Intramethod Variability in ReMi Dispersion Measurements and Vs Estimates at Shallow Bedrock Sites

The refraction microtremor (ReMi) method uses a linear array of receivers to record passive noise stress waves, thereby negating the need for a strong active source such as those typically employed in other linear-array surface-wave methods. The simplicity of such an approach is very appealing; however, there is a potential for significant uncertainty in shear-wave velocity (Vs) estimates obtained in this manner because much is unknown about the seismic wavefield that is being sampled. This article examines intramethod variability in ReMi dispersion measurements and Vs estimates at shallow bedrock sites. The focus is not on evaluating whether ReMi measurements yielded the “true” Vs profiles for the study sites, but rather on evaluating how the dispersion curves and Vs profiles at the sites were affected by variations in the seismic wavefield sampled by a linear array of receivers. It was found that changes in the sampled seismic wavefield, obtained through employing various array orientations at a site and inclusion of actively generated noise, resulted in significant variations in the ReMi-obtained dispersion curves and Vs profiles at the study sites, thus yielding a high level of intramethod variability for a given test location.