Frequency-dependence of velocity and attenuation of elastic waves in granite under uniaxial compression |
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Authors: | Hitoshi Oda Osamu Nishizawa Kin'ichiro Kusunose Takayuki Hirata |
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Institution: | (1) Faculty of Science, Okayama University, 700 Okayama, Japan;(2) Geological Survey of Japan, 305 Tsukuba, Japan;(3) Faculty of Applied Physics, Tsukuba University, 305 Tsukuba, Japan |
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Abstract: | Velocity as well as attenuation factorQ
–1 ofP-wave in a dry granitic rock sample under uniaxial compressions were measured in the range of frequency between 100 kHz and 710 kHz by using the pulse transmission technique. Above the stress of 0.5
f
, where
f
is the fracture stress, theP-wave velocity decreases with increasing axial stress, whereasQ
–1 increases. Particularly, the change ofQ
–1 is greater for high frequency than for low frequency. At a given stress level, the higher the frequency, the higher theP-wave velocity and the largerQ
–1. This result means that the velocity decrease with increasing stress is smaller for higher frequency. Because of this frequency-dependence of velocity decrease, theP-wave in the rock under dilatant state shows dispersion. The body wave dispersion is more remarkable at higher stress, and is not found in a homogeneous material with no cracks. Thus the disperison is attributed to the generation of cracks. When the frequency-dependence ofQ
–1 is approximated asf
n
in the present frequency range, the exponentn takes a value from 0.63 to 0.77. |
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Keywords: | Elastic wave velocity attenuation dispersion of body wave frequency-dependence of attenuation |
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