A quick glimpse into Internet chatrooms will show that the web is alive with theories about fracking and earthquakes. Many people believe that earthquakes, particularly the 2011 quakes in West Virginia and Oklahoma, could be caused by industrial activities such as mining and other deep-earth activities. One particular villain in these discussions is the process of shale gas extraction known as ‘fracking’.
Up to a point, the conspiracy theorists are right: in the words of the British Geological Survey’s report on two small earthquakes in the north-west region of England, ‘it is well established that fluid injection can induce small earthquakes’. New research from the USGS suggests that it possible to generate a rough idea of the maximum size of tremor which might be generated from fracking.
What is Fracking?
Fracking (short for ‘hydraulic fracturing’) is the name given to the process of extracting natural gas from shales by breaking up rock with water injected into it at high pressure – a process which, according to the EPA, ‘offers important economic, energy security, and environmental benefits’. Fracking is not, however, without risk and has been linked with groundwater pollution and radiation exposure, as well as earthquakes.
Fracking and Earthquakes – the Evidence
Most earthquakes occur in tectonically unstable areas as result of large-scale movements of the earth’s crust: but they can also occur where localised pressures cause smaller faults in the crust to move. Such earthquakes are generally smaller than those occurring at plate boundaries, though they may reach relatively significant magnitudes of M4-5 or even larger.
Although speculation that fracking caused the Oklahoma earthquake has been largely dismissed among the scientific community, the process of formation of natural oil and gas deposits rests upon a degree of crustal instability and so, regardless of human activity, it can be argued that there is a higher likelihood of earth movements where such deposits are present.
As noted above, it is widely accepted that fracking does cause earthquakes but that these are very small: the largest of these are probably those recorded at M1.5 and M2.3 in the northwest of England, and M2.8 in Oklahoma. Of greater potential concern, however, is the process of disposal of wastewater – which geophysicist Dr. Art McGarr of the United States Geological Survey told Decoded Science may, ‘lead to fairly large-magnitude earthquakes, magnitudes of 5 for example’.
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