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

by Sandi Doughton

  Growing up on Mercer Island, Pat Williams was fascinated by the submerged forests. They were marked on the charts he navigated by as he explored the lake in his skiff. Neighbors swapped stories about lost gear and theorized over what might lurk among the waterlogged trunks. “They were mythic,” Williams said.

  Even after he became a geologist, Williams never stopped wondering about those trees. Landslides big enough to sweep such huge tracts of forest into the lake would have dwarfed any slides that occurred since white settlers arrived. The charts from Williams’s boyhood mapped out three submerged stands in Lake Washington. There’s at least one in Lake Sammamish, to the east. He suspected they all got there because of earthquakes.

  Williams decided to collect samples from the underwater forest off the southeastern tip of Mercer Island where he fished and swam as a boy. A giant divot in the shoreline marks the slide’s origins. If the trees weren’t rotten, Williams thought he might be able to date the slide and the earthquake that caused it.

  Williams worked with Gordon Jacoby, a pioneer of dendrochronology and founder of the tree ring lab at Lamont-Doherty Earth Observatory, where samples from the Copalis ghost forest were analyzed. Jacoby was accustomed to extracting wood samples from tricky terrain, but neither man had worked under conditions so difficult and dangerous.

  “It was a really creepy place,” recalled Brendan Buckley, Jacoby’s lab assistant in the summer of 1991. “The whole thing was quite the debacle.” Buckley, Williams, and the team’s other SCUBA divers had to descend nearly thirty feet just to reach the tops of the trees. The trunks vanished into the inky depths, their roots embedded in the mud one hundred feet down.

  With only headlamps to penetrate the murk, the divers encountered a labyrinth of logs. Strands of algae wafted from the branches like the hair of drowned maidens. Snarls of fishing line threatened to entangle the divers. “It was pretty hard not to get snagged,” Williams recalled. “We always carried a sharp knife to cut ourselves out of the mess.”

  Buckley tried using a hydraulic chain saw to carve up the trunks, but the billowing sawdust hampered visibility so much he feared he might slice into his own limbs or someone else’s. “That spinning blade scared the hell out of us.” The best method proved to be the simplest: a two-man bow saw, like the crosscut saws loggers called misery whips. The divers positioned themselves on either side of a tree trunk, hammered stakes into the wood to brace their feet, and slowly pulled the blade back and forth.

  The work was so demanding they couldn’t stay down more than twenty minutes at a time. Under pressure to finish in two weeks, they pushed the limits until they were loopy from nitrogen narcosis—or ran out of air. Yet for all their efforts, they got no decent samples.

  The divers weren’t equipped to work much deeper than sixty feet. But at that level, the bark and outer layers of the trees were rotted away. Such crummy wood would never yield a useful date. The scientists knew the root ends of the trees were intact, preserved in the airless muck on the lake floor. But the prize was out of their reach.

  As they later testified in King County Superior Court, it seemed like a godsend when John Tortorelli turned up. A log salvager, Tortorelli was on the prowl for sunken trees he could sell to timber mills. He parked his barge nearby, and the scientists salivated at the sight of the crane and claw he used to pluck snags from the lake floor.

  Williams jumped in his skiff and hailed the barge. He proposed a deal: The divers could help Tortorelli locate logs, if the salvager would let them cut slices off the bottoms. Friendly and charming, Tortorelli agreed.

  The project was saved.

  “We would have left with nothing if he hadn’t been there,” Buckley said. It never occurred to the researchers that Tortorelli was breaking the law. “Who would have the balls to do it right in the open like that if he wasn’t legitimate?”

  Long after the scientists were gone, state regulators raided Tortorelli’s home and charged him with stealing $165,000 worth of trees. The researchers weren’t implicated in the crime, though some were subpoenaed by the prosecution. Tortorelli, who maintained his operation was legal, was convicted of theft, profiteering, and trafficking in stolen property. He was sentenced to eight concurrent terms ranging from twelve to forty-three months.

