I was interested in this a few years ago, with a relatively anti-fossil-fuel, environmental mindset. I came across the research summarised in the links below.
How many man-made earthquakes pre-fracking?
What size of earthquakes can be caused by fracking?
Apparently there are about 30-40 earthquakes above 1.5M every year in the UK. Not that 1.5 is a scary level (generally not felt at the surface), but is the level the BGS seismometer thingies pick up on a regular basis (the ones near blackpool are obviously especially sensitive to allow for the traffic lights for fracking to be monitored). The BGS website lists one last week north of the Shetland isles of 4.3M, and the week before in Wales at 2.4M.
About 20% of those are manmade – mostly due to coal mining. The biggest earthquake globally caused by fracking was 3.8 (in Canada), which was felt, but didn’t cause any surface damage. Much bigger earthquakes are caused by reservoir impoundment, injection of wastewater from oil and gas extraction into formations that it wasn’t taken out of (not what is happening here) and from geothermal works.
As I understand from speaking to a seismologist, fracking is meant to cause these little mini-seismic “quakes”, and they can be used by the industry to monitor where the fractures are in the rock and so on. They generally stay below 0.5M – but it isn’t unusual for them to go up to more than that – though the ones in Blackpool in 2011 were unusually high on a global scale. Its very unusual for them to be big enough to be felt by at the surface, as in 2011. The fact the limit the red traffic light is set so low in the UK now (triggered by the 0.5M and 0.8M last week) is precisely to stop anything larger happening. The fact it is being picked up by the media (even at magnitudes of less than 0 – which has to be the lowest “earthquake” ever reported!) is because of people’s (understandable) concerns over the process – not because anything has gone wrong, and in fact it seems to indicate that the system is working.
As it happens, my earlier research turned me from being generally suspicious of the process, to being cautiously supportive (or at least accepting). I realise that’s not a fashionable opinion but it is shared by most of my friends working in science-y, environmental fields – though not “paid by the industry” as has been implied. I still want to see a reduction in gas use, but while we continue to use gas, I’d rather it was produced from the UK rather than being shipped in as we do at present, as north sea gas can’t meet all our needs. And everything I’ve seen of how the process works in the UK convinces me that the issues in other countries aren’t relevant here. I am interested to see how this turns out though, as I’ll be the first to admit I’m wrong if my tap catches fire
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