Campaigners worried about the effects that fracking say they are concerned about the number of new tremors caused at a Fylde drill site.
Shale gas exploration firm Cuadrilla restarted hydraulic fracturing at the Preston new Road site this month.
To date there have been 23 tremors linked by the British Geological Survey to the fracking of the second well at the site, but all very small.
In Autumn last year, fracking had to be halted on several occasions as the tremors reached or exceeded the 0.5ML safety limit designed to protect residents’ property from damage.
But pressure is growing to raise the limit and the Department for Business, Energy and Industrial Strategy has hinted that it would consider scientific evidence that says raising the so-called traffic light safety system could be safe. But opponents say the tremors can cause underground well damage.
A spokesman for Frack Free Lancashire said: “We are obviously concerned that Cuadrilla’s fracking of the second well seems to be following the same pattern as when they tried, unsuccessfully, to frack the first one. In just four days, we have had 17 induced seismic events logged by the British Geological Survey.
“The current cluster is so far centered under people’s homes at Carr Bridge and Moss House Lane. The fact that events seems to be repeating themselves is clear evidence that Cuadrilla’s promises last year that they would not cause earthquakes cannot be trusted and that the seismic traffic light system must remain in place with its existing limits untouched.”
But industry body UK Onshore Oil and Gas said the Government should back fracking.
Ken Cronin, chief executive, said: "We're delighted that Cuadrilla have begun hydraulically fracturing the second well at their Preston New Road site in Lancashire.
“The operations begin as the Department for Business, Energy and Industrial Strategy reiterate support for shale gas exploration in the UK, an industry that will see new jobs, tax revenues and supply chain income benefiting both the communities that host development and our national economy.”