Size does matter Francis!

So Mr Egan is having a tough time right now as he gets wheeled in to studio after studio to explain himself about the seismicity which everyone assumes is caused by his company’s fracking operations. Maybe it’s all a bit tiring for him which may explain the  fact that he seems to be getting more preposterous at the same time as he gets more and more irritable.

On Saturday morning he treated us to the following exchange on Radio 4 Today

Egan: “Well the Richter scale as you probably know goes up in units of 10 and to cause damage generally you have to be at about a 3 or a 4. This was approximately 10,000 times smaller than that..”


”Than what?


Egan (continuing over him) “…at zero point .. than a 3 or a 4, cause it was a zero point .. we’ve had a number of these between 0.5 and the largest yesterday of 0.76  so these were roughly 10,000 times smaller than anything that could even begin to cause damage at surface”

Oh dear.

Firstly the Richter scale does NOT go up in units of 10. It goes up in units of one to a highest value of 10.

Secondly as  Robert Coontz explains here

The magnitude scale is logarithmic. That just means that if you add 1 to an earthquake’s magnitude, you multiply the shaking by 10. An earthquake of magnitude 5 shakes 10 times as violently as an earthquake of magnitude 4; a magnitude-6 quake shakes 10 times as hard as a magnitude-5 quake; and so on.

To compare two earthquakes in terms of shaking, you subtract one magnitude from the other and raise 10 to that power: 10^(M1-M2).

Shaking isn’t the only way to compare earthquakes. Another common approach is to talk about the relative amounts of energy they release. To do that, just insert one simple extra step: subtract the magnitudes and then add 50% before using the result as a power of 10. In mathspeak, the formula is 10^((M1-M2)*1.5).

Using this calculation we can see that talking about the size of the quake (it’s magnitude) comparing quakes of 3 and 0.76 (as Mr Egan claimed to be doing) the difference in magnitude  is in fact 174 times and not the 10,000 times that he suggests twice in the space of a few seconds. Even if we compare energy release and not size we only get a figure of just over 2,000.

Mind you a bit later on

“We stopped for 18 hours, there were no subsequent tremors and we are starting again this morning”

It would presumably have been too much for him to have checked the BGS website (as we did an hour before this interview was broadcast) to find that there had indeed been a further tremor the previous evening at 20:39

2018/10/26 20:39:22.7 53.786 -2.966 2 -0.1 BLACKPOOL,LANCASHIRE

I think if Mr Egan is expecting to capture that elusive social licence to operate that he needs so badly he’s going to have to be a little more truthful with the public.

You can hear the interview here:

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