Seattle at risk of giant earthquake

MONTEREY, Calif., April 10 (UPI) -- Seattle's tallest buildings are at risk of collapse during a rupture of the Cascadia fault zone in the Pacific Northwest, say U.S. seismic experts.

The Cascadia subduction zone is likely to produce the strongest shaking experienced from earthquakes in the lower 48 states, said seismic experts from the California Institute of Technology in Pasadena.

While the Pacific Northwest has experienced little seismic activity in 200 years, there is growing consensus the Cascadia subduction zone ruptures in giant earthquakes exceeding 9 on the Richter scale, Caltech scientists Thomas Heaton and Jin Yang said Thursday at the Seismological Society of America's annual meeting in Monterey, Calif. The Cascadia subduction zone last ruptured in 1700, Heaton and Yang said.

Simulations at Caltech show such earthquakes, which last for more than 4 minutes and are dominated by low-frequency motions, would be exacerbated by the geography of the Seattle basin and cause severe damage among modern high-rises, said Heaton and Yang.

The most vulnerable high-rises would be those built before code changes made as a result of California's 1994 Northridge earthquake, they said.