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Earthquakes near Newdigate, Surrey, 2018

Earthquakes with magnitudes of 2.7, 2.6, 2.4 and 3.0 ML were detected by BGS on 1 April, 27 June, 29 June and 5 July 2018, respectively, near Newdigate, Surrey, between Dorking and Crawley. The earthquakes were felt by local residents of Newdigate, Charlwood, Dorking and Crawley. Three smaller earthquakes with magnitudes of 1.8 .17 and 1.5ML were also detected in the same location.

To locate earthquakes we use a process a bit like triangulation and our closest monitoring station was over 50km away, so the errors in our location estimates are several kilometres.

To improve location and depth accuracy we are in the process of installing two additional monitoring stations within 10km of the area of activity. The location and construction of seismic monitoring stations is complex, in order to ensure good data quality. We hope to have this completed by the end of this week, subject to landowner agreement.

Although there have been no other instrumentally recorded events in the region in the last 50 years, there is evidence for historical earthquakes in the last 500 years, therefore a natural origin for these earthquakes canít be ruled out at this stage.

Earthquake clusters have occurred in the past in the UK (eg the Manchester cluster of 2002). It requires comparatively large amounts of equipment close to the cluster to image them in detail. For this reason, we hope to gain a better understanding of this scientific phenomena through the installation of additional stations, providing seismic activity continues in Surrey.

We are unable to say categorically if these earthquakes are related to hydrocarbon exploration or production, mainly because of the uncertainties in our estimates of the earthquake epicentres and particularly depths.

Our calculated epicentres for the earthquakes are approximately 4.5km from the Horse Hill well, which is within our calculated uncertainty.

While it is well known that hydrocarbon exploration and production can result in man-made or "induced" earthquakes, such events usually result from either long term hydrocarbon extraction, or the injection of fluids (eg hydraulic fracturing during production).

We contacted the Oil and Gas Authority (OGA) on 28 June to request the status of any operations in the area. Flow testing has been authorised at Horse Hill and the necessary equipment is on site, but flow testing has not yet been carried out. OGA are the regulatory body for oil and gas explorations and production in the UK.

Earthquake locations. CLICK FOR A LARGER VERSION