About7 million people in the U.S. live in areas with a greater risk of earthquakesdue to man-made seismicity, mainly from oil and gas drilling operations,according to a report from the U.S. Geological Survey.
Thatoil and gas activity includes wastewater disposal wells, which have alreadybeen cited as a source of earthquakes in Oklahoma. According to the USGS,regions of that state, along with portions of Kansas, have a chance of damagefrom all types of earthquakes "similar to that of natural earthquakes inhigh-hazard areas of California."
"Byincluding human-induced events, our assessment of earthquake hazards hassignificantly increased in parts of the U.S.," said Mark Petersen, chiefof the USGS National Seismic Hazard Mapping Project. The agency accompanied thereport with first-of-their-kind maps showing regions with increased risk ofman-made earthquakes. "This research also shows that much more of thenation faces a significant chance of having damaging earthquakes over the nextyear, whether natural or human-induced," Petersen said.
TheUSGS said the most significant hazards from induced seismicity are in sixstates, including four major oil and gas producers: Oklahoma, Kansas, Texas,Colorado, New Mexico and Arkansas. The states with the largest population areasexposed to increased activity, the survey said, are Oklahoma and Texas.
TheUSGS found that central and northern Oklahoma have the greatest increased riskfor earthquake activity during 2016, saying the 10% to 12% increase is duealmost entirely to man-made factors. The Dallas-Fort Worth region of northTexas also is among the areas at higher risk, with a potential increase inseismic activity of 2% to 5%. That area, particularly Forth Worth, is in theBarnett Shale play.
"Thecentral U.S. has undergone the most dramatic increase in seismicity over thepast six years. From 1973 to 2008, there was an average of 24 earthquakes ofmagnitude 3.0 and larger per year. From 2009 to 2015, the rate steadilyincreased, averaging 318 per year and peaking in 2015 with 1,010 earthquakes,"the USGS said. "Through mid-March in 2016, there have been 226 earthquakesof magnitude 3.0 and larger in the central U.S. region. To date, the largestearthquake located near several active injection wells was a magnitude 5.6 in2011 near Prague, Oklahoma."
Whilethe USGS cited wastewater injection wells as a primary reason for the increasedseismic activity, the survey rejected the idea that hydraulic fracturing wasalso a key cause of earthquakes.
"USGS studies suggest that this process is only rarelythe cause of felt earthquakes," the survey said.