Ruislip & Eastcote & Northwood Gazette
Londoners shaken up by ‘level 4’ earthquake
A 3.3 MAGNITUDE earthquake startled people around North and West London, leaving walls cracked, chairs on their backs, and some fearing ther had been an explosion.
The earthquake happened at 8.45am on Tuesday, September 8, with an epicentre at Leighton Buzzard in Bedfordshire, but tremors were felt across surrounding areas stretching into London.
Writing on the emsc-csem.org website, one person in Aylesbury said: “Wardrobe doors shook and felt the vibrations.”
Some may believe this was a very rare occurrence, but we see anything between two and three hundred earthquakes every year in the UK, according to top seismologist Glenn Ford.
But while earthquakes occur a lot in the UK, the British Geographical Survey (BGS) seismologist said there was still something unusual about this one in particular.
Mr Ford said: “What’s unusual about this is only about 10 per cent of these earthquakes are large enough to be perceived by the general public.
“It’s unusual in terms of it was felt.”
What caused the earthquake?
“This is typical UK seismic activity,” Mr Ford added. “Earthquakes occur in Britain due to crustal stresses in the means within tectonic boundaries, and that stress is basically relieved in these small movements we get in all pre-existing fault lines in the UK.”
Has there been a recent increase in earthquakes happening in Britain?
Giving a definitive answer, Mr Ford said: “No, definitely not.
“It remains constant, our sort of annual yield of activity.”
How did this earthquake compare to the biggest earthquakes London and Britain have ever felt?
This earthquake was slightly larger in size than most of the earthquakes we see in the UK.
Mr Ford said: “We get maybe two earthquakes a year of this size.
“It’s starting to get on the larger size – if you look at even the last 50 days of activity [in the UK], you’ll see most earthquakes are generally smaller than this.”
Despite this, the seismologist said it does not make the earthquake unusual in the area.
He said: “It’s not like it’s been a non-seismic area at all – there’s definitely been activity there recently.
“There’s not a lot, but they do certainly happen in the area.
“It’s just not as prevalent as you’d perhaps get in other parts of the country, like North Wales or the Scottish Highlands. But they do occur.”
Why was the earthquake felt?
There are many variables that determine why an earthquake is or is not felt.
“One is location,” Mr Ford said, “look at the location of this earthquake – it’s in a highly populated area of the UK.
Another factor is the time of day, and in this instance, “it happened at a time when all people are conscious.”
The other major variable is the depth of an earthquake – this one was just 10km beneath the ground in the Uxbridge area.
There are two ways in which earthquakes are measured – in magnitude, which never changes, and in intensity.
“This is a measurement of what people perceive, what happened,” according to Mr Ford.
“So, we would probably put this up to intensity 4 now that we’re getting so many calls.”
This is nothing compared to the “complete devastation” you see from earthquakes around the world, which reach up to intensity level 12. “We never get that in the UK,” Mr Ford said, “We maybe get a 6 now and again, but very, very rarely do we get anything above that. “Most earthquakes in the UK are around intensity 3 or 4.”
What’s unusual about this is only about 10 per cent of these earthquakes are large enough to be perceived by the general public. Seismologist Glenn Ford
How does this earthquake compare to others around the world?
“It’s a very small earthquake in world terms,” the seismologist said, “there’s tens of thousands of earthquakes this size around the world every year.
“To put it in context – comparing this earthquake to the earthquake that happened in Japan in 2011, it’s 380 million times smaller.”
So, why does London never get major earthquakes?
Mr Ford said: “Essentially, most of our stress getting built up on the mid-crustal areas gets relieved in other faultings in other parts of the country.
“When you think about it, the UK’s a tiny area.
“London has felt earthquakes, we’re just not getting them in the particular area right under London.
“But London has felt earthquakes throughout history.”
The Dogger Bank earthquake in 1931 was the strongest earthquake recorded in the UK since measurements began, and it’s 6.1 magnitude was felt across the entire nation.
Mr Ford said it “puts into perspective how small this one is – we’re looking at people feeling this earthquake maybe 20 to 30 kilometres from the epicentre.”
While the fact people felt this earthquake is what essentially makes it an unusual event in the UK, this is only because we do not expect to feel them like people do in other countries.
According to Mr Ford, “if this earthquake happened somewhere in Greece, you wouldn’t look up from your book or your newspaper for it.”