A previous version of this story from included information from The Associated Press that incorrectly stated that the study found a plausible connection between earthquakes and natural gas drilling. NBC DFW regrets the error.
A study released Wednesday says there's a plausible connection between a series of earthquakes in North Texas and a disposal process that's done after natural gas drilling.
The dozen or so minor quakes were reported in a few Dallas suburbs from the fall of 2008 through last spring. The largest was a 3.3-magnitude quake, and no major injuries or damage were reported.
The study said the quakes occurred during the time waste water from the gas extraction process was injected into a deep disposal well near the quake sites.
"The timing of those events and the timing of the injections seems to us to say that it could be a possible cause of the events," said Brian Stump, Albritton chair of geological sciences at Southern Methodist University's Dedman College.
Stump was one of the researchers involved in the study.
Stump also said the depth the earthquakes occurred and the depth at which the waste water is injected are similar. Stump said the disposal process can sometimes put between 8,000 to 10,000 barrels of waste water in the earth's crust per day.
The first quakes occurred after natural gas drilling began near Dallas/Fort Worth International Airport -- and none have been reported since that well stopped operating last fall.
"They did stop injecting this summer, and as I said, we haven't seen any earthquakes since then," Stump said.
The study doesn't include information about last summer's series of quakes in Cleburne.
In a statement, Brian Murnahan, a Chesapeake Energy Corp. spokesman said:
"Chesapeake appreciates the efforts of the scientists at SMU and UT Austin and agrees with their statement that natural gas drilling, hydraulic fracturing and production are not related to seismic activity near DFW International Airport. We believe this paragraph from their own paper adequately sums up our thoughts:
"More than 12,000 wells have been completed in the Barnett Shale of the Fort Worth Basin in the past decade and all received hydraulic fracture treatments. More than 200 saltwater disposal wells are active in the area of the Barnett production. If the DFW earthquakes were caused by saltwater injection or other activities associated with producing gas, it is puzzling why there are only one or two areas of felt seismicity," according to their article published in Leading Edge.
Currently, there are more than 24,000 active injection wells in Texas, making the likelihood of a relationship between saltwater disposal wells and seismicity extremely rare. In addition, while residents of the area may not actually feel seismic events, they often occur. Between 1973 and 2007, there were 103 reported earthquakes in Texas. The 11 seismic events that SMU has recorded with their local network near the DFW Airport C1DE SWD well were too small to be felt. The USGS estimates that there are more than one million seismic events annually around the world like those of the size near DFW Airport. These seismic events have been described as a "vibration like passing of light trucks," by UT researcher Cliff Frohlich in his book Texas Earthquakes.
Chesapeake maintains that a direct, causal relationship between saltwater disposal wells and seismic activity in the DFW area has not been scientifically proven."