Destruction and shock in Spain's earthquake 'hot zone'

People stand in front of a collapsed building in Lorca The shocks damaged more than 22,000 buildings in the Spanish town

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Eight people have died in the Magnitude 5.2 Lorca earthquake, with many more injured by falling debris.

A magnitude five earthquake occurs somewhere in the world around three times a day, and the earthquake in Lorca was about 1,000 times smaller than the recent Tohoku quake in Japan.

But Spain is a relatively low risk country for quakes, and buildings are not generally constructed to protect against seismic shaking.

Having said that, the Murcia region is the most seismically active in the country, and some of the medieval buildings that were badly damaged in this event may have been weakened by past earthquakes in the area.

This event was particularly damaging because it occurred at a relatively shallow depth, about 10km (six miles) below the Earth's surface.

Roger Musson from the British Geological Survey said it appears to have occurred along a fault line running from south-west to north-east.

Dr Musson told BBC News the quake was caused by an oblique slip movement, which means that rocks moved sideways and upwards along the fault.

Seismologists have reported that the 5.2 shock in Lorca was preceded by a Magnitude 4.5 event about two hours previously.

Infographic, BBC

The area has since experienced a series of aftershocks with magnitudes of up to 4.1.

Maria Jose Jurado, a scientific investigator at the CSIC Institute of Earth Sciences, Jaume Albera de Barcelona, told the newspaper El Mundo that it was likely the area could also experience aftershocks in coming days.

The Murcia fault line lies reasonably close to the subduction zone where Europe and Africa collide - though, as Dr Musson explains, "most of the action is taking place off the coast of North Africa".

The energy released in such quakes ultimately comes from the expansion of the Atlantic Ocean floor at the Mid-Atlanic Ridge. This expansion is pushing Europe in a south-easterly direction.

However, the eastern half of the Mediterranean is more seismically active than the west.

According to Dr Musson, the eastern Mediterranean is more "tectonically complex", with movement occuring not just on the Eurasian and African tectonic plates, but also the Anatolian plate that encompasses most of Turkey.

Several notable earthquakes have occurred along the Murcia fault in historic times. In August 1674, the town of Lorca was hit by a powerful shock that caused widespread damage and around 40 deaths.

Less powerful earthquakes occurred in the area during the 1970s, but caused far less damage.

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