(Updates throughout with detail, background)
By Susanna Twidale
LONDON, Oct 26 (Reuters) - British shale gas company Cuadrilla said it has paused fracking at its Preston New Road site in Lancashire, northwest England, after a small tremor was detected.
The company had restarted fracking for natural gas at the site just weeks ago after its activities at a nearby site were halted seven years earlier for causing tremors
Hydraulically fracturing, or fracking, involves extracting gas from rocks by breaking them up with water and chemicals at high pressure.
The British government, keen to cut its reliance on imports as North Sea supplies dry up, tightened regulation of the industry and gave consent earlier this year for Cuadrilla to start fracking at two wells Preston New Road.
It introduced a traffic-light system that immediately suspends work if any seismic activity of a 0.5 magnitude or above is detected.
Cuadrilla said on Friday the micro seismic event it detected early on Oct. 26 had a magnitude of 0.76, so it would temporarily pause activities under the traffic light system.
"Operations have now paused for the next 18 hours during which seismicity levels will continue to be measured," Cuadrilla said in a statement.
The company said the event was well below anything that would be felt on the surface and was only detected due to the sensitive monitoring system it has put in place.
"All the relevant regulators were informed without delay and we have verified that the well integrity is intact," Cuadrilla said.
It said it expects to resume fracking on Oct. 27.
Cuadrilla, 47.4 percent owned by Australia's AJ Lucas AJL.AX and 45.2 percent owned by a fund managed by Riverstone, said earlier this month it expects to spend at least three months fracking two horizontal wells to test flow rates to determine whether full-scale gas extraction would be viable.