As part of the monitoring requirements for their new wells in Lancashire, Cuadrilla are installing near-surface microseismic monitoring arrays. Geophones are buried to depths of 50 - 100m. They are capable of detecting the small "pops" and "cracks" as the shale is fractured, allowing the operator to map where the fractures are going as the stimulation progresses.
This video explains how the technique works, and how it is used both to allow operators to maximise the efficiency of their operations, and to minimise any environmental risks.
The video is made for an American audience, and I think to UK eyes it comes across as a little slick and "corporate", but it's well worth a watch.