There’s a been a lot of debate about what has caused the swarm of earthquakes in North Texas. A new study from the University of Texas at Austin and Southern Methodist University says humans are likely behind the quakes – not just in recent years, but for nearly a century.
The study, published Wednesday in the journal Seismological Research Letters, concludes that 59 percent of earthquakes across Texas since 1975 were likely caused by oil and gas activities. That includes wastewater disposal from fracking. But drilling methods used decades ago have also been linked to quakes.
"I think most people who produce petroleum act as if this is a new thing that just started happening, and I wanted to set the record straight that this has been happening in Texas for over 90 years," Cliff Frohlich says. He's the study’s senior researcher and is the associate director of the Institute for Geophysics at UT-Austin.
The study found that oil and gas activities “possibly” triggered another 28 percent, while only 13 percent of the quakes over the past few decades were considered natural.
In recent years, there have been dozens of earthquakes in North Texas. A 4.0-magnitude quake hit Johnson County between Venus and Lillian last May, which is the strongest to date. A 3.6-quake hit Irving last year.
The study also said wastewater disposal from hydraulic fracturing triggered most of the state’s earthquakes since 2008.
Frohlich said he hopes his research will help develop a greater understanding of the phenomenon.
"So that if we do have regulations they are sensible regulations, and if you are trying to manage a field, you can manage it to reduce hazards," he said. "We don’t understand it well enough to propose hard and fast regulations or rules just yet, but that’s certainly the objective."
The Texas Railroad Commission, which regulates the oil and gas industry, dismissed the study’s methods as “arbitrary” and “subjective.”
This isn’t the only study that’s explored the causes of Texas earthquakes. Last year, SMU seismologists linked oil and gas drilling to the swarm of quakes in Azle. Additional studies by academic scientists and those at the U.S. Geological Survey have also shown that pressure from high-volume wastewater injections has disturbed faults in Oklahoma, Texas, Kansas and Arkansas, which created earthquakes.
The UT-Austin study argues state regulators have been slow to acknowledge the link between the oil and gas industry and ground shaking. But Frohlich says they are coming around.
The railroad commission has tightened its rules for disposal wells in recent years. It's issued several permits with special requirements to reduce and record daily maximum injection volumes and pressure. Frohlich says regulators have also mandated that in order to permit a disposal well, there needs to be proof that it won't be built near a previous earthquake, and if so, that it won't cause more earthquakes.