Study: Quake-triggered landslides a significant hazard in Seattle

Thursday, October 24, 2013

Study: Quake-triggered landslides a significant hazard in Seattle

Posted under: Research, Science

This map traces the course of the Seattle fault across Puget Sound, through the city and across Lake Washington to the Eastside.

The next big earthquake on the Seattle fault could trigger destructive landslides in the city, potentially affecting a much larger area than previously thought, and in areas outside those currently considered to be landslide prone, a new University of Washington-led study shows.
“A major quake along the Seattle fault is among the worst-case scenarios for the area, since the fault runs just south of downtown.” said Kate Allstadt, a UW doctoral student in Earth and space sciences. “Our study shows the need for dedicated studies on seismically induced landsliding.”
Allstadt is the lead author of a paper documenting the research, published online Oct. 22 by the Bulletin of the Seismological Society of America. Co-authors are John Vidale, a UW professor of Earth and space sciences and Allstadt’s doctoral adviser, and Arthur Frankel of the U.S. Geological Survey, which funded the research.
The research offers a framework for simulating hundreds of earthquake scenarios for the Seattle area.

Map shows the path of the Seattle fault.

This map traces the course of the Seattle fault across Puget Sound, through the city and across Lake Washington to the Eastside.

While the region is vulnerable to deep earthquakes, shallow earthquakes and catastrophic quakes in the Cascadia subduction zone off the Pacific Northwest coast, a shallow crustal quake on the Seattle fault would likely be most damaging to the city.
The Seattle fault crosses Bainbridge Island and cuts across West Seattle and Beacon Hill, just south of downtown, then crosses Lake Washington to the eastern suburbs and the Cascade foothills. The last major quake on that fault was about 900 A.D., and scientists have documented that it triggered giant landslides that caused large tracts of forest land to slide to the bottom of Lake Washington.
The Seattle Basin that underlies much of the city amplifies ground motion and generates strong seismic waves that tend to increase the duration of the shaking. Allstadt said the hazard of landslides triggered by earthquakes is very high and warrants greater attention, in Seattle and in other areas prone to the phenomenon.

Read More Here