Mercer Island

Study: Nearly 8,000 Seattle buildings in landslide danger zones

Study: Nearly 8,000 Seattle buildings in landslide danger zones »Play Video
SEATTLE -- According to new study, Seattle could have close to 8,000 buildings in landslide danger zones.

The study, conducted by the University of Washington, is the first time scientist have looked at the locations and severity of local landslides.

It's no secret that coastal bluffs are prone to landslides, especially when they're wiped clean of vegetation and saturated in with water. But the new study looked at dry hillsides, concentrating more on what was on top of the land than underneath it.

Among other results, the study shows more areas that are vulnerable to earthquake-induced landslides than previously thought.

On the south tip of Mercer Island, 100 feet below the surface of Lake Washington, stands a well-preserved forest of trees that are 11,000 years old. Scientists believe a landslide slid the forest underwater after a major earthquake.

The unique forest led UW researcher Kate Allstadt to study the effects another large earthquake along the Seattle Fault would have on landslide-prone areas.

"We found you can actually under predict the hazards," Allstadt said.

She found Seattle has 30 percent more hillsides prone to earthquake-induced landslides than first thought.

"We found that areas directly over the fault, on what's called the hanging wall of the fault, are most prone. That's West Seattle, Delridge, Beacon Hill," she said.

And that's without hills being saturated with water. If the earthquake happens with soggy hillsides, you can add in other coastal bluff areas of North Seattle.

"People will say there will be a lot of landslides, but nobody says how much and where it will be," Allstadt said. "But we need to know these things because landslides can cut off access."

Lois Dunagan has lived through quakes and landslides, and the 91-year-old remembers when a 1946 landslide pushed her West Seattle house off its foundation.

"This use to sit back 40 feet from where it is now," she said.

That slide was weather related and not from an earthquake. Dunagan knows her home could be at risk, but she's losing sleep over it.

"What do you say, it will never happen to me? But really, I don't feel endangered at all," Dunagan said.

The last time Seattle had a major earthquake along the Seattle fault was in the year 900.