Deadly fault lines run down the spine of Italy

An aerial view of the destruction in the city of L'Aquila, central Italy. Photo / AP

This region of Italy has a long history of earthquakes dating from long before classical times. It is one of the most seismically active regions of Europe, essentially due to the collision of the tectonic plates of Africa and Europe which pushed up the Apennine mountain range, the geological 'backbone' of Italy.

The boundary between the African and European plates is particularly complex in this part of the Mediterranean, and the mountain-building process that created the Apennines has been an active feature of the region's geology and history for millions of years.

Italy is riddled with geological faults, and yesterday's earthquake near L'Aquila in the Abruzzo region, with a magnitude of 5.8 according to Italy's National Institute of Geophysics and 6.3 according to the US Geological Survey, probably was caused by a sudden movement in one of them as a result of the gradual sinking of the Apennines under the force of gravity.

"It is only relatively recently that the Apennines were created by being pushed up by tectonic forces, and now they are in the process of collapsing quite rapidly," said Professor Bob Holdsworth, of Durham University, who has studied the area.

"The evidence for these earthquakes is everywhere in Italian life, ranging from cataclysmic events recorded throughout history, through to the cliff-like fault scarps across the landscape."

The British Geological Survey said the earthquake's epicentre was close to the town of L'Aquila, about 96 kilometres north-east of Rome. The earthquake was just 140 kms north-west of a magnitude 5.9 tremor which struck the village of San Giuliano di Puglia on 31 October 2002, killing 28 people.

One of the worst recorded earthquakes in the region was in Avezzano in 1915, just 40 kms south of yesterday's quake; that killed 30,000 people.

John Whalley, principal lecturer in earth sciences at Portsmouth University, said there is a belt of seismic activity running parallel to the Apennines down the entire length of the Italian peninsula.

"These mountains form part of the major tectonic plate boundary marking the collision zone between the African and European plates," Dr Whalley said.

"This collision dominated the geological evolution of southern Europe for most of the past 50 million years and formed the Alps. Though we speak of a collision between two major plates, the collision zone is extremely complex with numerous microplates being trapped as the intervening ocean closed.

"As a consequence of this complexity, the Apennines run almost at right angles to the main trend of the Alps, having been formed when the western half of Italy was pushed over the top of the eastern half. Although the primary west-to-east motion has largely ceased, the area remains extremely unstable."

Dr Whalley said that a study in 2005 found that the town of L'Aquila was built on the bed of an ancient lake which may have amplified the vibrations of the quake, causing even more damage to buildings at the surface. "A magnitude 6.3 earthquake will nearly always be strong enough to cause significant damage but [the study] highlighted an increased risk in this area. The authors showed that the city was underlain by weak sediments, up to 820ft thick, which had accumulated in an ancient lake."

David Rothery, a senior lecturer in earth science at the Open University, said: "A magnitude 6 quake in the same region in 1997 took 11 lives and destroyed 80,000 homes. The latest quake was moderately large but more significantly shallow - its depth is preliminarily estimated at only six miles - so the shaking it caused at the surface was large. I expect the death toll will rise. Italian colleagues who arrived today from Rome and Padova felt the quake for themselves. Fabrizio, my colleague from Rome, was already awake, and, according to him, his house shook for 20 seconds."

Roger Musson, of the British Geological Survey in Edinburgh, said routine earthquake prediction is not possible anywhere and, that given the chaotic nature of earthquake occurrence, it may never be possible.

"In the case of the L'Aquila earthquake, some warning might have been taken by the series of foreshocks that preceded it," he said. "But there is no way to discriminate between foreshocks and normal small-magnitude seismicity, other than with hindsight. Aftershock activity has been intense. The possibility of a further event of similar magnitude cannot be ruled out."

More than 100 people in the Abruzzo region were crushed when their homes collapsed. Enzo Boschi, the chairman of Italy's National Institute for Geophysics and Volcanology in Bologna, said: "The damage involved buildings which were not built to withstand a quake that was not even particularly strong. It is always distressing to note that we do not have the mentality to build adequate structures in areas at risk of seismic activity. In other words, we don't construct buildings to withstand quakes nor do we revamp old ones to make them safe from collapse.

"We have detailed maps which indicate the areas most at risk of earthquakes and we have also indicated what actions are needed to make buildings safe. But little or nothing has been done."

- THE INDEPENDENT