CHARACTERIZING THE STIFFNESS OF A SHALLOW BEDROCK SITE USING THE MULTICHANNEL ANALYSIS OF SURFACE WAVES (MASW) METHOD WITH RAYLEIGH AND LOVE WAVES

Abstract

The Multichannel Analysis of Surface Waves (MASW) method continues to increase in popularity as a tool to characterize subsurface stiffness for geotechnical engineering purposes, particularly in cases where seismic site characterization is important. MASW is commonly performed using vertical impacts on the ground surface to generate Rayleigh waves (i.e., MASRW). The dispersive behavior of the Rayleigh wave is then imaged by transforming the raw waveforms from the time-space domain into the frequency-phase velocity domain. A characteristic dispersion curve for the site is selected based on examining the pattern of energy accumulation in the dispersion image. An inversion algorithm is then implemented to locate the most probable subsurface stiffness profile that caused the measured dispersion curve. While much research has been devoted to MASRW, horizontally-polarized Love waves have seen limited use in MASW investigations (MASLW), despite evidence to support some advantages in their implementation. In this study, MASW was performed using both Rayleigh and Love waves to characterize conditions at the same shallow bedrock site. To allow for a direct comparison between the results of Rayleigh waves and Love waves, the survey lines for both MASW tests were located in exactly the same position. Generally, the subsurface stiffness profiles resulting from inversion of the MASRW and MASLW dispersion curves agreed reasonably well. However, there were some subtle differences in interpretation of the dispersion images. This paper summarizes field conditions and testing configuration, followed by a discussion of data analysis and interpretation.