Full-Rip 9.0: The Next Big Earthquake in the Pacific Northwest

by Sandi Doughton

  Heaton was an unlikely choice to provide it. Just thirty-two years old, he was the newest hire at the U.S. Geological Survey’s (USGS) Pasadena office. His previous job was a one-year stint advising Exxon on earthquakes and offshore oil rigs. The son of a mathematician and a music teacher, Heaton never intended to go into geology. He wanted to play guitar. A pragmatic assessment of his prospects in the music industry quashed that plan, and a bad head for memorization bounced him out of chemistry, his second choice. He switched to physics, but the employment prospects were grim. At least there were jobs in the earth sciences.

  As a doctoral student at Caltech, he earned a reputation for cockiness—even among a group who considered themselves the Bronx Bombers of geoscience. NRC officials took note when Heaton challenged several top professors, all on the nuclear payroll, at a workshop on reactor safety. He thought they were exaggerating their ability to predict how the ground would shake during an earthquake. “They were using a lot of big words,” recalled Heaton, one of the only students in attendance. “But I thought it was a bit of a snow job, and I said so.”

  Heaton learned the hard way to question his own assumptions as well. In his first solo scientific paper, he used a mathematical trick to tease out an apparent correlation between tides and earthquakes. When he collected more data, he realized he was wrong. In one of the most humbling exercises for a scientist, he had to correct the record.

  “I really hated it,” Heaton recalled. “I realized I hadn’t been critical enough of my own thinking.”

  Even colleagues who called Heaton arrogant admired his willingness to poke at authority. The NRC probably figured it would take a touch of arrogance to step into the nuclear arena, where billions of dollars and political careers were at stake. At least the agency knew it hadn’t hired a yes man.

  One of the first things Heaton did after accepting the assignment was to charter the Cessna and fly nearly six hundred miles of coastline from Northern California to the Strait of Juan de Fuca. He was looking for evidence of giant earthquakes in a place where most geologists insisted they could never happen.

  Before he took to the air, Heaton spent several bleary-eyed days in his office slogging through reams of paperwork on the Satsop project. Despite reading a decade’s worth of seismic studies on the plant site and its environs, he was struck by how little was really known about earthquake risks in the Northwest.

  Professor Cobb’s earthquake-proof cushion had long since proved bogus. The region was not immune to damaging quakes. In 1949 a magnitude 7.1 earthquake north of Olympia rattled an area nearly the size of Texas and killed eight people. A quake south of Seattle in 1965 knocked every pier on the waterfront askew and caused more than $85 million of damage in today’s dollars. Hundreds of tiny quakes struck across the region every year. But few rose to the level of California-style disasters, and the scientific response was a collective yawn. There just wasn’t enough action to make it interesting.

  WPPSS reviewed the historical records, which went back about 150 years, and reached the logical conclusion: What’s past is prologue. The middling quakes since settlers arrived in the mid-1800s were what the region could expect in the future. The consortium added a margin of safety and for the Satsop plant set its worst-case scenario at a magnitude 7.5 quake near Olympia.

  As he tracked the logic through the documents, Heaton’s BS meter started to buzz. “I was there to be the devil’s advocate,” he recalled. “If they were making claims, I asked, ‘What’s the basis of those claims?’ ”

  Heaton knew 150 years is less than a gnat’s wing beat on geologic time scales. He also knew that geology itself had been turned upside down since WPPSS started planning the Satsop plant in the early 1970s. But the new thinking hadn’t budged the utility’s seismic bottom line.

  As late as 1975, some textbooks still ridiculed the notion that the planet’s crust was divided into plates that float like bumper cars on a cushion of semimolten rock. Most geoscientists Heaton’s age remember trying to make sense of the convoluted theories their professors offered to explain why California was jittery and Iowa wasn’t. One idea blamed quakes on stress in the Earth’s crust caused by the weight of mountain ranges. Another theory said the Earth’s surface was cooling from its fiery origins and wrinkling like the skin of a baked apple. The wrinkles were mountains, and cracks in the shriveling crust were earthquakes.

