Chapter 28: Application of the Spatial-autocorrelation Microtremor-array Method for Characterizing S-wave Velocity in the Upper 300 m of Salt Lake Valley, Utah
William J. Stephenson, Jack K. Odum, 2010. "Application of the Spatial-autocorrelation Microtremor-array Method for Characterizing S-wave Velocity in the Upper 300 m of Salt Lake Valley, Utah", Advances in Near-surface Seismology and Ground-penetrating Radar, Richard D. Miller, John H. Bradford, Klaus Holliger
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Spatial-autocorrelation (SPAC) microtremor-array data acquired at 14 sites in Salt Lake Valley, Utah, characterize S-wave velocities to depths as great as 300 m. Three data sets acquired at each site were analyzed simultaneously using equilateral triangular arrays with sensors deployed at 33.3-m, 100-m, and 300-m separation. Of the 14 sites, eight were within 1.2 km of active-source (vibroseis) body- and surface-wave acquisition sites, and two were within 0.7 km of boreholes logged for S-wave velocity (VS) to at least 50-m depth. A comparison to these existing active-source and borehole models indicates that these SPAC VS results typically differ by less than 10% on average to 100-m depth. At a majority of the investigation sites, SPAC modeling results can be interpreted confidently to more than 150-m depth. Linear ground-motion amplification spectra derived from these profiles of VS versus depth suggest amplification factors of more than three can occur at frequencies in the band of 0.5 to 4 Hz from the base of unconsolidated sediments in the upper 300 m.
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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.