This story was updated on May 20.
A new study suggests the oil and gas industry has triggered earthquakes across Texas since 1925. The research, which publishes Wednesday, attempts to set the record straight on what has become a hot-button issue across the state.
With citizens expressing concern about the state's growing number of quakes lately, scientists have published studies indicating that recent quakes are likely tied to the disposal of oil and gas wastewater, but state energy regulators say there's still not enough information to explain what's going on.
Last year, state regulators at the Texas Railroad Commission—the agency that oversees oil and gas exploration—cleared two energy companies of responsibility for causing more than two dozen earthquakes in North Texas with their waste disposal.
Researchers from the University of Texas at Austin and the Southern Methodist University in their latest study, to be published in the journal Seismological Research Letters, classified those North Texas events—and dozens more—as being "almost certainly induced" by the energy companies.
"There are many areas in Texas that have man-made earthquakes...and it's not a new phenomenon," said Cliff Frohlich, the study's lead author and the associate director of the Institute for Geophysics at the University of Texas.
Frohlich and his five colleagues devised a five-question survey on earthquake timing, location, research on the events and other details. With that data, they assessed the likely origins of the 162 quakes magnitude 3.0 or greater to shake Texas since 1975. They found 42 of them, or 26 percent, were most likely man-made, or "almost certainly induced" by the oil and gas industry. An additional 53 of them, or 33 percent, were classified in the second-likely category of "probably induced."
These suspected industry-linked earthquakes were mostly in the known oil basins, including the Eagle Ford Shale in South Texas and the Barnett Shale in North Texas. The researchers also showed that the likely cause of earthquakes changed over time as operators updated their methods for oil and gas extraction. While some early events were associated with the underground injection of water or gases such as carbon dioxide for oil recovery, the earthquakes after 2008 are mostly tied to wastewater disposal.
"It's a very systematic analysis about what's known about earthquakes in Texas going through the entire historic period and it's done by those who are really the experts on Texas seismicity," William Ellsworth, a geophysicist at Stanford University, told InsideClimate News. Ellsworth was not involved in the study.
Scientists reviewed dozens of older events, too, where less information was available, and found the oldest earthquake likely linked to oil and gas exploration struck in 1925, according to the study.
Using old studies, court documents and other available documentation, the researchers determined that some small earthquakes in 1925 along the Texas Gulf Coast were "probably induced" by the nearby withdrawal of oil and water. One of the side effects of the shaking: part of the local oilfield sank into the sea. Experts employed by the local oil company actually argued the event was man-made. Back in the 1920s, state officials, who could lay claim to the land if the events were proved natural, sued the energy company over the earthquake origins. The court decided the land's sinking was indeed an "act of man."
That is a major role reversal from today, when both the oil industry and Texas regulators are denying recent earthquakes are man-made, explained Frohlich.
Prior to 2008, Texas experienced an average of two earthquakes magnitude 3.0 or greater each year; after 2008, that number shot up to 12 per year. This coincides with an oil and gas boom sparked by hydraulic fracturing and horizontal drilling, when wastewater production jumped, too. Texas, the top state for oil and gas production, is one of several states in the country's midsection whose energy boom has been accompanied by a rise in earthquakes.
"There's certainly been an evolution in the understanding [of man-made quakes] in just the past couple of years," said Ellsworth. "The state of Oklahoma has embraced the science and taken some bold steps...to get the seismicity under control," he said, adding that Kansas and Ohio officials have adopted similar measures.
In contrast, Texas officials aren't publicly acknowledging a problem, said Frohlich, but he added that they are making moves to confront the issue. In 2005, Texas had only five permanent instruments, called seismometers, for detecting earthquakes. Last year, 11 more stations went online, and state lawmakers approved the addition of 22 new seismometers, which will go online in the coming years.
"The Railroad Commission takes the issue of seismicity very seriously and has taken several actions to address this issue," Gaye McElwain, spokeswoman for the regulatory agency, wrote in an email. Some of these actions include hiring a staff seismologist in 2014, requiring some new disposal well applications to include known earthquake-related data, and hosting a technical hearing to discuss the issue.
"The Commission will continue to use objective, credible scientific study as the basis for our regulatory and rulemaking function. However, this new study acknowledges the basis for its conclusions are purely subjective in nature," said McElwain.