A recently released United States Geological Survey (USGS) abstract, "Are Seismicity Rate Changes in the Midcontinent Natural or Manmade?," has added fuel to the debate over whether hydraulic fracturing can cause earthquakes. Noting that the increased rate of >3.0 magnitude quakes in certain regions in the Midwest is unprecedented outside of volcanic settings or main shock, the abstract authors conclude that "[w]hile the seismicity rate changes … are almost certainly manmade, it remains to be determined how they are related to either changes in extraction methodologies or the rate of oil and gas production."
To date, the "earthquake debate" has focused not on the fracking process itself, but on the disposal of fracking wastewater by way of deep well injection – a process that some claim caused the recent earthquakes in Arkansas, Oklahoma and Youngstown, Ohio. But the real debate will be over whether fracking as a technique for gas extraction can cause increased seismic activity, something that Cuadrilla Resources concluded happened last year in western England. While far from a definitive conclusion linking fracking to earthquakes, the language employed by USGS – "how they are related" – may suggest that USGS believes such a link to exist. Either way, USGS’s conclusions are certain to fuel a debate where the stakes already are high. If the fracking process can be causally linked to earthquakes, regulators may begin requiring seismic studies as a condition for obtaining a well permit; and such studies can be very expensive.
USGS will present the full results of its study on April 18 at the Seismological Society of America annual meeting.