London | Cuadrilla Resources, the Britain-based shale gas explorer half-owned by ASX-listed mining services company AJ Lucas, has been hit by a series of increasingly large earth tremors, threatening to revive the public concern over fracking that kept Cuadrilla off the site for seven years.

The company had only just resumed fracking at its Preston New Road site in northern England on August 15 after a nine-month pause when it triggered a spate of tremors above the regulatory threshold of 0.5ML on the Richter scale. If the threshold is crossed, operations must stop for 18 hours.