In theory, the chances of your house being shaken by a fracking-related earthquake are incredibly slim. In the UK, a traffic-light system is designed to minimise the risk of larger quakes occurring, with fracking halted if a tremor of magnitude 0.5ML (local magnitude) or above is recorded. So last week’s 2.1- and 2.9-magnitude fracking-related tremors near Blackpool came as a surprise, given a “red-light” 1.55-magnitude quake had occurred the previous Wednesday, and fracking at Cuadrilla’s Preston New Road site had been suspended.
“It suggests that the traffic-light scheme, even with what seemed like a conservative limit of [magnitude] 0.5, might not be appropriate,” says Stephen Hicks, a seismologist at Imperial College London. Trials in Finland have shown traffic-light schemes can help prevent quakes, so why didn’t it work on this occasion?
One possibility is UK shales react differently to other shale formations. Previously, geologists have pointed out that UK shales have been uplifted and deformed more than their US equivalents. “If UK shale reserves are more heavily faulted and fractured, the probability of induced quakes might be higher,” suggests Hicks. And the UK’s high population density increases the chances of even small quakes being widely felt.
