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Application of Resonant Ultrasound Spectroscopy to Determine the Elastic Properties of Macroscopic Rock Samples

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Resonant Ultrasound Spectroscopy RUS is a method whereby the elastic tensor of a sample is extracted from measured resonance frequencies. Typically, a rectangular parallelepiped sample is placed between two piezoelectric transducers, a source and a detector. The sample is driven at constant voltage as the frequency is swept through multiple resonances. The measured resonance frequencies are the input to an iterative inversion algorithm that finds the best match between the data and a set of resonances generated from a model. RUS has been used successfully to determine the elastic properties of single crystals of minerals found in the earths mantle e.g., Oda et aL, 1992. We are extending the applicability of RUS to macroscopic samples of rock. Rocks are potentially difficult samples on which to apply RUS, because of their high acoustic attenuation low Q, inhomogeneity, anisotropy, and the difficulty preparing suitable samples. In preliminary measurements, we have analyzed a variety of rock types to determine optimal sample sizes and aspect ratios, the minimum number of resonances necessary for obtaining an accurate inversion, the sensitivity of RUS to anisotropy in rock samples, and the precision of measurements on samples of varying sizes and aspect ratios. Assuming isotropy, we have found that RUS provides reliable results for relatively high Q materials such as basalt, primarily because a large number of resonance frequencies can be accurately determined.

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  • Geology, Geochemistry and Mineralogy
  • Acoustics
  • Mechanics

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