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

by Sandi Doughton

  During the Nisqually earthquake, geysers of wet sand sprouted nearby as particles in the already-loose fill rattled apart and water gushed out. Soil turned to thick slurry. Engineers have known for more than a century that reclaimed swamps are among the most dangerous places to build in earthquake-prone territory. Not only is the ground susceptible to liquefaction, but it also shakes harder and longer than more solid soils. The prospects weren’t improved by the discovery that the Seattle Fault zone passes directly under the reclaimed land. The fault doesn’t break the surface, but there’s little doubt the area will heave hard in the next big quake.

  Building a stadium under those conditions isn’t as tough as building one on the San Andreas Fault—but it comes close, said Martin Page: “That’s what made it fun for the engineers.” Page works for Shannon & Wilson, the Seattle-based firm that helped design the foundations for both arenas. The next time the ground shakes, he would be pleased to find himself sitting in the stands at either facility. “I think they would be some of the safest places to be during a big rupture on the Seattle Fault, and even in the tsunami that might follow.”

  To give the arenas a firm footing, Shannon & Wilson relied on a tried-and-true method for building in crappy soil: pilings. Collectively, the stadiums and their associated structures sit on more than 3,700 concrete-filled pilings, each two feet across. The steel piles are embedded in hard-packed glacial till. The ground beneath the ballparks could turn to soup and the structures wouldn’t sink or list.

  Long before the pile-driving started, the engineers conducted test borings to get a better idea of what lay beneath, Page said. They found a little bit of everything, from stumps and railroad ties to pockets of one-hundred-year-old construction debris. The fill ranges from fifteen to twenty feet thick. Below that are layers of muck, silt, and sand deposited over millennia by the ancient river and its estuary. In many spots the engineers had to bore down ninety feet before they struck solid glacial till.

  Pounding a flat-bottom piling that deep is like driving a skinny nine-story building straight into the ground. The tool for the job was a diesel hammer. With a driving ram that can weigh as much as twenty-five tons, the device harnesses the power of exploding diesel fuel to deliver up to fifty blows per minute to the head of a piling. “It’s like the difference between driving a railroad spike with a ball peen hammer versus a sledge hammer,” Page said. The noisy machines were able to sink a piling in less than half an hour. A few of the steel tubes buckled when they hit buried boulders. When in place, the pilings were packed with steel reinforcing rods and filled with concrete.

  Aboveground, both stadiums were built in sections to allow for thermal expansion and differential jiggling during a quake, said John Hooper, whose firm did the seismic engineering. “Safeco Field is really seven different buildings in one,” he said. The baseball stadium’s retractable roof posed a unique challenge. The engineers installed giant dampers on each of the interlocking sections. “They’re like the shock absorbers in your car, only twenty times bigger.” An earthquake could hit when the roof is open, closed, or somewhere in between, so the engineers ran computer simulations for multiple configurations.

  Safeco Field came through the mild Nisqually quake with no structural damage, though dozens of televisions, interior facades, and light fixtures took a beating. CenturyLink was under construction. The shaking knocked a scaffolding loose and delayed work by three days.

  The football stadium’s twin roofs were one of the trickiest puzzles the seismic engineers faced. The 720-foot-long canopies arch over the grandstands with no visible supports to block the view. The concrete pylons are tucked out of sight at either end. If the whole stadium torques in an earthquake, the roofs could tear themselves apart. To keep that from happening, Hooper and his colleagues employed the type of giant ball-bearing systems that many Japanese buildings rest on. This was the first time so-called friction pendulum dampers were used on such a large roof. At CenturyLink Field the bearings essentially allow the roof to float during an earthquake. The ground and the roof supports may shake like crazy, but the roof shouldn’t budge. Only one building in Washington incorporates a similar system in its foundation: the State Emergency Management Division’s headquarters near Tacoma.

