Fracking has been paused at British shale gas company Cuadrilla's Lancashire site after a fourth “micro seismic” event in four days.
Cuadrilla said it recorded the 0.8ML tremor at its Preston New Road site on Saturday morning and would continue to monitor seismic activity until before resuming on Monday.
The company said the activity did not reach the "red" level on the Oil and Gas Authority's warning system.
Work had been suspended for 18 hours following a seismic event of 0.76ML on Friday, and two smaller events were recorded on Wednesday and Thursday.
Hydraulic fracturing operations – to extract gas from rocks – resumed at the site last week for the first time since 2011 when it was halted after being linked with two earthquakes.
The resumption was met with a swathe of protestors, with one man even chaining himself to scaffolding in a bid to stop the controversial process getting underway.
The company said: “Cuadrilla can confirm following hydraulic fracturing this morning (27 October) a micro seismic event of 0.8ML, which can't be felt at surface, was recorded through the detailed seismic monitoring Cuadrilla and the British Geological Survey (BGS) are carrying out.”
Cuadrilla, 47.4 percent owned by Australia's AJ Lucas and 45.2 percent owned by a fund managed by Riverstone, was given permission to drill two wells at its Preston site by the government in 2016.
Work finally began on 15 October after campaigners failed with a last-minute legal intervention over safety risks.
The energy firm said the fracking was expected to last three months, after which the gas would be tested.
The Department for Business, Energy and Industrial Strategy supported the project and said shale gas had the potential to be a new domestic energy source and create jobs.
It added that it was “very clear” that shale developments must be safe and environmentally sound.