The Earth moves in Harmer Hill

Continents in collision: Shropshire village at the epicentre of earthquake as tectonic plates push Britain closer to Europe

TOM WILKIE

Science Editor

Eleven kilometres below the village of Harmer Hill, just north of Shrewsbury, the earth moved for the people of Shropshire at 11.41pm on Wednesday night.

The tremor, which measured 3.4 on the Richter scale, lasted for a couple of minutes and brought some worried residents out of their homes and into the street in their nightclothes. But the energy released at the surface was so slight that, at worst, a few roof tiles may have toppled and perhaps some cracks appeared in walls.

With a reluctance that must have gratified the local Euro-sceptic MP, Nicholas Budgen, the bowels of the Salopian earth were squeaking in protest as Britain is being physically forced away from North America into the arms of Europe. Down the middle of the Atlantic ocean runs a ridge, which is spreading outwards as molten rock wells up and creates new crust, pushing Britain away.

Because of this geological rather than political pro- European movement, "Britain is under stress all the time" according to Dr David Booth, a seismologist with the British Geological Survey's Global Seismology Group in Edinburgh.

Most large earthquakes take place around the boundaries of the tectonic plates which make up the earth's crust. The notorious San Andreas fault in California, for example, represents the grinding collision between the Pacific Plate and the North American Plate.

Although Britain is some distance from any plate boundaries, the effect of the ocean mid-floor spreading can be felt as far away as Shropshire. "Due to our very spectacular geological history, there are a number of weak points within the crust," Dr Booth said.

He pointed out that although, geologically, Britain "has settled down over the past few million years, there is still plenty of geological activity". The result is that there are "20 to 30 felt-events a year" - British earthquakes strong enough for people - rather than just delicate seismometers - to feel.

The Shropshire tremor, the largest in Britain for a year, follows quickly on the heels of the two biggest earthquakes in Britain this century - both of which were also in the same general area. The biggest British earthquake this century was centred on the Lleyn Peninsula in north Wales in July 1984. It was even deeper than this week's event, about 20 kilometres down, and registered 5.4 on the Richter scale.

In April 1990, the area was once again the epicentre of a sizeable, deep quake as a 20- second tremor, centred on Bishop's Castle, measured 5.1. Buildings across the West Midlands and the Black Country were evacuated and chimneys toppled.

All three tremors were so deep that seismologists cannot identify the local faults in the earth's crust that gave rise to them, and they are not linked to any features - such as hills or valleys - on the surface, according to Dr Booth.

But the Shropshire tremor was "most unlikely to be the harbinger of a large destructive earthquake in that area".We are not going to lose Shrewsbury, he said, although there may be minor aftershocks.

"A seismologist in California would fall about laughing when he saw the media attention given to an event of this magnitude."

But in a telling demonstration of current public anxiety, police 999 switchboards were jammed by people who feared they were victims of an IRA bomb attack.

Tremors that shook Britain

St Andrews, Fife, 811: earthquake said to have killed 1,400 people

Colchester, 1884: most damaging known quake, which killed four people, damaged 1,200 homes and flattened a church

North Wales, 1984: epicentre of the biggest quake in Britain this century, measuring 5.4 on the Richter Scale

Wrexham, 1992: epicentre of 20-second tremor which measured 5.2. It caused buildings across the West Midlands and Black Country to be evacuated, toppled chimneys and caused structural damage.