| Popis: |
An inconsistency in experimental stress-strain data for attenuation determinations is investigated. Attenuation (1/Q) calculated from the integrated areas of plotted hysteresis loops depend on the definition of maximum strain energy. If maximum strain energy is taken as the entire area under the loading segment of the hysteresis loop, the resulting 1/Q are approximately 4x < the 1/Q from the phase angle phi measured between cycled stress and strain 1/Q = tan phi. This inconsistency is resolved by locating the origin of zero stress and strain at the center of the hysteresis loop, regardless of the absolute sign of stresses and strains, and calculating the maximum strain energy during one cycle relative to that origin. Attenuation calculated from the ratio of hysteresis loop areas must be carefully interpreted before application to seismic wave propagation. Attenuation and dynamic moduli measurements on intact Sierra White granite samples were performed using 3 experimental techniques: hysteresis loop, resonant bar, and ultrasonic spectral ratio. Extensional attenuations and Young's moduli were measured at 0.1 Hz with the hysteresis loop and between 10 and 210 kHz with the resonant bar techniques. Ultrasonic P and S wave velocities and spectral ratio compressional and shear attenuations were measured in the 100-200 kHz and 0.6-1.1 MHz frequency bands, then converted into comparable extensional attenuations and Young's moduli. (EDC) |
