Experimental Investigation of Seismic Velocity Dispersion in Cracked Crystalline Rock

• Author / Creator

  Schijns, Heather M. E.

• Seismic velocity dispersion in crystalline rock is investigated through experimental measurements on two natural quartzite specimens. The quartzites are thermally damaged to induce low aspect ratio cracks and the shear and Young’s moduli are measured across a range of effective pressures, from 10-150 MPa, under dry, argon saturated and water saturated conditions. High frequency measurements (1 MHz) are made using the standard pulse transmission technique, while low frequency (0.01-1 Hz) shear measurements are made by forced torsional oscillation with the Australian National University apparatus. Low frequency Young’s modulus measurements are made using the innovative forced flexural method. Dry moduli do not show significant differences between low and high frequency results. Stiffening of argon saturated moduli is observed at high frequency, however, the low amplitude means it is not possible to confirm dispersion when compared to low frequency measurements. Both water saturated specimens display substantial dispersion, particularly at lower effective pressures when crack porosity is higher. Experimental results from one of the quartzites are compared to Gassmann and a combination of Biot and squirt flow elastic theories. Experimental low frequency shear moduli are invariant to pore fluid saturation as predicted by Gassmann, and Biot and squirt flow theory accurately describes the high frequency argon saturated shear modulus of the quartzite. Neither theory, however, adequately describes the behaviour of the Young’s modulus. The high frequency water saturated shear and Young’s moduli of the quartzites are substantially stiffer than is predicted by theory.

• Subjects / Keywords

  • Metamorphic rock
  • Shear modulus
  • Cracked rock
  • Velocity dispersion
  • Young's modulus
  • Ultrasonic
  • Seismic
  • Viscoelasticity

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R38W3898N

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.