Following the small tremors in Blackpool seven years ago new regulations 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
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Anything up to 0.5 is amber on the Government's traffic light scale and means fracking can proceed with caution and at a slower rate.
On the richter scale 8.0 is the highest grade of quake.
READ MORE>>> Fracking halted after tremor near Blackpool
Cuadrilla has pledge to frack slowly at Preston New Road and is also publishing all seismic activity here
When can people actually feel an earthquake happening? It would need to be at a level of at least 1.5 for it to be felt on the surface.
Blasts during quarrying can lead to tremors of up to 2.0