Experiments of elastic wave propagation through stacks of thin plates

Abstract

Ultrasonic experiments were performed to investigate the elastic behavior of systems of closely spaced (relative to wavelength) parallel linear interfaces [M. Schoenberg, J. Acoust. Soc. Am. 68, 1516–1521 (1980)], which have been used to model fractured media. The sample was composed of lucite plates with roughened surfaces and pressed together with controlled stress normal to the plates. Wavelengths were of the order of ten plate thicknesses. Compressional and shear velocities were measured normal and parallel to the plates. Quasicompressional and quasishear velocities were measured at a variety of oblique angles. The higher the confining stress, the less compliant the interfaces were, and the closer the medium behavior was to isotropic. According to the long wavelength linear slip model [M. Schoenberg and J. Douma, Geophys. Prosp. 36, 571–590 (1988)], the medium is transversely isotropic with certain constraints on the moduli and is characterized with four independent parameters: the Lamé constants of the background as well as two interface compliances. Data obtained at a variety of confining stresses agree very well with this model. Experiments were also conducted with some of the interfaces saturated with honey; the overall compliances measured were consistent with the mixing law derived from the linear slip model.