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CA Geological Survey Releases Landslide Susceptibility Map

via GCS
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The California Geological Survey (CGS) has released a new map showing the susceptibility of California to deep-seated landslides and where landslides are more likely to occur. The map is ranked on a scale of zero to 10 combining factors of rock strength and degree of slope; greater slope + weaker rock = highest susceptibility.State Geologist of California and head of CGS, Dr. John Parrish, says the information provides an overview for "emergency planners, those who own or operate infrastructure facilities, and the public at large," according to a release by the California Geological Survey.

“There are other landslide susceptibility maps out there, but those are very general. This map has a very robust data set behind it. Although you cannot use it to determine the risk potential at a specific site, you can get a good sense of whether landslides are something you need to be aware of in a given area.” The map was created in support of the recent ARkStorm Scenario, which described a storm that could result in more than $300 billion in property damage in California. The map, now available to the public, is the first step in estimating potential landslide losses from a major winter storm.

The coastal mountains between San Francisco and Los Angeles is the largest area of high landslide susceptibility while areas of the Coast Ranges north of San Francisco to the Oregon border, and the western Transverse Ranges in Los Angeles, Ventura and Santa Barbara Counties also have high-likelihood.
Landslides cause an estimated 25 to 50 deaths and more than $2 billion in damage each year in the United States. California has a significant share of that risk. When the state’s rainfall exceeds normal levels by 150 percent or more, landslides cause property damage in excess of $100 million on average, and as many as five deaths each year. More than 100 Californians have been killed by debris flows during the past 25 years.