  The old ideas persisted so long because there was nothing better to replace them. They weren’t much closer to reality than Benjamin Franklin’s notion that earthquakes were caused by a subterranean sea jostling the planet’s shell. In the third century BC, Aristotle invoked a kind of planetary flatulence caused by air currents that reverberate through caverns like the “wind in our bodies … [that] can cause tremors and throbbings.” In truth, early earthquake science was as frustrating as medicine before the discovery of germs. Earthquakes happened, and nobody knew why.

  That didn’t stop geologists from defending their flawed theories as ferociously as mother bears defend their cubs when German meteorologist Alfred Wegener suggested in 1912 that many of the mysteries could be explained by continents that drift. American scientists were particularly vicious. “Utter, damned rot,” declared the president of the American Philosophical Society. But within a few decades, seafloor surveys were turning up a lot of things that didn’t fit the old world view. Among them were canyons deep enough to swallow Mount Everest and underwater mountain ranges that girdled the globe like seams on a baseball.

  Some of the most pivotal evidence came from surveys off the Northwest coast. In the mid-1950s, British geophysicist Ronald Mason and marine engineer Arthur Raff of the Scripps Institution of Oceanography convinced the U.S. Navy to let them tag along on a series of hydrographic cruises. The scientists modified a magnetic sensor used to detect enemy subs and towed it behind the ship. What they found was a pattern of zebra stripes on the ocean floor that proved to be the key to a major puzzle: if continents drifted, what was the driving force?

  The stripes, tens of miles wide, revealed that molten rock is oozing up along underwater ridges to create new seafloor. As the magma flows outward and solidifies, its crystals align with the Earth’s magnetic field like compass needles. But the magnetic field flips every few hundred thousand years. The stripes on the seafloor were a record of those reversals stretching back through time. They also provided a yardstick by which to measure the seafloor’s annual expansion of an inch or two. Multiplied over millennia, that conveyor-belt motion was what nudged the continents—or more precisely, the huge slabs of rock called tectonic plates in which continents are embedded.

  For geologists it was as if somebody finally switched on the light. “Plate tectonics really set us free and flying,” said Tanya Atwater in Annals of the Former World. Atwater was a graduate student as the revolution dawned and used the new theory to explain the forces that created the San Andreas Fault. “It is a wondrous thing to have the random facts in one’s head suddenly fall into the slots of an orderly framework,” she said.

  That framework divides the globe into ten major plates and more than a dozen smaller ones. Made up of crust and a portion of the mantle below, the plates can be more than sixty miles thick. They slide atop a layer where heat and pressure give solid rock the consistency of Silly Putty.

  When geologists overlaid their new tectonic grid on maps of the world, they could instantly see that the action occurs at the boundaries where plates meet. Mountain ranges like the Himalayas are the crumpled fenders of head-on collisions. The North American and Pacific Plates grind past each other side by side to form the San Andreas Fault. But the most volatile boundaries of all are subduction zones: the places where the ocean floor plows into a continent. The land rides up over the seafloor like an Abrams tank rolling over a line of Mini Coopers. In what could be called the ultimate recycling process, the oceanic plate sinks—or subducts—back into the hot interior of the Earth.

  ACTIVE VOLCANOES, PLATE TECTONICS, AND THE RING O
F FIRE

  The planet’s surface is made up of ten major plates and dozens of smaller ones, all in motion. The Pacific Ring of Fire, where plates collide around the ocean basin, is where the majority of the world’s earthquakes and volcanic eruptions occur. (image credits 1.1)

  The world’s biggest earthquakes—the monsters that jolt the planet on its axis—all originate from subduction zones. Long before plate tectonics, the Pacific Ring of Fire was infamous for being home to three-quarters of the Earth’s volcanoes and 90 percent of earthquakes. Now the reason was clear as geologists traced out the plate boundaries that circle the Pacific basin.

  By the early 1980s, WPPSS couldn’t ignore the fact that the Pacific Northwest sits squarely on that ring, just inland from the boundary where a chunk of ocean floor called the Juan de Fuca Plate dives under North America. The nuclear plant proponents just didn’t think it was anything to worry about.

