Hydraulic fracturing and seismicity
Last year, two earth tremors were detected following Cuadrilla’s hydraulic fracturing operations at Preese Hall. The first took place on 1st April 2011 and measured 2.3 on the Richter Scale. To determine whether this was due to hydraulic fracturing, Cuadrilla worked with Keele University and the British Geological Survey (BGS) to set optimally placed seismometers to monitor ground movements around the active well sites as well as the surrounding area.
It was during the fourth fracture treatment at Preese Hall when a second tremor measuring 1.5 was recorded on 27th May 2011. Following this and after discussions with the DECC, we voluntarily paused hydraulic fracturing operations while a report was commissioned to discover if there was a link between seismicity and fracturing.
Shortly after the report into these tremors was released, Prof. Mike Stephenson, Head of Energy at the British Geological Survey (BGS), told the Shale Gas Environmental Summit:
“The tremors were way too small to cause any damage”
Professor Mike Stephenson, BGS, November 2011
Commenting in The Sunday Times, head of Seismology at the BGS Brian Baptie said:
“Weak rocks like shale break easily so they do not allow enough tension to build to generate big tremors.”
The Sunday Times, 12th February 2012
Earthquake magnitude scales are logarithmic, in this case that means that the energy released from a magnitude 2 earthquake is 32 times greater than a magnitude 1 earthquake.
This chart compares the actual energy released in various seismic events in the UK compared to an earthquake in Lincolnshire in 2008 which was the largest seismic event in the UK since 1984.
As the table below demonstrates, low level seismicity (2.9 and less) is common and does not cause damage. These figures and their associated descriptions are well established and used internationally.
Based on US Geological Survey documents, see more here.
What is the Richter Scale?
In 1932 Charles Richter devised the first magnitude scale for measuring earthquake size. This is commonly known as the Richter Scale.
The geology in the Bowland Basin means that seismic events, regardless of their cause, will not exceed this magnitude