Frictional discharge plasma from natural semiconductor/insulator junctions: Origin of seismo-electromagnetic radiation

By a pin-on-disk frictional experiment simulating the motion of an asperity on a fault plane, we observed photon emissions from the gap between the quartz disk and pins made of natural semiconductor or insulator minerals during friction. The patterns and intensities of photon emissions depended significantly on the gas pressure, on the normal stress and on the shape and material of the pins. The frictional contacts made of different grain sets or ore veins can be regarded as natural semiconductor/insulator junctions arising from the difference in electron states or work functions between the contacts. During seismic activities, such semiconductor/insulator junctions in natural fault zones would generate discharge plasmas that could be one of origins of seismo-electromagnetic phenomena. Finally, in addition to its effect on the geoelectromagnetic perturbations, the significances of the discovery of discharge plasmas on geochemical reactions on a fault zone arising from tectonic activities are discussed.