Establishing Confidence in Surface Wave Determined Soil Profiles

Abstract

This is an author-produced, peer-reviewed version of this article. The final, definitive version of this document can be found online at GeoRisk 2011: Geotechnical Risk Assessment and Management (GSP 224) ABSTRACTSurface waves can be used to determine the shear velocity profile from the ground surface to some depth limited by the spectral band of the seismic source. A number of factors influence the uncertainties of the determined profile. The field acquisition factors include the deployment geometry of geophones, the spectral characteristics of the geophones, recording instruments, and seismic source. A key data processing factor is the determination of a dispersion curve from the field recordings. Finally, there are important choices in conducting the inversion of the dispersion curve which leads to the final soil profile. Even if the field factors and acquired data are fixed, determination of the dispersion and the inversion decisions will have a strong influence on the final result. Different engineers will make different decisions, and a range of soil profiles can be expected. Assessment of this variability was the goal of the Surface Wave Benchmark Study sponsored by the Geophysical Engineering Committee of ASCE. Participants were invited to analyze as little or as much of the data as they wished. This paper documents one participant's analysis of a selected set of the data taken at a single location. A key finding documents how a lack of low frequency content limits the maximum depth for which one can have confidence in the soil profile.

Nonperturbational surface-wave inversion: A Dix-type relation for surface waves

“…We plot the inversion result in Figure 5e along with the depth profile obtained by Michaels (2011) using standard, iterative phase-velocity inversion. As can be seen, the Dix-type relation is able to recover several of the same features as the result from Michaels (2011).…”

“…To demonstrate that the Dix-type relation is capable of generating accurate velocity profiles in the near surface, we have processed a benchmark data set from the National Geotechnical Experimentation Site (NGES) at Texas A&M University (Michaels, 2011). These data were provided to the community by the American Society of Civil Engineers (ASCE) in 2010 to test surface-wave inversion methods.…”

Uncertainty in a Geophysical Survey for a Bridge Foundation Design

“…The final, definitive version of this document can be found online at Surface Waves: Air Gun Source The air gun sourced surface wave data were inverted for soil profile S-wave velocities. A discussion on the inversion method may be found in Michaels (2011). Continuing with the sample from SP15 on the island, the data of Figure 5B were inverted to a S-wave velocity profile (see Figure 6B).…”

Analyst A: Alternatives in Analysis of the UTexas1 Surface Wave Dataset

“…Inversion of the composite dispersion curve was done employing a 1-D-gradational soil profile in which the objects of the inversion are control points whose depth and shear-wave velocity assignment may vary. The reader is referred to Michaels (2011) for another example of this representation.…”