Seismic Monitoring of the United Downs Deep Geothermal Power Project (UDDGP) Site with Public Seismic Networks

The UDDGP located near Redruth, Cornwall, UK, consists of two adjacent deviated wells drilled in a hot granitic formation at depths of 5275 and 2329 metres, and intersecting the Porthtowan Fault Zone to allow a natural hydraulic communication between the wells. Shortly after flow-testing operations began in August 2020, a series of induced seismic events, with a maximum magnitude of 1.7 and a maximum intensity level 3 (i.e., weak vibrations) have occurred. Although these magnitude and intensity levels don’t represent significant seismic hazard to local communities or infrastructure, it’s important to have a detailed characterization of the microseismicity associated with operational wells to better understand the geomechanical processes associated with injection, and to assess the likelihood of continued operations leading to the occurrence of higher magnitude induced events. We utilize publicly-available data from stations within 20 km of the UDDGP site, including one BGS national network station and eight Raspberry Shake stations with short-period, vertical geophones, to relocate the epicentres of the induced events reported by the BGS, and to extract the focal mechanism of the highest-magnitude events. We then use the observed event magnitudes to forecast expected event magnitudes should induced seismicity continue to be generated at the site.