A few months ago, researchers from Durham University released a peer-reviewed paper —unfortunately, not widely reported – regarding the issue of hydraulic fracturing (“fracking”) and induced seismicity (earthquakes). According to lead author Richard Davies, hydraulic fracturing is not the earthquake inducing threat that anti-development activists claim.
Of 198 instances of human-caused earthquakes since 1929, the authors observed only one that was indirectly related to hydraulic fracturing, and this wasn’t in California. Other sources cite three other seismic events potentially related to the process, but the two in the United States were linked to wastewater injection, a process common to many industries.
As Davies states in the New Civil Engineer (sub req’d):
“It is worth bearing in mind that other industrial-scale processes can trigger earthquakes including mining, filling reservoirs with water and the production of oil and gas…we have concluded that hydraulic fracturing is not a significant mechanism for inducing felt earthquakes. It is extremely unlikely that any of us will ever be able to feel an earthquake caused by fracking.”
The paper examined published examples of induced earthquakes, looking at a variety of potential causes and the corresponding magnitudes for each event. How did hydraulic fracturing compare? According to the report:
“Hydraulic fracturing of sedimentary rocks, for recovery of gas from shale, usually generates very small magnitude earthquakes only, compared to processes such as reservoir impoundment, conventional oil and gas field depletion, water injection for geothermal energy recovery, and waste water injections. We have proposed four primary mechanisms for fault reactivation by hydraulic fracturing. Although there are approaches for mitigating the risks (e.g., Brodylo et al., 2011; Green et al., 2012) and faults can often be imaged by seismic reflection data, and avoided, it cannot be ruled out that reactivation of preexisting faults could induce felt seismicity. It should be noted, however, that after hundreds of thousands of fracturing operations, only three examples of felt seismicity have been documented. The likelihood of inducing felt seismicity by hydraulic fracturing is thus extremely small but cannot be ruled out.” (p.18, emphasis added)
The authors point out four mechanisms by which hydraulic fracturing can potentially trigger seismicity by causing an increase in the fluid pressure in a fault zone. They also note, however, that the role of hydraulic fracturing in felt seismic events is very low.
“To date, hydraulic fracturing has been a relatively benign mechanism compared to other anthropogenic triggers, probably because of the low volumes of fluid and short pumping times used in hydraulic fracturing operations. These data and analysis should help provide useful context and inform the current debate surrounding hydraulic fracturing technology.”
So yes, like many other processes associated with energy development, hydraulic fracturing is capable of producing small scale seismic events that in almost all cases are too small to be felt at the surface.
As we have noted before, and as other scientists and regulators have reiterated time and again, hydraulic fracturing (unlike some other human-generated activities) simply does not pose a serious risk of creating felt seismic events. Of course, here in earthquake-prone California, we should be concerned about seismicity, and that is why strong regulations are in place.
The good news for California, though, is that with regard to hydraulic fracturing, there is little reason to keep yourself awake at night in fear. This is because, as Mark Zoback, Stanford University geophysicist and advisor to the Obama Administration, has stated:
[E]xtremely small microseismic events occur during hydraulic fracturing operations. These microseismic events affect a very small volume of rock and release, on average, about the same amount of energy as a gallon of milk falling off a kitchen counter.”
This is something that solid operating practices, and appropriate regulations, can manage – as they have for many decades in this state and throughout the country.