Hattix

I felt it. Up late, room lit by a small four-watt flourescent tube and the slightly more powerful TFT monitor when a few tremors rolled me in my seat a little. I knew what it was instantly, I felt the Dudley quake of 2002 and it was exactly the same. The gentle rolling lasted maybe five seconds before a rapid series of sharp jolts took over; That’s when I realised this was somewhat stronger to say the least! Things fell. Shelving toppled. Neighbours went outside to see what was going on, to be told by me that it was just an earthquake.

An earthquake strong enough to be felt at any one specific place happens every five to ten years in the UK, whereas one strong enough to be felt at all at any place in the UK happens around twice a year. These are typically fairly weak events, maybe magnitude two or three. The widely felt Dudley earthquake of 2002 was a 4.7 and enough to be felt across the whole of England and Wales; It hit South Yorkshire, where I am, at about 3.0.

The Market Rasen earthquake of 2008 was a 5.2 at its epicenter (just 50km away) and still a good 5.0 when it reached me. Each integral, each one point, on the Richter scale is an energy difference of over thirty times. The 9.3 in Sumatra, 2006, yielding the deadly Asian Tsunami of Boxing Day, was over a million times more powerful.

But why do we get ‘quakes at all in the UK? We’re not on a faultline, we’re not anywhere near any volcanoes. Britain should be seismically dead, right? The reality isn’t quite so clear cut. Britain is on the move, but upwards, still rising back up after the ice melted only ten thousand years ago, two kilometers thick of ice depressed the land. We’re also being pushed east by the Atlantic seafloor spreading.

These forces, though gradual, build up. Britain’s geology, the rock that makes up the British Isles, is a mess. Old oceanic basalts from half a billion years ago, shales from the Jurassic, sandstones from the Cretaceous, coals from the Carboniferous, we’ve more geologic diversity beneath our feet than almost anywhere on Earth. All these rocks are bent, twisted by the incalculable forces of millions of years of tension, torsion and shifting. The rocks themselves are broken and faulted.

The current forces from our interglacial rebound and the mid-Atlantic ridge get caught up when our broken rocks snag on each other. Every few months, the rock breaks and the pressure is released; We get an earthquake. They’re usually small but every so often, maybe every five or ten years, we get one able to pass magnitude four.

Further reading on the British Geological Survey’s website, as well as realtime seismometer data.