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Seattle Skyline Could Collapse in Big Quake

Michael Reilly, Discovery News

In Yang and Heaton's simulation the crucial difference was laid bare; a giant earthquake shook buildings for up to five minutes, and those with brittle welds were five times more likely to collapse.

The key is that giant quakes generate a lot of low-frequency shaking, often as slow as one strong, wobbling shake per second. This motion particularly affects taller buildings, which begin to resonate with the shaking, leaning further and further as their weight lolls back and forth. If the building tilts much beyond five degrees from vertical, its steel frame will bend, and eventually it will collapse.

"I definitely see this as being a useful study," Barb Graff, director of the Office of Emergency Management for the City of Seattle. "It's not quite at the same level of tangible experience that makes you change building code, but if it gets tested further in the community and becomes more concrete down the road, it could change code."

However, Graff stressed that engineers at the city's Department of Planning and Development are acutely aware of the seismic hazards posed by the Cascadia and nearby Seattle faults, and comb the latest research for information relevant to upgrading earthquake protection in buildings.

"There are still many unknowns and uncertainties in our simulations," Jing Yang of the California Institute of Technology said. "But we want to express our concern about the possibility of building collapse. Residents and insurance companies should know these buildings are not strong enough to prevent collapse."

Related Links:

Discovery Earth: Seismic Week

How many earthquakes occur everyday?

Discovery Blog: Earth Impacts