Derecke Palmer, 2010. "Characterizing the Near Surface with Detailed Refraction Attributes", Advances in Near-surface Seismology and Ground-penetrating Radar, Richard D. Miller, John H. Bradford, Klaus Holliger
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The tomographic inversion of near-surface seismic-refraction traveltime data is fundamentally nonunique. It is possible to generate tomograms, which range from the geologically improbable to the very detailed, all of which accurately satisfy the traveltime data. A comparison of the starting models with the final tomograms demonstrates that refraction tomography usually does not improve lateral resolution significantly. Therefore, if important geotechnical features are to be delineated, it is essential that they be included in the starting model, especially zones with low seismic velocities. Suitable detailed starting models for both traveltime and full-waveform inversion can be derived using a suite of parameters, generally known as seismic attributes. Refraction attributes can be computed readily from all near-surface seismic-refraction traveltimes, amplitudes, and waveforms, using the generalized reciprocal method (GRM) and the refraction convolution section (RCS). Furthermore, refraction attributes can be employed as a priori information to resolve nonuniqueness before the acquisition of any a posteriori information, such as borehole or other geophysical data. Narrow and wide zones with low seismic velocities are delineated with detailed attribute-based tomograms and are consistent with other refraction attributes derived from head-wave amplitudes and the RCS. Those zones are not detected with refraction tomograms which use low-resolution starting models, such as the smooth vertical velocity gradient. Additional models of the near surface, such as scaled density ratios and the P-wave modulus, can be computed from combinations of the refraction attributes. The use of a suite of attributes and combined attributes as well as the seismic velocity facilitates derivation of more comprehensive quantitative models of the near surface and thus more effective integration of seismic with borehole and other geotechnical data, using either multivariate geostatistics or full-waveform inversion.
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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.