rescue crews and relief operations targeting the hardest-hit areas.
The Indian Ocean disaster prompted the United States to triple its funding for tsunami research, modeling, and preparedness. Bernard’s six-person team expanded to more than two dozen scientists and technicians. Much of the new money went to bolster the country’s fledgling network of tsunami detection buoys, which Bernard and his colleagues had spent more than a decade developing. In 2004 there were six buoys anchored in deep water off Alaska, the Pacific Northwest, and Hawaii. By 2012 a network of forty U.S. instruments and fifteen from other nations stood watch over the world’s ocean basins, lowering the odds that another giant tsunami would take people on distant shores by surprise.
The heart of the instruments is a sensitive pressure sensor that sits on the seafloor. As a tsunami passes by, the sensor detects the shift in water pressure and calculates the wave’s height. Even a centimeter-high tsunami can’t sneak past unnoticed. The buoy beams the data direct to labs and government agencies around the globe.
Before the network existed, determining whether a tsunami would be destructive was a tough call. Two out of every three warnings were false alarms. The only thing forecasters had to go on were seismograms, which provided a quick estimate of the earthquake’s size and location. But size alone isn’t enough to tell whether a tsunami will be generated or how big it may be. By directly measuring the wave, the buoys eliminate most of that uncertainty. Japanese forecasters realized they had vastly underestimated the size of the 2011 tsunami when the wave reached the closest buoy. The measurement was a whopping 5.5 feet, the largest ever detected in the open ocean. “When we saw that, we could see that it was going to be huge,” Titov said.
As Japan’s 2011 calamity unfolded, Titov was finally able to show that his model could get ahead of the curve. Using data from the buoys, he accurately forecast the arrival times and heights of the modest waves that came ashore along the U.S. West Coast and Hawaii. One town on the island of Maui experienced damaging floods, which the model predicted six hours in advance. Titov’s model is also helping communities map out areas that are likely to flood in a Cascadia tsunami and plan evacuation routes.
But on the day the megaquake strikes, neither the high-tech model nor the state-of-the-art tsunami detection buoys will be of much help to people in Seaside, Cannon Beach, Ocean Shores, and other communities close to ground zero. The buoys are stellar sentinels for tsunamis that arrive from far away, affording the luxury of hours to evacuate. For a tsunami that will slam into shore in less than half an hour, the data they provide arrive too late to help with the initial warning.
It will take about fifteen minutes for Cascadia’s tsunami to reach the closest buoy off the Northwest coast. If everything works perfectly, Titov might be able to feed that initial wave height into his model and produce a flooding forecast within thirty minutes. That will be welcome information for communities along the Strait of Juan de Fuca and northern Puget Sound, where the tsunami won’t arrive for one to two hours. But communities on the coast will have already been hit by the time the forecast is finished.
The first formal alert will come from the West Coast and Alaska Tsunami Warning Center near Anchorage. Based on initial seismic readings, which often underestimate quake size, the center should be able to push out a warning within five minutes. Data coming in from the buoys will help update and refine subsequent alerts and track the multiple tsunami surges. But in the chaos and blackouts following one of the world’s most powerful earthquakes, it’s a crapshoot whether those messages will get through to the people in harm’s way.
In the final analysis, the best advice Titov, Bernard, Dengler, and every other tsunami expert can offer is the same mantra Corcoran preaches: Don’t count on sirens or other technology. Don’t wait for official confirmation. If you feel the earth quake, head for high ground.
“If you want to sit around and argue about it, go right ahead,” Corcoran added. “I just hope you haven’t bred yet and you’re out of the gene pool.”
The videos of 3/11 that hit Stephanie Fritts hardest were from Sendai. Cars were creeping like ants across an expanse of rice paddies, their drivers trying hopelessly to outpace the water. “That wave was going so much faster than the cars,” Fritts said, shaking her head as if to block out the image. “That big,
black, dirty wave.”
As emergency management director for Pacific County, Fritts’s territory includes a section of the Washington coast that looks a lot like the Sendai Plain. With twenty-eight miles of beach that gleam like mother-of-pearl, the Long Beach Peninsula isn’t nearly as developed as Sendai is. But it’s just as flat.
The spit owes its existence to the Columbia River. As the waterway merges with the Pacific, the freshwater current swings north, dumping sediment as it goes. The peninsula measures about two miles across at its widest point. Some five thousand souls live there year-round in homes that open onto the sea or sit tucked behind grassy dunes. As many as twenty-five thousand people crowd hotels and campgrounds during the annual kite festival in August. An abundance of bogs makes this prime country for growing cranberries. Oysters love it, too. Some of the highest spots around are the mountains of shells piled outside local seafood plants.
At the county building in the town of Long Beach, Fritts unfolded the tsunami hazard maps for the peninsula on a fall day in 2012. Except for green patches at each end designating high ground, the entire spit is colored various shades of yellow. The only reason it’s not red is because the maps are designed with the color-blind in mind. Yellow is as bad as it gets. A Cascadia tsunami half the size of Japan’s biggest waves would completely submerge most of this narrow tongue of land, just as the black water engulfed the flat fields around Sendai. The outlook is equally grim on the Ocean Shores Peninsula to the north, Washington’s most popular beach resort. Even by car there wouldn’t be enough time to evacuate, and the roads are likely to be jumbled blocks of pavement anyway.
With nowhere to run, folks in these vulnerable spots are considering a very Japanese option: engineering their own high ground. The town of Long Beach, where a cheerful arch welcomes visitors to “The World’s Longest Beach,” is applying for federal grants to build the country’s first tsunami evacuation structure. Working with architects and engineers from the University of Washington, residents decided on a high, grassy berm that could be incorporated in the elementary school’s athletic fields. With gently sloping access ramps and a broad top, the artificial hill could provide refuge to one thousand people.
Full-Rip 9.0: The Next Big Earthquake in the Pacific Northwest Page 17