Relaxation Spectra of Wave Attenuation in Single-crystal Quartz and Sandstone

The experiments have been conducted to investigate the effect of strain amplitude on the compressional and shear wave velocity, Vp, Vs, attenuation, Qp-1, Qs-1 and dynamic Poisson’s ratio, Vd in quartz samples of three types: the intact quartz, fractured quartz and smoky quartz and sandstone. The measurements were performed using the reflection method on a pulse frequency of 1 MHz with changing strain in the range 0.3 < e < 2.0 m-strain under a confining pressure of 10 MPa and at ambient temperature. The anomalous inelastic behavior occurs owing to the change in value of the strain-amplitude. The evident strain-amplitude effect takes place only on Q-1, Vd - parameters. P- and S- wave velocities are little sensitive (~1%) to changing strain amplitude. The greatest decrease in Q-1 (to 16%) takes place in the smoky quartz whereas in other quartz, effect is practically absent. Amplitude variation leads to the modification of relaxation spectrum. The broadening of peaks width with increasing strain amplitude that takes place for P- wave attenuation in the smoky quartz. Such behavior of attenuation can be explained by a joint action of viscoelastic and microplastic mechanisms in the material with defects.