‘It Is Safe’: Six Key Takeaways from StatesFirst’s New Report on Injection and Induced Seismicity

A new report conducted by StatesFirst, an initiative of the Ground Water Protection Council and Interstate Oil and Gas Compact Commission, takes a comprehensive look at potential induced seismicity associated with Class II injection wells.

The report – which included input from state regulators, seismologists, academics and industry experts – finds that seismicity linked to oil and gas development is rare; that the risk associated with those rare occurrences is minimal; and that understanding of induced seismicity is growing and mitigation techniques are proving effective.

Its primary message was summarized by Ohio Department of Natural Resources Oil & Gas Chief and study co-chair Rick Simmers:

“It is safe,” Simmers said of wastewater injection. “We monitor the operations very carefully as do our counterparts in other states.”

Unfortunately, the Associated Press buried that in the 10th paragraph of its story on the report, choosing to open the piece with the following instead:

“A group of U.S. drilling states, seismologists, academics and industry experts issued guidance Monday in a frank new report on handling human-induced earthquakes caused by hydraulic fracturing or the disposal of fracking wastewater.” (emphasis added)

This misleading lead paragraph only serves to reinforce one of the common misunderstandings the study was trying to address. By greatly overstating the exceedingly limited link between fracking and induced seismicity — and incorrectly suggesting fracking and wastewater injection are one in the same — the story offered more of the same when it comes to mainstream media coverage of the issue.

That said, here are six key takeaways from the report that the AP either glossed over or left out:

Takeaway #1: Induced seismicity attributable to fracking is exceedingly rare – only two instances      

Contrary to some of the recent headlines, the report is very clear that hydraulic fracturing does not pose a credible threat for seismic activity. As the report emphasizes,

“[S]cientific evidence suggests hydraulic fracturing has a far lower potential to induce ‘felt’ earthquakes than underground disposal.”

The report states there have been just two instances of felt seismic events attributed to the hydraulic fracturing process in the U.S. Looking at one particular incident in Ohio, the report notes, it was

“only the fourth time hydraulic fracturing had been linked to seismic activity (and the second time in the United States).”

For perspective, more than one million wells in the U.S. have been hydraulically fractured since the technology was developed nearly 70 years ago. That is why the authors concluded:

“Although public concern has focused on hydraulic fracturing as a major source of induced seismicity… Incidents of felt-level seismicity associated with hydraulic fracturing occur far less frequently than those associated with Class II disposal wells and typically have lower magnitudes than injection-induced seismicity.”

For further distinction, the report devotes an entire section to addressing ongoing public confusion regarding the difference between fracking and wastewater disposal – confusion that continues to be exacerbated by misleading headlines and media reports. The report properly defines fracking as a well completion technique conducted for just a few days prior to a well going into production, while defining wastewater injection as a continuous process than is conducted after a well begins producing.

“The process of hydraulic fracturing is significantly different from the process of injecting fluid into a permeable and porous disposal zone. The volume of fluid injected over the short term is typically higher than with a disposal well; however, the hydraulic fracturing procedure lasts only a short time compared to a long-term disposal well.”

It is also important to understand that almost ALL oil and gas wells – whether hydraulically fractured or not – produce brine, which is completely different than fracking fluid and represents a vast majority of the total volume of fluid disposed into Class II injection wells.

For example, much of the brine, also known as produced water, in central Oklahoma has nothing to do with hydraulic fracturing at all – a fact alluded to in the press release accompanying a recent report on induced seismicity in Oklahoma conducted by Stanford University geophysicists Mark Zoback and F. Rall Walsh:

“Because the pair were also able to review data about the total amount of wastewater injected at wells, as well as the total amount of hydraulic fracturing happening in each study area, they were able to conclude that the bulk of the injected water was produced water generated using conventional oil extraction techniques, not during hydraulic fracturing.”

