An natural disaster of 0.5 has the TNT equivalent of 5.6kg - or a large hand grenade.
It was detected on Saturday after drilling for shale gas resumed in Lancashire following a 0.8 tremor on Friday.
The UK's Energy Minister Claire Perry had a private meeting with oil and gas firms in May, months before fracking resumed in the UK earlier this month for the first time in seven years, but she failed to record that meeting in a transparency register, The Guardian reported on Friday.
One said: "Great to see such potent community resistance against this disgusting industry".
Critics claim fracking poses a serious risk to people and the planet through effects such as toxic air pollution, contamination of water and seismic events. Neither was felt at surface.
The campaign to stop fracking could be boosted by the continued seismic activity.
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A second tremor of 0.8 magnitude has been recorded within 24 hours at the UK's only active site for fracking.
Cuadrilla was hydraulically fracturing the shale rock adjacent to a well when the seismic activity was recorded, the spokesman said.
Operations have been paused for 18 hours, during which seismicity levels will continue to be measured.
"Events such as these result in tiny movements that are way below anything that would be felt at surface, much less cause any harm or damage", a spokesman said. Without sophisticated monitoring at Cuadrilla, they would not be detected.
A government-appointed panel recommended greater monitoring and said operators should observe a "traffic light" regime, with tremors of 0.5 or above triggering a "red light" and an immediate halt. "As per the hydraulic fracture plan in place at Preston New Road, work will now pause for at least 18 hours and is expected to recommence in the morning (Saturday, October 27, 2018)".
The energy firm said the fracking was expected to last three months, after which the gas would be tested.
Lord Chief Justice Lord Burnett said the sentences were "manifestly excessive" and replaced them with conditional discharges.