  But Tortorelli’s tree sections allowed the scientists to say with confidence that the forests had slid into Lake Washington about 1,100 years ago—a time when Mayan culture was reaching its apex and the Byzantine Empire was battling for control of eastern Europe. The link between the underwater forests and the earthquake was cemented after backhoes at the West Point sewer plant unearthed a Douglas fir trunk carried ashore by the tsunami.

  The scientists compared ring sequence bar codes and found that the tree from the sewer plant and the trees from Lake Washington all died in the same season of the same year, fellow victims of the Seattle Fault. The exact year remains unknown, but radiocarbon tests of the sewer plant log narrowed the window to three decades. The quake struck sometime between 900 and 930 AD.

  The tsunami waves that raced through Puget Sound 1,100 years ago also drowned native settlements, including one at West Point. The layers exposed in Atwater’s trench showed that many decades passed before the beach was inhabited again.

  Ancient Native American stories from around Puget Sound warned of a’yahos, shape-shifting spirits that appeared sometimes as double-headed snakes, sometimes as monsters with the head of a deer and the hindquarters of a snake. The places where the spirits dwelled were perilous, the land torn and the trees twisted. Shamans described rushes of turbid water and ground shaking when the a’yahos stirred.

  Ruth Ludwin, the UW seismologist who had studied earthquake and tsunami stories from Pacific coast tribes, joined with experts from Seattle-area tribes to compile several of the accounts. They found the spirit sites fell roughly along the route of the Seattle Fault. A’yahos lurked near Lake Washington’s underwater forests. Their malevolent power was in evidence on Alki Point. Nearby, at what is now a ferry terminal, a large “spirit boulder” still marks the spot where native stories reported havoc caused by the shape-shifters. Geologic mapping revealed a good reason for those stories: That site and several others linked to a’yahos were buried by giant landslides in the past.

  Five of the studies validating the Seattle Fault’s menace were published simultaneously in the December 4, 1992, issue of Science magazine. A commentary dryly noted, “There has not yet been time to assess the hazard implications.” But there was no question that a similar quake would be devastating today. The problem was, scientists had no idea how often the fault might rip or how big future quakes might be.

  The urgency to learn more about the fault increased in 1995, with the Robinson Point earthquake. The magnitude 5 temblor struck just before 11:30 PM on January 28. Centered on Vashon Island, about midway between Seattle and Tacoma, it didn’t do much damage. But when geologists analyzed its source, they realized it occurred on, or very close to, the Seattle Fault.

  The USGS embarked on a series of field investigations that stretched over several years to uncover all they could about the fault’s structure and scope. Research vessels cruised the length and width of Puget Sound towing twenty-ton arrays of air guns that fired off earsplitting blasts. The sound waves penetrated the seafloor and bounced back. Based on the same principle as prenatal ultrasound, the technology is able to look below the surface. On land, scientists dug two-hundred-foot shafts, poured in explosives, and set off charges along a transect from the Olympics to the Cascades. More than one thousand sensors tracked the way the shock waves ricocheted through the ground. The USGS even ponied up $50,000 to buy the data from oil company surveys in the 1970s.

  Combined with old-fashioned observations of the type that inspired Professor Daneš’s original surveys, the results revealed the Seattle Fault as a major force in sculpting the surrounding landscape. It’s not too much of an exaggeration to say that the city owes its existence to the fault.

&n
bsp; Unlike the strike-slip San Andreas Fault, where blocks of rock move sideways past each other, Seattle’s Fault is of the thrust variety. In an earthquake, rocks on the south side of the fault thrust up and over the north side. That’s what caused the uplift on Bainbridge Island and Alki Point. It’s also what formed a line of hills east of Seattle called the Issaquah Alps. On the tops of those peaks, geologists found bedrock that had been lifted nearly five miles. All that movement occurred during earthquakes, which means the Seattle Fault has been grinding away for millions of years.

  Some of the features that lured settlers are the fault’s handiwork. The 900 AD earthquake raised the broad valley of the Duwamish River enough to turn sandy tide flats into fertile soil. The depth of Elliott Bay, which the city’s founding fathers first measured with horseshoes attached to a clothesline, may be due to the uneven terrain created by the Seattle Fault. Some scientists suspect the steep gradients could have funneled glacial meltwater, gouging out an exceptionally deep hole on Seattle’s waterfront.

