Do I Think That Fracking Causes Earthquakes?

Alan Kafka
Weston Observatory
Department of Earth and Environmental Sciences
Boston College

Note: My analysis presented here is based on what was known about this issue at the time that I wrote this (June 2014). I don’t think the essence of this story has changed (yet?), but as more earthquakes occur near fracking sites the details of the issue are evolving.

These days, I can hardly go anywhere without being asked: “So, tell me, does fracking cause earthquakes?” Not wanting to get into a complex scientific and political argument on the spot (especially in social situations), I generally try to change the subject.

But, I guess there’s no avoiding it. Being a seismologist, I do have a responsibility to answer. So, here’s my take on it.

Short and simple answer: Yes.
Longer answer: But, it’s complicated…

“Hydraulic fracturing,” also known as “fracking”, is a method of injecting fluid into the ground to fracture rock for extracting natural gas and oil. Since an earthquake is the release of energy due to fracture of rock inside the Earth, we would have to say that the process of fracking definitely creates many small earthquakes. These small earthquakes are generally too small to be felt and are not (so far?) the earthquakes that have been considered the big problem in terms of causing structural damage or injury. However, part of a fracking operation involves the use of high volumes of water to release natural gas from dense rock, and disposing of the associated wastewater involves injecting it into deep rock formations. That wastewater injection can “induce” or “trigger” earthquakes in faults that have been dormant (and might have otherwise remained dormant) for a very long time. These wastewater-injection induced earthquakes are not necessarily so small, and can be damaging. And that is (so far?) where the fracking/earthquake problems and controversies lie.

Here’s my summary of the story:

  • There are well-documented cases of earthquakes clearly associated in time and space with fracking operations. But it’s not really the fracking itself that is the most likely source of damaging earthquakes. It’s the disposal of fluids via injection of highly pressurized wastewater into faults that more likely tends to induce the larger, potentially damaging earthquakes.
  • Most earthquakes associated with fracking operations have been smaller than magnitude 3. But a few larger and damaging earthquakes are suspected of having been induced by the injection of wastewater from natural gas (and also oil production) operations. On the seismogram shown below, you can see the Weston Observatory/BC-ESP recording of a magnitude 5.6 earthquake that occurred in Oklahoma on November 6, 2011 and is suspected of having been induced by injection of wastewater from oil extraction. Although that earthquake has not been directly linked to fracking, the injection of wastewater from oil extraction is essentially the same process as what occurs in fracking operations.
  • There is a well-known theoretical explanation of why injection of highly pressurized wastewater into faults could induce earthquakes. The increased pore pressure along the fault effectively lubricates the fault, causing it to release stress that might have been building up for many years, but might not have slipped without the excess pore pressure.
  • Out of many thousands of fracking operations, and the associated disposal of wastewater, so far only a small percentage of those operations have been clearly identified as being related to induced earthquakes of any significant size. The majority of operations have not, so the probability of a given fracking operation inducing damaging earthquakes is probably quite low.
  • Just how large and damaging a fracking/wastewater injection-related induced earthquake could be remains unknown. Although such earthquakes are generally smaller than magnitude 3, and the largest earthquakes claimed to be fracking-related are less than magnitude 6, even larger future earthquakes can not be ruled out. More research on this topic will be necessary to answer the question of just how big future wastewater injection-related induced earthquakes might ever be.
  • There are many other environmental issues related to fracking, such as heavy truck traffic and contamination of nearby well water used by local communities for drinking water. These are important issues to consider regardless of the question of whether or not fracking operations induce earthquakes.

Bottom line for me: These kinds of things are complicated. I think a more relevant question than “Does fracking cause earthquakes?” is: Given that wastewater injection procedures associated with fracking operations can induce earthquakes big enough to cause damage in some (small?) percentage of cases (and that there are other environmental hazards associated with fracking), what should we do about it? Fracking provides new sources of natural gas that could enhance our ability to generate electricity, heat homes, and provide fuel for transportation. Given the uncertainties, how do we find the right balance to make informed decisions about the extent to which the risks associated with fracking, or with any other process for finding new sources of energy, are worth the benefits?

This is the challenge for all of us as citizens of planet Earth.

