The technique has already been used to successfully predict an earthquake in Iceland.

Dr Stuart Crampin, at the University of Edinburgh, warned the Icelandic authorities in late October last year of an impending quake. He said there would either be a magnitude five tremor soon or a severe earthquake of magnitude six before February 1999.

Accurate predictions could help evacuation before a quake

He then issued a final warning on 10 November and, three days later, the earthquake duly arrived. It was magnitude five as predicted.

Dr Crampin believes his studies have revealed "a new understanding of the nature of rock deformation prior to fracturing, with important implications and applications".

The new technique allows the time and magnitude of an earthquake to be predicted but not the exact location. However, the information should allow geologists with knowledge of the local area to suggest which fault is most likely to rupture.

Stress and strain

The system is based on gathering information about the build up of stress in rocks in earthquake-prone areas.

The data comes from seismic waves that shake through rocks after minor earthquakes, which people would not feel but can be recorded on sensitive seismometers.

Some of the characteristics of the waves are determined by tiny cracks in the rock which are filled with salty water. As the stress builds up, the cracks are deformed and the seismic waves change.

Careful monitoring of these changes means the predictions can be made.

At the moment, the forecasting technique can only be used in areas where seismometers of sufficient sensitivity can be deployed.