MINING-INDUCED SEISMICITY IN THE NOTTINGHAMSHIRE COALFIELD

Between July 1989 and August 1990 over 130 earth tremors were felt and reported by people living in the Edwinstowe district of Nottinghamshire. In order to determine whether the tremors were caused by mining activity, a small aperture array of eight temporary surface seismometer stations was established around the area of coal extraction from Thoresby Colliery. Over the following 11-month period, 785 microseismic events were detected. The spatial and temporal patterns of this seismicity can clearly be seen to be associated with the commencement, the continuing extraction and the closure of faces. Activity is at a minimum at weekends, holidays and during periods of enforced closure due to the weather, rising to a maximum on the Wednesday of each week. Events occur within days of a face going into full production and cease at the end of the production, with good correlation between face advancement and hypocentral position. While the location of events outside of the array is inferior to those within the Thoresby take, it is clear that there are very strong indications that the majority of these events originate from the adjacent collieries, especially Welbeck, Ollerton and Clipstone. While the results establish a definite causal relationship between coal production and the local microseismicity, frequency magnitude studies suggest that the seismic hazard and risk of damage to properties is low, as the maximum magnitude recorded during this period was less than 2.5.