Scientists say it’s not a matter of if, but of when a devastating earthquake will hit the Pacific Northwest.
University of Washington researchers have now done detailed simulations to find out just how intense the shaking from such a quake off the Oregon and Washington coast would be.
The last time a magnitude 9.0 quake was felt here was in 1700. According to geologists, another one could happen at any time.
Geophysicist Erin Wirth and her team did 50 simulations based on various scenarios. Wirth says a quake farther from Seattle would actually cause more damage than one closer. It all depends on which way the fault ruptures.
“The seismic waves pile up as they rupture towards a location. So, in the case of Seattle, if the earthquake is pretty far off shore and then the earthquake ruptures toward Seattle that can cause strong ground shaking.”
That shaking would be stronger than a quake with a closer epicenter that ruptures along a fault going the opposite direction.
In the various scenarios, the researchers also looked at what they call "sticky points" along the subduction zone. These are areas between the plates that can catch and generate more shaking. Such zones were evident in both the 2011 Tohoku, Japan, earthquake and the 2010 Chile earthquake.
The simulations reveal the average duration of very strong shaking of a 9.0 magnitude quake here would be 100 seconds. That’s four times longer than the shaking during the Nisqually quake in 2001.