July 18 (Reuters) - Sixteen states are at high risk of damaging earthquakes over the next 50 years and certain areas of the United States face a higher threat of temblors than previously thought, a federal geological survey agency said.
The findings come from updated earthquake hazard maps that were released by the U.S. Geological Survey on Thursday. The maps are used to help define safe building codes, help emergency responders plan after a quake, and influence insurance rates, the report said.
"The cost of inaction in planning for future earthquakes and other natural disasters can be very high, as demonstrated by several recent damaging events across the globe," Mark Petersen, chief of the USGS National Seismic Hazard Mapping Project, said in a statement.
The western United States faces a high risk of damaging earthquakes up and down the coast and in the intermountain region, the report said. The California cities of San Jose, Vallejo and San Diego all saw a heightened threat, as new fault lines have been recently discovered, the report said.
The cities of Irvine, Santa Barbara and Oakland had their threats downgraded however, the report said.
It also upgraded the risks facing parts of the central and eastern United States, singling out areas near New Madrid, Missouri, and Charleston, South Carolina. Scientists did however lower the threat facing New York City's skyscrapers, as slow-shaking quakes which impact taller buildings are less likely in the area than previously thought.
The 16 states with areas facing the highest risk are Alaska, Arkansas, California, Hawaii, Idaho, Illinois, Kentucky, Missouri, Montana, Nevada, Oregon, South Carolina, Tennessee, Utah, Washington, and Wyoming.
The survey noted a sharp spike in the number of earthquakes over magnitude 3, potentially driven by hydraulic fracturing in states like Texas, Oklahoma and Arkansas. Between 2010 and 2012 more than 300 quakes were recorded, compared to an average of just 21 per year over recent decades in the region.
While those quakes were not included in the analysis of earthquake risk, researchers said that planners should consider higher potential for shaking given the increased seismic activity.
The maps are based on over a century of observed earthquake data. The last assessments were published in 2008 and were updated to account for new scientific modeling and studies on quakes, the report said. (Reporting by Curtis Skinner in New York; Editing by Eric Beech)
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