  The most recognizable structure in the Pacific Northwest was built long before anyone knew what a subduction zone was, or dreamed that Seattle’s hilly landscape harbored tectonic cracks. The Space Needle graced the cover of Life Magazine on February 9, 1962, just weeks before the Seattle World’s Fair opened. It was constructed in a rush. Engineers were sketching out plans a few steps ahead of workers bolting sections of steel together. Yet the graceful spire is likely to hold up to big earthquakes far better than many modern buildings. “If there’s anything left standing in Seattle, the Space Needle will be there,” said Gary Noble Curtis, one of the project engineers.

  Curtis answered the phone in Pasadena the day the Needle’s architects called to recruit his boss, structural engineer John K. Minasian. An expert in tower design, Minasian practiced what he called “sound engineering.” That meant being a fanatic for detail. Every calculation was checked, rechecked, and checked again, all by hand or slide rule. “He was very demanding,” Curtis recalled. “Everything had to be just so.” But after all the numbers were run, Minasian would tug on his ear and explain to his protégés that a design had to sound good, too. What he meant, Curtis said, was that an engineer needs an intuitive sense of the way mechanical stresses will flow through a structure.

  Minasian also had a healthy sense of caution, born from investigating tower collapses. Lacking any earthquake hazard maps, he just doubled the existing seismic code. He also upped the wind specs, building for nearly twice the original loads. The result is a much stronger structure than engineers would build today, even with all their knowledge about the seismic risks.

  The Needle sits on a thirty-foot-deep foundation of reinforced concrete. For extra strength Minasian insisted on a single, continuous pour. The job took twelve hours and 467 truckloads of concrete. Seventy-two giant bolts, more than thirty feet long and four inches wide, anchor the tower to the foundation. Because the schedule was so tight, Minasian had to order the steel based on back-of-the-envelope calculations. He pulled out a catalog and picked the biggest beams available, Curtis said. “It’s probably over-designed by 50 percent.” The structure is also highly redundant. If the steel legs fail, the inner core is strong enough to resist earthquake motion, and vice versa.

  None of that makes the Needle a fun place to be in an earthquake. The manager of the rotating restaurant likened his experience in the 1965 quake to riding a flagpole. “A couple of Space Needle employees were said to have fled, never to return,” wrote Knute Berger in Space Needle: The Spirit of Seattle. The women’s gymnastic team from Western Michigan University was on the observation deck 520 feet off the ground when the Nisqually quake struck. “Once we realized it was an earthquake, terror kind of ripped through you because you have no control over what’s going to happen,” the coach told a reporter. The mayor of Issaquah, east of Seattle, clung to a beam and tried not to scream as the saucer tossed from side to side.

  But a thrill ride at the top doesn’t mean serious trouble for the steel tower. The Needle is so strong it should be able to whip around for the duration of a Cascadia megaquake and then some, Curtis said. “It could do that forever. The structure would take it just fine.”

  Northwest historian Murray Morgan estimated Minasian’s caution boosted the project’s cost by $1 million, pushing the final price tag to about $4 million. It probably wouldn’t be possible to erect such a strong structure in today’s economic environment, Curtis said. No one pressured Minasian and his crew to shave their safety margins. “There was no complaining that we put too much steel in it,” he said. “Today, you’d get in big trouble for wasting somebody’s money.”

  CHAPTER 12:

  NUTS, BOLTS, AND CHIMNEYS

  THE DUST HAD BARELY SETTLED from th
e Nisqually earthquake in 2001 before Derek Booth was cruising the streets of West Seattle. As he drove slowly past Craftsman homes and bungalows built in the Roaring Twenties, Booth counted cracked and crumbling chimneys. The quakes of 1949 and 1965 had rocked this blue-collar neighborhood with surprising force, toppling brick flues like bowling pins. Booth’s initial reconnaissance convinced him that the pattern had repeated itself again. This time the University of Washington geologist hoped to get to the bottom of the mystery.

  “The working hypothesis was, ‘There’s something about West Seattle,’ ” recalled Booth, who splits his time between the UW and the University of California at Santa Barbara. But without a broader survey, he couldn’t be certain West Seattle really was hammered harder than other neighborhoods. The city was buzzing with geologists and students, and Booth had no trouble recruiting volunteers to help. In two-person teams, the group fanned out across Seattle and nearby cities. One volunteer would drive at a snail’s pace while the other recorded chimney conditions and used a handheld GPS to log coordinates. “We looked at every single chimney we could see from the street. It was a very quick, very crude survey.” The scientists were racing to get the job done before homeowners started making repairs.

