Study: Modern Oilfield Activities Not Linked to Quakes in Southern California

EID has previously highlighted the fact that no seismic activity has been linked to either injections wells or hydraulic fracturing in California. A study released today in the Bulletin of the Seismological Society of America by two California-based U.S. Geological Survey (USGS) underscores how modern oilfield practices in Southern California are a big reason why.

The study, by researchers Susan E. Hough and Morgan Page, is based largely on old state oil drilling records. It is an interesting examination of whether some early-20th Century earthquakes in the region may have been associated with energy production or produced water injection, at a time when oilfield practices – particularly reinjection of fluids to balance pressures — were not as scientifically advanced as they are today. This was also when the Los Angeles basin contributed around 20 percent of the world’s total oil production.

The authors conclude that a possible association between old production practices and seismicity nearly 100 years ago “cannot be ruled out,” but, as they would admit, this is not a claim that there is such an association, it is merely a suggestion for further study. Most importantly, the USGS scientists also highlight the safety of now-routine current practices like produced water reinjection.

Agreement between academics and regulators

The authors cite numerous studies that confirm what leading scientists and state regulators have concluded: modern oil and gas drilling has not led to felt seismic activity in California, the nation’s most earthquake-prone state.

The authors draw on the work of Egill Hauksson of the California Institute of Technology (CalTech), among others. From the abstract [emphasis added]:

“Considering seismicity from 1935 onward, Hauksson et al. (2015) concluded that there is no evidence for significant induced activity in the greater Los Angeles region between 1935 and the present.”

“Although Los Angeles basin fields accounted for roughly 20% of the world’s total production of crude oil by 1923 (Franks and Lambert, 1985), Hauksson et al. (2015) recently concluded that, apart from the six small events in the Wilmington area identified previously by Kovach (1974), there is no evidence for significant induced earthquakes in the greater Los Angeles area between 1935 and the present.”

Last year, Hauksson explained to the Los Angeles Times why earthquakes are not observed in Southern California oilfields. In addition, California State Geologist John Parrish and former USGS geophysicist William Ellsworth spoke with Science  magazine and further explained:

Ellsworth: Why does California see so many fewer induced earthquakes than places like Oklahoma?

Parrish: Our geology is quite a bit different from the geology in the midcontinent and the eastern states. For one thing, their production formations are very old. California, we have very poorly consolidated sediments that are much younger.

Ellsworth: The change has been when water begins to be injected in virgin formations, places where no perturbations have happened before. That seems to be to me at least one of the signatures for situations where can say these earthquakes have been induced.”

In addition, a 2012 study examined hydraulic fracturing (“fracking”) in the Inglefield Oilfield in Los Angeles, the nation’s largest urban oilfield. While fracking does not currently take place in Los Angeles, the study found that fracking– used for the purposes of the study only – did not induce any felt seismic events.

The Los Angeles Times article on the new USGS study also emphasized the safety of modern exploration and production:

The report’s finding does not mean that oil drilling is causing earthquakes in Southern California today.

The study only focused on earthquakes between 1900 and 1935. Different scientists have looked at earthquakes during more recent decades and have not found any reason to blame oil production for triggering earthquakes more recently in the L.A. Basin.

The reason could be that oil drilling practices in the L.A. Basin have changed dramatically since the years when oil was first discovered in this region, and today’s techniques may be safer and thus unlikely to trigger earthquakes as they might have done long ago.”

“Scientists don’t believe that wastewater injection — or oil production in general — is causing earthquakes in the L.A. Basin. A study last year found no obvious connection between oil production and earthquakes in the basin after 1935, around the time modern seismic sensing equipment was developed.

‘If the Los Angeles Basin were like Oklahoma today, we would know about it. We’re obviously not inducing magnitude 5 earthquakes on a regular basis,’” [study co-author] Hough said.

As study co-author Page told the Times: “It is … probable that changes to industry practices have largely mitigated the hazard.”

The Times chronicles the interesting genesis of the report in old, almost forgotten, state records. The authors pointed to some interesting implications from their work:

“One promising implication of the study is that, if true, the L.A. Basin is not as naturally seismically active as it’s currently believed to be.

‘If these earthquakes were in fact man-made by industrial processes that are no longer employed, the present-day earthquake hazard might be lower than we estimated in our models,’ Page said.

In other words: ‘Maybe geologically, the L.A. Basin could be safer than we have thought. It’s a possibility, at least,’ Hough said.

This is interesting. Hough and Page note that modern drillers use reinjection –replacing water (with oil removed) taken from an underground formation during production and reinjecting it back into the formation, which is something that drillers in the early 20th century didn’t do. The researchers posit that perhaps that removing the oil and not replacing it could have changed the balances between tectonic plates, leading to a higher incidence of felt earthquakes between 1900 and 1935. By reinjecting in the drilling process, Hough and Page believe it is possible  that production has very little or no overall effect on seismic interactions, thus maintaining the stability of the San Andreas Fault zone, although they allow for other possibilities. Further study will be needed to assess the validity of this hypothesis.

The Times goes on:

But one thing is certain: nothing in this study suggests that a halt to oil drilling would stop earthquakes from happening in Southern California. The state sits on the edge of two gigantic tectonic plates that are moving past each other, and that strain must be released through earthquakes.

‘If oil drilling in the L.A. Basin stopped today, we would still have earthquakes,’ Page said. ‘You can’t stop plate tectonics.’”


The current study is a fascinating piece of “seismological detective work,” as CalTech professor Jean Paul Ampuero told the Times, that adds depth to our understanding of both early-20th Century energy development in the Los Angeles Basin and the proximity of seismic events to industry activities. No causal connection is established, though the authors note that “a better identification of induced and tectonic events would improve our characterization of background (tectonic) earthquake rates in the region.”

Most noteworthy, however, is that no evidence is provided of any induced seismicity caused by the 42,000 Class II underground injection wells in California, the topic of most pressing present-day concern. The USGS researchers do not provide any evidence of induced seismicity post-1935, but they do recommend further study.

The good news for Californians is that, while we always live with the potential threat of earthquakes, experts do not think that modern oil production – and the benefits it brings to all of us – is materially increasing that risk.



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