Estimation of near‐surface shear‐wave velocity by inversion of Love waves

Abstract

Love waves are a type of surface wave formed by the constructive interference of multiple reflections of SH waves in the Earth's crust and upper mantle. Unlike Rayleigh waves, the dispersion of Love waves is independent of P‐wave velocity. Love‐wave phase velocity of a layered earth model is a function of frequency and three layer parameters: SH‐wave velocity, density, and thickness of layers. In theory, fewer unknowns make the inversion of Love waves more stable and reduce the degree of nonuniqueness compared to Rayleigh waves. There has been much less attention on utilizing Love waves than on Rayleigh waves in the near‐surface community, in significant part because acquiring SH‐wave data is not as easy as acquiring vertical‐component data. With improvements in data acquisition techniques, acquiring SH‐wave data is getting easier. Analyzing SH‐wave data using Love‐wave inversion for near‐surface applications may attract as much attention as Rayleigh‐wave inversion because it provides SH‐wave velocities that are critical for S‐wave and anisotropy analysis. In this paper, reprocessing SH‐refraction data acquired in two U.S. states to isolate Love waves and carrying out Love‐wave inversion has produced encouraging results in terms of sharp dispersion images and stable inversion; this suggests that we could benefit from a revisit to existing SH‐refraction data to extract Love waves for determining S‐wave velocities from Love‐wave inversion.