An Experimental Study of Microwave Emissions from Compression Failure of Rocks

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  • MAKI Ken-ichiro
    School of Engineering, University of Tokyo Present Address: Terahertz Sensing and Imaging Laboratory, RIKEN
  • TAKANO Tadashi
    Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency
  • SOMA Eriko
    Faculty of Engineering, Tokyo University of Science
  • ISHII Kentaro
    Faculty of Engineering, Tokyo University of Science
  • YOSHIDA Shingo
    Earthquake Research Institute, University of Tokyo
  • NAKATANI Masao
    Earthquake Research Institute, University of Tokyo

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  • 岩石圧縮破壊に伴うマイクロ波放射の観測
  • ガンセキ アッシュク ハカイ ニ トモナウ マイクロハ ホウシャ ノ カンソク

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Abstract

Electromagnetic emissions observed in a series of rock fracture tests are described. Four kinds of rocks, basalt, gabbro, granite and quartzite were pressed by uniaxial compression to fracture, for all of which many signals were detected at two microwave bands (2GHz and 300MHz). These detected signals consist of intermittent pulses of a short duration. Comparing the microwave records and the observation with a high-speed digital video camera, we found that the pulse signals were generated after the decrease of the axial load, and even after the macroscopic fracture (deformation) was completed. This differs from the occurrence of lower frequency emissions (0.3-300kHz) monitored as well, which became active and was strongest during the load decrease. The occurrence of signals at the two microwave bands did not always coincide, but a signal at 300MHz often followed a signal at 2GHz with a short interval of 50-100ns. An additional detector at 22GHz picked up emissions only for quartzite, which occurred exclusively during the decrease of axial load.

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