  As the south side of the fault jerked upward over the eons, the north side sank. The result is a depression five miles deep, filled with sediment and topped with the hard-packed till left behind by glaciers. Most of Seattle sits on this basin, as do Bremerton, Bellevue, and everything else across a huge expanse of the urban corridor. But the USGS team quickly realized that living on top of a basin is not the best place to be in an earthquake. Seismic waves can get trapped and reverberate in the same way water sloshes around in a bathtub.

  The USGS team tested the effect in March 2000, when Seattle’s old baseball stadium, the Kingdome, was imploded. The blast created the equivalent of a magnitude 2.3 earthquake. More than two hundred temporary seismometers recorded the ground shaking. Just as they had suspected, the scientists found that the ground shook two to three times harder inside the basin than out. “The whole Seattle basin is going to have such an extra kick it’s going to shake like a bowl of Jell-O in an earthquake,” said Craig Weaver, chief of the USGS earthquake contingent in Seattle.

  But what locals really want to know about the Seattle Fault is, where is it? You’d think there would be an answer by now, but the exact route has proved elusive. Unlike the San Andreas and other faults whose presence is announced by scars on the ground, Seattle’s fault is what scientists call blind: It doesn’t split the surface during earthquakes (though some of its offshoots do). The grainy images pieced together from seismic and ultrasound surveys revealed that the fault isn’t a single crack but a five-mile-wide swath of fault strands. Between downtown Seattle and Vashon Island, as many as eight separate strands extend east and west. “You can pretty much figure that if you’re in that zone, you’re on top of a fault or near a fault,” Sherrod said.

  But ask three geologists to point out the strands on a map, and you’ll get five different answers. The images are ambiguous enough to leave room for interpretation and argument.

  Most geologists think the major strands bisect the city just south of the stadiums where the Seahawks, Mariners, and Sounders play. The fault takes a jog around the base of Beacon Hill, then tracks Interstate 90 across Lake Washington and continues to North Bend in the Cascade foothills. But some scientists think the fault zone extends further north, with strands that run right under Seattle’s downtown waterfront and beneath the city’s center.

  Proximity matters in earthquakes. Damage is always worst closest to the fault. But no matter the strands’ exact path, a powerful quake anywhere on the Seattle Fault zone will be more damaging and deadly to the city and its environs than a megaquake on the coast. When the subduction zone rips, the ground will shake much longer, but the motion in Seattle will be muted by distance. “With the Seattle Fault, the strongest shaking will be right in the middle of where we live and work,” Weaver said.

  A detailed scenario for a magnitude 6.7 quake on the Seattle Fault put the death toll at 1,600. The violent lurching would knock pedestrians off their feet and collapse bridges, roads, and power lines, the report warned. It would take months or longer to repair the shattered transportation system. The waterfront seawall would collapse into Puget Sound, pulling the supports out from under docks and ferry terminals. The nation’s sixth busiest seaport would slide into Elliott Bay—cranes, container terminals, and all. Sloshing waves in Puget Sound, Lake Washington, and Lake Sammamish would swamp waterfront property.

  The numbers are numbing:

  • $33 billion in property damage, on a par with the Northridge quake

  • 24,000 people injured

  • Nearly 10,000 buildings destroyed and more than 180,000 unsafe or restricted due to change

  • A third of homes closest to the fault unfit for habitation

  When this scenario was released in 2005, an emergency planner summed it up in five words: “It’s going to be ugly.”

  But the realization was a long time coming, Weaver said. For more than a decade after Bucknam and the other scientists laid out the evidence of a massive quake on the Seattle Fault, the local community didn’t take the threat seriously. The response ranged from puzzlement to hostility. Builders were especially dubious. In their view, a fault that had last slipped in 900 AD wasn’t worth fretting over. Who knew when, or if, the thing might quake again? The USGS didn’t.

