Earthquakes at Fracking Sites May Indicate Larger Tremors to Come

A drill rig at the Fayetteville Shale gas play in Arkansas. The area was shaken by earthquakes in 2010 and 2011 following injections of wastewater from natural gas operations into deep underground wells. (Image: Bill Cunningham via USGS)

Researchers have developed a new technique that can be used to monitor the seismic activities around fracking operations that may help to reduce the likelihood of larger and potentially damaging earthquakes at fracking sites from occurring.

The tiny tremors, which are caused by hydraulic fracturing of natural gas near the surface, may be an indication of the stressful conditions deep underground that could destabilize faults and trigger larger earthquakes.

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Stanford geoscientists have developed a way of detecting the thousands of faint earthquakes at fracking sites that have been previously missed. Clara Yoon, the lead author of the study published in the Journal of Geophysical Research, said in a statement:

Study co-author William Ellsworth, a professor (research) of geophysics at Stanford’s School of Earth, Energy & Environmental Sciences, went on to say:

October 2010 Arkansas earthquakes

Citizens nearby an Arkansas natural gas field were rocked by a magnitude 4 earthquake; it was then followed by two larger aftershocks in February 2011.

Scientists said that the two larger aftershocks were caused by the injection of wastewater from fracking sites into deep underground wells, and not by fracking operations closer to the surface.

Since the Arkansas earthquakes, Oklahoma, Texas, and other gas and oil-producing states have subsequently been rattled by earthquakes of a magnitude 4 and higher.

The analysis

Yoon and her colleagues were able to conduct a retrospective analysis of seismic activity in Arkansas before the magnitude 4 event by using an advanced data-mining algorithm developed by the research team.

Using earthquake-pattern recognition, the algorithm was able to generate detailed records of seismicity. Yoon said:

When the algorithm was used, it was discovered that there were more than 14,000 small, previously unreported earthquakes.

The researchers were able to show that most of the earthquakes were the direct result of fracking operations at 17 of the 53 production wells, after comparing the timing and location of the tremors with fluid-injection data that was provided by the state of Arkansas.

Co-author Gregory Beroza, the Wayne Loel Professor of Geophysics at Stanford, explained:

The earthquakes at fracking sites larger than expected

It was found that most of the earthquakes at fracking sites were larger and more persistent than expected, indicating potential trouble ahead. Earthquakes generated by fracking are usually no larger than magnitude 0, this equivalent to a milk carton hitting the floor after falling off a counter.

However, there were several earthquakes at fracking sites observed to be a magnitude 1, 31 times stronger than a magnitude 0. There were also a few that were above magnitude 2, 1,000 times stronger than magnitude 0.

Small earthquakes at fracking sites can be induced during hydraulic fracturing.
Small earthquakes (yellow stars) can be induced during hydraulic fracturing when high-pressure fluid (blue arrows) is pumped into horizontal wells to crack rock layers containing natural gas. Earthquakes (green stars) can also be induced by the disposal of wastewater from gas and oil operations into deep vertical wells. Over time, the disposal layer migrates away from the well (dashed green arrows), destabilizing preexisting faults. (Image: via Clara Yoon)

Even though most fracking-induced quakes occur near the well and dissipate quickly, some Arkansas earthquakes were located a distance from the wellbore and had continued weeks after the fracking operations had ended.

Ellsworth believes fracking near wastewater wells induced thousands of earthquakes that were too big and lasted too long; this indicates the stress conditions deeper down were primed to create the instability that triggered larger earthquakes

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