HR: 1340h
AN: MR33A-0157    [Abstracts]
TI: Effects of Shock-induced Cracks on the Ultrasonic Velocity and Attenuation in Rock
AU: * Ai, H
EM: ahr@gps.caltech.edu
AF: Caltech, Caltech, 252-21, Pasadena, CA 91125 United States
AB: Measurements for compressional wave velocity and attenuation coefficients of 1-cm cubes were conducted. Samples were taken at various radii and depths beneath the impact crater on a 20x20x15 cm San Marcos granite block, impacted by a lead bullet at velocity of 1200 m/s. Damage parameters of the cubes are calculated from the measured pre- and post-impact P wave velocities, V_p0 and V_p, by D = 1-(V{p}/V{p0})², and crack density is inverted from the measured P wave velocities using the theory of Kachanov [1993] with the assumption of the average aspect ratio of cracks being constant. Anisotropic orientation of cracks is observed from the ultrasonic velocity and attenuation measurement. Whereas P wave velocity and the normalized distance from the impact point follow an exponential decay relation, the damage parameter, crack density, and attenuation coefficient are expressed by a power-law decay relation with the distance. The damage parameter and attenuation coefficients are approximately linearly related. Attenuation coefficient is found to be a more useful parameter than elastic velocity in describing the anisotropic orientation of cracks.
DE: 5100 PHYSICAL PROPERTIES OF ROCKS
DE: 5104 Fracture and flow
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005