Why Seattle's big quake had little impact
Good building codes, a federal project, and the quake's depth all helped minimize the damage.
In the end, even the tropical fish were safe.Skip to next paragraph
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Here in downtown Seattle, Wednesday's 6.8-magnitude earthquake rattled walls and workers, sending a snowfall of cracking plaster onto the heads of employees and causing a panicked evacuation of the blue-and-cream-colored terra-cotta Medical Dental building.
But when everyone eventually returned to the office later in the day, the ceilings were still sound and the office's collection of tropical fish were still swimming happily in their tanks.
It's an aquatic example of how Seattle escaped the massive damage and widespread loss of life that has accompanied quakes of similar magnitude - from Northridge, Calif., to Kobe, Japan.
Ultimately, damage may reach into the billions of dollars, yet only one person died and few buildings had significant structural damage. By contrast, the Kobe temblor left more than 6,000 people dead and turned the city inside out.
Seattle's relative good fortune came from a combination of factors, including improved building codes and increased preparedness. Perhaps the greatest factor, though, was pure science - the underlying geology and tectonics of the Pacific Northwest.
Unlike the events in Northridge and Kobe, the Seattle-area quake took place deep within the earth - as many as 30 miles down. The result is obvious.
"With a deep earthquake, the shaking tends to last longer, but the vibration you're feeling is [weakened] by the shock waves moving through 30 miles of soil," says Charles Roeder, a professor of civil engineering at the University of Washington here. "The earthquakes we have here tend to be deep - whereas, the earthquakes they have in Los Angeles tend to be fairly shallow."
Indeed, the strongest Seattle earthquakes of the 20th century all have taken place in roughly the same place that this week's event did. Each occurred as one plate of the earth's crust slowly slid farther beneath another.
In California, earthquakes happen as plates simply grind against each other, meaning they're much closer to the surface - and therefore more damaging.
A similar kind of grinding fault, named the Seattle Fault, runs directly through the city, but that remained quiet.
"If it were a 6.8 on the Seattle Fault, we'd be looking at a lot more damage, more like what happened to Kobe," says William Steele, coordinator of the seismology lab at the University of Washington. "We'd be looking at hundreds of billions of dollars of damage - and many casualties."
That's not to say deep earthquakes can't be damaging. Scientists say deep earthquakes could actually be more dangerous for big buildings, causing entire areas of earth to give way. But Wednesday's temblor didn't appear to cross that threshold for intensity.
Moreover, scientists are quick to point out that Seattle's increasing earthquake awareness has led to better buildings.
"The engineers have learned their lessons," says Dr. Steele. "They've studied the California quakes; they've looked at why buildings break apart."