Italy is on one of the most seismically active regions of Europe, where the African tectonic plate pushes up against the Eurasian plate. The situation is further complicated by a microplate beneath the Adriatic Sea that is moving northeast, pulling apart the rocks that make up the Apennine mountain range running down the country’s spine. The result, according to John McCloskey, Professor of Geophysics at the University of Ulster, is an “extremely complicated geology” in which “the entire country is crisscrossed by lots of faults”.

Most of these are clustered along the Apennines, which is where most of Italy’s significant earthquakes occur. The L’Aquila disaster is the fourth severe quake in this region in the past three decades. Its epicentre was 85km southeast of the magnitude 5.6 and 6.0 earthquakes that struck Umbria and the Marche in September 1997, killing 11 people and damaging Assisi. It is also 140 km northwest of a 5.9 quake that hit Puglia in October 2002, killing 28 people. A still more devastating quake, of magnitude 6.9, hit Irpinia, near Naples, in 1980, killing an estimated 3,000 people.

Professor Bob Holdsworth, of Durham University, said that in the Apennines “recently created mountains are now slowly collapsing due to a complex large-scale interaction between plate tectonic forces and gravity.

“The evidence for these earthquakes is everywhere in Italian life, ranging from cataclysmic events recorded throughout human history and legend through to the steep, cliff-like fault scarps that can be traced across the landscape.”

Professor McCloskey, whose team has analysed the 1997 Umbria-Marche quake in detail, said that the geology of the region meant there would be a risk of aftershocks, several of which were reported yesterday.

“The quake is in a similar location to the 1997 Umbria-Marche sequence of eight earthquakes over two months,” he said.

The L’Aquila quake is likely to have been caused by a “normal fault” which occurs when the Earth’s crust is being extended or stretched. As this happens, the crust periodically fails on diagonal planes, forcing down the block of crust on one side while the other moves slightly upwards.

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