Geologists Set the Record Straight on Earthquakes, Injection, and Fracking

The June 10th edition of Seismological Research Letters (SRL) is focused entirely on the topic of induced seismicity, an issue that has been producing a lot of headlines recently, especially in Texas and Oklahoma. Despite researchers’ efforts to clearly articulate what is and is not potentially causing these activities, there still seems to be quite a bit of misconceptions on fracking and injection wells in relation to such events. After all, when every headline starts with “Fracking causes…” it can be a little confusing to hear thatfracking is not causing most of the induced earthquakes,” or even thatmost injection operations do not appear to induce earthquakes.

This is exactly what researchers from the United States Geological Survey (USGS) and the Geological Survey of Canada (GSC) have attempted to clear up in the lead SRL article for this edition called, “Myths and Facts on Wastewater Injection, Hydraulic Fracturing, Enhanced Oil Recovery, and Induced Seismicity”. The USGS has also followed up the report with an article outlining six facts about induced seismicity, which makes for a great companion piece.

As E&E News reported,

“Although the message that these earthquakes are induced by fluid injection related to oil and gas production has been communicated clearly, there remains confusion in the popular press beyond this basic level of understanding,” Rubinstein’s paper states.

So what are the myths and facts surrounding waste water injection wells and induced seismicity? Let’s take a look at some of the myths from SRL and the facts laid out by USGS in its follow-up.

Myth #1 (SRL): “Hydraulic fracturing is causing all of the induced earthquakes.”

Fact #1 (USGS): “In the United States, fracking is not causing most of the induced earthquakes. Wastewater disposal is the primary cause of the recent increase in earthquakes in the central United States.”

Fracking has actually caused so few instances of induced seismicity that a previous USGS report stated:

“USGS’s studies suggest that the actual hydraulic fracturing process is only very rarely the direct cause of felt earthquakes. While hydraulic fracturing works by making thousands of extremely small ‘microearthquakes,’ they are, with just a few exceptions, too small to be felt; none have been large enough to cause structural damage.” (emphasis added)

A seismologist with Southern Methodist University, who was the lead author of a major study on induced seismicity, has also stressed that “fracking” is not the cause:

We’re not talking at all about fracking,” Dr. Matthew Hornbach, a scientist at Southern Methodist University who recently released a study on quakes in North Texas, told Congress Tuesday. “In fact, it’s been driving us crazy, frankly, that people keep using it in the press.” (emphasis added)

The focus instead is on wastewater disposal, a separate process. But even fluid injection isn’t an inherent threat for causing earthquakes:

Myth #2 (SRL): “All injection wells (hydraulic fracturing, wastewater disposal, and enhanced oil recovery) induce earthquakes.”

Fact #2 (USGS): “Most injection wells do not trigger felt earthquakes.”

The U.S. Environmental Protection Agency (EPA) has actually applauded states for how they manage their disposal well programs, saying “very few” of the nation’s disposal wells have been linked to felt seismic events. In fact, the National Research Council estimated in 2012 that only “one out of every 4,000 disposal wells nationwide are associated with triggered seismicity.”

EID also released a report looking at data on earthquakes in the Barnett Shale of North Texas, showing how 99.9 percent of the region’s injection wells have not been associated with felt seismicity.

And in California, where earthquakes are almost a cultural fact of life, there have actually been no cases of induced seismic activity from injection wells or any other oil and natural gas activity. And that’s with over 42,000 injection wells in the state.

Myth #3 (SRL): “The wastewater injected in disposal wells is spent hydraulic fracture fluid.”

Fact #3 (USGS): “The content of the wastewater injected in disposal wells is highly variable.”

The USGS goes on to say (emphasis added):

In many locations, wastewater has little or nothing to do with hydraulic fracturing. In Oklahoma, less than 10 percent of the water injected into wastewater disposal wells is used hydraulic fracturing fluid. In some parts of Oklahoma where very high volumes of wastewater are injected, no hydraulic fracturing is occurring at all, so the wastewater is purely saltwater that comes up with oil in the extraction process.” (emphasis added)

That brings us to a fourth myth, as the scientists have recently laid out:

Myth #4 (SRL): “There would be no need for wastewater disposal if hydraulic fracturing was not used.”

