Two earthquake tremors in north-west England earlier this year were probably caused by controversial operations to extract gas nearby, a report by the company responsible has concluded.

The two tremors, which were felt by people just outside Blackpool, but did not cause any known damage, were reported in April and May, measuring 2.3 and 1.5 on the Richter scale. Since the second event, Cuadrilla Resources has stopped "fracking" operations – where water is injected into rocks at high pressure to extract gas from the cracks.

The report, by a team of European seismic experts not usually employed by the company, concluded it was 'highly probable' that the two main tremors and a series of aftershocks were caused by Cuadrilla's operations at the Preese Hall-1 Well in Lancashire.

It said, however, that the cause was an 'extremely rare' combination of factors including a pre-existing fault in the rocks, and that it was 'unlikely' to occur at other sites in the Bowland Basin, where Cuadrilla is hoping to exploit an estimated 200 trillion cubic feet of shale gas.

'If these factors were to combine again in the future, local geology limits seismic events to around magnitude three on the Richter scale as a "worst-case" scenario,' added a company statement.

The report, and plans for an early warning system so the company can monitor work more carefully or even stop operations if seismic activity is felt in the future, will be sent to the government's Department for Energy and Climate Change and the British Geological Survey for approval before the company can resume operations at Preece Hall.

The study was criticised, however, by opponents of fracking, who called for a full investigation by the government before Cuadrilla or other companies are allowed to continue operations in the UK.

'The main concern is it's just one of a long list of environmental concerns and no [full assessment] has been done into the full environmental and human risks,' said Helen Rimmer, north-west campaigner for the environment campaign group Friends of the Earth.

Opinion is split over the huge and growing gas fracking industry in north America. Opponents say the industry contaminates groundwater and adds to greenhouse gas pollution from burning fossil fuels, leading to the practice being banned in some places, including France. Supporters say fracking is safe, and contributes valuable energy at a time when conventional gas and oil supplies are supposed to be running out and prices soaring.

Cuadrilla announced in September that it had "gas in-place" in its licence area in Lancashire of 200 trillion cubic feet. A report commissioned by the company also estimated that the operations would create 5,600 jobs, about one-third of them in Lancashire.

This article is reproduced courtesy of the Guardian Environment Network

	READ MORE...
	INVESTIGATION UK shale gas boom 'may be dirtier than coal' Despite outrage in the US over ‘fracturing’ techniques used to extract shale gas and new evidence its greenhouse gas footprint may be higher than that of coal, the UK has given the go-ahead to companies here to begin drilling. Tom Levitt reports from the centre of this potential unconventional gas boom near Blackpool
	SPECIAL CONTENT EFU Film: Fracking Hell – the environmental costs of the new US gas drilling boom The gas stored in the Marcellus Shale formation is the subject of desperate drilling to secure US domestic energy supplies. But the process involved - hydraulic fracturing - is the focus of a bitter dispute over environmental damage and community rights
	NEWS Europe's scramble for gas sees controversial hydraulic fracturing cross the Atlantic In the US, gas-extraction in the Marcellus Shale has been linked to pollution and social conflict. Now Halliburton, Chevron and Exxon, among others, want to bring the so-called 'fracking' process to Europe, reports Luke Starr
	NEWS UK's 'fracking' gas-extraction is not unconventional says industry The controversial gas-extraction process known as 'fracking' is safe, says UK-based Cuadrilla Resources, and not a threat to ground or surface water supplies
	INVESTIGATION US natural gas drilling boom linked to pollution and social strife The gas stored in the Marcellus Shale formation is the subject of desperate drilling to secure US domestic energy supplies. But the process involved - hydraulic fracturing - is the focus of a bitter dispute over environmental damage and community rights