Fifty separate earth tremors have been caused in the Blackpool area by "fracking", the drilling method used to extract shale gas, The Independent has learnt.
The huge number of seismic movements was admitted yesterday by one of the authors of a report into two very noticeable earth tremors likely to have been caused by the fracking operations of Cuadrilla Resources, which says it has discovered enormous supplies of shale gas in the Blackpool area.
The report, which the energy firm commissioned, concluded it is "highly probable" that Cuadrilla's operations were responsible for two tremors which hit Lancashire. The first, of magnitude 2.3 on the Richter scale, hit the Fylde Coast on 1 April followed by a second of magnitude 1.4 on 27 May. The report, which is being sent to the Government, has intensified the controversy around "fracking", or hydraulic fracturing, which involves pumping water, sand and chemicals at high pressure into shale rock, to release the gas it holds.
The company sought to play down the impact of its activities, saying that it had probably triggered "a number of minor seismic events". But when The Independent interviewed Stefan Baisch, one of the report's authors, he admitted that the actual number was 50.
In the same interview, Mark Miller, Cuadrilla's chief executive, accepted that 50 sounded like a lot of tremors but dismissed their significance. "There's a certain level of seismic activity that can occur even with a truck going past a house," Mr Miller said.
"But just because it doesn't do any damage, doesn't mean we're not concerned about it. It's not good for us if the public is concerned and it's not good for the production of gas."
Mr Miller said the report's findings were not sufficient to stop the company from using the controversial method. "Cuadrilla is working with the local and national authorities to implement the report's recommendations so we may resume our operations," he said.
Cuadrilla stopped fracking at its site in Weeton and commissioned yesterday's report into whether the practice causes seismic activity on 31 May, after concerns were raised about the tremors.
David Loveday, a shale gas expert at the Inenco energy consultancy, said the report demonstrated a "pressing need to understand the mechanism which potentially caused these earth tremors to prevent a re-occurrence".
A spokesman for the Department of Energy and Climate Change (DECC) said: "The implications of this report will be reviewed very carefully before any decision on the resumption of these hydraulic fracture operations is made."
The findings coincided with a day of environmental opposition to the practice, as protesters from the Frack Off campaign group occupied another Cuadrilla site near Southport, shutting it for the day. Frack Off also staged a rally in London.
The Cuadrilla findings are likely to feature in the Commons today, when the Energy minister, Charles Hendry, appears before the Energy and Climate Change Select Committee.
Before the publication of yesterday's report, which was conducted by a team of independent experts, Cuadrilla had stressed that there "was no proven link between the seismic events and the hydraulic fracturing". Yesterday, it conceded that 50 such events had occurred in eight months.
The company said: "The seismic events were due to an unusual combination of geology at the well site coupled with the pressure exerted by water inject. This combination of factors was extremely rare and would be unlikely to occur together again."
The report stressed that while a "worst-case scenario" could result in a magnitude 3 earthquake in the Blackpool area, this "would be unlikely to occur" and, if it did, "there is no threat to people or property". Cuadrilla claimed that an earthquake of 2.6 on the Richter scale would be "the maximum level allowed".
Dr Brian Baptie, a seismologist at the British Geological Survey, which is advising DECC on whether to allow the resumption of fracking in the UK, said: "Fifty seismic events does seem a lot, but most were very, very small."
He added that a magnitude 2.6 earthquake, at this depth, would not cause any structural damage but "might cause strong shaking that would be widely felt by people indoors and out".
Cuadrilla is at the forefront of shale gas exploration in the UK and raised strong hopes for the future of the industry in September when it revealed that its field in Lancashire contained up to 5,660 billion cubic metres. About a fifth is expected to be recoverable.
Mr Miller said: "We unequivocally accept the findings of this independent report and are pleased the report concludes that there is no threat to people or property in the local area."