Every expert tends to exaggerate the importance of his special field in proportion to the length of time spent on it and to the difficulties overcome.— Max Planck (1858–1947)
In this chapter, we consider seismic-velocity anisotropy and how it depends on frequency. We restrict our comments to vertical transverse isotropy (VTI), a kind of anisotropy that represents velocity variation with respect to the vertical axis in a horizontally layered earth (Backus, 1962; Thomsen, 1986; Berryman et al., 1999; Bakulin, 2003). Laboratory-scale rock samples can show significant velocity anisotropy. When it occurs on this fine scale, we call this intrinsic anisotropy to distinguish it from apparent anisotropy, which results in layered media (Figure 1). Intrinsic anisotropy is not a function of frequency, and it represents a rock property such as density or bulk modulus.
Figures & Tables
Elements of Seismic Dispersion: A Somewhat Practical Guide to Frequency-dependent Phenomena (SEG Distinguished Instructor Series No. 15) covers selected effects encountered in the acquisition, processing, and interpretation of reflectionseismic data. The material, based on the 2012 SEG Distinguished Instructor Short Course, shows how those phenomena arise, how they can be characterized, and the important information they contain. The text shows how spectral decomposition and time-frequency methods have led to improved understanding and use of nonlinear harmonics, near-surface guided waves, layer-induced anisotropy, velocity dispersion and attenuation, interference, and Biot reflection. Accessible discussion is augmented by examples, figures, and references to primary literature for further study. This book will interest technical managers and those who work in acquisition, processing, and interpretation of seismic data. (DISC on DVD, 761A, is also available.)