Effect of Dislocations on Polycrystal Anelasticity Inferred From In Situ Forced Oscillation Test

To understand the effect of dislocations on the velocity and attenuation of seismic waves, the anelasticity of polycrystalline samples was measured in situ during dislocation creep. We used polycrystalline borneol as a rock analog. Because the effects of grain boundary mechanism on the anelastic properties of this material are well known, dislocation effect can be detected as a deviation from them. We developed a new experimental apparatus and conducted the forced oscillation tests continuously on the sample deforming under various creep stresses ranging from diffusion to dislocation creep regimes. The testing frequency was mostly fixed at 5 Hz, but was sometimes scanned from 16 to 0.5 Hz. When the creep stress was higher than 2 MPa, the dominant deformation mechanism changed from grain boundary diffusion creep to dislocation creep. However, modulus reduction was not observed, indicating that dislocations significantly affected creep, but did not affect anelasticity. The different effects of dislocations on creep and anelasticity were explained in terms of the viscous resistance to dislocation motion.