The depth of the quake, at 1.9 miles, is roughly the same depth at which the fracking, a process for extracting oil and gas, is carried out.
The past year has seen an extraordinary amount of fracking in Karnes County as a result of the development of the Eagle Ford Shale.
A seismologist employed by the University of Texas said in a report on the kutnews.org web site that hydraulic fracturing itself does not cause earthquakes. But he says earthquakes have been associated with the disposal of fracking fluids.
“They [drilling companies] pump the water back into the ground into a deep aquifer to get rid of it,” earthquake researcher Cliff Frohlich at UT’s Institute for Geophysics told KUT News.
“The quakes have been associated with the pumping of water back into the ground, not the producing of the gas,” he said, pointing to seismic activity in North Texas and in Arkansas.
In September, Arkansas banned the use of deep wells to store waste water, according to the report. StateImpact Pennsylvania points to a study by Southern Methodist University and UT that linked small earthquakes in the North Texas Barnett Shale with the practice, and says the Army Corps of Engineers has expressed concern about drilling for natural gas near dams.
Frohlich said it’s too soon to say if waste water disposal activities were related to today’s 4.6 magnitude quake in South Texas. “That’s a question,” he said.
The area southeast of San Antonio has felt earthquakes before. There was a 4.3 magnitude earthquake in 1993 near the same location, and there have been smaller quakes recorded back to the 1970s, Frohlich said.