SIMULTANEOUS RAYLEIGH AND LOVE WAVE GENERATION FOR MASW DATA

Abstract

Multichannel Analysis of Surface Waves (MASW) has become an increasingly popular geophysical method for characterizing subsurface properties. During MASW, a linear array of geophones is used to record the motion generated by Rayleigh waves (vertical motion) or Love waves (horizontal motion). The use of Rayleigh waves for MASW has been well-researched and documented. Although less work has been devoted to understanding the full potential of Love waves, previous research efforts have indicated that Love waves present several situational advantages over Rayleigh waves. Rayleigh and Love waves are dispersive, meaning the phase velocity of the waves is frequency-dependent in a vertically heterogeneous medium. Using the data collected from the generation of Rayleigh or Love waves, a dispersion image is created. Dispersion curves are extracted from this image and an inversion process converts the dispersion curve into a shear velocity (VS) profile that is used to estimate soil stiffness. This inversion process is fundamentally nonlinear and ill-posed, without a unique solution. In other words, there are more unknown than known values and multiple “correct” solutions exist. One way in which the issue of solution non-uniqueness can be mitigated is by collecting and analyzing data from both Rayleigh and Love waves. However, Rayleigh and Love waves are typically generated by different impacts on a source – vertical and horizontal strikes, respectively. Therefore, data acquisition time is significantly increased if both Rayleigh and Love wave data is collected. No studies have systematically examined the simultaneous generation of Rayleigh and Love waves for MASW using a single impact on a single source. An angled source capable of producing both Rayleigh and Love waves with a single strike could significantly improve acquisition times of Rayleigh and Love waves and encourage their joint use for MASW applications. This research effort aims to explore optimal techniques for the simultaneous generation of Rayleigh and Love waves and compare the results to traditional MASW techniques.