Semi‐Analytical Modeling of Love Wave Propagation in Heterogeneous Fractional Viscoelastic Media With Slip Interfaces: Applications to Inversion of Field Data and Subsurface Characterization

ABSTRACT A fractional viscoelastic Love‐wave dispersion model is developed for a two‐layered heterogeneous medium with slip interfaces. In this formulation, the top layer is modeled with depth‐dependent heterogeneity in shear modulus and density, characterized with independent rates of heterogeneity and nonlinearity parameters. This configuration allows for a more realistic representation of near‐surface geological complexity. In comparison, the second layer is assigned a milder linear heterogeneity, while the half‐space is assumed to be homogeneous. This independent treatment of material heterogeneity in the top layer is a key novelty of this study, as it relaxes the commonly adopted assumptions in literature of proportional or identical depth‐dependent variations of elastic parameters. Owing to the nonanalytical solution of the corresponding governing equations, a hybrid semi‐analytical/numerical scheme based on Runge–Kutta method is implemented to obtain the dispersion relation. The effectiveness of the proposed model is demonstrated by its application to real dispersion data recorded at a site in Nirsa (India). A Monte‐Carlo‐based inversion is subsequently carried out to recover the subsurface parameters. The inverted shear‐wave profile is found to be consistent with the Rayleigh wave and HVSR joint inversion reported in the literature and also shows agreement with a Love‐wave inversion for isotropic elastic layered media with bonded interface obtained by the Hv–Inv software. Parameter sensitivity indicates that the near‐surface parameters exert the dominant control on the dispersion behavior, with the most significant variations occurring within the 0–20 Hz band, implying that low‐frequency sensitive geophones are more suitable for exploiting the capabilities of the present model. Overall, a practical tool for interpreting measured dispersion curves is thus provided to the seismological community, while the numerical scheme developed here can directly be applied to general layered wave‐propagation studies involving heterogeneity.