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Scientific Investigations Report 2005–5012
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S-Wave Refraction Survey of Alluvial Aggregate

By Karl J. Ellefsen, Gary J. Tuttle, Jackie M. Williams, and Jeffrey E. Lucius

This survey was part of a Cooperative Research and Development Agreement between the U.S. Geological Survey and the Lafarge Corporation

thumbnail image of Yampa River Valley

An S-wave refraction survey was conducted in the Yampa River valley near Steamboat Springs, Colo., to determine how well this method could map alluvium, a major source of construction aggregate. At the field site, about 1 m of soil overlaid 8 m of alluvium that, in turn, overlaid sedimentary bedrock. The traveltimes of the direct and refracted S-waves were used to construct velocity cross sections whose various regions were directly related to the soil, alluvium, and bedrock. The cross sections were constrained to match geologic logs that were developed from drill-hole data. This constraint minimized the ambiguity in estimates of the thickness and the velocity of the alluvium, an ambiguity that is inherent to the S-wave refraction method. In the cross sections, the estimated S-wave velocity of the alluvium changed in the horizontal direction, and these changes were attributed to changes in composition of the alluvium. The estimated S-wave velocity of the alluvium was practically constant in the vertical direction, indicating that the fine layering observed in the geologic logs could not be detected. The S-wave refraction survey, in conjunction with independent information such as geologic logs, was found to be suitable for mapping the thickness of the alluvium.

Version 1.0

Posted June 2005

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Aerial photograph of field site.
Geologic Logs for drill holes.
Seismic cross sections for field site.
Data for each seismic spread.
OFR-02-0176: pick_sw -- A program for interactive picking of S-wave refraction data logo