This volume is of particular interest to geophysicists, engineering geologists and geologists who are engaged in the interpretation of seismic measurements on rock engineering and petroleum engineering projects. The treatment is deliberately non-mathem.

Seismic measurements take many forms, and appear to have a universal role in the Earth Sciences. They are the means for most easily and economically interpreting what lies beneath the visible surface. There are huge economic rewards and losses to be made when interpreting the shallow crust or subsurface more, or less accurately, as the case may be.

Much work is presently being done concerning small scale heterogeneities in the earth's crust. These heterogeneities range from pores in sedimentary rocks up to fluctuations in the density and seismic constants of the earth's crust with scale lengths of kilometers. The ability to study and quantify these heterogeneities using seismic methods would be a major advance in the earth sciences. Physical modeling has been shown to be a useful technique for investigating various aspects of wave propagation. In this thesis, two physical modeling experiments (one three-dimensional and one two-dimensional) are used to investigate the scattering of seismic waves from small scale heterogeneities and the changes in seismic velocity and apparent attenuation resulting from this scattering. The effects of both isotropic and anisotropic scattering on velocity and apparent attenuation are calculated. These experimental results are compared to theoretical results. The theory used for isotropic scattering for the three-dimensional experiment is a modified version of Wu's single scattering theory, where instead of calculating the scattering for a single scatterer using the Born approximation, the exact results for scattering from a cylindrical shape are used. While the results for compressional waves and both components of shear waves compare reasonably well for small scatterer volume fractions, at larger scatterer volume fractions, where the need for multiple scattering is more likely, the results for all waves do not compare as well. Many theories used to test anisotropic scattering predict changes in velocity rather than changes in apparent attenuation. The velocity changes are used primarily in this work due to geometrical focusing by a seismic lens that biases the amplitudes (and hence the estimates of apparent attenuation) at low frequencies where most theories predict apparent attenuation. Velocities are calculated from the data using travel times and low frequency phase shifts for the compressional waves and for one component of the shear waves measured in this two-dimensional experiment. Theories that are used to predict compressional and shear wave velocities for both isotropic and anisotropic scatterers are based on a fractional volume method (isotropic), two crack methods (isotropic and anisotropic), and a finely layered method (anisotropic). The isotropic experimental results have much larger, non-linear changes in the velocities than do the isotropic theoretical results. The anisotropic experimental results have similar shapes to both theoretical anisotropic methods for compressional waves and to the theoretical anisotropic crack method for shear waves. Attenuation is computed using log spectral ratios and compares as well with the theoretical results as can be expected within the limits set. A method using anisotropic apparent attenuation to help quantify the scatterers is developed for use with field data.

Understanding Seismic Anisotropy in Exploration and Exploitation (second edition) by Leon Thomsen is designed to show you how to recognize the effects of anisotropy in your data and to provide you with the intuitive concepts that you will need to analyze it. Since its original publication in 2002, seismic anisotropy has become a mainstream topic in exploration geophysics. With the emergence of the shale resource play, the issues of seismic anisotropy have become central, because all shales are seismically anisotropic, whether fractured or not. With the advent of wide-azimuth surveying, it has become apparent that most rocks are azimuthally anisotropic, with P-wave velocities and P-AVO gradients varying with source-receiver azimuth. What this means is that analysis of such data with narrow-azimuth algorithms and concepts will necessarily fail to get the most out of this expensively acquired data. The issues include not only seismic wave propagation, but also seismic rock physics. Isotropic concepts including velocity, Young’s modulus, and Poisson’s ratio have no place in the discussion of anisotropic rocks, unless qualified in some directional way (e.g., vertical Young’s modulus). Likewise, fluid substitution in anisotropic rocks, using the isotropic Biot/Gassmann formula, leads to formal errors, because the bulk modulus does not appear, in a natural way, within the anisotropic P-wave velocity. This updated edition is now current as of 2014.