Fact #4 (USGS): “Wastewater is produced at nearly every oil and gas well, not just hydraulic fracturing sites.”

The SRL article continues:

“Salt water is produced at virtually all oil wells, whether the wells were hydraulically fractured or not. In fact, hydraulic fracturing is not used in the Hunton Dewatering Play in central Oklahoma, yet it is one of the largest producers of salt water in the United States.”

But we can also take this discussion out of the realm of oil and gas, because the reality is there are many uses for disposal wells. Now, when talking about oil and gas waste, we’re typically referring to Class II wells, but check out some of the other by-products that can be placed into underground disposal. From the EPA:

  • Class I Injection Wells – “Isolate hazardous, industrial and municipal wastes through deep injection.” The list actually leaves off radioactive waste which is mentioned here. Waste in these wells may originate from:
    • Petroleum Refining
    • Metal Production
    • Chemical Production
    • Pharmaceutical Production
    • Commercial Disposal
    • Food Production
    • Municipal Wastewater Treatment
  • Class III Wells – “Minimize environmental impacts from solution mining operations.” These wells are “used to mine uranium, salt, copper, and sulfur.”
  • Class IV Wells – “Prevent ground water contamination by prohibiting the shallow injection of hazardous waste except as part of authorized cleanup activities.” The only thing allowed in these wells is “ground water that has been contaminated with hazardous chemicals.”
  • Class V wells are used to inject non-hazardous fluids underground.” “In your community there may be industrial waste disposal wells, storm water drainage wells, large capacity septic systems, and other Class V injection wells.”
  • Class VI wells are wells used for injection of carbon dioxide (CO2) into underground subsurface rock formations for long-term storage, or geologic sequestration.”

So waste injection isn’t new and isn’t singular to oil and gas. It’s actually how we dispose of everything from salt water to human waste. When scientists talk about potential induced seismicity, they stick to Class II wells and the results are few wells being able to be linked to activity. Can you imagine how much more insignificant that number becomes when one adds in all of the other injection wells in a region?

Myth #5 (SRL): “Induced seismicity only occurs close to the injection well and at a similar depth as injection.”

Fact #5 (USGS): “Induced seismicity can occur at significant distances from injection wells and at different depths.”

The SRL article goes on to say:

“Seismicity can be induced at distances of 10 km or more away from the injection point and at significantly greater depths than injection. In the classic case of injection‐induced seismicity at the Rocky Mountain Arsenal, seismicity was induced at distances of at least 10 km laterally from the well and at depths of at least 4 km greater than the depth of injection. More recent reports have argued that seismicity may be induced at 20 km or more from the injection point.”

There is no blanket answer for why one well may induce seismic activity and another may not. As EID noted previously, one of the key highlights of a recent SMU study was that researchers acknowledged this:

“This study also gives further credence to the need for ongoing site specific assessments. The potential for seismic activity must be addressed based on downhole pressure, injected volumes, and location, including the orientation of certain faults. Peer-reviewed studies have consistently identified these variables as necessary to understand induced seismicity, and not to convey a blanket, one-size-fits-all approach that suggests geological or pressure conditions in any given area are analogous to operations in other parts of the country.”

Researchers have consistently noted that location alone cannot be the determining factor. Pressure, volume, location, time and other factors all have to be evaluated, since similarly operating wells in two different areas may or may not be associated with seismicity.


It’s no wonder Dr. Hornbach of SMU felt the need to vent his frustrations before Congress or the geologists who put out these reports saw a need to better inform the public. The media has sensationalized this issue, using a hot button word like “fracking” to draw people in while disregarding the media’s duty to accurately inform that very public. When a headline reads, “Report: Fracking ‘most likely,’ causing Texas earthquakes,” a direct contradiction to the science being reported on, what other choice do these researchers have than to come forward and try to set the record straight?

It is unfortunate that they had to spend precious time explaining these inaccuracies their studies clearly do not support. And the fact they did so is proof the media needs to focus more on getting the information correct—even if it means leaving out that favored “f” word, fracking. They owe it to their readers to do at least that.


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