A controversial technique for extracting gas deep underground was the "highly probable" cause of earth tremors in Lancashire earlier this year, according to a report. The Blackpool area was rattled by two minor quakes with magnitudes of 2.3 and 1.5 in April and May, which resulted in test drilling being suspended. Independent experts now say the fracking technique, which injects water, sand and chemicals into shale rock under high pressure to release trapped gas, was almost certainly to blame. They concluded that an unusual combination of high pressure injection and geology at the Preese Hall well triggered the seismic events. "This combination of geological factors was extremely rare and would be unlikely to occur together again," the experts said in their report. Even in a "worst case scenario" any future tremor would be limited to magnitude 3 and would be so far underground that any impact on the surface would be minimal, they added. HOW DOES FRACKING WORK? But environmental groups have seized on the report as further evidence that fracking can have unpredictable consequences. In the United States, where fracking is already widely used, local residents claim to have ignited shale gas that has leaked into domestic water supplies. The World Wildlife Fund called for a moratorium on shale gas extraction. Head of energy policy Nick Molho said: "These findings are worrying and are likely to add to the very real concerns that people have about fracking and shale gas." Activists from the Frack Off campaign group have taken over one of the test rigs owned by the company Cuadrilla. Spokeswoman Jenny Boykin said: "Fracking uses huge amounts of water mixed with toxic chemicals, a large fraction of which are never recovered. "Contamination of irrigation water means that everyone's food supplies could potentially be affected." But the industry insists the technique is safe if properly regulated. Chief Executive Mark Miller said the report into the Lancashire quakes showed there was "no threat" to people or property. "We are ready to put in place the early (seismic) detection system that has been proposed in the report so that we can provide additional confidence and security to the local community," he said. The Department of Energy and Climate Change will now consider the report before deciding whether drilling activity can resume. Vanessa The Google Girl.