Cuadrilla Resources was the company responsible for the fracking operation. They have now released a report, Geomechanical Study of Bowland Shale SeismicityGeomechanical Study of Bowland Shale Seismicity, 2 Nov 2011, confirming that it caused the earthquakes.
In the report there are a number of factors that were said to have contributed to the seismic events, including the following:
- There was a pre-existing critically stressed fault.
- The fault was "transmissible" so accepted large quantities of fluid.
- The seismic events were induced after repeated injection of fluid into the same fault zone.
The report states that repeat occurrences are unlikely at future well sites and gives magnitude 3 as a worst-case scenario.