A lot has changed since two minor tremors in 2011 were attributed to test fracking in Lancashire
There's some information about fracking-related earthquakes here in our Fracking Facts pages, but we thought it might be useful to dive into this a little deeper seeing as its one of the concerns that crops up most prevalently in any public discourse about shale gas.
Let's start by looking back at what happened back in 2011.
As far as we can tell (distilling a lot of highly technical information in two expert reports commissioned at the time) it appears that it boils down to this: firstly, there was a previously unidentified underground fault line (where two opposing faces of rock meet) and that this was "lubricated" with fracking fluid; and, secondly, the pumping of fracking fluid caused a build-up of energy in the rock which then caused it to "slip" along the now lubricated fault.
So how will this be avoided in the future?
It seems that there are three things that mean a repeat is now very unlikely.
1. The fracking companies have all acquired 3D seismic images of the sub-surface
This means that they can "see" the sub-surface in much more detail now, and therefore plan their drilling and fracking so that they avoid any existing fault lines from now on.
2. Fracking operations are going to be conducted differently
We understand that the volume of fluid injected at any one time will be smaller, and that pressure will be reduced at the surface much sooner so that there's less chance of a build-up of energy in the rock.
3. There's a Traffic Light System
Sensitive, real-time monitoring will be in place during and after fracking operations. If a tremor is detected at above a very low threshold of just 0.5 magnitude on the Richter scale, operations will temporarily cease while an investigation is conducted to make sure it's safe to resume.
Although the UK is not tectonically active, there are still lots of recorded tremors every year. If you've got the time and inclination, check out the British Geological Survey earthquakes website where you'll find details of all the tremors recorded in the British Isles during the last 50 days. You'll find several that are of a similar or even higher strength to the 1.1 magnitude and 2.3 magnitude tremors linked to Cuadrilla's activities in April and May 2011 respectively, but there are no reports of any damage to property or injury to people.
It really doesn't seem that more fracking-related tremors are all that likely and even though there's still going to be risk, there's almost no chance of any harm being caused.