HR: 0800h
AN: T51B-0446    [Abstracts]
TI: Electric-discharge Luminescence between Frictional Natural Quartz by Pin-on-disk Method: Possible Origin of Seismo-electromagnetic Radiation
AU: * Muto, J
EM: mutoh@mail.tains.tohoku.ac.jp
AF: Department of Geoenvironmental Sciences, Graduate School of Science, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Nagahama, H
EM: nagahama@dges.tohoku.ac.jp
AF: Department of Geoenvironmental Sciences, Graduate School of Science, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai, 980-8578 Japan
AU: Miura, T
EM: takashi.miura@gakushuin.ac.jp
AF: Department of Physics, Gakushuin University, Mejiro, 1-5-1, Toshima-ku, Tokyo, 171-8588 Japan
AU: Arakawa, I
EM: ich.arakawa@gakushuin.ac.jp
AF: Department of Physics, Gakushuin University, Mejiro, 1-5-1, Toshima-ku, Tokyo, 171-8588 Japan
AB: To elucidate mechanisms of electromagnetic radiations before and during earthquakes, electric-discharge luminescence around a frictional quartz interface was investigated using a vacuum tribometer with a pin-on-disk arrangement. A pin with a quartz tip slides on a quartz disk under various normal forces and sliding velocities. The disk and the pin were made from a single crystal of Brazilian quartz. The quartz disk was cut normal to c-axis and polished on both sides. The thickness and the radius of the disk were 1 mm and 17.5 mm, respectively. An optical microscope and a charge coupled device (CCD) video camera were used to take luminescence images through the transparent quartz disk. The frictional experiments can be conducted under sliding velocities ranging from 10 mm/s (0.1 rps) to 102 mm/s (1 rps) and normal forces ranging from 50 mN to 150 mN. From the total area of contact points, normal stress can be estimated ranging from 4 MPa to 11 MPa. All experiments were performed under controlled ambient gas pressure of Ar and N$_{2}$ and a room temperature. Based on these experimental conditions, we investigated the dependences of luminescence intensities on normal stresses and gas pressures. Under a constant gas pressure (Ar: 1.2$\times$10$^{4}$ Pa) and a constant sliding velocity (51 mm/s), luminescence intensities per unit area increase with normal stresses. Moreover under a constant sliding velocity (102 mm/s) and a constant normal stress (11MPa), luminescence intensities increase with N$_{2}$ gas pressures up to 1.2$\times$10$^{3}$ Pa and decrease with further increases in N$_{2}$ gas pressures. Our preliminary results indicate that densities of electric charge between a frictional interface increases with increases in normal stresses, and electric-discharge luminescence (plasma luminescence) due to dielectric breakdown of the ambient gas occurs at the interface. The contact electrification (triboelectrification) around frictional quartz interfaces, which causes the electric discharge and the dielectric breakdown of the ambient gas, can generate electromagnetic radiations (Hertz radiations or radiations from electric discharges) or electric-discharge luminescence accompanied with earthquakes.
DE: 8010 Fractures and faults
DE: 5104 Fracture and flow
DE: 0600 ELECTROMAGNETICS
DE: 0654 Plasmas
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting