Reuters

Hyrdaulic fracking has handed the United States a remarkable (and remarkably lucrative) oil and gas boom. In some corners of the country, though, it also seems to have led to something of an earthquake boom.

Past research has connected earthquakes in seismically mellow states like Oklahoma and Ohio to the process companies use to dispose of the water and chemicals used in fracking. Drillers inject those spent fluids into deep wells underground, which can weaken faults and trigger a quake. An important caveat: only a handful of the 30,000 disposal wells around the country have ever been implicated.

A new paper, by a team from the University of Texas, however, adds a new wrinkle to the fracking-earthquake connection. In this case, it's not the process of fracking itself that's at fault, just the volume of drilling it's enabled. As the Wall Street Journal reports, researchers found that the sheer quantity of oil and gas being removed from Texas's Eagle Ford Shale formation has actually made the region more quake-prone. Per the WSJ:

The new study doesn't find much evidence that the man-made fracturing is causing earthquakes all by itself. The connection is more indirect, the study found: New wells are extracting nearly 600,000 barrels of oil a day and a considerable amount of water as well. Given the scale at which oil is now being removed, enough liquids are being disturbed that rocks are settling and faults slipping, causing the small earthquakes.

As the Journal notes, Southern California experienced a similar spate of drilling-induced quakes during its own oil rush, in the 19th century.