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Story by the Dallas Morning News

The day after the most powerful earthquake recorded in North Texas, the Texas Railroad Commission announced it will require operators of five wastewater wells to perform tests to help determine whether there is a link between well activity and earthquakes.

The wells are within 100 square miles of the the estimated epicenter of Thursday’s magnitude-4 earthquake near Venus.

The operators — Bosque Disposal Systems LLC, EOG Resources Inc., MetroSaltwater Disposal Inc. and Pinnergy Ltd. — have agreed to temporarily shut down for testing, which will happen within days.

Researchers at Southern Methodist University said Friday that they will work with state and federal scientists to investigate the quakes.

Thursday’s quake near Venus hit just before 6 p.m. and was felt in Arlington and Mansfield, from Midlothian to Alvarado, and from Cleburne to Dallas, according to the U.S. Geological Survey. There were even reports from as far as Austin and Houston.

Scientists are already studying two other earthquake clusters — one near Azle and Reno, recently tied to oil and gas activity; and one in Dallas and Irving.

Researchers said they had expected to see stronger quakes in the area.

“I’m not at all surprised to read about an event of that magnitude occurring,” said Art McGarr, a USGS seismologist in Menlo Park, Calif. “That area has had quite a few induced earthquakes. There are a lot of wastewater disposal wells near there that have been injecting quite substantial amounts of wastewater from unconventional energy production.”

The USGS has blamed wastewater wells, where companies dispose of fluids used in oil and gas operations, for the increased rate of earthquakes in parts of Texas, Oklahoma, Colorado and other central U.S. states. Underground fluid pressure from the wells can disturb nearby faults.

The agency said last month that North Texas’ earthquake risk has tripled since 2008, mainly because of the increased use of disposal wells.

“We should understand that some parts of Texas are in earthquake country now,” said Mark Petersen, chief of the USGS National Seismic Hazard Modeling Project in Golden, Colo.

Thursday’s earthquake is the 23rd in a series of tremors that began in 2009 near Midlothian. Five, including Thursday’s, registered above a magnitude of 3, according to SMU.

“If you have movement on a fault and change the stresses, you increase the likelihood of additional earthquakes,” said SMU seismologist Heather DeShon in a statement. “In other words, one earthquake frequently leads to another.”

After the quakes, the Railroad Commission of Texas dispatched inspectors to the area to check wells for damage.

As to whether the wells may be to blame for Thursday’s tremor, Commissioner Ryan Sitton said, “We don’t want to speculate on anything.”

He said that beyond testing the wastewater wells, the commission was taking additional steps to evaluate quakes in North Texas.

The agency is hiring a second seismologist and will have a public hearing in early June to help determine what further action to take.

The Railroad Commission has invited SMU seismologists, other researchers and representatives from oil and gas companies to speak at the hearing.

SMU has 26 earthquake monitors deployed in North Texas, split between the Azle and Irving-Dallas areas. Most of the equipment is borrowed from agencies such as the USGS.

The SMU seismologists are hoping to get 10 monitors for the Venus area. So far the USGS has sent them three; there’s a shortage of equipment in part because of the Nepal quake.

Legislation pending in Austin would provide $2.5 million for a new statewide network of seismic stations. SMU scientists spoke in favor of the bill at a House committee hearing on Monday.

“We emphasized to the House Committee on Energy Resources the need for a permanent regional network, supplemented by portable instruments, that we can deploy in a time-sensitive manner when earthquakes occur,” said SMU associate professor of geophysics Matthew Hornbach in a statement.