The National Research Council published a report today, reviewing and analyzing peer-reviewed literature, federal and state documents, data requested from private companies, and more ... all in an effort to better understand the link between earthquakes and natural gas fracking techniques.
Because this is the National Research Council, you can read the whole thing online for free. But here are the three key takeaways:
First: The actual process of hydraulic fracturing—injecting fluid into the ground to break rocks and release trapped natural gas—doesn't seem to come with a serious seismic risk. This process has been definitively linked to small earthquakes—no greater than 2.8 magnitude—at one location.
Second: Injecting wastewater from fracking back into the ground has a much more noticeable seismic effect. What's more, this effect goes far beyond fracking. Injecting liquids into the ground is part of advanced recovery for oil, conventional drilling for oil and gas, carbon capture and storage, and geothermal electricity generation. This should not be a surprise. We've known that human can induce small earthquakes since the 1920s and injecting large amounts of liquids into a space that previously didn't hold much liquid—what the NRC calls a fluid imbalance—is part of that.