  Within a couple of weeks, Booth and his colleagues had eyeballed 60,000 chimneys, nearly 1,600 of them with obvious problems. Just as he had suspected, West Seattle was a hot spot. “It wasn’t just that the people of West Seattle are whiners,” Booth said. “They really did have the most damage of anybody.” In one narrow zone, almost every other chimney was a mess. Yet just a few blocks over, it was as if the earth hadn’t budged. The patchy distribution was nearly identical to what geologists documented after the 1965 quake. “You could try to explain it by saying that maybe some people just had a crappy mason build their chimneys,” Booth said. “But unless the same guy did all the chimneys in a three-block area then retired, it just doesn’t make any sense.”

  Chimneys act as crude seismometers, Booth explained. Made up of bricks pasted together with mortar, they’re usually the first thing to fail when the ground jerks back and forth. The amount and type of chimney damage in an area is a good indicator of the intensity of shaking. “There are a lot more chimneys than there are seismometers, so that’s really useful information.” The four real seismometers in West Seattle at the time confirmed the chimneys’ informal readings: An instrument close to the area where damage was most severe registered ground motions nearly three times stronger than a seismometer half a mile south. Distance from the quake’s epicenter couldn’t explain the pattern of damage, nor could the underlying soil. West Seattle sits on the same hard-packed glacial deposits as much of the city and its suburbs.

  The scientists also found heavy chimney damage in Bremerton, a Navy town west of Seattle across Puget Sound. As they mapped their observations, the researchers couldn’t help but notice that much of the damage lined up on an east-west axis, tracing the route of the Seattle Fault. “We thought, ‘Gee, that’s interesting,’ ” Booth said. A powerful quake on the Seattle Fault about 1,100 years ago uplifted beaches in West Seattle and mudflats near Bremerton. But the Nisqually quake originated forty miles south, deep under the delta of the same name. The Seattle Fault didn’t move an inch.

  Still, Booth and his colleagues suspected that the fault wasn’t as blameless as it looked. “It occurred to us that the presence of a major [fault] could certainly influence the way in which earthquake waves from depth might be transmitted up to the ground surface.” A few years later another group of scientists confirmed that hunch with a series of experiments. The researchers rolled into West Seattle in a truck mounted with a Vibroseis, a pistonlike device used to shake the ground. By recording the way the signals bounce back, scientists generate a subterranean image. What they saw more than quarter of a mile down was an abrupt step, or fold, in the bedrock. A step marks the edge of the Seattle Fault zone and probably explains why the same part of West Seattle seems to lose chimneys in every major quake.

  As seismic waves radiate through the ground, they bend and refract like rays of light when they pass from one kind of rock into another. Scientists think the edge of the Seattle Fault acts like a lens, concentrating and focusing that seismic energy and beaming it straight into West Seattle. Neighborhoods directly in the line of fire shake harder than those a few blocks away. It’s a neat solution to a puzzle that has vexed scientists for more than four decades. But what does it mean if you’re shopping for a house in West Seattle? “That’s a fair question,” Booth said, “but I don’t want the real estate agents after me. Besides, there’s much more to the safety of a house than how hard the ground shakes during a moderate earthquake.”

  The chimney study is tucked away in a mountain of scientific information Northwesterners can take a shovel to if they want a more complete picture of the seismic risks where they live and work. The problem is that scientists are often more interested in the general than in the particular. The maps of chimney damage in Booth’s report don’t zoom down to the block level. Nor do research papers on the South Whidbey Island Fault do much for homeowners trying to figure out if a strand runs through their backyards.

