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If a 9.0 earthquake were to strike the Cascadia Subduction Zone on Washington's Northwest tip, Seattle could get off relatively easy compared to if it was located far off the coast. That's according to results of 50 new simulations just released by the University of Washington.
This effort has been in the works for years as part of the Magnitude 9 project, trying to get a better handle on just how the Cascadia threat could unfold.
The 9.0 quake is something that scientists and emergency disaster planners have said is a matter of "when" not "if." An offshore Cascadia Subduction Zone quake could spread deadly shaking from Canada to California.
The last major quake happened in 1700, according to UW researchers, when the Juan de Fuca oceanic plate jolted under the the North American plate off the Washington and Oregon coasts -- and that happens every 500 years or so. Researchers warn it could happen again any day.
UW says the project ran simulations looking at the epicenter of the earthquake, how far inland the earthquake will rupture, and which sections of the fault will generate the strongest shaking.
"Surprisingly, Seattle experiences less severe shaking if the epicenter is located just beneath the tip of northwest Washington," said project leader Erin Wirth in a press release. "The reason is because the rupture is propagating away from Seattle, so it's most affecting sites offshore."
That means communities beyond Seattle, such as Aberdeen or Portland, would face the worst of the shaking.
Then there is the flip side -- if the epicenter is located far off the Washington or Oregon coast.
"But when the epicenter is located pretty far offshore, the rupture travels inland and all of that strong ground shaking piles up on its way to Seattle, to make the shaking in Seattle much stronger," Wirth said.
The overall results of the 50 simulations find that coastal areas would be hardest hit, according to UW. Sediment-filled basins, such as downtown Seattle, would shake more than hard, rocky terrain.
But researchers make it clear that the results can vary with each possible scenario, and none of them are good.
"We are finding large amplification of ground shaking by the Seattle basin," said collaborator Art Frankel, a U.S. Geological Survey seismologist and affiliate faculty member at the UW, in a press release. "The average duration of strong shaking in Seattle is about 100 seconds, about four times as long as from the 2001 Nisqually earthquake."
The research will be presented Tuesday at the Geological Society of America's annual meeting in Seattle.