For years, there were some things you couldn’t find inside the city limits of Cleburne, Texas. One was a place to buy beer; another was robust natural-gas exploration. A third: earthquakes. Now you can find all three in this rural outpost south of Fort Worth, and some residents wonder if a causal relationship exists between two of the town’s new features. (Hint: Hardly anyone blames the earthquakes on beer sales.)
The quakes began recently, with five over seven days in early June. The tremors were small—none measured more than 2.8 on the Richter scale, and most were lower. But in an area with a scant history of seismic activity, the sudden series of quakes prompted 911 calls, general low-grade panic, and an emergency meeting of city officials on June 9. They voted to seek help from geological experts to determine the cause of the earthquakes. A team of scientists from Southern Methodist University soon arrived and placed seismographic equipment in the area.
Brian Stump, a geological scientist at SMU, notes that those who suspect a connection between natural-gas extraction and the recent earthquakes could be right. He says research has documented a causal relationship between some extraction techniques—specifically fluid injection—and small tremors. “It is difficult to establish a causal relationship, and earthquakes caused by extraction are very rare,” Stump says, “but it happens.”
Early in this decade, gas exploration reached frenzied levels, spurred by Cleburne’s location atop the natural-gas-rich Barnett Shale. Ten years ago, there were no gas wells in the area. City Manager Chester Nolen says Johnson County now has some 2,000 wells, with 200 inside Cleburne proper. Fear about the quakes hasn’t halted the lucrative drilling.
The question of whether drilling can cause stronger earthquakes—a 4.0 quake is 900 times more powerful than a 2.0—motivated the City Council’s decision to seek help. “We wanted to find out if this would begin to significantly challenge our quality of life,” says Robert Kelly, a local dentist and City Council member. “The big question is whether it is safe to continue gas exploration.”
The answer sits at the far end of some serious scientific study and will likely be a long time coming.