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The process of hydraulic fracturing or fracking uses fluid pressure to extract hydrocarbons from rock. There have been media reports in the UK linking a fracking operation to some minor earthquakes.

The controversial new drilling operation for natural shale gas in Lancashire has been suspended following a second earthquake in the area that may have been triggered by the process.

The British Geological Survey is claiming there may be a link. How established is the science behind this?

Earthquake experts from the British Geological Survey said that the 1.5 magnitude quake last week was similar to a 2.3 earthquake in April in the same area and that both may be linked to the experimental fracking for shale gas at Preese Hall on the Fylde coast.

Brian Baptie from the BGS:

"We had a couple of instruments close to the site and they show that both events were close to the site and at a shallow depth.

"The timing of these two events in conjunction with the ongoing fracking at the site suggests that they may be related." He added: "It is well-established that drilling like this can trigger small earthquakes."

So how well established is it? And can it trigger larger earthquakes, perhaps not in the UK but in areas of greater geological sensitivity?

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    If you're willing to accept the word "earthquake" down to low enough energies fracking is an earthquake; but a some point the word gets less applicable. – dmckee Aug 6 '11 at 23:31
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    Notably 1.5 and 2.3 magnitude earthquakes are common, and hardly noticable. Also, keep in mind that they may have stopped drilling not because they are afraid they're causing the quakes - they have to stop once quakes occur, and let things settle down, since earthquakes can cause disruptions in the shaft and drilling equipment. Better to wait until the area is geologically stable before resuming drilling. – Adam Davis Aug 7 '11 at 0:26
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    This is and article for a canceled project in Switzerland for HDR geothermal powerplant. They use some very advanced drilling techniques that are borrowed from the oil and gas industry. nytimes.com/2009/12/11/science/earth/11basel.html?_r=1 disclaimer - first learned about it from energybulletin.net but cannot find it now. The report cited here concludes that there is link, but that the earthquakes are harmless. – Daniel Iankov Aug 7 '11 at 6:56
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    Not entirely harmless in this case: On the other hand, the report also found a 15 percent chance that the project could set off an earthquake that could cause over half a billion dollars in damage. Every year, the project would probably produce some $6 million in damage, the report found. – z7sg Ѫ Aug 7 '11 at 10:02
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    @DJClayworth "There may be a link" is not a clear statement. Since I can't easily ask the BGS how the evidence stacks up, I'm asking random guys on the internet. If you don't feel qualified to answer, there's no pressure. – z7sg Ѫ Aug 8 '11 at 18:11
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Cross-posting from my answer here: while fracking can theoretically cause earthquakes in specific rare scenarios (see the accepted answer); most earthquakes attributed to mining are caused by non-fracking mining activity, specifically, wastewater disposal wells according to a Texas specific study.

The Academy of Medicine, Engineering and Science of Texas (TAMEST) 2017 pre-publication study "ENVIRONMENTAL AND COMMUNITY IMPACTS OF SHALE DEVELOPMENT IN TEXAS" says in chapter on earthquakes:

  • There has been an increase in the rate of recorded seismicity in Texas over the last several years. Between 1975 and 2008 there were, on average, one to two earthquakes per year of magnitude greater than M3.0. Between 2008 and 2016, the rate increased to about 12 to 15 earthquakes per year on average.
  • Under certain unique geologic conditions, faults that are at or near critical stress may slip and produce an earthquake if nearby fluid injection alters the effective subsurface stresses acting on a fault.
  • Mechanisms of both natural and induced earthquakes in Texas are not completely understood, and building physically-complete models to study them requires the integration of data that always will have irreducible uncertainties.
  • To date, potentially induced earthquakes in Texas, felt at the surface, have been associated with fluid disposal in Class II disposal wells, not with the hydraulic fracturing process.
  • The TexNet goals address an integrated research portfolio that considers seismicity analysis, geologic characterization, fluid-flow modeling, and geomechanical analysis.

Additionally, the linked answer's question has a previous answer which also produced the similar conclusion from Oklahoma study (most earthquake increase is due to wastewater injection, not fracking)

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Cuadrilla Resources was the company responsible for the fracking operation. They have now released a report, Geomechanical Study of Bowland Shale Seismicity, 2 Nov 2011, confirming that it caused the earthquakes.

In the report there are a number of factors that were said to have contributed to the seismic events, including the following:

  • There was a pre-existing critically stressed fault.
  • The fault was "transmissible" so accepted large quantities of fluid.
  • The seismic events were induced after repeated injection of fluid into the same fault zone.

The report states that repeat occurrences are unlikely at future well sites and gives magnitude 3 as a worst-case scenario.

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    Seeing as a magnitude 3 is barely noticeable does this really count? As I recall the duration of the quakes is generally much lower than those of naturally occurring quakes as well. – Chad Nov 2 '11 at 15:25
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    Link in answer is broken. It should be worth pointing out that a magnitude of 3 is apparently barely felt or noticed: geo.mtu.edu/UPSeis/magnitude.html Only a quake of 5.5+ would cause damage to buildings. – Django Reinhardt Sep 5 '13 at 14:45
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    "Only a quake of 5.5+ would cause damage to buildings." You're missing a word such as "significant". The UK has fairly regular earthquakes around magnitude 4 and these often cause minor damage to buildings, such as cracking walls and toppling chimneys. (Though a toppled chimney can be pretty significant if it causes several tens of kilos of bricks or stone to fall through your roof and into your house.) – David Richerby May 15 '15 at 9:05
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    I think that you should really mention that a magnitude 3 quake is unnoticeable. Thunder can cause more shaking than that! I know, I experienced the latter! Each level up you get 31.6 times the energy. A magnitude 4, 31.6x more energy, won't damage any buildings. – zagadka314 Nov 25 '15 at 2:39
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I would be very surprised if it did not cause earthquakes. Back in 1993, the Dutch established that even conventional gas exploitation causes earthquakes up to a magnitude of 3.5. Since a 2.3 earthquake is 16 times weaker, it's quite believable that you could get such an earthquake even with experimental drilling.

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    all depends on what you call "earthquake". Such small magnitude seismic events are NOT called earthquakes but tremors except by people trying to stir up negative sentiment against drilling. – jwenting Nov 2 '11 at 13:54
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    Not to mention that releasing energy at smaller levels reduces energy available for catastrophic seismic events. – Chad Nov 2 '11 at 15:25

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