Thursday, October 23, 2014

The results of some just released landslide research should come as no surprise to residents of the city of Astoria.  The Oregon Department of Geology and Mineral Industries (DOGAMI) has released shallow and deep landslide susceptibility maps that will aid planners for the City of Astoria indicating many high risk areas.

DOGAMI scientists Bill Burns and Kate Mickelson used lidar, a laser-mapping technology that allows for amazingly detailed and accurate mapping of the earth's surface, to locate 120 landslides within the city limits - 83 of these have moved in the last 150 years and several have caused significant damage.

With a protocol developed at DOGAMI, Burns and Mickelson then used the inventory of mapped landslides to create landslide susceptibility maps. These maps show areas that have the potential for landslide hazards. About 55 percent of the city of Astoria is classified as highly susceptible to shallow landslides - slides where movement occurs along a plane less than 9.5 feet deep. About 37 percent of the city is highly susceptible to deep landslides- slides that move along a plane at depths greater than 15 feet.

With this information and a Federal Emergency Management Agency (FEMA) tool called Hazus, Burns and Mickelson conducted a regional risk analysis. The risk analysis indicates that a loss ratio of about 65 percent can be expected in a major earthquake, with about 50 percent of the damage and losses resulting just from landslides. Similarly, an exposure analysis indicates that roughly one quarter of the city is at risk to landslides.

These maps and loss estimation products can be used by city planning and emergency management officials to develop and refine emergency response plans, public outreach activities, the selection of appropriate safe-haven sites, and mitigation of critical facilities and infrastructure. For example, by combining the hazard maps with transportation data, potential road blockages can be identified and alternative routes located. Similarly, the hazard maps can be combined with other information such as the locations of hazardous waste facilities to evaluate potential effects and to plan for emergency response.

"It is important to remember that these maps and results are valuable for regional screening," says Bill Burns."They aren't for site specific evaluations. However, they give planners an idea of what is out there and where to focus their efforts."

To see a preview of Open-File Report O-13-05, Landslide inventory, susceptibility maps, and risk analysis for the City of Astoria, Clatsop County, Oregon, visit:
http://www.oregongeology.org/pubs/ofr/p-O-13-05.htm

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