Accession Number : ADA131983

Title :   Effects of Microstructure and Pore Fluids on the Acoustic Properties of Granular Materials.

Descriptive Note : Final rept. Feb 82-Jan 83,


Personal Author(s) : Nur,Amos

PDF Url : ADA131983

Report Date : 08 Aug 1983

Pagination or Media Count : 133

Abstract : The purpose of this paper is to explain the effects of granular microstructure and effective pressure on low frequency velocities in water saturated granular materials. Micromechanical models are developed for the dry frame moduli. Unambiguous predictions are stated explicity for Vp, Vs, and Vp/Vs as a function of grain characteristics, porosity, and effective pressure. The predictions of each step are systematically tested by laboratory measurements of Vp and Vs in glass beads and quartz sands. Signal velocities were measured by an ultrasonic pilse transmission technique at frequencies approx. 200 kHz. All measurements were obtained in vacuum dry (10 micrometers) samples. Although signal velocities are generally equivalent to group velocities in dissipative media, we are aware of no evidence for dispersion in vacuum dry samples of similar composition. Errors in the moduli are expected to be less than 5%. These moduli are in fact frequency-independent, dry frame moduli and as such are expected to apply across seismic, acoustic, and ultrasonic frequency ranges.

Descriptors :   *Sediments, *Granules, *Ocean bottom, *Acoustic properties, *Porosity, Fluids, Geoacoustics, Geophysics, Dissipation, Measurement, Mathematical prediction, Grain size, Sand, Modulus of elasticity, Microstructure, Ultrasonic frequencies, Depth, Velocity

Subject Categories : Physical and Dynamic Oceanography
      Geology, Geochemistry and Mineralogy

Distribution Statement : APPROVED FOR PUBLIC RELEASE