The great quake of '08

It was hardly San Francisco in 1906, but this week's tremor was Britain's worst in decades. Esther Addley travels to the epicentre in search of a fault line no one has mapped
Earthquake in England
A seismograph showing the earthquake with a magnitude of 5.2 on the Richter scale. Photograph: British Geological Survey/ PA

At 5.12am on April 18 1906, the reporter Fred Hewitt would later record, "the hand of a vengeful God" fell on his home city of San Francisco.

"The ground rose and fell like an ocean at ebb tide. Then came the crash ... To me it seemed like an eternity. I was thrown prone on my back and the pavement pulsated like a living thing. Around me the huge buildings, looking more terrible because of the queer dance they were performing, wobbled and veered. Crash followed crash and resounded on all sides. Screeches rent the air as terrified humanity streamed out into the open in agony of despair."

They know just how he felt in Market Rasen, Lincolnshire, which at 12:56am on Wednesday attracted its own burst of the Almighty's ire. "My husband said, 'What's that?'" Joan, a shop assistant at China Choice on Queen Street recounted earlier this week. "I said, 'It's a big lorry,' and rolled over. But he went out in his pyjamas and talked to the neighbours. He came back and said, 'I think you just slept through your first earthquake.'"

It was not just any tremor. The 5.2 magnitude quake, which struck the small market town, was the largest to shake Britain in a quarter of a century, releasing forces in excess of those unleashed by the Nagasaki atomic bomb. Its ripples were felt as far afield as Aberdeen, Northern Ireland and the Netherlands.

But if God was enraged by northern California in 1906 (and evidently more than a little irked last week by David Bates, 19, whose pelvis was broken by falling masonry as he watched TV in Wombwell, south Yorkshire), he seems to have been barely put out by the folks of rural Lincolnshire. Several bricks were slightly dislodged in the chimney of the Gordon Arms, opposite Market Rasen's main square, and another a little further down the street was also left a bit wonky. Two small stone crosses pitched off the roof of St Thomas's church, damaging 20 or so slates. A handrail fell off the wall inside Walton's estate agents. China Choice, to Joan's amazement, escaped without one of its hundreds of ornaments being damaged, though a few doors up, in Market Rasen Pet Centre, Bridget Pitman did have some birdseed fall off the shelves, while her three parrots went "totally berserk".

"Well it's not really the tsunami, is it?" said Heather Tyson, smoking a cigarette out the back of her gift shop. "You would understand it if there were chimney pots everywhere and the streets were full of debris and missing limbs and things. But really everything was very quickly back to normal, apart from all the news vans and helicopters and stuff."

As disasters go, the Great Lincolnshire Earthquake of 2008, as it will doubtless never come to be called, was a very British catastrophe. (As it happens, the so-called Great English Earthquake in 1884 Colchester was significantly weaker). Awoken by Wednesday's quake, variously described as a "low horrible grumble" or a "loud cracking bang", hundreds across Britain called their local police forces, just to make sure they knew about it. Many turned on the TV. But a great number, judging by an unscientific poll at its epicentre this week, grunted and went back to sleep.

"My wife said, 'Hey, what's that?' and woke me up," said Rex Saunby, pausing in his van for a cup of tea after replacing the tiles on the roof of St Thomas's. "She went downstairs and said a picture had fallen off the TV. But that was it." Nick Patton, the clerk of the Market Rasen racecourse, said a few of his cupboard doors had swung open. In Portland Terrace in nearby Gainsborough, one of the most affected spots, Sharon Brooks said she initially thought the rumbling was an explosion. "The house shook and then my daughter came in and said 'My hamster's upside down.' The earthquake had knocked over its cage."

Earthquakes happen all the time in Britain - at least one every other day, on average - and some of them are even big enough to rattle teacups. A tremor in Kent last year measured 4.2 and led to five streets in Folkstone being evacuated. Manchester had a "swarm" of six quakes in the space of three weeks last August, the last measuring 2.4 ("It felt like a patio door was being closed," said Gwen Graham, 51). A 5.0 boneshaker emanating from the junction of High Arcal Road and Himley Road in Dudley in 2002 prompted 12 people to walk into the local police station in their pyjamas.

