Cuadrilla are investigating after the biggest quake yet was recorded near the UK’s only active fracking site.
Operations have been suspended at the Preston New Road site near Blackpool following the 2.9 magnitude tremor on Monday morning.
It comes after two other tremors in five days which were both recorded as the strongest at the time.
In a statement, Cuadrilla said no hydraulic fracturing was being carried out at the time of the latest tremor and none was carried out over the weekend.
The firm added: “We appreciate this has caused concern for local people and by way of reassurance it is worth noting that this event lasted for around a second and the average ground motion recorded was 5mm per second.
“This is about a third of that permitted for construction projects.
“We are working with the team of regulators who intensely monitor our activity at Preston New Road to investigate the event and will provide more updates in due course.
“Hydraulic fracturing operations will remain suspended during this time.”
On Wednesday, operations were paused at the site for 18 hours after a “micro seismic” event of magnitude 1.55 was detected.
On Saturday, an even larger 2.1 magnitude tremor was reported. That tremor also occurred when no fracking was taking place.
Environmental campaign group Friends of the Earth has called for a complete ban on fracking, with spokesman Jamie Peters saying: “This issue of earthquakes in connection to unwanted fracking has always been serious but now it is getting out of hand.”
Heather Goodwin, a resident of Lytham St Anne’s near the plant, said: “The walls of my house shook, there was a really deep, guttural roar. For a moment, I really thought my house was going to fall down.
“It only lasted a few seconds but I felt the need to go all round the house and check for damage. We’ve been afraid of this happening. How long before there’s real damage done and people injured?”
Under UK rules, work must be suspended for 18 hours if seismic activity with a magnitude exceeding 0.5 is detected.
Cuadrilla has previously described this limit as “exceedingly low” and wants a review of the rules, which are much tougher than in the US.
Fracking, or hydraulic fracturing, involves injecting water and chemicals at high pressure to break up rock and extract gas.
However, it can cause tremors and is opposed by environmentalists who say it contaminates drinking water, pollutes the air and water and contributes to climate change.
There have been regular protests at the Lancashire site.
Cuadrilla says fracking work will be completed by the end of November, followed by flow testing of the well, with results expected early in 2020.
It hopes exploratory tests will show the potential of shale gas for the UK and estimates around 1,300 trillion cubic feet of gas is contained in the area.
The government says shale gas could be an important new domestic energy source reducing dependency on imports, as well as delivering economic benefits.