November 21, 1999

Hidden Risk That Science Saw

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Why Insurers Shrink From Earthquake Risk

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By JUDITH BERCK

ORTLAND, Ore. -- This wasn't supposed to be major earthquake country. Floods, landslides, even the occasional volcanic eruption, perhaps. But there has not been a major quake in the Pacific Northwest since European settlers first arrived here, so few people in Oregon, Washington or British Columbia ever worried about the ground shaking.

But scientists now believe that the potential makings of a giant earthquake -- of 8 or 9 magnitude -- have been quietly building here. Using new data from Global Positioning System satellites, oceanographers from Oregon State University who were studying minute movements in the earth's crust found to their surprise that the Juan de Fuca Plate, a section under the Pacific Ocean, is moving northeast and shoving under the North American mainland much faster than was previously thought.

Worse, rather than passing smoothly, the two plates are snagged somewhere, probably under the Coastal Range west of Portland, leading to growing pressure that can be relieved only by an earthquake.

The affected region extends 750 miles, from British Columbia to northern California, and inland to the Cascade Mountains east of Portland and Seattle, where the same geological forces have created active volcanoes.

Preliminary data shows that the Juan de Fuca Plate, once thought to be almost motionless, may be moving 10 to 15 millimeters a year -- "about as fast as your fingernail grows," said Chris Goldfinger, assistant professor of oceanography at Oregon State and a co-author of a report presented at the Seismological Society of America meeting in Seattle last May.

"This is very, very fast, geologically," he said. Because of the motion, he added, "the North American plate is being compressed like a spring."

When the spring finally breaks free of the snag, the region will suffer a subduction-zone earthquake, a more potentially destructive type than California usually experiences. Most quakes there occur along faults where the ground moves laterally, and severe damage is fairly localized. Subduction-zone quakes affect wider areas and can be much stronger, like the 9.2-magnitude quake that struck Alaska in 1964.

The last major earthquake in the Cascade region occurred in 1700, and the average interval between such quakes seems to be about 600 years, but could be less, Goldfinger said.

Other research has found that small crustal faults in the Portland hills, thought to be inactive, may be able to produce significant quakes.

Reactions to these alarming reports have varied from fatalism to urgent concern. Demand for residential earthquake insurance has picked up somewhat, though not explosively. And some homeowners, including Portland's mayor, Vera Katz, have made alterations to their homes to make them safer in a quake.

"A lot of our community is in a denial stage, yet they are informed," Mayor Katz said. "One of the first questions I asked as mayor was about the potential of an earthquake. There was a deadly silence in the room."

Much of downtown Portland was built using methods and materials, like brick and terra cotta, that often fare poorly in earthquakes. The city government has begun a program to retrofit public buildings and bridges and to improve emergency plans.

The state's urban building codes took little account of earthquake risk until a moderate 5.6-magnitude temblor near Salem, the state capital, did $30 million in damage in 1993. Since then, the codes have been tightened somewhat, but they are still less strict than those in coastal areas or in quake-prone California, and apply only to new construction, not existing buildings. State officials say they need more data from the latest studies before taking new action.

In recent years, the Oregon legislature has been reluctant to appropriate money for seismic upgrades of the state's highways and bridges or for new maps of earthquake hazard zones.

Without actual experience of a quake to go by, officials have trouble deciding how much preparation is needed. "I'm so ambivalent about this," Mayor Katz said. "If it's a very severe quake, I don't know if we've planned far enough. I don't know if any community can plan far enough."