Seismicity at Newdigate, Surrey, during 2018-2019: A candidate mechanism indicating causation by nearby oil production Rob Westaway, James Watt School of Engineering, University of Glasgow, Glasgow G12 8QQ, UK
[email protected] Supplementary material Contents: Page 1 Section 1: Reporting of activities in the Brockham and Horse Hill wells Page 7 Section 2: Geo-location issues Page 12 Section 3: State of stress Page 14 Section 4. The Davis and Frohlich criteria for anthropogenic seismicity 1..Reporting of activities in the Brockham and Horse Hill wells As is evident from the extensive media coverage (e.g., BBC, 2018; Hayhurst, 2018; McLennan, 2019), from the outset, on 1 April 2018, a potential connection between the ‘swarm’ of earthquakes in the Newdigate area of Surrey and local oilfield activities (in the nearby Brockham and Horse Hill wells) was immediately suspected, but was dismissed by one developer (Hayhurst, 2018). Concerns about the possibility that activities in these wells were indeed causing these earthquakes were raised through correspondence in The Times newspaper in August 2018 (Gilfillan et al., 2018). A workshop, convened by the Oil & Gas Authority (OGA), followed on 3 October 2018, a summary of its proceedings being reported by OGA (2018), including the statement that ‘the workshop participants concluded that, based on the evidence presented, there was no causal link between the seismic events and oil and gas activity although one participant was less certain and felt that this could only be concluded on “the balance of probabilities” and would have liked to see more detailed data on recent oil and gas surface and subsurface activity.’ The workshop presentations included a candidate conceptual model linking the seismicity to site activity, by Haszeldine and Cavanagh (2018), which – its authors admitted – could not be tested at that stage because essential data needed were unavailable.