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| Quake complacency 02/27/02 by RICHARD L. HILL of the Oregonian, used with permission. Bob Norris vividly recalls his bewilderment when the chunky federal-issue Suburban yawed as if it had struck a speed bump. With the truck rocking and power lines swaying, it didn't take long for the veteran seismologist to figure out that he had run into "an unholy big earthquake." Along with millions of others at 10:54 a.m., Feb. 28, 2001, Norris found himself stunned by the largest earthquake to strike the Northwest in the past half-century. For most people, the strong undulating motion of the magnitude 6.8 earthquake lasted 15 to 20 seconds. But Norris found himself on the loose fill of Harbor Island south of downtown Seattle, which recorded one of the region's strongest ground movements. The most powerful shaking lasted for about 20 to 30 seconds before fading and halting a few minutes later. "I got a good ride out of it," said Norris, who is with the U.S. Geological Survey in Seattle. "The shaking was so strong that I couldn't find the door handle on the truck to open it, and I couldn't put the truck into drive to get out of there. I wasn't panicking, but I was thinking that this really isn't cool." Norris won't forget that alarming experience. But he and other scientists fear that many people will look back on those few startling moments as amusing rather than recognizing the serious implications they have for the Northwest. "We got off really easy for a 6.8," Norris said. "There's concern that people will say, 'Shoot, we went through a 6.8 and had no problem.' We shouldn't let the fact that we did so well with this one lead us to feel that we might do as well with the next one." More than 400 people were injured, and one death was attributed to a stress-induced heart attack. Damage estimates from the Nisqually Earthquake, as it is officially known, range from $700 million to $1.5 billion. The reason the quake didn't cause more destruction is that its source -- or hypocenter -- was 321/2 miles below the surface on a fault within the Juan de Fuca Plate. The plate is moving eastward beneath Oregon and Washington, under the North American Plate. Such deep quakes are called intraplate or slab earthquakes. They affect a large area and produce a distinctive rolling motion, unlike the sharper jolts from shallower quakes on near-surface faults. With an epicenter in the Nisqually River Delta about 11 miles northeast of Olympia, the Ash Wednesday quake occurred at almost the same site as the magnitude 7.1 earthquake that killed eight people April 13, 1949. Another large earthquake centered south of Sea-Tac Airport hit the region April 29, 1965, killing seven people. Those also were slab quakes. The Nisqually Earthquake is being compared to the magnitude 6.7 quake that struck in 1994 near Northridge, Calif. Because that quake occurred at a shallower depth of 11 miles, it killed 57 people and resulted in an economic loss of $40 billion, the costliest disaster in U.S. history. That's why scientists worry about a magnitude 6.8 quake along the shallow Seattle Fault or the Portland Hills Fault, rather than in the Juan de Fuca Plate. "We would have a very different outcome than we did with the Nisqually quake," Norris said. "That definitely wasn't the worst-case scenario for a quake of that size." Real-time data Norris, who coincidentally had been on Harbor Island to inspect a portable seismometer, was able to download data from the instrument as the quake continued. He also is one of the few scientists to have witnessed a sand boil in action. Sand boils, also called sand blows or sand volcanoes, are geysers of water and sand created during an earthquake as a result of liquefaction, which happens when shaking turns wet soil into a jellylike liquid. "I thought it was a water-main break," he said. "The water was emitted for more than an hour. There was a lot of pressure." Sand boils occurred throughout the Puget Sound area. But geologists say one fortunate aspect of last year's quake is that it occurred during a dry winter. Although the quake triggered landslides, the dry soil prevented more from occurring. Because of the instruments scattered throughout the Puget Sound area, the earthquake was the first of its type in the United States to be well-monitored. Using the global positioning system, for example, scientists found that the quake moved Seattle south-southwest 5 millimeters, or one-fifth of an inch. Since the earthquake, nine new GPS stations have been placed throughout the region to measure ground movement, said Meghan Miller, a professor of geological sciences at Central Washington University. Scientists speculate Some scientists speculate that the quake might have been caused by the buildup of additional stress that is created by an arch in the