A company using "fracking" to drill for gas in Lancashire has had to suspend operations following a 1.5 magnitude earthquake near Blackpool on Friday.
It is the second earthquake to strike Lancashire since April, and experts say it may be a result of the controversial practice, a process of drilling for natural shale gas which involves injecting water and rock-dissolving fluids underground at extremely high pressure to break apart hard shale rocks and release gas.
Cuadrilla Resources, the company carrying out the fracking at Preese Hall, Weeton, close to the Fylde coast, said it had suspended operations to examine data collected by the British Geological Survey before deciding whether it was safe to resume. Neither quake was large enough to cause any structural damage.
Mark Miller, the company's chief executive, said: "We take our responsibilities very seriously and that is why we have stopped fracking operations to share information and consult with the relevant authorities and other experts.
"We expect that this analysis and subsequent consultation will take a number of weeks to conclude and we will decide on appropriate actions after that."
Drilling is likely to be suspended for a long time as Cuadrilla investigates the cause of the quakes with the help of outside experts. The BGS said it could not say conclusively if the first earthquake, on 1 April, was linked to the fracking but the organisation's website stated: "Any process that injects pressurised water into rocks at depth will cause the rock to fracture and possibly produce earthquakes.
"It is well known that injection of water or other fluids during the oil extraction and geothermal engineering, such as shale gas, processes can result in earthquake activity."
The BGS said that last week's 1.5 magnitude earthquake was very similar to a larger 2.3 quake that centred on nearby Poulton-le-Fylde at the beginning of April. "It seems quite likely that they are related," said Brian Baptie, the survey's head of seismology. "The recorded waveforms are very similar to those from the magnitude 2.3 event last month, which suggests that the two events share a similar location and mechanism."
WWF Scotland has repeated its call for fracking to be banned, following news that a company was seeking permission for Scotland's first shale gas exploration at Aith, near Falkirk.
Its director, Dr Richard Dixon, said: "Whether the shale gas drilling and the earthquake are linked certainly needs investigated. However, we already know enough about the environmental problems associated with fracking to know that it should be banned in Scotland."
"Shale gas would be a disaster for the climate and its production could contaminate groundwater. Scotland should follow France's example and ban it before it even gets going. Scotland should become the home of clean energy not another dirty fossil-fuel. Shale gas projects in Scotland would quickly tarnish our global claim to green credentials."
Pollution fears
Fracking has been heavily criticised by environmentalists in the US, who say the process can end up polluting drinking water in the surrounding area. Last year in Pennsylvania, a natural gas company was banned from drilling for at least a year because methane from a faulty well polluted drinking water.
This April, the New York Times reported that Congressional Democrats had found that "oil and gas companies injected hundreds of millions of gallons of hazardous or carcinogenic chemicals into wells in more than 13 states from 2005 to 2009". Despite this, a report last month by the Commons energy and climate change committee found there was no evidence that fracking was unsafe, saying a ban on shale gas drilling was not necessary in the UK as there was no evidence that it posed a risk to water supplies from underground aquifers. "There appears to be nothing inherently dangerous about the process of fracking itself and as long as the integrity of the well is maintained shale gas extraction should be safe," said Tim Yeo, the committee chairman.
