EXPERIMENTAL-STUDY OF A VAN NETWORK IN THE FRENCH ALPS

In 1989, a telluric and magnetotelluric network was installed in the northern part of the French Alps by the Laboratoire de Detection et de Geophysique (LDG). The purpose of this experiment was to check the applicability of the Greek VAN method to earthquake prediction in a different geotectonic and seismic context from the Greek one. The sites were selected according to several criteria for geology and potential noise sources. A complete station consists of six telluric non-polarisable dipoles of Petiau type, 2 magnetometers of Mosnier type and an acquisition unit run by solar energy. The interesting signals are not correlated with the geomagnetic field variations. Anthropogenic noise, electrochemical variations and atmospheric storms are not listed. Synthetic graphs sum up the seismic and telluric activities during 3 months and 2 weeks. For the correlation between earthquakes and potential telluric precursors, we consider first the multiple epicentres, then the near-field ones and finally the most significant events. Some encouraging results are presented. This experiment must be continued over a longer period and the network completed with low-frequency radio-electric receiving stations.