Seattle prepares for the big quake

March 4, 1999
Web posted at: 10:40 AM EST

Seattle areas most prone to earthquake damage are being mapped by scientists from the U.S. Geological Survey and the University of Washington.

It has been 35 years since a major earthquake hit the Seattle area and scientists warn that another may occur at any time. Recent research shows that the Seattle Fault, which runs from Bainbridge Island through downtown Seattle and east toward Lake Samamish, has experienced large earthquakes in the past.

"That fault wasn't even recognized 40 years ago when the existing Seattle geology map was produced," said Derek Booth, a professor of geological sciences and civil and environmental engineering at the University of Washington.

The new maps are being created as part of Seattle's Project Impact to help prepare the city for an earthquake. Using geographic information system technology, the geologic maps will contain basic information on the materials that make up the region's hills and valleys.

"The result will be highly detailed three-dimensional maps showing the subsurface layers under Seattle," said Kathy Goetz Troost, a geological sciences researcher at the University of Washington.

The maps and an accompanying database will be a resource for city agencies and the public seeking up-to-date geological information, Troost said. They also are necessary to predict how different areas of the city with different soil types and varying geology will shake during an earthquake.

U.S. Geological Survey seismologists, who have been collecting ground motion data from small earthquakes in Seattle for the last several years, will analyze the data.

"Combining the geology with the ground motion data will produce a much better estimate of shaking effects in Seattle than is now available," said Craig Weaver of the federal agency. That will result in a second set of maps that chart where ground motion will be most severe during a large earthquake, maps that could be useful in picking sites for new critical facilities and in setting priorities for seismic retrofitting.

The geological data also will be used by the state Department of Natural Resources to re-evaluate Seattle's susceptibility to liquefaction, and by the U.S. Geological Survey to produce landslide susceptibility maps for which ground shaking, rather than intense rainfall, is the landslide trigger.

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