VAN Method - Description of VAN

Description of VAN

Prediction of earthquakes with this method is based on the detection, recording and evaluation of Seismic Electric Signals or SES. These electrical signals have a fundamental frequency component of 1 Hz or less and an amplitude proportional to the magnitude of the earthquake. According to the VAN team the SES are emitted by rocks under the stress caused by the movement of tectonic plates. They are perhaps attributed to the piezoelectric behaviour of some minerals, especially quartz, or to effects related to the behaviour of crystallographic defects under stress and they appear when the mechanical stress on rocks reaches a critical value, a few weeks before the earthquake, and the generation of electric signals by minerals under high stress leading to fracture has been confirmed with laboratory experiments. In one model, the seismic electric signals propagate with relatively low attenuation along the tectonic faults, due to the increased electrical conductivity caused either by the intrusion of ground water in them or by the ionic characteristics of the minerals. Alternately, a mechanism has been proposed relying on the electrokinetic effect associated with the motion of groundwater during a change in pore pressure.

Seismic electric signals are detected at stations which consist of pairs of electrodes (oriented NS and EW) inserted into the ground, amplifiers and filters. They are then transmitted to the headquarters of the VAN team in Athens where they are recorded and evaluated. The VAN stations have a degree of spatial selectivity. For example the station IOA, located near Ioannina, detects seismic electric signals which correspond to tectonic activity in Western Peloponnese and the Ionian Sea, while it does not detect signals related to tectonic activity around Ioannina. Currently the VAN team operates 9 stations, while in the past (1999) they could afford up to 17.

The VAN team claims that they are able to predict earthquakes of magnitude larger than 5, with an uncertainty of 0.7 units of magnitude, within a radius of 100 km, and in a 2-hour to 11-day time window. Several papers confirm this success rate, but the earthquake sample size is too small to make a statistically significant conclusion. For example, there were eight M ≥ 5.5 earthquakes in Greece from January 1, 1984 through September 10, 1995, and the VAN network forecast six of these.

In recent years the VAN team has tried to improve the accuracy of the estimation of the time of the forthcoming earthquake by introducing the concept of natural time, a parameter which indicates the evolution of the process from the generation of the seismic electric signal to the fracture at the tectonic fault.

The VAN method has also been used for investigation of seismic electric signals in France and in Japan. Though not strictly a VAN methodology, China plans to launch a satellite in 2014 to compare changes in the ionosphere with ground-based seismic and electrical measurements, as ionospheric changes have been successfully charted as precedent to seismic phenomena. The results of such a study could lend credence (or criticism) to the VAN method.