Commentary on fracking by Dr Rosemary Quinn of GNS Science - 8/11/ 2011
There are many examples of activities that cause human-induced seismicity, of which hydraulic fracturing (or ‘fracking’) is just one.
There is a large body of published data that indicates that seismic activity caused by fluid injection (for solution mining, hydrocarbon production, geothermal energy generation, hazardous and non-hazardous waste disposal purposes for example) cause small seismic events i.e. less than or equal to magnitude (ML) 3.9.
The seismic activity associated with hydraulic fracturing is generally less than magnitude 2.0, with the magnitude and number of events depending on local geology, the pressure and duration of the fluid injection, and the injection-rate. The small-size of earthquakes induced by hydraulic fracturing (compared to those generated by other activities) is partly due to the fact that fluid injection is for shorter duration (days as opposed to weeks or years) than for other activities.
This induced seismic activity will probably be minor compared to natural background seismicity. In New Zealand, for example, GeoNet records about 18,000 magnitude 2.5 and larger events in an average year. At the lower end of this scale, most people are unaware that anything is happening – a passing truck generates as much if not more vibration – so the effects of seismic activity that are typically induced by hydraulic fracturing would be hard to separate from the background level of seismicity.
The fact that we experience natural earthquakes does not mean that we should be complacent: hydraulic fracturing operations need to be designed and monitored to ensure that they do not present undue risk to people and resources. The minimum pressures and flow-rates required to achieve the desired outcome should be used. If that is done, it is very unlikely that hydraulic fracturing operations will result in any noticeable seismic impact.