Fracking in Lancashire: When does seismic activity mean fracking has to stop?
Following the small tremors in BlackpoolÂ seven years agoÂ new regulationsÂ mean very low levels of seismic activity lead to a suspension in fracking.
If seismic sensors detect anything above 0.5 magnitude on the Richter scale – far below what people can feel at the surface – the company has to stop and review its operations. Yesterday's was 0.4 magnitude, recorded at 3.45am at a depth of 3km
On the richter scale 8.0 is the highest grade of quake.
Blasts during quarrying can lead to tremors of up to 2.0