Induced seismicity at preese Hall, UK - A review

Hydraulic fracturing activities during shale gas exploration at Preese Hall, near Blackpool, UK induced a series of anomalously large microseismic events, including two that were felt at the surface. The unexpected nature of this seismicity meant that microseismic monitoring of these operations was limited, with only two surface stations being deployed after a M-1 2.3 event was detected by the British Geological Survey's regional seismic network. The small size of the available dataset means that we must try and extract as much information from it as possible if we wish to fully understand what went on, and how risks might be reduced in future. Towards this end, we have used waveform inversion to determine moment tensors for a number of the induced events; events predominantly occurred with a pure strike-slip mechanism. To investigate the state of stress in the sub-surface from a different direction, we have also performed shear wave splitting analyses of the available dataset. These two techniques yield principle horizontal stress orientations that are in good agreement with each other, and that are also consistent with in situ measurements.