Expert: Well activity could be to blame for Timpson earthquakes
By by Peggy Jones firstname.lastname@example.org
May 17, 2012 at 10 p.m.
One of the state's leading experts on earthquakes said Thursday that two recent quakes near Timpson might be connected to commercial injection wells operating in the area.
Cliff Frohlich was studying the May 10 earthquake northwest of Timpson when the earth shook again there early Thursday.
The U.S. Geological Survey reported that a magnitude 4.3 quake rattled Shelby County a little after 3 a.m.
"I thought, 'Whoa!' I was working on the May 10 earthquake yesterday and now there's another one." said Frohlich, associate director of the University of Texas Institute of Geophysics.
Frohlich specializes in the study of Texas earthquakes.
"That area (around Timpson) is not very seismically active," Frohlich said. "It is possibly human activity-related."
Timpson, in Shelby County, is in the Haynesville shale formation - a hotbed of activity for natural gas exploration and extraction.
Frohlich said he feels certain the two recent quakes were not caused by drilling or hydro-fracturing (known as fracking), which is the practice of injecting water into a well to extract natural gas.
"I don't know of any cases where drilling caused an earthquake," Frohlich said. "With fracking there is a tiny chance. Production rarely causes an earthquake - only if there were huge fields. But disposal has, occasionally, been connected to earthquakes."
Salt water is a by-product of natural gas extraction that is disposed of in deep injection wells, where it is contained so that it does not contaminate groundwater.
According to the Texas Railroad Commission, there are 39 permitted commercial injection disposal wells in Shelby County.
Ramona Nye, spokesperson for the railroad commission, said there are three permitted injection wells within a five-mile radius of the epicenters of the earthquakes. Two are active, she said.
Nye said railroad commission inspectors checked each of the wells Friday, the day after the first earthquake.
"They found no violation of any rules," Nye said of the well inspections. "They were operating under their permitted conditions."
Nye said the wells are permitted at 6,000 feet, while the depth of each earthquake was about 15,000 feet.
It is easier to determine the epicenter of an earthquake than to determine the depth it occurred, Frohlich said.
"Saying it occurred at 5 kilometers simply means it was shallow," the earthquake expert said. "No one really knows exactly what depth it occurred at."
"These wells have been permitted to inject since 2006," Nye said. "Texas has a long history of safe injections, and staff has not identified a significant correlation between seismic activity and injection practices."
But Frohlich said a series of minor earthquakes in 2008-09 near Cleburne, south of Dallas, were linked to injection wells in that area. Cleburne is in the Barnett shale formation.
"Even if it turns out these are caused by human activity - they will be small. Human activity earthquakes don't tend to get very large," he said.
John Bellini, a geophysicist with USGS National Earthquake Information Center in Golden, Colo., said, "There are probably - I'll say - two dozen of that size or larger earthquakes happening in the world every day."
Will there be more around Timpson?
"I wouldn't be surprised if there were," Frohlich said. "And I wouldn't be surprised if there weren't."