SEISMIC DAMPING AND CREEP IN THE MANTLE.
BOEING SCIENTIFIC RESEARCH LABS SEATTLE WASH
Pagination or Media Count:
A unified theory of viscosity and viscoelasticity of the molecular-rearrangement type is given in which the two phenomena appear as special cases. The Becker theorem is reviewed with the Becker distribution of relaxances, the distribution function of activation energies is a constant, viscoelastic creep is logarithmic and the specific damping 1Q is frequency insensitive in wide ranges of time and frequency. The vibrating-string theories of dislocation damping in general are not feasible because the mean thermal kinetic energy of the basic mode is smaller by order of magnitude than the Peierls-Nabarro dissipation already for amplitudes equal to the Burgers vector for most materials. Low-amplitude damping is treated as a consequence of the perturbation of the activation energies of thermally activated jumps of dislocation segments by the applied stress since the distribution function of the activation energies is probably close to the Becker distribution, the resulting damping is insensitive to frequency and amplitude and increases steeply with the temperature. The Amontons law of solid friction breaks down at very small amplitudes of displacement, such as those between the walls of small cracks in rocks. The simplest generalization of the Amontons law to include small amplitudes leads to an amplitude- and frequency-independent damping.
- Geology, Geochemistry and Mineralogy
- Solid State Physics