A scenario study of seismically induced landsliding in Seattle using broadband synthetic seismograms

Bulletin of the Seismological Society of America
By: , and 

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Abstract

We demonstrate the value of utilizing broadband synthetic seismograms to assess regional seismically induced landslide hazard. Focusing on a case study of an Mw 7.0 Seattle fault earthquake in Seattle, Washington, we computed broadband synthetic seismograms that account for rupture directivity and 3D basin amplification. We then adjusted the computed motions on a fine grid for 1D amplifications based on the site response of typical geologic profiles in Seattle and used these time‐series ground motions to trigger shallow landsliding using the Newmark method. The inclusion of these effects was critical in determining the extent of landsliding triggered. We found that for inertially triggered slope failures modeled by the Newmark method, the ground motions used to simulate landsliding must have broadband frequency content in order to capture the full slope displacement. We applied commonly used simpler methods based on ground‐motion prediction equations for the same scenario and found that they predicted far fewer landslides if only the mean values were used, but far more at the maximum range of the uncertainties, highlighting the danger of using just the mean values for such methods. Our results indicate that landsliding triggered by a large Seattle fault earthquake will be extensive and potentially devastating, causing direct losses and impeding recovery. The high impact of landsliding predicted by this simulation shows that this secondary effect of earthquakes should be studied with as much vigor as other earthquake effects.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title A scenario study of seismically induced landsliding in Seattle using broadband synthetic seismograms
Series title Bulletin of the Seismological Society of America
DOI 10.1785/0120130051
Volume 103
Issue 6
Year Published 2013
Language English
Publisher Seismological Society of America
Contributing office(s) Earthquake Science Center
Description 22 p.
First page 2971
Last page 2992
Country United States
State Washington
City Seattle