*UPDATE* Just the Facts: Hydraulic Fracturing and Seismicity

For two new reports linking earthquakes and shale gas production, there’s more than meets the eye.

There have been countless stories this week about two new reports – one from the United Kingdom and the other from the state of Oklahoma – drawing a connection between seismic activity and hydraulic fracturing. The headlines paint a bleak picture for such a safe and important technology: Reuters says, “UK firm says shale fracking caused earthquakes.” Rolling Stone asks rhetorically, “Wait, Now Fracking Causes Earthquakes?” By the time the Natural Resources Defense Council chimed in, the message was that hydraulic fracturing triggered two “relatively large earthquakes, with magnitudes 2.3 and 1.5.”

But were these seismic events “relatively large” as the NRDC claimed? Not really. In fact, in both the U.K. and Oklahoma the seismic activity measured was less than a magnitude 3. The U.S. Geological Survey – filled with people who actually study such things for a living – states that even magnitudes as high as 3.9 are often unnoticeable to those in the area.

So we’re not talking about roads being twisted or buildings and houses slipping off their foundations. Heck, we’re not even necessarily talking about your cup of coffee rattling on the table. What we are discussing is, according to the USGS, “similar to the passing of a truck.”

But don’t just take our word for it. We’ve read through the reports and gathered the key facts, so you can now see for yourself what these reports actually say about hydraulic fracturing.



  • “These events were reportedly felt by a small number of people but neither had any structural impact on the surface above.” (p. 1, Executive Summary)
  • “If these factors were to combine again in the future local geological limits seismic events to around magnitude 3 on the Richter scale as a worst-case scenario.” (p. 2, Executive Summary) — [NOTE: What does a magnitude 3 seismic event feel like? According to the U.S. Geological Survey, “many people do not recognize it as an earthquake” and vibrations are “similar to the passing of a truck.”]
  • “Even the theoretical maximum seismic event of magnitude 3 would not present a risk to personal safety or damage to property on the surface.” (p. 3, Executive Summary)
  • “In the past, mining induced earthquakes in the UK with magnitudes up to ML=3 caused no or only minor damage (Bishop et al., 1993). The associated earthquakes were located at shallower depth compared to the induced seismicity in the Bowland Shale.” (p. 44, Full Report)
  • “Even the maximum seismic event is not expected to present a risk. In the UK area near Lancashire there have been many seismic events induced by mining induced seismicity that caused events up to magnitude ML=3.1.” (p. 52, Full Report)


“There have been more than a million similar treatment operations in the world over the last 50 years or so and there are only two cases where similar seismic reactions occurred.”

–Stefan Baisch, German seismologist and one of the report’s authors (Nov. 3, 2011)

  • Although the report concludes that it is “highly probable” that hydraulic fracturing “triggered the recorded seismic events,” the report also notes that this was due to “an unusual combination of factors including the specific geology of the well site, coupled with the pressure exerted by water injection.” The report finds that this “combination of geological factors was rare and would be unlikely to occur together again at future well sites.” (p. 2, Executive Summary)
  • “[I]t is unlikely that another well in the Bowland basin will encounter a similar fault with the same critical stresses and high permeability into which fluid can be pumped.” (p. 2, Executive Summary)
  • “[T]he probability of a repeat occurrence of a fracture-induced seismic event is very low due to the unlikelihood of specific factors combining in the same way again.” (p. 3, Executive Summary)
  • “Since the chance for any single factor to occur is small, the combined probability of a repeat occurrence of a fracture induced seismic event with similar magnitude is quite low.” (p. iii, Full Report)
  • “[I]t is quite likely that the new wells will show no strong seismicity at all.” (p. 48, Full Report)
  • “Since earthquakes in Lancashire are rare we can be confident that the chance of triggering large earthquakes [with hydraulic fracturing] is negligible.” (p. 49, Full Report)
  • “[I]t cannot be concluded that all stimulation treatments are likely to cause unusual seismicity. We deal with just a single case and it is possible that this was just a very unlikely event that happened in the first try.” (p. 50, Full Report)


