Shake, rattle & roll in the Mediterranean sun: A series of recent tremors is regarded as normal seismic activity. Susan Watts reports

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The Independent Online
THE Mediterranean, favoured holiday destination of millions of Britons, suffers thousands of earthquakes each year, although most are too small to be felt.

Last week's series of large tremors across the region alarmed locals and tourists alike, but experts said yesterday that these should not deter anyone from taking holidays there.

Although at least six quakes hit the headlines towards the end of last week, such seismological activity is not unusual; the Mediterranean is notorious for its frequent, and sometimes violent, earth movement.

On Monday last week, a powerful earthquake rocked the Greek island of Crete, with tremors felt in western Turkey. Earthquakes are measured according to the Richter scale - a crude, roughly logarithmic scale where the energy of a quake of magnitude 5 is 15 times that of a quake of magnitude 4, which in turn has 225 times the energy of a quake of magnitude 3.

The Cretan quake measured 5.9 on that scale. It was offshore, some 25 miles (40km) north-west of Iraklion. The quake caused only minor damage, but shook people enough to bring them out on to the streets. The following day, a moderate earthquake of magnitude 4.5 shook western Turkey itself. Turkey's western and southern coastal areas and the entire eastern region sit on top of a quake-prone belt known as the Anatolian fault.

Last Thursday, reports were received of a Portuguese quake measuring 5.8 on the Richter scale. Officials said later that the epicentre was about 250 miles (400km) south-east of Portugal - nearer to the Moroccan coast.

Urs Kradolfer, from the Swiss Seismological Service, said people should be aware that they were entering a part of the world that was earthquake-active: 'Unfortunately we still cannot predict when earthquakes are going to happen - just the zones most likely to have them.'

Roger Musson, a seismologist with the British Geological Survey in Edinburgh, has analysed data from the past 20 years in the region. Statistically, the region experiences one and a half quakes every year of magnitude 6 or more, and a quake of a magnitude greater than 7 once every three years. Some years there have been no severe earthquakes at all - others have seen four or five.

The Mediterranean is vulnerable to earthquakes because of its position above the border between two of the Earth's tectonic plate systems. A plate is a chunk of the Earth's crust floating on top of a more viscous layer, the mantle. Earthquake activity is most likely to occur at the boundaries of these plate systems.

The Mediterranean was once much larger - part of the Tethys ocean. When the African continent moved upwards to close off the Mediterranean, the two continental land masses and the plate boundaries beneath them met untidily.

The African plate rotates in an anti-clockwise direction relative to the Eurasian plate. Geologically, Italy and the Adriatic Sea belong to the African plate. Thus, any movement of the African plate creates tensions that result in earthquakes in Greece and

Italy.

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