  Beyond the scientific reports are several resources that do provide practical information for those who know how to interpret them. Geologic maps are available online for many areas. Perhaps the most powerful predictor of earthquake damage is whether a structure sits on solid ground or loose dirt, and the maps can tell you that—as long as you can decipher terms like “advance outwash deposits” (not a bad footing for a house, it turns out). Most people already know if their property is vulnerable to earthquake-triggered landslides. But many cities, including Seattle, offer maps that highlight the risky slopes. In terms of ground shaking from earthquakes, USGS seismic hazard maps are the best guides to what the future may hold. Although the measure of shaking that’s mapped is confusing (peak ground acceleration expressed in g-values), the color coding makes it clear which areas are likely to be rattled the hardest.

  If you live in West Seattle, you could extract enough information from Booth’s paper to roughly determine where your house sits in relation to the epicenter of chimney carnage. But Booth also found clusters of broken chimneys in other parts of the city where the Seattle Fault can’t be blamed. The next earthquake may strike from an entirely different direction or on a different type of fault. Tacoma could get the hardest shaking, or Portland.

  Given the capricious nature of the threat, geologists, engineers, and emergency managers agree that the best strategy is to assume your house, apartment, business, or condo will get a good shaking one of these days and plan accordingly. “Just do the reasonable, prudent things anybody in a moderate to high earthquake hazard zone should do,” Booth advised. “So the chimney falls down? There are worse things that can happen.”

  It’s possible to rebuild an old chimney to modern standards, but the cost is so steep few people bother. Roger Faris got rid of his instead. The old stack teetered over his daughter’s bedroom and made him nervous. So Faris dismantled the bricks to below the roofline, replaced the fireplace with a gas-burning facsimile, and installed a stainless steel stove pipe. The rest of Faris’s 1906 Craftsman in Seattle’s Phinney Ridge neighborhood is equally squared away.

  The former barge operator and contractor probably wasn’t the first person in Seattle to give his house a seismic makeover, but he was the first to champion the simple fixes that can help people protect their biggest investment. Sitting at his dining room table in 2012, Faris flipped through the 1985 issue of Fine Homebuilding that got him thinking about earthquakes. The well-worn magazine fell open to a picture of a two-story California bungalow slumping in on itself like a fallen cake. A quake had knocked the house off its footings and collapsed its lower supports. The article described how to prevent that kind of damage by bolting the house to the foundation and bracing vulnerable spots. Faris followed the step-by-step directions to retrofit his own house, then set out to spread th
e word.

  “You don’t need to be very skilled,” he said, ducking into the narrow stairwell that leads to his basement. “It’s just repetitive tasks.” Faris did the seismic work before he Sheetrocked the basement, adding a bedroom and a nook for the ping-pong table. One section of the original wall remains exposed in a storage room.

  Faris explained that he started the project by using bolts to fasten the mudsill—the two-by-four that is the base of the house’s frame—to the concrete foundation it rests on, but usually isn’t attached to, in older homes. “What keeps it there is the force of gravity and friction, the weight of the building just sitting on it,” Faris said. An earthquake that shakes the house back and forth can overcome that friction and essentially pull the rug out from under the house. The resulting damage is like totaling a car.

  In Faris’s basement, the bolts are hidden by plywood panels that are an equally important part of the retrofit. He pointed out how the panels extend from the mudsill to the floor joists above, strengthening what are called the pony or cripple walls. Without plywood bracing, the side-to-side shoving from a quake can cause the pony walls to fall like dominoes.

  In 1990, just as awareness of the Cascadia Subduction Zone was dawning, Faris started teaching other homeowners how to do the job themselves. He worked at a cooperative called the Phinney Neighborhood Association, where he taught a wide range of DIY skills and helped pioneer one of the country’s first tool lending libraries. The association added retrofit equipment to its collection—tools like air-powered palm nailers for working in tight spaces and rotohammers. “You just pull the trigger and they drill through concrete like butter,” Faris said, admiringly.

  When the Federal Emergency Management Agency launched an initiative to boost earthquake preparedness in the Puget Sound area, they recruited Faris and incorporated his classes into what was called Project Impact. In a poorly timed move, the Bush administration announced it was cancelling the program on the day of the 2001 Nisqually quake, saying it wasn’t effective. Faris begged to differ and along with the City of Seattle helped keep the retrofit classes going. “You don’t solve a problem like earthquake preparedness in a few years,” he said. “It takes decades.”