Earthquake Prediction Research Center,
Tokai University. Shimizu 424, Japan and Geodynamics Research Institute/Department of Geology and Geophysics, Texas A&M University, College
Station, Texas 77843, USA
prediction has been in practice in Greece for more than a decade by the so
called VAN method. The method is based on detection of characteristic
changes in the geoelectric potential, the so-called Seismic Electric
Signals (SES) that appear prior to earthquakes. SES are distinguished from
noise through a set of criteria based on simple physical principles. It
has been found that SES are observed only at particular locations
(sensitive sites) and that a sensitive site is selectively sensitive to
SES from particular seismic source area's), making epicentral prediction
possible to within about l00 km. Magnitude of an impending earthquake is
predicted, to within 0.7 units, from its relationship, also empirically
discovered, with epicentral distance and intensity of SES.
Former two classes of predictions, mainly based on the past history of fault movement and seismicity, can be useful for long-term planning for mitigation of earthquake hazard. On the other hand, short-term prediction is based on precursory phenomena immediately before earthquakes. A wide variety of phenomena, including seismological, geodetic, geochemical, hydrological, electro-magnetic or even meteorological and biological phenomena, has been postulated to be potential precursors. Except for a few cases like Haisheng prediction, however, there has practically been no success but frequent failures. Although some success may be hoped in the future, owing to the development of new technologies and data handling techniques, such as GPS, satellite interferometry, water table monitoring, so far, at best, most of the reported precursory phenomena have been noticed only after earthquakes. They are called post-predictions.
The VAN method, named after the initials of Professors P. Varotsos, K. Alexopoulos and K. Nomicos, stands out as a notable exception in that it has been actually making short-term predictions before, not after, earthquakes. Soon after the disastrous earthquake in Athens area in 1981, the VAN group started monitoring geoelectric potential changes, because solid state physicists Varotsos and Alexopoulos anticipated theoretically that some electric current would be generated in the earthquake source region just prior to earthquake. Nomicos developed the necessary data acquisition system. The VAN group now claims that earthquakes in Greece with Ms(ATH) (magnitude announced by the Seismological Institute of the National Observatory of Athens, SI-NOA) greater than 5 can be predicted within the error of 100 km in epicentral location and 0.7 unit in magnitude. The time of earthquake occurrence is claimed to be from several hours to II days after detecting the signals, but it can be several weeks for repeated and prolonged signals.