Active Sourced Wavefield Modeling for Layered Half-Space

Traditional free vibration-based forward models generate theoretical dispersion curves under the assumption of planar waves, neglecting the influence of the actual source-receiver configuration. The 2D/3D discretization-based numerical wavefield modeling approaches can mimic real field scenarios considering active source-receiver information. However, numerical methods are computationally inefficient. This study introduces an active sourced semianalytical wavefield modeling approach for laterally homogeneous horizontally stratified media, incorporating source-receiver data acquisition layouts. The method considers a cylindrically spreading wavefield described by the Hankel function instead of the planar wave assumption. The approach considers both propagating waves characterized by real wavenumbers and decaying waves with complex wavenumbers, allowing for the calculation of surface displacements in both the far and near fields. The proposed model captures the complete wavefield, including source-offset effects and leaky waves, while maintaining computational efficiency comparable to any free vibration-based approaches. The method entails solving the eigenvalue problem constructed through the higher-order thin-layer method. Subsequently, it calculates the frequency domain vertical and radial surface responses at any desired location in space generated by a vertically positioned active source. The proposed method's overall performance is investigated on diverse subsurface profiles, including regularly dispersive media, low-velocity layer models, and a field cross-hole model. The Rayleigh wave's vertical and radial component dispersion images obtained from the proposed method are validated against the numerical approach. The proposed method is at least two orders of magnitude faster than the numerical approach. Notably, it addresses mode misidentification issues arising from modal osculation at low frequencies and effectively captures the smooth transition of modal energy from fundamental modes to higher modes. Note that the present method is limited to laterally homogeneous media. However, this method provides a valuable tool for advancing the accuracy and efficiency of active surface wave methods in various engineering applications.