Comparative analysis on penetrating depth of high-frequency Rayleigh and Love waves

• Penetrating depth of surface waves is a critical factor in geophysical investigation.
• Sensitivity analysis provides a relationship between wavelength and penetrating depth.
• The fundamental mode of Rayleigh waves can “see” 1.3–1.4 times deeper than Love waves.
• Higher-modes of the two waves penetrate the same depth for a given wavelength.
• Both waves are insensitive to those of layers under an HVL or LVL and the HVL itself.

A particular mode of surface waves possesses a unique phase velocity for each wavelength. Different wavelengths primarily reflect geological information at different depths. In practice, knowledge on penetrating depth of surface wave data is extremely important to define an earth model for inverting their phase velocities. For a layered model, we use the Jacobian matrix to investigate the relationship between wavelength and penetrating depth. The results show that a different mode of surface waves is sensitive to a different depth range. No matter for Rayleigh or Love waves, higher mode waves can penetrate deeper than fundamental mode waves do. For a normal model (S-wave velocity increases with depth) and given the same wavelength, the fundamental mode Rayleigh-wave data can “see” 1.3–1.4 times deeper than that of Love waves. In addition, the higher-mode components of the two waves can penetrate the same depth. Our numerical studies based on sensitivity analysis of fundamental mode waves of two kinds of irregular models, HVL (high-velocity-layer model) and LVL (low-velocity-layer model), suggest that both Rayleigh and Love waves are insensitive to the layers beneath an HVL or LVL and the HVL itself. Therefore, wavelengths required for estimating S-wave velocity of these layers are much longer than the normal model.