New research from the University of Washington has determined that buildings in the Puget Sound lowlands and Willamette Valley will shake more than previously thought in a 9.0 Cascadia fault zone earthquake. Existing high-rise buildings may have a 20-25 percent chance of collapse.
Seismologists and structural engineers associated with the M9 Project at the University of Washington used supercomputers to run dozens of three-dimensional simulations of a magnitude 9.0 rupture of the offshore Cascadia fault zone. UW professor Jeff Berman said the modelling showed enhanced shaking in the vast, sediment-filled basins beneath the Puget Sound lowlands and Willamette Valley. Affected cities include Seattle, Tacoma and Everett, as well as Portland and nearby Tualatin, Oregon.
Berman said when “The Really Big One” hits, the geology of these basins could magnify seismic energy through what he called the “bowl of Jello effect.”
“If you shake a bowl of Jello, you can get the Jello to move a lot faster than the bowl,” he explained in an interview. “That is exactly what is happening in the basin. The ground motions are coming in and you’ve got this bowl that is not as strong and stiff as the surrounding volcanic rock underneath.”