  During his aerial reconnaissance, Heaton saw ample evidence of a landscape shaped by tectonic forces. As the Cessna skirted Washington’s wild beaches, the massifs of the Olympic Mountains crowded the horizon. Oregon’s coves and sandy beaches blended into a backdrop of rumpled hills. The collision of plates could account for that kind of buckling. To the east the Cascade volcanoes dotted the skyline like a string of giant pearls. Volcanic arcs are a by-product of subduction. They form as molten blobs of the recycled plate rise through cracks and vents. It was clear the Northwest’s offshore subduction zone, called Cascadia, had been active in the past. But was it still capable of causing trouble?

  The Cascadia Subduction Zone, where the Juan de Fuca Plate meets the North American Plate, lies offshore and stretches seven hundred miles from Vancouver Island to Northern California. The plates converge at a rate of about forty mm per year. The adjacent Pacific Plate moves northward at forty-five mm per year. The toothed line represents the plate boundary. (image credits 1.2)

  Despite the bravado of youth—“I thought I was a hotshot,” Heaton recalled with a chuckle—he realized he needed help. Luckily, he didn’t have to go far to find it. The clapboard colonial that housed the USGS Pasadena office sat across the street from Caltech’s Division of Geological and Planetary Sciences and the office of Hiroo Kanamori. No one knew more about subduction zones at that time than the Japanese-born scientist, and it’s probably still true. “I’m not sure I could have pulled it off without him around,” Heaton said.

  Kanamori was the first to delve into the subset of earthquakes so powerful they blew the needle off the Richter scale. The replacement he devised, called the moment magnitude scale, is universally accepted today, though Richter’s name still sticks. Kanamori is also a nice guy in a discipline in which egos can soar off the charts. Heaton can be brusque; Kanamori is gracious. Yet the two scientists share a probing intellect that drew them together, first as student and mentor, then as colleagues.

  It was Kanamori who suggested Heaton fly the coast. In parts of Japan, subduction zone quakes jerk up shorelines several feet at a time. After thousands of years and dozens of quakes, some Japanese coasts look like stair steps. Heaton chartered the Cessna in Eugene, Oregon, and scanned cliffs and headlands from Cape Mendocino to Cape Flattery for these uplifted terraces. He didn’t find many.

  He and Kanamori later spent two weeks in an SUV driving the region with colleagues from Japan. Nothing they saw screamed out a history of giant quakes. Maybe WPPSS was right in arguing that the Cascadia Subduction Zone was in a class by itself: an earthquake-free class.

  The power consortium wasn’t alone in that assessment. Most geologists agreed. Even Heaton’s employer considered Cascadia unworthy of mention in the national earthquake hazard maps. The USGS scientist in charge of mapping at the time dismissed any suggestion of subduction zone quakes as antinuclear propaganda.

  At a time when geologists were just beginning to get the hang of their new paradigm, Cascadia didn’t seem to fit the mold. Subduction zones are usually seismically noisy places. Slabs of rock more than five hundred miles long and hundreds of miles wide don’t grind past each other easily. They stick in spots, build up pressure, then slip. Each slip makes an earthquake. Japan, which sits at the boundary of four plates, experiences tiny temblors every five seconds and more than one thousand quakes a year big enough to be felt.

  The Northwest had occasional quakes, but they weren’t on the subduction zone. The Cascadia plate boundary was “quiet as Kansas,” as Bob Yeats put it. The Northwest’s elder statesman of seismology, Yeats moved to Oregon from California in 1977 and counted himself among the most adamant skeptics of Cascadia’s menace.

  Scientists concocted a grab bag of theories to explain the subduction zone’s silence. One even suggested the Juan de Fuca and North American Plates were pulling apart, not converging. Another group pointed out that Cascadia lacks the deep offshore trench characteristic of many active subduction zones.

  Several scientists argued that size matters. Compared to the world’s major tectonic slabs, the Juan de Fuca Plate is little more than a postage stamp—though it didn’t start out that way.

