Earthquakes occur where large stresses build up in the rocks along fault lines which are associated with movements of the crustal, or tectonic, plates.

As the plates jostle against each other, becoming distorted, tremendous strain builds up.

From time to time this is discharged in zones where the rocks are weakest, causing a series of shock-waves known as seismic waves.

These can have highly destructive effects on the earth's surface as they cause the ground to undulate and shake from side to side.

Most earthquakes take place along tectonic plate boundaries, or fault lines, although occasionally they occur as a result of movements within the interior of plates.

Many fault-lines are located around the Pacific Rim, giving rise to regular earthquakes in the west of the United States and Latin America, China, Japan and the south Pacific region, but North Africa, Italy, the Balkans and Turkey are also located near fault-lines involving the African plate and the Eurasian plate.

The Anatolian fault that lies between the two plates runs east-west across Turkey, with the Eurasian landmass inching eastwards. The fault is under additional pressure from the Arabian plate which is shifting northwards at a rate of inches per year.

Earthquakes can occcasionally be predicted by knowledge of locations and cycles of past earthquake activity, by minor tremors immediately prior to a major event, and sometimes by abnormal animal behaviour.

Most deaths resulting from earthquakes are caused by collapsing buildings rather than the direct effects of the earth's movements.

SPACE.WIRE