“I said it wasn't possible. It's the most uninformed thing I've ever publicly said,” Frohlich says now, laughing. When he learned about the Barnett Shale natural gas boom, and realized he'd been wrong, Frohlich decided to sort through the history of Texas earthquakes to see if there were any potential links to oil field activity.
That work has now resulted in a new study, "A Historical Review of Induced Earthquakes in Texas," published on Wednesday in the journal, Seismological Research Centers. The study, conducted by researchers at the University of Texas-Austin and Southern Methodist University, compares the state's long history with oil and gas activity with the state's equally long history with earthquakes and it finds that about 90 percent of the quakes in the last four decades may have been caused by oil field activity.
Frohlich, the lead author of the review, has studied Texas earthquakes for about 30 years, but he'd never considered the possible connection between the oil field and shifting tectonic plates. “I'm an earthquake guy, but I didn't know much about oil field technology. I'd looked at what happened with Goose Creek, for example, but I'd never looked at it all together with what else was going on in the Goose Creek oil field,” he says.
When looking into the older incidents, Frohlich and the other researchers relied on old studies, scientific papers and court records. They started with Goose Creek, a once-booming oil field located in modern-day Baytown that ended up submerged by water after several earthquakes in the 1920s. The researchers found that Humble Oil's own scientists were pushing hard to make a connection between the oil field and the earthquakes that covered the oil field in water . “It's hard to believe it today, but back in the 1920s Humble Oil scientists actually fought to prove that oil companies had caused the earthquakes,” Frohlich says.
Of course, Humble Oil, an ancestor of ExxonMobil, had good reason – the state had filed a lawsuit trying to claim the land since any submerged land belonged to Texas by law. "The oil industry scientists found this link between the activity and the earthquakes decades ago, but they buried the information, or lost it, after it was no longer useful," Frohlich says.
When reviewing earthquakes that have occurred in the past 40 years, the researchers used a five-question test to evaluate the strength of evidence suggesting an earthquake was caused by oil field activity. Of the 162 Texas earthquakes of magnitude 3.0 or greater between 1975 and 2015, a quarter were “almost certainly” induced by oil and gas activities, while 33% were “probably induced and 28 percent were “possibly induced,” according to the study.
The researchers also tied the Eagle Ford Shale in South Texas, the Permian Basin in West Texas and the Barnett Shale in North Texas to some of the most recent earthquakes. They chide the Texas Railroad Commission, the state oil and gas regulatory board, for being “slow to acknowledge that induced earthquakes occur in Texas.”
(The RRC has yet to publicly acknowledge a link between quakes and drilling, but it has quietly changed the regulations so now any company that wants to drill within 10 km of an area with a history of earthquakes has to explain why their drilling won't cause more earthquakes, according to Frohlich.)
Frohlich decided to do the review after learning that the state legislature was setting up Tex Net Seismic Monitoring Program, an earthquake monitoring program that is slated to start monitoring earthquake activity this year. “I wanted to pull together a picture of what we knew about the earthquakes before the monitors went in this year,” he says. “We'd like to find a silver bullet, a simple way to solve the problem in all of the oil fields, but scientific research is incremental and it takes years to get piece everything together. This is a start though.”