Weston Observatory/BC-ESP seismogram of magnitude 5.6 earthquake that occurred in Oklahoma on November 6, 2011. This earthquake is likely related to injection of highly pressurized wastewater (from oil extraction operations) into wells. It was big enough to cause injuries and damage more than a dozen homes. (Click on seismogram to enlarge.)

Further Reading:

For an excellent, more complete, analysis of the situation, see the USGS Science Feature article Man-Made Earthquakes Update, and follow the links in it.

Clear and Simple Illustration of Mechanism to Explain Earthquakes in the Central and Eastern United States

This is a clear and simple illustration (adapted from the South Carolina Earthquake Education and Preparedness Program) of the commonly accepted “ancient zones of weakness” model for the cause of earthquakes in the Central and Eastern United States (and other “intraplate” regions far from plate boundaries). According to this model, preexisting faults and/or other geological features formed during ancient geological episodes persist in the intraplate crust, and, by way of analogy with plate boundary seismicity, earthquakes occur when the present-day stress is released along these zones of weakness.

IP_Quakes_Logs_AdaptedAlso see:

Why Does the Earth Quake in New England? and South Carolina Earthquake Education and Preparedness Program

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Broken Garage Door Springs, Earthquake Prediction, and Earthquake Triggering

Alan Kafka
Weston Observatory
Department of Earth and Environmental Sciences
Boston College

(Originally Posted: April 27, 2012)

A few days ago, one of the huge springs on our garage door opener broke, with quite a big KABOOM!

It seems to me that this is a perfect example of the problem of earthquake prediction. Here’s what I see as the connection:

In the morning, the garage door repair guy (who happened to be there fixing something else) looked up at the spring and said, “That deformed spot in the spring is ‘metal fatigue’ – it might break in 5 minutes, or it might break in 10 or 20 years.” Then, two hours later, it broke! (Perhaps he disturbed the internal stress field while he was fixing something else?)

This seems to be a perfect analog of the Elastic Rebound Theory of earthquakes, and the phenomenon of Earthquake Triggering!

It also explains why we knew that an earthquake was lurking in Haiti, but we couldn’t tell when it would occur: The tectonic stresses were ready to be released in an earthquake, but nobody could tell if the earthquake would occur in minutes, in years, in decades, or in centuries…

New Updated Seismicity Maps for Northeast U.S.

Click on the maps below to see the Weston Observatory seismicity maps of the Northeast United States, updated as of early February 2014.

The first map shows historical seismicity (from June 1638 to December 1974), and the second map shows network seismicity (from January 1975 to early February 2014).



The Detective Work of Seismologists: Earthquake or Blast?

Justin Starr
Weston Observatory
Department of Earth and Environmental Sciences
Boston College

Residents of the city of New Bedford, MA and the surrounding area felt something very strange at 10:52 am on January 9th, 2014. They heard a loud blast and felt a distinct rumble.

A seismic event had occurred.

Weston Observatory scientists quickly determined that the magnitude of this seismic disturbance was 1.9 and that it was located very close to New Bedford. Not very big, but shallow enough to be heard by many people in the area.

While speaking to the Massachusetts Emergency Management Agency (MEMA), Weston Observatory scientists were informed that there may have been blasting in the New Bedford harbor around the same time as the earthquake and very close to the possible epicenter. So was this a real earthquake? It was up to the scientists to find out.

Several phone calls went out and eventually, Weston Observatory scientists reached the New Bedford harbormaster who put them in touch with the Captain of… the Kraken! The Kraken is a drilling and blasting barge located in New Bedford and is tasked with widening the shipping lanes. As it turns out, the Kraken did not blast until 12:09 pm, over an hour after the earthquake occurred. In fact, the Captain received many phone calls asking if it was they who blasted and caused the shaking… but it was the earthquake!


The two seismograms shown below are from a USArray seismic station in Tiverton, RI. On those seismograms, you can see the Kraken Blast and the earthquake. Notice the big difference in magnitude (the earthquake is an order of magnitude larger).


And notice (below) the well-defined, high amplitude wave labelled “Rg” on the seismogram of the blast. The presence of these “Rg” waves on a seismogram are one of the ways that seismic “detectives” use to identify blasts, and distinguish them from earthquakes.


These “Rg” waves have been studied by seismologists, and are one of the ways that seismologists can distinguish between earthquakes and explosions. See, for example:

Kafka (1990): Rg as a Depth Discriminant for Earthquakes and Explosions