Earthquakes triggered by fluids injected deep underground, such as during the controversial practice of fracking, may be more common than previously thought, a new study suggests.

Fluid injections into Earth are not uncommon. For instance, in hydraulic fracturing, or fracking, water, sand and other materials are injected under high pressure into a well to fracture rock, opening fissures that help natural gas flow out more freely. Fluid-injection operations are also used to help get power from geothermal energy, and to dispose of waste.

However, researchers have long known that fluid-injection operations can trigger earthquakes. For instance, in 2006 one geothermal energy site triggered four earthquakes in Basel, Switzerland, ranging from 3.1 to 3.4 on the Richter scale. Fracking also appears linked with Oklahoma’s strongest recorded quake in 2011, as well as a spate of more than 180 minor tremors in Texas between Oct. 30, 2008, and May 31, 2009.

It remains unclear why some injection wells set off earthquakes whereas others do not. To find out, seismologist Cliff Frohlich at the University of Texas at Austin analyzed seismic activity in the Barnett Shale of northern Texas between November 2009 and September 2011 and compared the properties of injection wells located near quake epicenters. […]