Despite Headlines, UCSC Study Inconclusive on Link between Seismicity and California Injection Wells

Recently, researchers at University of California Santa Cruz (UCSC) released a paper analyzing a potential relationship between seismic activity and produced water disposal from oil and gas operations in California’s Central Valley.

To date, scientists and regulators – including John Parrish, the State Geologist —  have reported that produced water injection has not been a cause of felt seismic activity in our fault-laden state. Contrary to misleading claims from activist groups like Californians Against Fracking and the Center for Biological Diversity, the authors of the current paper found no direct causal link between “wastewater” disposal and seismicity.

While this paper is a thoughtful first-look at employing and using numerical model-based projections to study potential correlations between a wide-range of crustal conditions and seismic activities in areas where wastewater injection occurs, it does have some built-in limitations as well as inconclusive results.  It’s important that Californians have access to the facts.

Inconclusive Results

The UCSC paper falls short of finding any definitive link between produced water injection and seismic activity, which the researchers admit. At this stage of the research, they are dealing in correlation, not causation. For example, in the opening section, the researchers state:

“We then investigate a possible correlation between fluid injection and seismicity, including variation in frequency-magnitude distribution with the onset of injection rate increase” (emphasis added)

The authors’ guarded language continues in the first paragraph of the second section, when stating the purpose of the research:

“This study concentrates on a potentially injection induced earthquake swarm in 2005, which is associated with the White Wolf fault (WWF) and occurred at the southern end of the Central Valley, CA…The White Wolf Swarm is suspected to be connected to fluid-injection activity based on a statistical assessment of injection and seismicity rate changes” (emphasis added)

Even the conclusion of the paper is not definitive on any relationship between wastewater disposal and seismic activity, as the report states:

“Our results suggest a connection between wastewater disposal and seismicity with events up to Mw4.6 at the southern end of the Central Valley” (emphasis added)

Possible, potentially, suspected – all of these words used to describe wastewater disposal and seismic activity throughout the report do not infer causation, no matter how much activist groups twist them to seem like they do. While this is a problem for activists who “want” the research to support their ideology, it is a sign of the researchers’ intellectual honesty that they do not make claims that their science does not support.

In fact, “a suggested connection” does not mean that injection wells cause an increase in seismic activity of magnitudes of any concern to humans; it means that the safe practices we already have in place make sense and should continue – a view the UCSC researchers share.

Natural Seismicity

Another reason anti-industry activists’ claim of causation is unfounded is because, with active faults and natural seismic activity already occurring in this area, determining a link between disposal injection and seismic events is extremely complicated. As the researchers point out, the fault near the examined swarm was active prior to injection:

“The presence of background seismic activity on the upper portion of the Tejon fault revealing that part of the fault was seismically active prior to injection.”

A 2015, a peer-reviewed report from the California Council on Science and Technology (CCST) mentions this same difficulty, making it seem almost impossible to know definitively that fluid injection has anything to do with seismic activity in California. As the report states:

California has frequent naturally occurring earthquakes – so many that seismologists have a hard time determining if any of these earthquakes were actually induced by fluid injection.”

Even so, a very small percentage of seismic events have been tied be to disposal injection wells. There are currently over 52,000 class II disposal wells in California and yet few recorded seismic events potentially related to the disposal process. The authors acknowledge the rarity of such events:

Up to now, few injection-induced earthquakes outside of geothermal reservoirs have been observed in California.”

Scientists and Experts Agree

In addition to this UCSC research, several other recent major studies have examined a potential relationship between induced seismicity and produced water injection. Most notably for California, last year the California Council on Science and Technology (CCST) released its peer-reviewed study on the impacts of well stimulation, including produced water disposal, in the state.

In addition to finding no link between hydraulic fracturing (“fracking”) and induced seismicity, the report also found no instance of induced seismicity from produced water disposal. As the report states:

Fluid injection in the process of hydraulic fracturing will not likely cause earthquakes of concern…To date, there have been no reported cases of induced seismicity associated with produced water injection in California” (p. 48; emphasis added)

Outside of California, the scientific consensus on wastewater disposal and induced seismicity falls in line with the UCSC researchers’ findings. As a recent analysis from the U.S. Geological Survey concluded:

“Although the disposal process has the potential to trigger earthquakes, not every wastewater disposal well produces earthquakes. In fact, very few of the more than 30,000 wells designed for this purpose appear to cause earthquakes” (emphasis added)

You may have read that felt seismic events have, in fact, been linked to produced water disposal elsewhere in the country, and this is true in a very limited way: less than one percent of U.S. injection wells – 0.15 percent of Class II injection wells and 0.55 percent of disposal wells –

have been potentially linked to seismicity. Not one of these wells is in earthquake-prone California where we have been disposing of produced water, and employing hydraulic fracturing, for many decades. With our safety record, we are clearly doing something right.

Fracking is not disposal

Anti-energy activists are notorious for linking a host of things to hydraulic fracturing. Some are absurd, some are offensive and some are downright bizarre. Activists are no different on the issue of induced earthquakes. They swear that “frackquakes” exist even though scientists and regulators confirm that the fracking process – as opposed to disposal – does not cause felt seismic events, even in states with increased seismic activity.

This is because, as Stanford University geophysicist Mark Zoback told the United States Senate,

“It is important to note that the extremely 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.” [emphasis added]

Activists and the media frequently conflate fracking and disposal, but disposal happens regardless of whether fracking is used. Oil and gas production “produces” water in much greater quantities than hydrocarbons. Whether a well is hydraulically fractured or not, water will be produced and will be recycled, used in enhanced oil or gas recovery operations, or, in a majority of cases, it will be disposed of. It is critical to have an extensive monitoring regimen in play precisely because disposal is such a routine and integral part of the oil and gas – in California, almost exclusively oil – production process. The fact that our state has had not seismic activity linked to the process is a testament to industry best practices and a historical commitment to environmental protection which, yes, includes sensible but strict regulations.

Rigorous Monitoring Continues

A main point made by the UCSC researchers is that, while no definitive proof of a link between produced water disposal and seismicity exists, monitoring efforts and safety are a top priority. As the authors’ introduction notes:

“Our results suggest that induced seismicity may remain undetected in California without detailed analysis of local geologic setting, seismicity, and fluid diffusion” (emphasis added)

Oil and natural gas companies could not agree more and in California comprehensive monitoring programs are already in place. In fact, not only is there agreement that disposal activities should be monitored, but the UCSC paper’s recommendations are entirely consistent with the industry’s scientifically rigorous and careful approach to resource development.

For obvious reasons, oil and gas companies take the safety of their workers and the communities in which they operate very seriously. Since the passage of Senate Bill 4 the industry operates under the nation’s most rigorous regulatory rules to protect the environment and increase energy production accountability. The sweeping legislation establishes a comprehensive permitting system, increases transparency, includes the strongest disclosure requirements in the country, and requires extensive monitoring and testing to ensure safe production.

So, when fringe environmental groups like the Center for Biological Diversity try to scare the public with inflammatory claims like the need “to act immediately” to protect Californians from events potentially related to produced water disposal – even though such events have never, to the best of our knowledge, happened in more than 100 years of energy production in the state – they are intentionally failing to acknowledge that robust “action” is already occurring and working well.


For years, opponents of oil and gas development have fomented not only concern but the “run for your life” kind of alarmism that helps raise money but confuses, rather than clarifies, issues. Today, this includes stoking a fear of inducing seismic events via produced water injection or fracking. The reaction to the UCSC study is no different and, as noted above, the alarmism is misplaced.


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