The tremor, which notched up a local magnitude of 2.9 last Monday, is the largest to be associated with fracking so far in the UK. It followed another event of 2.1ML on Saturday evening.
The oil and gas explorer said it was “aware of the concern” of those who felt the minor earthquake close to its Preston New Road site near Blackpool, Lancashire.
It has repeatedly called for seismic safety limits on fracking to be eased but appeared to acknowledge that fracking might have resulted in damage to a small number of nearby homes.
In a statement the company said: “This event lasted for between two and three seconds and was felt by many in the locality. We are sorry for any concern this has caused. We are in the process of visiting local people who have raised concerns about minor damage to their property and will repair any damage that is assessed to have been caused by the seismic events.”
Cuadrilla’s operations remain suspended while the Oil & Gas Authority (OGA) gathers and analyses data on the events, which were among dozens of smaller ones in recent weeks that are associated with Cuadrilla’s activities. The regulator said it will consider “whether or not the hydraulic fracturing operations, mitigations and assumptions set out in the operator’s hydraulic fracture plan continue to be appropriate to manage the risk of induced seismicity” at Preston New Road.
Such plans must be approved by the OGA and the Environment Agency, with the Health and Safety Executive as a statutory consultee. They must be persuaded that fracking will not mobilise geological faults.
Under the ‘traffic light’ regulatory system, operators must suspend the injection of fluids, reduce pressure and monitor ground motion if induced seismicity of 0.5ML or more is detected. A 2.3ML event halted hydraulic fracturing at the nearby Preese Hall site in 2011. It was permanently shut in 2015.
The 2.9ML event released around four times more energy than the 2011 quake and 251 times more than the 0.5ML ‘red light’. Although small by global standards, local people reported that even the 2.1 ML event left caused their houses to move, books to fall off shelves and floorboards vibrate.