Takeaway #2: Induced seismicity from wastewater injection is also very rare

The report also provides proper context regarding the rare occurrences of induced seismicity linked to wastewater injection, noting there are 168,000 active Class II injection wells in the U.S., however,

“The vast majority of injection wells do not cause felt earthquakes. There are approximately 34,000 active wastewater disposal wells, over 134,000 active enhanced oil–recovery wells, and tens of thousands of wells are hydraulically fractured every year in the United States. Only a few dozen of these wells are believed to have induced felt earthquakes.”

The report also notes that a “vast majority of earthquakes are tectonic, or attributable to natural causes,” something the USGS has pointed out previously,

“Of more than 150,000 Class II injection wells in the United States, roughly 40,000 are waste fluid disposal wells for oil and gas operations. Only a small fraction of these disposal wells have induced earthquakes that are large enough to be of concern to the public.” (emphasis added)

The U.S. Environmental Protection Agency agrees, stating in a major report intended to help clarify induced seismicity for the purpose of better managing risks, that “very few” of the tens of thousands of disposal wells in the United States have produced any notable seismic activity.

Takeaway #3: A ‘one size fits all’ approach is not the answer

Various geological considerations and varying risk levels across the U.S. add to the complexity of the induced seismicity issue, which is why the report emphasizes that such efforts are best handled at the state and local level and that simply shutting down all injection wells is not the answer:

“… A one-size-fits-all approach is infeasible, due to significant variability in local geology and surface conditions, including such factors as population, building conditions, infrastructure, critical facilities, and seismic monitoring capabilities.”

For instance, a sweeping, nationwide ban on injection wells would shut down production in California, where there have been zero instances of induced seismicity, due at least in part to the state’s unique geology. California has 42,000 Class II injection wells, none of which have been linked to earthquakes in the most seismically active state in the U.S. Would shutting more than 40,000 wells with absolutely no link to induced seismicity make any sense in a scientific sense?

Not only is sweeping ban on wastewater disposal wells not scientific, it would be an economic disaster as well. For example, the oil and gas industry has accounted two thirds of the jobs created in Oklahoma since 2010. That said, a ban of all injection wells – which the report identifies as being a “critical component” of continued U.S. oil and gas production – would effectively shut down all oil and gas production in the state and devastate the economy. That’s another reason the report recommends states use case-by-case mitigation measures instead.

Takeaway #4: Increased understanding of induced seismicity is leading to effective mitigation measures

Another reason the report recommends site-specific mitigation measures is because that’s the best way to achieve results.

The report notes that although plenty of questions remain when it comes to differentiating between naturally-occurring and induced seismic events – as well as mitigating measures to address the latter – progress is being made due to increased scrutiny of induced seismic activity.

Many in the scientific community, including Zoback and Walsh, believe felt injection-induced seismicity has been the result of direct injection into basement rocks or formations in hydraulic communication with the basement rock. The authors of the StatesFirst study agree:

“The main physical mechanism responsible for triggering injection-induced seismicity is the increased pore pressure on critically stressed fault surfaces, which effectively unclamps the fault and allows slip initiation. These faults generally are located in the Precambrian basement.”

Based on that general consensus, mitigation measures have been implemented in Oklahoma and Kansas to avoid deep injection into basement rock or formations that might be in hydraulic communication with basement rock, as well as scaling back injection frequency, volume and pressure and seizing injection into active faults.

The report also highlights the effective mitigation measures of other states that have had seismic activity linked to injection wells. As the report puts it:

Ohio: The Ohio department of Natural Resources selected disposal wells for seismic monitoring based on the geology and proximity of the injection zone to the Precambrian basement rocks, where most of the seismicity in Ohio occurs. Seismic monitoring occurs prior to injection and continues after it has begun. If no significant induced seismicity is detected, the seismic instrumentation may be  moved to another location. This program is implemented on a case-by-case basis.

