Establishing Confidence in Surface Wave Determined Soil Profiles

Surface 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.