A light earthquake shook the Dallas-Ft. Worth area of North Texas on Saturday night, leaving no known damage or casualties but stirring concern about the potential of the area’s oil and gas fracking industry to generate seismic activity.

The magnitude 3.3 earthquake struck about 9:15 p.m. Central time on Saturday, said Dale Grant, an geophysicist with the U.S. Geological Survey.

The epicenter was near the border of the cities of Dallas and Irving, near the site of the former Texas Stadium, where the Dallas Cowboys football team played for nearly 40 years.

Comments on Twitter from the Dallas Ft. Worth area indicate that the quake was felt across the region.

“We have not received any reports of damage, nor are we expecting any,” Grant said.

Grant said earthquakes of that size are not uncommon in the Barnett Shale Field of North Texas, near the area hit by Saturday’s temblor.

Critics said the quake was a reminder of the threat posed by hydraulic fracturing, or fracking. The technique, pioneered in the Barnett shale formation, is the driving force behind the U.S. energy boom.

“We are guinea pigs in the middle of this fracking experiment. Texas homes are built to withstand wind, not earthquakes,” Sharon Wilson, an organizer for Earthworks, an advocacy group, said on Sunday. “Who will pay for the damage to private property?”

Fracking involves the injection a mix of pressurized water, sand and chemicals to unlock hydrocarbons from rock can trigger earthquakes. Many environmental groups say the technique is wasteful, polluting and noisy, but the industry says it is safe.

Even so, the Texas Oil & Gas Association, an industry lobby group, concedes that the issue deserved more careful study.

“The oil and natural gas industry agrees that recent seismic activity warrants robust investigation to determine the precise location, impact and cause or causes of seismic events,” Todd Staples, the association’s president, said in an email.

The city of Denton, about 40 miles (65 km) north of the Dallas Ft. Worth area, earlier this month banned fracking in the city limits, after activists complained that the process leads to earthquakes.

(Reporting by Jim Forsyth in San Antonio, Texas; Writing By Frank McGurty; Editing by Marguerita Choy)