  Weaver recalled several tense meetings with local engineers and architects. “They were really skeptical,” he said. “We were basically told to prove it.” If the Seattle Fault was really dangerous, it would have slipped repeatedly over the past thousands of years, not just once. The builders told Weaver and his team to come back to the table when they had evidence of more earthquakes.

  Thanks to a new technique that revolutionized earthquake science in the Pacific Northwest, that wouldn’t be long.

  CHAPTER 6:

  SEEING THE FAULTS FOR THE TREES

  ASK GEOLOGISTS ABOUT LIDAR, and here’s what they say:

  “It knocked our socks off.”

  “I look at it first thing in the morning.”

  “Every new batch of data is like unwrapping a Christmas present.”

  “Crack cocaine for geologists.”

  But the best way to grasp the power of the airborne laser imaging technique is to visit a spot like the northwest slope of Mount Hood, a Cascade volcano in Oregon where Ian Madin led a small expedition on a September morning in 2011. Shouldering through a tangle of subalpine fir, hemlock, and bear grass wet with dew, he followed fluorescent flagging and backhoe tracks to a freshly dug trench. Madin, chief scientist for the Oregon Department of Geology and Mineral Industries, pointed to the low ridge bisected by the ditch. “That was really tough to find,” he said. A team of USGS volcanologists who mapped the area years ago didn’t notice it, even though the road is just a stone’s throw away.

  On a lidar (lie-dar) map it took only a glance to see the innocuous-looking ridge for what it is: the scar created when an earthquake ruptured the ground from the volcano’s flank all the way to the Columbia River. “It just jumps out at you,” Madin said. “It looks like somebody drew it in with a Sharpie.”

  Before lidar, geologists knew of a single earthquake scar west of the Cascade Mountains and north of California. They stumbled across that one only because it showed up on aerial photos of a clear-cut. Everywhere else the region’s dense forests concealed features like the eight-foot-high ridge slicing across Mount Hood National Forest. But lidar can distinguish wrinkles on the ground as small as six inches high.

  Thanks to the technique’s near-magical ability to “see” through trees, geologists now count more than a dozen faults, all with big quakes in their pasts, knifing across the region from northern Oregon to the Canadian border. The list is growing so fast there’s a backlog of scarps waiting to be trenched—the best way to tell how often a fault has snapped. “Everywhere we look these days, we find more faults,” said Madin. Lidar revealed the fault on Mount Hood in 2008. It took him three years to scrape together the money to dig into it.

  Beyond th
eir astonishment at the sheer number of faults, geologists were surprised to learn that Seattle’s is by no means the biggest, nor was the 900 AD quake a solo event. Several other faults snapped around the same time, as did the Cascadia Subduction Zone. The sequence of the concatenation is blurry, but a similar barrage in the future is a real possibility.

  Lidar is also revealing a network of faults running through the sagebrush flats near the Hanford Nuclear Reservation, home to the region’s only nuclear power plant and North America’s biggest radioactive waste dump. Insights gained from lidar are helping geologists piece together a unified theory of the region’s seismic hazards and quantify the forces that are loading the faults for the next earthquakes. “We’re finally starting to see the big picture,” Madin said.

  Lidar’s first contribution to seismic science in the Northwest came as geologists were struggling to get a better handle on the Seattle Fault. They knew it had ripped in spectacular fashion at least once—but that was more than a thousand years ago. Maybe what happened around 900 AD was a fluke. The people and builders of Puget Sound were anxious to know how often the urban corridor might be jolted.

  The USGS team hit a wall in their search for answers. Scientists spread out across the region looking for beaches, bluffs, and wetlands uplifted by earlier quakes. They didn’t have much luck. Brian Sherrod, who got his start assisting Robert Bucknam with the early Seattle Fault studies, pulled cores and hacked into stream banks at more than one hundred marsh sites across the region.

  It was frustrating, because geologists knew that a fault that snapped as recently as a thousand years ago couldn’t possibly be dead. Sediment cores from the bottom of Lake Washington pointed to repeated landslides, probably triggered by earthquakes. But the overall record was too paltry to draw conclusions. Then a tiny, public utility went bargain hunting and came back with a treasure.