HR: 0800h
AN: T51B-1335    [Abstracts]
TI: Experimental Studies on Luminescence of Visible Light Associated With Rock Fracture
AU: * Kato, M
EM: mkato@gaia.h.kyoto-u.ac.jp
AF: Graduate School of Human and Environmental Studies, Kyoto Univ., Sakyo, Kyoto, 6068501 Japan
AU: Mitui, Y
T51B-1335 AF: Faculty of Integrated Human Studies, Kyoto Univ., Sakyo, Kyoto, 6068501 Japan
AU: Yanagidani, T
EM: yasan@rcep.dpri.kyoto-u.ac.jp
AF: Disaster Prevention Research Institute, Kyoto Univ., Gokasho, Uji, Kyoto, 6110011 Japan
AB: The sky being illuminated before and during an earthquake is one of the phenomena that are often referred as macroscopic anomaly. Since the first unambiguous photographs of the illuminated sky were taken during swarm activities in Matsushiro, Japan, in mid-1960s, reports of similar observations, some of which are less credible than others, follow large earthquakes in Japan, such as 1995 Kobe Earthquake, as interest in this phenomenon, in accord with interest in short-term earthquake prediction, is high in Japan. Brady and Rowell [1986] was first to experimentally investigate luminescence during rock fracture, and postulated from spectrographic observations that luminescence is caused by exoelectrons emitted from fresh rock surfaces which are created during fracture. In other experimental studies on electromagnetic behavior of rocks subjected to compression [e.g., Yoshida, 2001], piezoelectric effect of quartz is asserted to play an important role, and it appears that luminescence and emission of other electromagnetic waves do not share the same origin. We have experimentally studied luminescence of rock in uniaxial compression. Rock samples such as granite, sandstone, and basalt are prepared in both dry and wet conditions, and are compressed with high strain rates in ambient atmosphere. Luminescence of rocks is weak but visible to naked eye when conditions are met. Photographic records of faint luminescence with digital cameras are also possible. Emission of light is instantaneous, and appears to be dominant at the final explosive failure. Its intensity significantly decreases when samples are in wet condition. Mineralogy controls luminescence, as, for example, quartz-rich samples usually emit stronger light than quartz-poor samples. Grain size is another controlling parameter, as we observe stronger light from granite with coarser grains. These observations are not successfully explained by the exoelectron hypothesis of Brady and Rowell, but rather suggest that discharge of piezoelectric field is primarily responsible for luminescence.
DE: 5104 Fracture and flow
DE: 7209 Earthquake dynamics (1242)
DE: 8010 Fractures and faults
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Tectonophysics [T]
MN: Fall Meeting 2005