Poor Athens! Coming as it did so soon after the devastation in Turkey, Tuesday's Athenian tremor generated a much greater terror than might otherwise have been the case. But it has been a major tragedy in its own right. And it will be interesting to see if VAN predicted it.
VAN is the acronym for three Greek seismologists, Varotsos, Alexopoulos and Nomicos, who several years ago announced a new technique for predicting seismic tremors. Their methodology is based on the fact that very weak electric currents flow to and fro in the ground because of minor voltage differences between one place and another on the Earth's crust. The assumption is that these "earth currents" may be disrupted by the kind of crustal stress that precedes a major earthquake.
The three became interested in earthquakes in the 1980s when Varotsos was a researcher at the University of Athens. They were conducting experiments whereby dry rocks were subjected to abnormal pressures, and the electrical characteristics of the rocks were monitored. They found that, in such circumstances, just before fracturing, a rock would generate a transient and weak electric current as crystal imperfections caused a separation of the charges. Because earthquakes are, in essence, much larger versions of such rock fractures, the VAN trio reasoned that they should generate precursory electrical signals in the Earth's crust.
To test their theory, VAN constructed a network of monitoring instruments in Greece that are in effect giant voltmeters, comprising wires perhaps two or three miles in length connected to electrodes inserted in the ground. By analysing the signals from their monitoring instruments, they claim to have predicted several weeks in advance every major earthquake in the region in the past 10 years.
But there is much scepticism in the seismic world about the VAN technique. Critics say that VAN are merely measuring electrical noise, and that any anomalies they find are just due to some problem with the instruments. The claimed predictive skill, they say, is just coincidence.
Last year in the scientific journal Nature, for example, a group of colleagues were dismissive: "Our analyses show the VAN claims to be without foundation. Some of the geoelectrical signals are artefacts of industrial origin, and there is no compelling evidence linking any of the geophysical signals to earthquakes. Controversy lingers primarily because Varotsos's claims have not been stated as unambiguous and objectively testable hypotheses."
So as I said - it will be interesting to see how VAN has coped with this latest incident in Athens.