But though historically quakes have certainly made themselves felt in this country - early cathedrals at Lincoln, Wells, St Davids and Canterbury were all damaged or destroyed in the 12th to 14th centuries - British tremors have always been a more of a shiver than a shake. Even the largest recorded, a magnitude 6.1 centred on Dogger Bank off the North Sea coast in June 1931, caused no more than a few chimneys to collapse in Hull - though by the time they reached London the shockwaves still had enough force to knock the head off of the model of Dr Crippen at Madame Tussauds.

The truth is that compared with much of the world, seismic activity in Britain is embarrassingly underwhelming. The US Geological Survey records 550 seismic occurrences within its borders each week, while Japan sits atop such a troubled seismic zone it regards major quakes as almost every day. It even had one yesterday, measuring 3.6, off the coast of Fukushima.

The most recent major Japanese quake was in January 1995 when a 7.2-magnitude tremor that struck Kobe killing 6,500 people and destroying 250,000 homes. Because quake magnitude is a logarithmic rather than linear measurement, 7.2 is not, as it might appear, just a bit more intense than Market Rasen's 5.2. Each whole number increase on the scale represents a tremor 31 times more powerful than the last. The Sumatran quake that caused the 2004 tsunami, for instance, measured 9.3 but was almost 1 million times more powerful than Wednesday's Lincolnshire wobble.

Though earthquakes have been recorded from the earliest times, our present understanding of them is in fact remarkably recent. The theory of plate tectonics, now widely accepted as explaining why the earth's crust behaves as it does, did not fully emerge until the late 1960s - the science of seismology was also aided by all the probes the superpowers had been developing to measure each other's nuclear tests.

The theory identifies the Earth's crust as made up of a number of major plates that are continually moving, driven by heat originating deep within the planet's core. Where the plates meet, they may find themselves compressing together, pulling apart or slipping under one another. The massive friction forces these generate can give rise to quakes. This is why parts of the globe located on plate boundaries, such as the west coasts of the Americas, or the Pacific "ring of fire", experience such severe quakes. And why Britain, which sits in the middle of the Eurasian plate well away from anywhere terribly seismically interesting, gets such feeble ones.

Brian Baptie, a seismologist at the British Geological Survey, acknowledges that for those who monitor quakes, British tremors are not exactly earth-shattering. "The work that we do in impact terms is much less significant than other places," he said. "What we are doing is really trying to understand why we get earthquakes in the UK."

Thanks to measurements gathered from as far afield as Canada and Alaska, the BGS has pinpointed Wednesday's focus at a spot 12.4 miles below ground. Since the Earth's crust under Britain averages only 18.6 miles in depth, he said, "that's pretty deep".

"We're down in what's called the early Palaeozoic basement. These rocks are probably 300m to 400m years old. And the fault that caused the earthquake would be in those rocks."

The problem for British scientists is that unlike more seismically adventurous parts of the world, it is pretty difficult to work out where the fault lines under Britain actually lie. Unlike the San Andreas fault on America's west coast, which has created several enormous fissures on the Earth's surface, the comparatively tiny cracks and weak spots at the centre of a plate are often very difficult to detect.

There is the Great Glen fault, which runs through Loch Ness, and the Highland Boundary fault, also in Scotland. A fault system called the Variscan Front runs from south-east England towards Cornwall, and another known as the Church Stretton fault which runs roughly from Wales to the southeast.

But Market Rasen sits on none of them. "In this case, we just don't know," said Baptie. "Whichever fault caused this earthquake, it doesn't have a name. It's just not mapped by geologists."

Professor Lynne Frostick, the director of the Environmental Research Institute at University of Hull, said to think of the UK, or at least the plate on which it sits, as "a great, stately galleon moving across the earth":

"As we are going up and down over the waves, the boards creak and groan against each other."

As for predicting which of the boards will creak next, however, "we have got lots and lots of faults beneath us. Which one will take up the stress? Who knows".

Climate change might seem a more pressing concern for Britain than the risk of seismic disaster, yet Britain's future does hold the prospect of what one Gainsborough resident, yesterday called "proper earthquakes".

"There is a change going on that will affect Britain," said Frostick, "and that's in the Red Sea-Gulf of Aden area. It is actually opening up into an ocean, at a rate of 2cm a year, and we are being gradually pushed away. If that really starts to open up then Africa will rotate, and will crash into Europe. And that will push us to the edge of a plate, where the real seismic activity is."

Happily, that leaves the residents of Market Rasen a little time to straighten their chimneys first.