  • The study evaluated the potential for groundwater contamination and found that hydraulic fracturing operations in the area “occurs at a depth of around 3km, whereas groundwater aquifers do not exist beyond a depth of around 300m. There is a very thick, impermeable formation of rock above the Bowland shale with acts as a confinement layer. There is another rock barrier above this impermeable layer that will prevent any fluid migrating upward. The confinement layer and the barrier prevent any fluid getting into permeable layers of rock above.” (p. 3, Executive Summary)
  • “[T]here is negligible risk of fluid breaching into permeable layers.” (p. v, Full Report)
  • “[I]t can be concluded that it is very unlikely that the fluid would ever leave the Containment Layer.” (p. 41, Full Report)




  • “[T]he uncertainties in the data make it impossible to say with a high degree of certainty whether or not these earthquakes were triggered by natural means or by the nearby hydraulic-fracturing operation.” (p. 1)
  • “South-central Oklahoma has a significant amount of historical seismicity” (p. 2)
  • “The Eola Field…contains a highly folded and faulted thrust system” (p. 3)
  • “Given the analog recording history for most of the Oklahoma Geological Survey’s recording history it is difficult to determine whether the character [of the earthquakes in question] is uniquely different from that of earthquakes previously observed in the area. There have been significant numbers of earthquakes occurring in this area in the past…” (p. 21)
  • The authors note that many pieces of evidence “suggest that the earthquakes observed in the Eola field could have possibly been triggered” by hydraulic fracturing, but they further caution: “Simply because the earthquakes fit a simple pore pressure diffusion model does not indicate that this is the physical process that caused these earthquakes. The number of historical earthquakes in the area and uncertainties in hypocenter locations make it impossible to determine with a high degree of certainty whether or not hydraulic-fracturing induced these earthquakes.” (p. 25)


  • “The earthquakes range in magnitude from 1.0 to 2.8” (p. 1) — [Again, the U.S. Geological Survey on magnitude 3 seismicity: “many people do not recognize it as an earthquake,” vibrations are “similar to the passing of a truck.”]
  • Although there is “a clear correlation between the time of hydraulic-fracturing and the observed seismicity in the Eola Field…subsequent hydraulic-fracturing stages at Picket Unit B Well 4-18 did not appear to have any earthquakes associated with them.” (p. 21)
  • “Whether or not the earthquakes in the Eola Field were trigged by hydraulic-fracturing these were small earthquakes with only one local resident having reported feeling them.” (p. 25)


What’s the takeaway here? After being used more than 1.2 million times over nearly 65 years in more than 25 states, hydraulic fracturing has a clear record of safety, most notably in the fact that there has not been one confirmed case of groundwater contamination linked to this important well completion technology. Proper modeling and mapping of the subsurface is an ongoing process, and as technology improves so does our understanding of things deep below the ground, including fault lines. This technological advancement allows companies to see things – and in the case of fault lines, avoid things – that previously would have been tough to do.

The industry’s record of safety has not been a static process, but rather the result of a dynamic approach that constantly looks for ways to improve. Although the seismic events described here are minor, these two reports nonetheless include some important recommendations about how best to address subsurface issues in the future, and companies the world over will likely be paying pretty close attention.

UPDATE (Jan. 10, 2012; 2:10pm ET)

According to Bloomberg, scientists in the U.K. have confirmed the safety of hydraulic fracturing, especially as it relates to hydraulic fracturing. From that story:

Drilling for shale gas in the U.K. won’t cause dangerous earthquakes and poses little risk to the environment given appropriate safeguards, scientists said.

“Most geologists think this is a pretty safe activity,” Mike Stephenson, head of energy science at the British Geological Survey, said at a briefing in London today. “We think the risk is pretty low and we have the scientific tools to tell if there is a problem.”

That’s good news, too, because it looks like the U.K. is going to increase its estimate of recoverable natural gas from shale. Also from Bloomberg:

The U.K. could have more shale gas the previously thought, Stephenson said. The British Geological Survey is reviewing its estimates for U.K. onshore shale gas resources. The survey originally estimated that there is about 150 billion cubic meters of shale gas onshore, compared with about 300 billion cubic meters of conventional gas resources…Cuadrilla Resources Ltd. says it’s found more natural gas trapped in the shale rock around Blackpool in northwest England than Iraq has in its entire reserves.


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