Juan de Fuca Plate as it inches beneath the Puget Sound area. "No one knows exactly what the mechanism is for generating an earthquake in the subducting slab, because it's 30 miles deep," said Steve Palmer, a geologist with the Washington Division of Geology and Earth Resources. "There are a number of different theories, but I don't think anyone has a provable idea about the cause of earthquakes at that depth." The biggest surprise about the Nisqually Earthquake is that it was "almost a dead ringer" for the 1949 quake, Palmer said. "And the major thing we learned is that we didn't learn anything from the previous quakes in 1949 and 1965. If you take a look at the damage to structures and the ground failures last year, they were essentially where you had those types of failures and events in those previous quakes." There were notable exceptions because of Seattle's seismic-retrofit ordinance, which resulted in several of the city's older structures performing well during the earthquake, he said. But the Capitol still awaits repairs, and a key thoroughfare called the Deschutes Parkway in Olympia isn't expected to open until at least late next year. In Oregon, the quake helped generate support for five earthquake-related bills that passed the Legislature, said Yumei Wang, director of geohazard programs for the Oregon Department of Geology and Mineral Industries. Drills required One bill requires state and local agencies, along with businesses with more than 250 employees, to hold earthquake drills. Two other bills require surveys of public schools, colleges, hospitals, and fire and police stations to identify structures at risk from quakes. The Legislature also placed two measures on the ballot this November asking voters to decide whether the state should issue general obligation bonds to help make public schools and emergency service buildings more quake-resistant. Sen. Peter Courtney, D-Salem, who introduced the bills, said he was disappointed that the $500,000 he had wanted for conducting the surveys failed to win approval. He hopes the geology department is able to obtain survey money from federal programs or elsewhere to help pay for them. "I'm particularly concerned about older schools," he said. "There are schools that would just explode in a large earthquake." Three types of earthquakes can strike in the Northwest: Intraplate or slab quakes. The 1949, 1965 and 2001 quakes have been the most destructive Northwest events in recent decades. They also are called Benioff zone earthquakes, which occur 25 to 40 miles deep within the Juan de Fuca Plate. Crustal earthquakes. The most common type, produced by faults as deep as 15 miles below the surface. The magnitude 5.6 Spring Break Quake in March 1993 near Scotts Mills, which caused $30 million in damage, was a crustal quake. Cascadia subduction zone earthquakes. Scientists worry about this type of quake because it could devastate the entire region. Like the Nisqually quake, the Juan de Fuca Plate plays a key role. Subduction zone quakes occur offshore, where the heavier Juan de Fuca Plate plunges, or subducts, beneath the North American Plate. Evidence shows that the plates are sticking as they pass each other, building up tremendous pressure that is unleashed in magnitude 8 or 9 earthquakes. Unlike the crustal or slab earthquakes that can produce strong shaking for a minute or less, subduction zone quakes produce shaking that can last four or five minutes along with deadly tsunamis. Similar subduction zones have produced the two largest recorded earthquakes: a magnitude 9.5 quake in 1960 in Chile and a magnitude 9.2 quake in 1964 in southern Alaska. Scientists have found evidence in recent years that the last subduction zone quake struck the Oregon coast in 1700. Wang has estimated that a magnitude 8.5 subduction zone quake on the Oregon coast would cause more than 13,000 casualties and $12 billion in damage to buildings. She was part of a team from the state agency that visited the Puget Sound area after the quake to see what could be learned. They found that the damage primarily was to old buildings and bridges in areas of poor soils and steep slopes. "I think it would be useful for us to strengthen buildings and structures that we know will fail in an earthquake," Wang said. "The Nisqually Earthquake wasn't 'the big one,' so we need to prepare." Palmer agrees. "Some people have the perception that this was the earthquake we were waiting for," he said. "It gave them a false hint of what a magnitude 6.8 earthquake can do. It wasn't even a comprehensive test of the building code. So there's still a lot of work to be done because they will happen again, and next time we might not get off so easily." You can reach Richard L. Hill at richardhill@news.oregonian.com or 503-221-8238. |
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