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Open-File Report 2006-1139

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## Shallow-Landslide Hazard Map of Seattle, Washington

#### By Edwin L. Harp, John A. Michael, and William T. Laprade

| *Open-File Report*PDF (10 MB)                    Right-Click to 'Save As' or 'Download'*Open-File Report*PDF (10 MB)                  Right-Click to 'Save As' or 'Download'**Abstract**
Landslides, particularly debris flows, have long been a significant cause of damage and destruction to people and property in the Puget Sound region. Following the years of 1996 and 1997, the Federal Emergency Management Agency (FEMA) designated Seattle as a “Project Impact” city with the goal of encouraging the city to become more disaster resistant to the effects of landslides and other natural hazards. A major recommendation of the Project Impact council was that the city and the U.S. Geological Survey (USGS) collaborate to produce a landslide hazard map of the city. An exceptional data set archived by the city, containing more than 100 years of landslide data from severe storm events, allowed comparison of actual landslide locations with those predicted by slope-stability modeling. We used an infinite-slope analysis, which models slope segments as rigid friction blocks, to estimate the susceptibility of slopes to shallow landslides which often mobilize into debris flows, water-laden slurries that can form from shallow failures of soil and weathered bedrock, and can travel at high velocities down steep slopes. Data used for analysis consisted of a digital slope map derived from recent Light Detection and Ranging (LIDAR) imagery of Seattle, recent digital geologic mapping, and shear-strength test data for the geologic units in the surrounding area. The combination of these data layers within a Geographic Information System (GIS) platform allowed the preparation of a shallow landslide hazard map for the entire city of Seattle.     | Version 1.0

Posted July 2006
-  **Report** PDF (*10 MB)  (This report is accessible as defined in Section 508 of the Rehabilitation Act of 1973, Amendments of 1998.)  **Downloading Suggestion*It is best to download a large file to your hard drive rather than open it inside your browser. A standard click may automatically open the file inside the browser but doing so will result in a very slow load. Downloading the file may take several moments but will be worth the wait. Once it is downloaded, open it from your hard drive—it will open in a fraction of the time it would take to open over the Internet.   *Downloading SuggestionIt is best to download a large file to your hard drive rather than open it inside your browser. A standard click may automatically open the file inside the browser but doing so will result in a very slow load. Downloading the file may take several moments but will be worth the wait. Once it is downloaded, open it from your hard drive—it will open in a fraction of the time it would take to open over the Internet.  
-  **Sheet 1** Map PDF (938 KB) 
-  **Sheet 2** Map PDF (4.2 MB) |
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| U.S. Department of the Interior | U.S. Geological Survey      URL: https://pubsdata.usgs.gov/pubs/of/2006/1139/Questions or Assistance: USGS Web ContactPage Last Modified: Sat Jan 12 21:14 EDT 2013 |  |

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