Shale gas, correlation and earthquakes

 

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There is a bridge between earthquakes and shale gas exploration – but exactly where and what is that bridge?

“Correlation is not evidence of connection or causation.”

 Sorry, this is a bit long but it is intended to put a balanced view about the complexities of the hot and moving inside of the living earth which is 24,000 miles round at the equator.

A special report on Sky News UK, 19 April 15, looked at a relationship between fracking and earthquakes in Texas. That report portrayed Professor Brian Stump, SMU University, Dallas, quietly saying that “there is undoubtedly a correlation between fracking and earthquakes”. The professor is an acknowledged expert seismologist. Not taking his statement seriously would be foolish.  However, what does it mean?

Many years ago, when I was a student learning about statistics, it was pointed out that there is a correlation between the divorce rate in the UK and the rate of importation of wooden rolling pins. The point is that it is not difficult to find sets of figures which have similar patterns and therefore appear to be related.  They might be.  They might not be.  What the word “correlation” does is to alert that there might be a relationship.  To establish that there is a real connection, there has to be a logic or understood mechanism and there has to be evidence. When I used to do a great deal of work as an expert witness in court, if I wanted the judge to believe me, then I had to state a clear opinion, give  a common sense explanation for that view and show evidence that is was true.  The essence of scientific thinking is to have a hypothesis, have a logical explanation, and be able to test to provide evidence.  Frankly, Professor Stump is dramatically more competent than I to comment or test that correlation.  Nevertheless, I am left wondering and it may be that this is so complex, or at least so variable from one location to another that we will never be able to be definitive.  It seems logical to observer that there are, from time to time, new areas of seismic activity where none had been recorded before.  These may be that nobody had bothered recording before (so there was no record) or they had recorded no activity but, all of a sudden, there was some – that may be due to the earth itself which is still very hot at its core and still cooling. So, if there was  a situation where in the USA, as Professor Stump observed, adequate records showing more seismic activity after shale fracking than before, it may have been due to that fracking, it may not. Until more is known, it seem to me that the following is a reasonable position to take.

The first shale gas well drilled in the UK was near the Northern seaside resort of Blackpool.  There were reports of earthquakes and the drilling of the shale well was immediately blamed.. You don’t have to be a qualified seismologist to understand something about fracking and earthquakes. Consider a few billion tonnes of rock a mile or two below the surface and put some water under pressure into a crack in that rock.  Mostly it is not necessary but suppose also that you stick in a small explosive charge. What does common sense tell you is going to happen?

For those old enough to remember the cold war between the West and The Soviet Union, each testing bigger and bigger hydrogen bombs usually below the ground, they may remember that there was a fear that we might crack the surface of the earth’s crust. These weapons were hundreds, even thousands of times larger than the bombs dropped on Japan during the Second World War. Hiroshima’s bomb was around 15 k tonnes   (equivalent to 15,000 tonnes of TNT explosive) and the USSR’s largest 50,000 k tonnes.  In the case of fracking for shale gas, we are not talking of tonnes of explosive, more of kilos and iit maybe that no explosives are used, just high pressure fluids, mainly water

The process of fracking always uses water under pressure. Sometimes it uses small charges of explosives – we are talking kilos, not even tonnes of explosives against millions, or even billions, of tonnes of rock.  Blackpool has always had earthquakes. These have been noticeable maybe 2 or 3 times a year but never done any damage.  Millions, even trillions, of tonnes of earth’s crust is under tension and stress and, occasionally, it moves a bit.  Now, if that tension and stress was on the edge of moving and causing a detectable quake, what fracking might do is trigger the quake which would have happened anyway. More than that, what the injection of fluids are more likely to do is lubricate the movement which was about to happen anyway and make a series of short movements which would reduce the effect of the quake. Blackpool might well have less detectable earthquakes, not more.

Sensibly, we do need Professor Stump and others to keep an eye on this and keep investigating.  Nevertheless, at present, the evidence we have is that this is, at worst, not a serious risk of earthquake damage in the UK.

Bill Butterworth  7 November 15

Next week; Shale gas exploration and pollution.