Major Seattle quake could trigger thousands of landslides

by: Chris Legeros Updated:

SEATTLE - Seattle has a history of landslides. They're usually on steep slopes near the water after heavy rains have saturated the soil.

“The ground is always moving here,” said West Seattle resident Bob Strandberg.

 Now, a University of Washington study gives us a look at what could happen if more than just gravity caused mud to move downhill.

Using computers, researchers simulated a shallow magnitude seven earthquake, similar to the one that rocked the Philippines in October.

They placed their simulated quake along the Seattle fault that runs under the city. If it hit when the ground was wet, Geophysics Professor John Vidale said it could trigger more than 30,000 landslides and potentially damage more than 10,000 buildings.

“That is the worst case scenario and we can't really say exactly which building would be damaged,” said Vidale.

Vidale said the graduate student who conducted the study, Kate Allstadt, was able to map what areas would be prone to slip in a quake.

She was surprised to find some spots where the landslide risk was assumed to be low previously. They included inland neighborhoods in North Seattle and along Beacon Hill near the Interstate.

"Those are areas that may well be in worse shape than we thought,” said Vidale.

 There's no reason to panic or be alarmed by the study. Vidale said you've got to keep it in perspective.

The last big quake on the Seattle fault was more than 1,000 years ago. There's a good chance we may never see another one in our lifetimes.

 He said we should use more research like the study just completed, as we plan new buildings, and try to make sure that critical lifelines like roads, water, sewage and power systems work after a major quake.

He calls the UW study a bit of a wake up that the problem is worse than we thought.