Chapter 9: Analysis of the Velocity Dispersion and Attenuation Behavior of Multifrequency Sonic Logs
Ludovic Baron, Klaus Holliger, 2010. "Analysis of the Velocity Dispersion and Attenuation Behavior of Multifrequency Sonic Logs", Advances in Near-surface Seismology and Ground-penetrating Radar, Richard D. Miller, John H. Bradford, Klaus Holliger
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Modern slim-hole sonic-logging tools designed for surficial environmental and engineering applications allow for measurements of the phase velocity and the attenuation of P-waves at multiple emitter frequencies over a bandwidth covering five to 10 octaves. One can explore the possibility of estimating the permeability of saturated surficial alluvial deposits based on the poroelastic interpretation of the velocity dispersion and frequency-dependent attenuation of such broadband sonic-log data. Methodological considerations indicate that for saturated, unconsolidated sediments in the fine silt to coarse sand range and typical nominal emitter frequencies ranging from approximately 1 to 30 kHz, the observable P-wave velocity dispersion should be sufficiently pronounced to allow for reliable first-order estimations of the underlying permeability structure based on the theoretical foundation of poroelastic seismic-wave propagation. Theoretical predictions also suggest that the frequency-dependent attenuation behavior should show a distinct peak and detectable variations for the entire range of unconsolidated lithologies. With regard to the P-wave velocity dispersion, results indicate that the classical framework of poroelasticity allows for obtaining first-order estimates of the permeability of unconsolidated clastic sediments with granulometric characteristics ranging between fine silts and coarse sands. The results of attenuation measurements are more difficult to interpret because the inferred attenuation values are systematically higher than the theoretically predicted ones, and the form of their dependence on frequency is variable and is only partially consistent with theoretical expectations.
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Near-surface seismology and ground-penetrating radar (GPR) have enjoyed success and increasing popularity among a wide range of geophysicists, engineers, and hydrologists since their emergence in the latter half of the twentieth century. With the common ground shared by near-surface seismology and GPR, their significant upside potential, and rapid developments in the methods, a book bringing together the most current trends in research and applications of both is fitting and timely. Conceptually, near-surface seismology and GPR are remarkably similar, and they share a range of attributes and compatibilities that provides opportunities to integrate processing and interpretation workflows, which makes them a perfect pair to share pages in a book.
With growth in numbers and professional emphasis have come sections, focus groups, and even professional societies specifically promoting near-surface geophysics. The emergence of near-surface geophysics groups, beginning in the late 1990s and extending into the early twenty-first century, has fueled a diversity of opportunities for professional collaborations. A range of workshops and shared publications has been the fruit of collaborative efforts. The near-surface community continues to extend and develop methods and approaches necessary to satisfy increasing demands in some of the socioeconomically pertinent disciplines such as civil and environmental engineering and hydrology. This book represents the first formal cooperative effort undertaken by the near-surface communities of the Society of Exploration Geophysicists, the American Geophysical Union, and the Environmental and Engineering Geophysical Society.