Earthquake damage
Credit: martinluff /

Unless you've been pulling a Rip van Winkle for the past twenty years, you've probably heard people talking about "fracking"; maybe a lot. Make no mistake, there is a great deal of controversy surrounding the topic, with alarmists on one hand shrieking that the very appearance of a frack truck in their neighborhood caused their cows to give sour milk and industry shills on the other side saying with that telltale trained calm that fracking is so safe that they'd have no problem with Chevron doing a frack job in their basement. Who's lying? Who's telling the truth? Well, the answer is the same as always: both of them are lying, though to be politically correct we should say both of them are "spinning the truth."

While incidences of contaminated water and air pollution have been reported for years, a more recent claim is that fracking causes earthquakes[2]. True or false? Let's have a look...

What is this "Fracking" Anyway?

Fracking is shorthand for a process called "hydraulic fracturing," which is used to stimulate wells drilled into low-permeability reservoirs. Oops: let's back up a bit.

Not Lakes: Reservoirs

Porosity and Permeability in Sand Grains
Credit: Australian Government's Cooperative Research Centres Program

The concepts of porosity and permeability in pictures. Those brown blobs are sand grains about the size of a period on this page.

Oil and gas are not contained in pools, puddles, lakes, rivers, or pockets deep underground. Instead, oil and gas (and water, too) are contained in tiny spaces between grains of rock, most smaller than the period at the end of this sentence. If a rock has a lot of these pores, it's called "porous." An oil well is a way to empty the oil and gas out of billions and trillions of those pores over the large volume of rock called a "reservoir." That only works, however, if the oil or gas can move from pore to pore to get to the well; sort of like passengers have to get off a tram or subway car through a single door. If it's easy for the fluids to move from pore to pore to pore, the rock is called "permeable"; if not, it's "impermeable."

You with me so far?

Unconventional Reservoirs

Drilling Rig on the Hunt for Oil in Wyoming
Credit: gvgoebel /

A drilling rig "making hole" on the plains of Wyoming.

Some rocks are inherently porous but impermeable; the rock known  as shale is the best example. Shale is also the rock type that is most likely to contain the organic material that changes into oil and gas. For generations, petroleum geologists have lamented this conflict: there's lots of oil and gas in the many pores of shale, but they aren't connected so there's no way to get the oil out.

Cartoon of a Horizontal WellCredit: Geophysik_Geothermie / wikimedia commonsAbout twenty years ago, oil companies combined two existing techniques to produce oil and gas from shale and other impermeable reservoirs. The first is horizontal drilling, the second is fracking. Horizontal drilling is easy to explain, though not that easy to do: instead of running straight down, the well takes a big right-angle bend and ends up running parallel to the surface: a horizontal well (the well actually runs parallel to the rock strata, whatever their angle). The wells run horizontal for long distances - in some cases, up to two miles. This exposes long stretches of hydrocarbon-rich porous, but impermeable rock to the well.

Now for the Dirty Part

Credit: U. S. Geological Survey

A frack job in progress on a Marcellus Shale well, eastern US.

Hydraulic Fracture SchematicCredit: U. S. Environmental Protection AgencyIn simplest terms, hydraulic fracturing is a way to make impermeable rocks more permeable. A short stretch of the well is blocked off and huge pumps push a slurry of chemical-laden water and sand into the will under extreme pressure. Water can't be compressed (the hydraulic principle), so something has to give and that something is the rock. Tiny man-made cracks - fractures - propagate into the rocks for tens to hundreds of feet in all directions, carrying the chemicals and sand. When the pressure is released, the sand remains behind to "prop" the fractures open and provide a permeable path to the well. This process, called a "stage," may be repeated as many as thirty or forty times in a single well.


Earthquakes, You Say?

The Richter Scale of Earthquake Magnitude
Credit: South Dakota State Geological Survey

The Richter Scale in pictorial form. 

Let's ignore for now any discussion of groundwater contamination or air pollution: the question is whether fracking causes earthquakes. The simple answer is "yes." The not so simple answer is "it depends on your definition of earthquake."

If you know anything about earthquakes at all, it's probably the Richter Scale, which quantifies the "strength" of an earthquake. It's a logarithmic scale, so a big earthquake is a large number and a little earthquake is a small number. Also, each increase of one means an increase of ten in strength: a 7 (like the 2010 Haiti quake) is ten times as powerful as a 6, and 100 times as powerful as a 5. Below about 2, the events are called "microseismic," and cannot be sensed by humans. To break the rocks in a well, a frack job creates seismic events in the range of about -2 to -4; or about 1/10,000th of the power of the smallest earthquakes humans can feel.

Like I said, the simple answer is "yes," but the real answer isn't simple.

So Why do People Keep Saying "Fracking Causes Earthquakes"?

Frack jobs use water, and lots of it. The laughably misnamed Texas Railroad Commission says that an average frack job in the state's Eagle Ford Shale uses about 14 acre-feet of water. It being Texas, they're not inclined to use familiar units that might cast the oil industry in a bad light, but 14 acre-feet of water is more than 4.5 million gallons. Some of that chemical-laced water gets pumped back to the surface and some of it remains down-hole and comes up along with the oil or gas later. All of it has to be taken care of, and not much of it gets recycled (though more than there used to be). The rest of it gets trucked to a waste disposal well somewhere and is pumped underground for "permanent storage."

Now a little tale: back in the 1960s, a swarm of minor earthquakes (magnitude 4-5)  hit the Denver, Colorado, region. Seismologists eventually concluded that the quakes were caused by the injection of wastewater more than 12,000 feet below the Rocky Mountain Arsenal just north of the city[3]. Geologists have known for about fifty years that injection into deep wells can cause earthquakes. A simple explanation is that the fluids "lubricate" deep faults, a more complex explanation involves changes in the pressure system and redistribution of regional stress - let's just stick with "lubricate."

In recent years, there's been an uptick in earthquakes associated with deep injection wells, including quakes in Oklahoma in November, 2011, that injured two. A study published in a mainstream geological journal concluded that the quake was caused by injection into waste disposal wells. Other earthquakes linked to wastewater disposal wells (either by proximity or actual science) have occurred in Arkansas, Texas, Ohio, Colorado/New Mexico and England[1][2]. There is still, however, no known earthquake directly linked to fracking that was powerful enough for people on the surface to feel it.

So: DOES Fracking Cause Earthquakes?

Seismograms of an Earthquake
Credit: Crickett / wikimedia commons

Seismograms are recordings of the passage of seismic waves generated by earthquakes. Large movements essentially mean that the earthquake was large, nearby, or both.

Well, no: it doesn't.

Wastewater injection does occasionally cause earthquakes, a fact that's not really news - seismologists have known that for more than forty years[3]. What's new is the frequency of seismicity associated with injection wells, a frequency that happens to track the increased use of hydrofracking. In other words, the two phenomena are at most indirectly related: the more fracking industry does, the more wastewater is produced. The more wastewater is produced, the more gets shoved into injection wells. That's where the relationship should break.

Injection-related seismic events are preventable, even if fracking continues. There are a number of ways to approach the problem[1]:

  • More stringent regulation of injection well siting, such as prohibiting wells near subsurface faults.
  • Regulation to require recycling of fracking water instead of disposal (this would also reduce fracking's inordinate impact on freshwater supplies in some areas).
  • Reduction in demand for oil and natural gas through conservation and development of renewable energy sources