Texas: The Railroad Commission requires reporting of all historic earthquakes that occurred within a 100-square-mile area, considering a 9.08-km radius, from a proposed injection well location using data from the USGS (RCT 2014). When establishing the historic seismicity in a local area, it is important to recognize the location error associated with reported events.”

Several states — including Ohio, Oklahoma, Kansas and Texas — have already deployed or are planning to deploy permanent state seismic networks. Temporary seismic networks are also being used more frequently, which are effective for identifying the location and depth of quakes.

The latter helps experts determine if earthquakes might be induced based on the proximity epicenters to injection wells. But considering the science of natural quakes is nearly identical to that of induced quakes, causation is never a black and white issue.

Takeaway #5: Water quality has not been negatively affected

The “Frequently Asked Questions” supplement to the report clearly states that induced seismicity has in no way affected groundwater quality:

“At this time, there is no evidence to suggest that induced seismicity creates a risk to groundwater, as in many cases these events are either unrecognizable as as an earthquake or not felt at all, and according to the USGS, with very few exceptions, induced earthquakes have been too small to cause structural damage.”

The report notes that injection wells are regulated by the U.S. EPA’s Underground Injection Control (UIC) program under the Safe Drinking Water Act or state agencies that have been granted regulatory authority over the program (primacy states). The programs are designed to protect against water contamination, and their effectiveness was noted in a recent EPA study that found that fracking and related oil and gas development activities have “not led to widespread water contamination.”

Takeaway #6: The risk of harm to people and property from induced seismic activity is also exceedingly low

Despite all the media attention induced seismicity has received in recent years, the report notes that not only is the likelihood of induced seismicity low, but the risk of harm to people or property is low as well.

This assessment is based on the definition of a hazard as being a source of potential damage from induced seismicity, whether it be a fault of concern, buildup of pore pressure, or a hydraulic pathway to the basement rock, where most earthquakes occur. The presence of a hazard does not necessarily constitute a risk, however. Instead, the probability of harm from a hazard — whether it be the presence of people or structures, potential for a high magnitude earthquake or ground motion — must be present for substantial risk to be present.

The authors have determined that the latter isn’t present when it comes to induced seismicity:

“To date, the likelihood of induced seismicity associated with a particular injection site has been very low, as has the risk of harm to people or property.”

Interestingly, the report states the reason many induced-seismicity events are felt despite being very low magnitude (between 2.0 and 3.0 on the Richter scale) is due to the fact that they are occurring at shallow depths.

“This shallow depth often explains why induced earthquakes as small as M 2.0 can be felt. In general, natural earthquakes occurring in the central and eastern United States are not felt at that low a level of magnitude unless they are very shallow.”

The report also notes that earthquakes capable of causing structural damage almost always occur at much greater depths, including the only two magnitude 5.0 or greater earthquakes potentially linked to Class II injection – 2011 events in Prague, Okla., and Trinidad, Colo. (And the scientific community continues to have differing opinions concerning whether the Prague and Trinidad events were induced or were natural).

That considered, a vast majority of earthquakes tied to wastewater injection have not been strong enough to cause structural damage. As the report states,

“It commonly is accepted that structural damage to modern engineered structures happens only in earthquakes larger than M 5.0. Very few cases are known in which injection-induced earthquakes have caused structural damage because they generally are smaller than M 5.0. However, historical or poorly designed/constructed structures could be susceptible to structural damage in earthquakes of this magnitude or lower. In rare cases, nonstructural damage has been reported in earthquakes as small as M 3.0.” (emphasis added)


The increase in seismic activity linked to wastewater injection— specifically in the mid-continental U.S. — has been well-documented in the past five years. However, the experts from academic community, industry, state regulatory agencies and state geological surveys consulted for this study agree that induced seismicity is still rare and the public risk from induced seismic events is low. The phenomenon is something industry is taking very seriously however, as it continues to seek increased understanding and implement effective mitigation procedures.

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