Strange electromagnetic signals were detected two months before a major earthquake hit Japan. The signals support controversial work by Greek researchers, who say they could one day be used to predict earthquakes.
For several years seismologists have intensely debated whether or not you can forecast earthquakes by the electromagnetic signals emitted by rocks under stress.
Proponents of the idea 鈥� known as the VAN method after the initials of the Greek researchers who developed it, Panayiotis Varotsos, Kessar Alexopoulos and Konstantine Nomicos, all of the University of Athens 鈥� maintain that electrical and magnetic activity in the ground can predict the location, time and magnitude of some earthquakes.
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Other researchers have had difficulty repeating the Greek team鈥檚 results. But now Seiya Uyeda鈥檚 team from the Earthquake Prediction Research Center at Tokai University in Japan reports measuring anomalous changes in the Earth鈥檚 electrical and magnetic fields in Japan鈥檚 Izu islands, from the end of March 2000. And a couple of months later, a series of earthquakes started on 26 June.
The researchers used telephone wires as antennas, to measure extremely low frequency electromagnetic waves every 10 seconds.
Rock faults
They say their geoelectrical field readings showed 鈥渃lear, unusual changes鈥�. The strength of the signals increased over time, reaching a peak just before the first large earthquake of magnitude 6.4 on the Richter scale on 1 July 2000. After the seismic activity died down, the fields returned to normal.
The group also saw changes in the Earth鈥檚 magnetic field strength over the same period. After allowing for other possible causes of magnetic noise, such as rainfall or man-made sources, the researchers saw a tiny but unexplained distortion. The variations were about a million times smaller than the Earth鈥檚 natural magnetic field.
The signals were picked up at only two antennas, which the researchers admit is puzzling. They think that the stress signals may be propagated along highly conductive channels, such as faults in the rock that contain pools of water, making them detectable only in certain areas.
鈥淕rasping at straws鈥�
Seismologists are divided over the significance of the results. Varotsos says that Uyeda鈥檚 experimental results are impressive, and confirm the signals he has seen in Greece over the past 20 years.
Max Wyss of the University of Alaska Fairbanks, on the other hand, dismisses the Japanese measurements. The group鈥檚 assertions that these signals predict earthquakes are 鈥済rasping at straws鈥�, Wyss says. 鈥淭hey simply want to believe that, no matter what the facts are.鈥�
Phil Reppert of Clemson University in South Carolina says that while Uyeda鈥檚 work doesn鈥檛 prove it will ever be possible to predict earthquakes, it does show the need for more research. 鈥淚 agree with the authors that the chances of their signals being man-made noise are slim.鈥�
More at: Proceedings of the National Academy of Sciences (vol 99, p 7352)