Comparative analysis on sensitivities of Love and Rayleigh waves

Love waves are generally less employed than Rayleigh waves in near-surface shear-wave (S-wave) investigations because acquiring S-wave data is not as easy as acquiring P-wave data. The dispersion of Love waves, however, is independent of Poisson’s ratio. This character can be the valuable basis to improve the S-wave velocity imaging. The sensitivity of earth properties to the dispersion curve of surface waves (Love and Rayleigh waves) is fundamental to determining the accuracy of an S-wave velocity model. By analyzing sensitivities to the dispersion curves of Love and Rayleigh waves comparatively, modes and frequency ranges of surface-wave dispersion data can be chosen appropriately during the inverse procedure, which helps to improve the accuracy of S-wave velocity profiles. For layered earth models, the sensitivities are defined by the percentage changes instead of partial derivatives. Analysis based on a regular model and an irregular model shows that, for earth properties such as the S-wave velocity and the thickness of each layer, Love waves are more sensitive than Rayleigh waves in most frequency ranges. Although the low velocity layer can dramatically influence the sensitivities of both Love and Rayleigh waves, the sensitivity of Love-wave to changes in S-wave velocity is much higher at low frequencies. Furthermore, Love waves are more sensitive than Rayleigh waves to the change of Swave velocity in half-space. That means Love waves can recovery the S-wave velocity of the half-space more easily. All these indicate that the joint inversion of multimode Love waves with Rayleigh waves would obtain a more accurate S-wave profile.