Frac-induced seismicity
How often are there earthquakes in the UK?
The UK usually has only very small earthquakes. The British Geologic Survey (BGS) has historic records (from written reports of earthquakes back to 1700) and digital records of earthquakes since the 1970s. From their national network of seismometers, the BGS records about 1700 events in Britain every year but only a few are strong enough to be felt by people.
Why don’t more people feel these small earthquakes?
Small earthquakes are not noticed by humans because the ground motion they produce is too small to be felt or they are swamped by other ground motion we are used to feeling every day; trains, traffic, even waves, wind and jets flying overhead which result in bigger ground motion.
How are earthquakes monitored?
Scientists record the ground motion onthe BGS national network of seismometers and they can identify where the earthquake source is; whether it was a large event which was recorded around the world or a smaller event in Britain. The BGS publishes the earthquake events they record on their website using the Richter scale of magnitude, where the very weakest earthquakes have negative Richter values, which just means they are very small. There are many more small earthquakes than big ones.
Do earthquakes cause damages?
What really matters is the ground motion, so that a large magnitude earthquake at depth would result in much less ground motion than asmallershallow event. Cosmetic damage (e.g. cracks in plaster) has been reported for shallow (depth < 1 km) earthquakes caused by long-wall mining. However, most earthquakes are much deeper and it is very rare for damages, even cosmetic ones, to occur at magnitudes less than 4.
Does fracking cause earthquakes?
In the US, over 1.8 million hydraulic fracturing operations for shale gas have been carried out and there are a few documented cases of associated earthquakes, but none of these have caused any damages. In the UK, a hydraulic fracturing operation in Lancashire produced some small earthquakes.
What are the OGA doing to regulate this?
The Oil and Gas Authority requires detailed geological studies to be undertaken by an operator to prevent such operations taking place near geological faults, which greatly reduces the likelihood of an event. The OGA requires seismic monitoring before any operations begin and a traffic light scheme during injection, so that if abnormal events are detected, the pressure is reduced and then monitoring of the ground motion begins to make sure that larger events do not occur. Further information can be found here:
How can I be assured that this regulation is strong enough?
These regulations are more cautious than any other measures in place to reduce man-made earthquake risk worldwide. For example in the US, where a traffic light scheme has been introduced for hydraulic fracturing, the red light is set at magnitudes of 2.7 to 4.5 depending on the state and in Western Canada the red traffic light for hydraulic fracturing injection has a high threshold (magnitude 4). In the Netherlands where production from the giant Groningen gas field caused earthquakes associated with subsidence,ground motion is monitored and earthquakes of greater magnitude than 1.5 are reported. In Switzerland, earthquakes resulting from geothermal operations use a similar traffic light system that incorporates both magnitude and ground motion monitoring (Red = 2.9 magnitude and >5mm/s ground motion).
Recent increases in earthquakes in the central United States have been linked to wastewater injection in deep disposal wells rather than hydraulic fracturing. While some of the US wastewater comes from hydraulic fracturing, much of this is produced water from regular oil and gas wells. There are no proposals to collect and dispose of wastewater from hydraulic fractured wells or any other oil and gas wells in deep disposal wells in the UK.
Will the regulation stop earthquakes from happening?
No, earthquakes are a natural phenomenon, and the process of hydraulic fracturing creates micro-earthquakes which are not felt at the surface, but these regulations are aimed at to minimise any disturbance to those living and working nearby and to prevent the risk of damage to buildings.
References:
BAPTIE B., SEGOU M., ELLEN R. and A. MONAGHAN. 2016., Unconventional Oil and Gas Development: Understanding and Monitoring Induced Seismic Activity. British Geological Survey Open Report, OR/16/042. 92pp.
M.P. Wilson et al, 2017 Anthropogenic earthquakes in the UK: A national baseline prior to shale exploitation. Marine and Petroleum Geology 68 (2015) pp 1-17
Predicting and Monitoring Ground Motions Induced by Hydraulic Fracturing
OGA-commissioned paper by Dr Julian J Bommer, May 2017