  When subduction began along the Northwest coast about 200 million years ago, the oceanic plate offshore was gigantic. Geologists call this tectonic ancestor the Farallon Plate. Much of the modern Northwest landscape originated in a succession of volcanic islands and microcontinents that rode the conveyor belt of the subducting Farallon Plate until they collided with North America. Too bulky to be crammed down into the Earth’s interior, these chunks of land fused with the continent. Each arrival extended the Northwest coastline westward from its original position near Idaho’s border with Washington and Oregon.

  The Okanogan Highlands latched on about 175 million years ago, followed by the Blue and Wallowa Mountains. The North Cascades docked about 95 million years ago, and were crushed, folded, and fractured in the impact. Vancouver Island and much of Northwestern British Columbia arrived the same way. Scientists estimate the Farallon Plate delivered at least fifty chunks, called terranes, over its long history.

  But in the process, the plate itself was largely consumed as it subducted under North America. All that remains is the Juan de Fuca Plate and another nub called the Cocos Plate off the coast of Central America. Someday, even those vestiges will be swallowed up completely. So it didn’t seem unreasonable for geologists to speculate that the subduction process had already run out of steam.

  The first studies on the Satsop plant flatly stated that subduction sputtered to a halt half a million years ago. Even the 1980 eruption of Mount St. Helens didn’t change many minds. It takes a long time to stop a tectonic train, Cascadia skeptics pointed out. The fact that residual blobs of magma were popping up in volcanoes didn’t mean the subduction zone was still active.

  The newest Satsop studies in Heaton’s pile presented a different argument. Cascadia would never rank among the planet’s seismic bad boys, WPPSS argued, because the plates were slipping past each other as smoothly as skis over snow. No sticking. No buildup of tension. No earthquakes. The reasons were a mystery, but sediments from the Columbia River might be acting as a lubricant to grease the skids.

  Heaton considered the arguments from every angle he could think of, asking himself whether the evidence justified the conclusions. The WPPSS case struck him as a house of cards balanced on a skimpy historical record. “It was almost like reading a legal case instead of a scientific case,” he recalled. Heaton and Kanamori discussed a more ominous explanation for Cascadia’s silence—one that WPPSS chose to discount.

  The reason subduction zones produce the most powerful quakes is a simple matter of geometry. The bigger the fault, the bigger the quake. Subduction zones are a kind of fault—a boundary along which rock layers move past each other. No other faults, not even the mighty San Andreas, can match them for size. Subduction zones can extend for 600 miles or more, but it’s not just their length that makes them treacherous. The interface where rocks jerk past each other in a quake, called the rupture zone, is immense. A
magnitude 9 subduction zone quake can rupture an area bigger than the state of Maine.

  Subduction zones are at their most dangerous when the down-going plate and the overriding plate lock up along their entire length. When the pressure reaches the breaking point, the result is what scientists call a megathrust quake. Japan’s 2011 disaster was a megathrust. So was the 2004 giant that triggered the Indian Ocean tsunami and Alaska’s 1964 magnitude 9.2 monster.

  Was it possible the entire Cascadia Subduction Zone was locked up tight? That would explain the lack of smaller quakes. The subduction zone could be building toward its next rupture. In that case the passage of 150 quake-free years didn’t mean the region was safe. It just meant that not enough time had passed for the fault to reach its breaking point.

  BIGGER FAULT = BIGGER QUAKE

  Subduction zone quakes are the world’s biggest because they involve a huge surface area. (image credits 1.3)

  On his final Cessna flight, Heaton felt uneasy. He had seen the damage done when subduction zone quakes rocked the coastlines of Alaska and Chile: roadways buckled, towns turned upside down, communities awash. The landscape unfurling beneath him was so reminiscent of those places that he could imagine similar mayhem visited upon the quiet fishing towns and harbors of the Northwest. “I was struck by a deep sadness,” he recalled. “I thought, ‘What a tragedy it would be if it happened here.’ ”

  While Heaton was surveying the coast, WPPSS’s finances were already starting to implode. The last thing the project needed was a seismic bogeyman.

  The difference between the type of quake the Satsop plant was designed to withstand and a coastwide megathrust is like the difference between twenty-five atomic bombs and twenty-five thousand. Ground shaking can last ten times longer—up to five minutes. How much more would it cost to build a nuclear plant to stand up to something that big?