Diagnostics of the acoustic properties of unconsolidated media under natural conditions

Results of experimental studies carried out at the Bezvodnoe test area in 2005 and 2006 are presented. The goal of the studies is to investigate the potentialities of vibration diagnostics of the surface layers of soil under natural conditions. The most attention is given to the problem of measuring the shear modulus of soil and determining the power of seismic acoustic radiation with the help of an impedance method. The results obtained testify to the high sensitivity of the impedance method soil diagnostics and to the possibility of monitoring the variations of soil properties. Sources of nonlinear distortions and the problem of stability of radiation characteristics are also considered. A comparison with theoretical estimates is performed. It confirmed a special role of the contact region as the major source of radiation signal distortions. The results of the study are important for seismoacoustic investigation of the structure of natural media under natural conditions.     

Nonlinear acoustic spectroscopy of carbonate rocks

The paper presents the results of experimental research into the nonlinear acoustic properties of carbonate rocks depending on saturation. The linear acoustic properties of the same sample depending on saturation were presented earlier in Physical Acoustics. The previously obtained data point to the isotropy of the material, which makes it possible to restrict analysis to only two vibration modes. Responses for finite deformations were measured for the longitudinal and shear modes of an isotropic sample, which made it possible to analyze the nonlinear properties of macroscopic deformations with a change in volume and pure displacement. A heretofore unknown feature of the response was revealed for finite deformation values; it is related to the occurrence of a jumplike transition from classical nonlinearity to a hysteresis type of nonlinearity. As well, the deformation amplitude corresponding to the transition depends on fluid saturation. We studied the slow relaxation that occurs after long-term excitation of a sample with a deformation amplitude on the order of 10^?6. Data are presented on relaxation for deformation from pure displacement and deformation with a change in volume, which made it possible to isolate features related to the type of deformation and to compare the obtained data with the earlier published theoretical model. These data are compared with the results of other research groups.