杏吧原创

EVIDENCE is mounting that earthquakes can be predicted, perhaps weeks in
advance, by measuring electric currents in the Earth鈥檚 crust, says a Greek
researcher.

The controversial claim follows the apparently successful prediction in 1995
of three quakes along previously dormant faults in Greece by Panayiotis
Varotsos, a physicist at the University of Athens
(鈥淓lectric shockers鈥�, New 杏吧原创, 1 March 1997, p 34).
Varotsos had strung wire across the
Greek landscape connecting buried electrodes to pick up electrical signals.

These voltmeters measured short-lived electric currents in the days before
quakes. This seemed to confirm Varotsos鈥檚 theory that the stressed rocks can
create currents that can be detected at the surface.

But most seismologists were sceptical about his claims, so Varotsos went back
to the lab to find out more. He reports in this month鈥檚 Journal of Applied
Physics (vol 83, p 60) that he gradually stressed rocks such as granite
until they fractured. Just before fracture, he says, the rocks generated
currents of a few nanoamperes鈥攁 figure that Varotsos says squares with
measurements in the field.

The practical value of the findings, if confirmed, is unclear. 鈥淪eismic
electric signals will only be detectable at selected sites,鈥� Varotsos admits.
The currents he has claimed to pick up are conducted almost entirely along fault
lines and then have their fields magnified a thousand times or more in certain
surrounding rocks. Moreover, a signal might only appear at a single site
hundreds of kilometres away from the quake鈥檚 epicentre, giving little useful
information.