By Marice Richter
DALLAS (Reuters) - A series of earthquakes that rattled a small community northwest of Fort Worth, Texas, more than a year ago were linked to oil and gas operations, according to a scientific study released Tuesday.
The study published in the science journal Nature Communications concluded that the 27 earthquakes that occurred in Azle, Texas, were the result of high-pressure injection of drilling wastewater injected into the ground and other industry activity.
"On the basis of modeling results and the absence of historical earthquakes near Azle, brine production combined with wastewater disposal represent the most likely cause of recent seismicity near Azle," said the study's authors, who included researchers from Southern Methodist University, the University of Texas and the U.S. Geological Survey.
The earthquakes from November 2013 to January 2014 caused cracks in building foundations, large sinkholes and other damage to property in Azle, which is about 20 miles northwest of Fort Worth.
Azle sits atop the large underground Barrett Shale natural gas formation. The in-ground disposal of wastewater that results from hydraulic fracturing – the injection of water and chemicals into the shale to recover oil and gas – has been linked to earthquakes in previous scientific studies.
The Texas Railroad Commission, the state's regulatory agency for the oil and gas industry, said in a statement to the study's authors on Tuesday that it takes "very seriously the issue of seismicity."
The agency has previously denied a link between the earthquakes and drilling operations. But the agency adopted a rule last year that allows it to restrict or shut down disposal wells, the agency said in a statement.
"Cities across the state should be very, very worried," Sharon Wilson, an organizer based in Dallas for the environmental group Earthworks, said in a statement. "It is only Texas state regulators and lawmakers who are living in denial."
A research study last summer also linked a series of earthquakes in Oklahoma to wastewater disposal wells.
The Oklahoma Geological Survey, which documents earthquakes in the state, said Tuesday the number of 3.0 magnitude earthquakes has risen to about 2.5 per day from a historic level of 1.5 per year before 2008.
The agency said in a statement the rash of earthquakes, mostly in central and north-central Oklahoma, are caused by oil and gas wastewater injected into disposal wells.
A series of earthquakes in the Dallas area earlier in 2015 is still being studied.
(Reporting by Marice Richter in Dallas; Editing by David Bailey and Sandra Maler)