Today I learnt something very interesting that I didn’t know before – that intraplate earthquakes in the UK mostly occur in western England and Scotland, not Ireland, eastern Scotland or southeast England (where I grew up).
The cause of this is that the lithosphere in that region is thinner – 80 km rather than around 100 km – and presumably weaker; I have written before about how intraplate earthquakes tend to be focussed in regions of relative weakness within the plate, where the strain rate is higher.
As for what is causing this variation in lithospheric thickness, there is a fairly good correspondence between the thinned lithosphere and extent of the British Tertiary Igneous Province – the UK part of the North Atlantic Igneous Province, a region of widespread (probably mantle plume related) volcanic activity that accompanied the rifting of the North Atlantic Ocean around 55 million years ago. Since lithospheric mantle is just sufficiently cooled asthenosphere, heating = thinning.
It’s pretty cool how earthquake patterns can so tangibly reflect a deep tectonic history that played out tens of millions of years before the combination of plate motions and stresses that proximally cause them.
Of course, there are potentially damaging intraplate earthquakes outside of this region – the most destructive earthquake in the last 400 years – estimated magnitude 4.6 – had an epicentre very close to where I grew up. And whilst all of these earthquakes might seem very small in the grand scheme of things, but remember the UK is not a country that builds anything with earthquake shaking in mind, so damage from even a minor shake is potentially significant.
Nice plan for content warnings on Mastodon and the Fediverse. Now you need a Mastodon/Fediverse button on this blog.