Natural-gas production linked to quakes in England, Arkansas, and North Texas, but more study needed

Following oil and gas exploration that began in the 1950s, long before fracking of the Eagle Ford got underway, the area southeast of San Antonio started to see minor earthquakes as early as the 1970s, occurring mostly within natural gas fields, Frohlich said.

Julie Dutton, a geophysicist with the U.S. Geological Survey, said last week the area has seen more than a dozen earthquakes over the past two decades. “At a 4.8, though, this is of course the largest that we’ve seen,” she said.

Still, even before the Eagle Ford boom spiked drilling permits across the region, there have been number of known gas fields buzzing with activity in South Texas for decades, Frohlich said. Frohlich coauthored a study after a magnitude 4.3 earthquake, the region’s previous record-holder, rattled the region in 1993 and suggested the quake was tied to natural gas production. Both the 1993 earthquake and last week’s occurred across the Fashing gas field, just west of Karnes City, which has been actively exploited since the late 1950s — Houston-based Momentum Oil & Gas most recently announced buying up a swath of new property and wells in the Fashing in May.

“It’s funny, the analogy I make is like smoking,” Frohlich said. “If your grandfather dies of lung cancer, it’s hard to prove smoking caused it, but on the other hand, you can run statistics for hundreds of people and say, ‘Yea, smokers are much more likely to have lung cancer.’ It’s a lot like that.” Looking southeast of San Antonio, historically most of the area’s earthquakes have occurred in active gas fields, Frohlich said. “We’re unaware of any earthquakes that occurred before gas development began in the 50s, and so a logical person would probably conclude it’s related to that,” he said.

Of last week’s earthquake, Frohlich said, “My intuition is that there is a relationship, but it’s hard to prove.” •

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