The Government's plan to allow fracking to restart has been described as a "charter for earthquakes", but how many were being recorded last time fracking went ahead?
Business and energy secretary Jacob Rees-Mogg described concerns around human induced seismic activity as "hysteria", blaming a lack of public understanding. He also said limits on level of potential earthquake activity that could be caused by fracking – 0.5 on the Richter scale – was too low and should be revisited.
He was responding to an urgent question from shadow shadow secretary of state for climate change and net zero Ed Miliband, who accused the Government of breaking a 2019 Conservative manifesto promise not to restart fracking unless it could be show to be safe. He said the Government had provided no evidence that it was safer and instead was changing the safety limits.
Mr Miliband said: "I look forward to him and his colleagues explaining his charter for earthquakes to the people of Lancashire, Yorkshire, the Midlands, Sussex, Dorset and, indeed, Somerset who will be part of his dangerous experiment. Let me tell the Conservatives that we will hang this broken promise round their necks in every part of the country between now and the next general election."
Responding, Mr Rees-Mogg said: "It is safe, it is shown to be safe, and the scare stories have been disproved time and again. The hysteria about seismic activity fails to understand that the Richter scale is a logarithmic scale. It seems to think it is a straight arithmetic scale, which of course it is not."
The Richter scale measures the magnitude of an earthquake - the amount of energy it released. This is calculated using information gathered by a seismograph. The scale is logarithmic, which means each whole-number jump is a tenfold increase in wave amplitude, which is what the lines on a seismograph are recording.
So the wave amplitude in an earthquake with a magnitude of 2.0 is 10 times greater than an earthquake with a magnitude of 1.0, and the amplitude increases 100 times between 1.0 earthquake and 3.0 earthquake. The amount of energy released increases 31.7 times between whole number values.
Regulations require fracking work to stop if tremors above 0.5 on the Richter scale are detected - previous work to extract shale gas was stopped over tremors being caused. However, Mr Rees-Mogg said other industries had higher limits on seismic activity.
He said: "As regards seismic activity, there are millions of seismic events of a magnitude of 2.5 or lower in the world every year. We should not assume that every seismic event is the San Francisco earthquake."
In 2019, Blackpool was the UK’s earthquake hotspot - and fracking got the blame. The area experienced 135 earthquakes that year according to data from the British Geological Society (BGS).
That was more than anywhere else in the UK and comes on top of 57 more in 2018. Most of the earthquakes reported in the Blackpool area were during hydraulic fracturing operations at Preston New Road.
They included a 2.9-magnitude tremor in August 2019. While the Richter scale is one way to measure earthquakes, another is to measure intensity - or the degree of shaking caused by an earthquake at a given place - on the European Macroseismic Scale (EMS).
The BGS lists the Blackpool earthquakes as having an intensity of six - meaning it would be felt by most people indoors and many outdoors, and could cause minor damage, like small cracks, falling plaster and falling objects.
The Oil and Gas Authority halted fracking indefinitely at the Preston New Road site following the August 2019 earthquake. The Government then stopped fracking across England in November, saying then that it would only allow its resumption if science supported it and communities wanted it.
BGS said hydraulic fracturing, or fracking, is generally accompanied by “microseismicity” - very small earthquakes too small to be felt. The high number of earthquakes recorded in Blackpool is likely also due to higher numbers of monitoring stations being placed by BGS in the area.
The BGS permanent network of sensors across the UK is usually able to detect most earthquakes with a magnitude of 2.0 or above anywhere in the UK, although this may vary from place to place and at different times. The vast majority of the events detected near Preston New Road had magnitudes far below the normal detection threshold and were only detected because of the increased number of seismic stations.
Last year, Carharrack, near Redruth in Cornwall, experienced 70 earthquakes according to data from BGS - that was more than anywhere else in the UK, making it the nation's hotspot, and comes on top of 163 more in 2020. However, no tremors have been recorded in the area in 2022.
Carharrack's spate of earthquakes may have been much more numerous but the majority were so small they couldn't be felt by people. Last year, the biggest were two 1.1 magnitude earthquakes and one 1.2 magnitude, each with an intensity of three - which is a weak intensity felt by a few people.
The high number of earthquakes in the area may be due to geothermal energy work in the area. Following a 1.7 magnitude quake in December 2020, an investigation was launched at United Downs Geothermal, a local geothermal energy power plant, where drills are sent deep into the ground to extract heat for use in homes and businesses.
United Downs Geothermal had previously confirmed some earth tremors in the area were linked to its operations.
The area with the highest number of earthquakes so far in 2022 is Poolewe, in Highland, Scotland, which has had 11. These include a 1.7 magnitude quake in April and a 1.6 magnitude one in May, which was felt by a single resident in Poolewe, who described "a moderate rumbling".
