Mécanismes de génération de bruits telluriques dans la bande ultrabasse fréquence (UBF) : sources possibles des signaux dits «signaux électro-sismiques » (SES)

Some anomalous transient electric signals in the ULF band, the so-called SES, are claimed to be earthquake precursors. However, their origin remains widely unknown. Anomalous signals having the same characteristics as the SES have been observed at the ‘Centre de recherche géophysique’ (CRG), Garchy (France) and their origin has now been clearly identified with the leakage of electric and phone networks of the CRG. They can be generated by two electrochemical mechanisms of the metallic electrode polarization: the galvanic cell and the AC electrolytic cell. These two mechanisms were controlled by field experiments, and their existence can be generalized and extrapolated to different scales. Any lack of insulation of grounded metallic bodies (underground electric and phone networks, pipelines, gas and water metallic conduits, railways, grounded towers of high power electric lines etc.) could lead to the generation of DC signals looking like the so-called SES. The greatest care must then be taken when claiming the existence of electric precursors of seismic or volcanic significance.