For its upcoming National Seismic Hazard Map, used by engineers to update building and construction codes and by insurers to set policy rates, the U.S. Geological Survey (USGS) will take into account risks posed by induced or man-made earthquakes. For North Texas, where earthquakes are historically uncommon, an increase in earthquake risk is likely as the Dallas area has suffered more than 120 earthquakes since 2008. The increase will be small, said Mark Petersen, chief of the USGS’s National Seismic Hazard Project in Golden, Colorado. The hazard map predicts the location, the frequency, and the strength of earthquakes in a given region.
The Dallas Morning News reports that earthquakes are occurring in parts of the country where previous hazard maps did not predict a risk. Scientists have attributed these earthquakes to nearby fracking operations. USGSscientists have linked two Dallas-area earthquake clusters with wastewater injection wells, where oil and gas companies dispose fluids used in the fracking process.
“We’re putting a lot of effort into understanding this,” Petersen said.
Between 2010 and 2013, residents of central and eastern U.S. states felt an average of five times as many earthquakes per year as they did between 1970 and 2000. Most of these man-made earthquakes are small, but in 2011 a 5.7-magnitude earthquake struck near injection wells in Oklahoma.
The current USGS hazard map, released in 2014, predicts a region’s 50-year earthquake risk based on how many quakes the area has sustained over hundreds of years. Induced earthquakes, however, strike and disappear over a shorter timeframe. “It’s very difficult to assess where induced seismicity might occur,” Petersen said. “They’re based on economic and policy decisions which are difficult to forecast, especially over a 50-year time period.”
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