Chapter 7: Laboratory techniques for determining seismic velocities and attenuations, with applications to the continental lithosphere
Published:January 01, 1989
Nikolas I. Christensen, William W. Wepfer, 1989. "Chapter 7: Laboratory techniques for determining seismic velocities and attenuations, with applications to the continental lithosphere", Geophysical Framework of the Continental United States, L. C. Pakiser, Walter D. Mooney
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The interpretation of seismic data is dependent on laboratory investigations of the elastic and anelastic properties of rocks. Important constraints on the composition of the continental lithosphere have been provided by comparing laboratory and field determined seismic velocities. Much less is known about the nature of attenuation in the crust and upper mantle. Furthermore, laboratory attenuations have not been studied as extensively as velocities. Nevertheless, the utilization of laboratory attenuation measurements to tie seismic data to the anelastic properties of rocks is promising. Laboratory velocity measurements are usually obtained with a pulse transmission technique, whereas measurements of seismic attenuation in the laboratory are determined by resonance techniques, ultrasonic pulse propagation, stress-strain hysteresis loop analysis, and torsion-pendulum oscillations. Velocities in rocks increase with increasing pressure, whereas attenuations decrease. The greatest changes, which occur over the first 100 MPa, are attributed to the closure of microcracks. Velocities decrease with increasing temperature. At temperatures below the boiling point of a rock’s volatiles, attenuation appears to be temperature-independent, and above this, attenuation decreases. Increasing pore pressure, which lowers compressional and shear-wave velocities in sedimentary and crystalline rocks, produces a marked increase in Poisson’s ratio. The influence of pore pressure on attenuation in crystalline rocks is at present poorly understood. At high pressures, velocities are primarily a function of mineralogy, whereas mineralogy may only be of secondary importance for attenuation. Anisotropy, which is common in velocities of many crustal and upper-mantle rocks, may also be an important property of rock attenuation. Attenuation may vary significantly with frequency for saturated rocks, but appears to be frequency-independent for dry rocks. The effect of frequency on velocity is minimal.