Stanford geoscientists have demonstrated that fracking-related activities were the direct cause of a number of small earthquakes. Clara Yoon, then a Ph.D. student, studied seismic activity that occurred between June and September 2010, using data mining techniques to conclude that fracking, as well as wastewater injection, caused both small, magnitude 0 quakes and larger quakes in October 2010 and 2011.

The technique can be used to monitor seismic activities at fracking operations, giving geoscientists an early warning that larger, more damaging quakes could be on the way. This advance notice of problems would enable well drillers to help reduce the likelihood of bigger, potentially damaging earthquakes from occurring.

Fracking releases trapped shale gas by injecting high-pressure fluid underground. This cracks rock open,Map showing shift of Arkansas earthquake locations after Feb. 15, 2011. Source: U.S. Geological SurveyMap showing shift of Arkansas earthquake locations after Feb. 15, 2011. Source: U.S. Geological Survey which produces very small earthquakes. Conventional earthquake-spotting tools miss the tiny quakes that data analysis reveals.

“In our study, you can actually see individual earthquakes occurring next to the section of a well that’s being fracked,” said Yoon, lead author of the study published in the Journal of Geophysical Research.

Arkansas' earthquakes were the first in the U.S. to draw attention to the potential role fracking played in quake genesis. Texas, Oklahoma and other states have also experienced these quakes. Scientists believed the likely cause to be the practice of injecting waste fluids deep into the earth.

Yoon developed an advanced data-mining algorithm to examine seismic activity in Arkansas. She found 14,000 small, previously unreported earthquakes and compared their timing and location to fluid-injection data. She was able to demonstrate the direct relationship between fracking and quakes in 17 of 53 production wells — an unexpected result.

An additional unexpected result was the discovery that some fracking-induced quakes were larger, with magnitudes 1 and 2, than the many tiny magnitude 0 tremors. Since the differences between Richter-scale magnitudes increases geometrically, a magnitude 1 quake is 31 times stronger than a 0 magnitude quake. These quakes also persisted longer than expected.

Wastewater-induced quakes identified in the research point out that faults deeper down can also cause quakes when stressed.

The Stanford team encourages continuous seismic monitoring from the beginning of a fracking operation. Applying Yoon’s algorithm to data gathered from this monitoring could help pinpoint activity leading to larger tremors.