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Earthquakes: Scientists struggle with predictions

Last July a panel of Japanese seismological experts admitted, for the first time, that they were unlikely to be able to predict when a catastrophic earthquake would happen, because predicting earthquakes was (to quote them) "difficult".

On its own, that is a statement of the blindingly obvious, but earthquakes have financial and social implications. China had earthquake detectors long before the Western world, because they could be critical in so large a country with limited grain stocks.

Predicting when an earthquake will strike is only half the problem; the other half is saying how big it will be. Seismologists willingly admit they are not terribly good at either, although there is a growing body of evidence that an earthquake is preceded by electromagnetic disturbance (which, intriguingly, animals seem to be sensitive to).

This is because most significant quakes are the result of "slips" between two colliding pieces of the Earth's crust. The San Andreas fault in California, for example, consists of a northward-moving piece of coastline and a southward- moving land mass. Because the crust contains magnetised minerals, the strain that builds up before they move can show up with very sensitive instruments.

The latest evidence comes from a researcher who appears to have correctly predicted three events along previously dormant faults in Greece. According to New Scientist magazine, Panayiotis Varotsos, a physicist at the University of Athens, strung wire across the landscape to detect electrical signals and found brief currents before the earthquakes.

The currents were tiny - a few nanoamperes, or billions of times less than that in household items. And Mr Varotsos is not sure how the finding could be used for larger-scale faults: "Seismic electric signals will only be detectable at selected sites," he said, perhaps hundreds of miles away from the quake's epicentre. Predicting anything more than the likelihood of a seismic event will remain - as the Japanese team said in their understated way - "difficult".

- Charles Arthur,

Science Editor