(Updates throughout with detail, comment)
By Susanna Twidale
LONDON, Oct 29 (Reuters) - British shale gas company Cuadrilla has paused fracking at its Preston New Road site in northwest England for the second time in two weeks, after a tremor with a magnitude of 1.1 was detected on Monday, the company said.
The tremor is the third recorded at the Lancashire site over a 0.5 magnitude limit, set by the government, since the company restarted fracking for natural gas on Oct. 15, although Cuadrilla said one was a so called "trailing event" which didn't stop production.
Fracking, or hydraulically fracturing, involves extracting gas from rocks by breaking them up with water and chemicals at high pressure.
It is opposed by environmentalists and green groups who say extracting more fossil fuel is at odds with Britain's commitment to reduce greenhouse gas emissions.
However, Britain's government is keen to reduce the country's reliance on imports of natural gas, which is used to heat around 80 percent of Britain's homes.
Cuadrilla said Monday's 1.1 magnitude tremor was way below anything that can be felt at the surface and a very long way from anything that would cause damage or harm.
"In line with regulations, hydraulic fracturing has paused for 18 hours now, during which seismicity will continue to be closely monitored... Well integrity has been checked and verified," Cuadrilla said in a statement.
The company, which is 47.4 percent owned by Australia's AJ Lucas AJL.AX and 45.2 percent owned by a fund managed by Riverstone, first attempted to frack gas near the coastal town of Blackpool in northwestern England in 2011, but the practice led to a 2.3 magnitude earth tremor.
It said then that the quakes at that site were caused by an unusual combination of geological features, but they led to an 18-month nationwide ban on fracking while further research was carried out.
The government has since introduced a traffic-light system that immediately suspends work if seismic activity of magnitude 0.5 or above is detected.
Cuadrilla said earlier this month it expects to spend at least three months fracking two wells to determine whether full-scale gas extraction would be viable.