Anyone following our blog knows that the issue of whether fracking activities cause earthquakes is one receiving a lot of press and has been the subject of various studies. A seismologist at the United States Geological Survey (USGS) has added to the mix with a recently published study examining earthquakes in the central and eastern United States. The study, entitled “Shaking from Injection-Induced Earthquakes in the Central and Eastern United States” and appearing in the Bulletin of the Seismological Society of America (Vol. 104, No. 5) (August 2014), evaluated the effects of 11 earthquakes that the study considered “generally acknowledged or suspected to be induced by fluid injection.” The study relied on the USGS’s “Did You Feel It?” database, in which private citizens report that they felt an earthquake and rate its intensity. Using the database, the report compared reports for the earthquakes suspected to be related to fracking to reports for known natural earthquakes of similar magnitude in the same area. Based on this comparison, the study concluded that earthquakes allegedly produced by fluid-injection from fracking operations may cause less damage overall than earthquakes naturally induced by seismic events.
While the conclusion of the study is interesting, it underscores the need to rely on sound science and evidence before making conclusions about what may or may not have caused a seismic event in the first place. In fact, perhaps the most striking aspect of the study is how the earthquakes that are allegedly attributable to fracking-related activity were chosen–the study merely states that the earthquakes in question are “generally acknowledged or suspected” to have been induced by fracking fluid or wastewater injection, without providing any further analysis. Therefore, it is not clear how it was determined that these earthquakes are attributable to fracking activities. Additionally, the study only analyzed the data for 11 earthquakes, which represents a small sample size. Finally, questions about the reliability of the data arise because the impact of the earthquakes is quantified solely based on the USGS’s “Did You Feel It?” database, which consists of the subjective reports of private citizens. Not only are the reports subjective, but because “Did You Feel It?” depends on voluntary reporting, the individuals who elect to report data to the USGS may not be representative of the broader population of residents. In fact, the reporting rate varied dramatically among the 11 earthquakes that were analyzed; for some earthquakes, the number of “Did You Feel It?” responses was as low as several hundred reports, while for other earthquakes there were over 66,000 reports recorded in the system. This wide variability in responses calls into question what motivates people to participate in the “Did You Feel It?” system after a given earthquake, and whether these motivations distort the data and render it unreliable.