Higher-order thin layer method (HTLM) based wavefield modeling approach

Traditional free vibration-based forward modeling approaches provide only the theoretical modal solution that lacks information regarding modal amplitudes. Moreover, they ignore the influence of source-receiver layout on the wavefield. Numerical wavefield modeling approaches can generate a dispersion spectrum mimicking the actual field test; however, numerical methods are not efficient in terms of computational time and produce numerical artifacts. Furthermore, they can be contaminated with leaky waves for soil strata with a high Poisson's ratio. This study presents a new wavefield modeling approach for developing full dispersion spectra of stratified media incorporating source-receiver configuration. The proposed method calculates the theoretical modal amplitude using the higher-order thin layer method and determines the vertical displacement responses at specified virtual receiver positions in the frequency-space domain. Afterward, it searches for spectral values at each frequency over a broad range of trial phase velocities to create a full dispersion spectrum. The accuracy and computational efficacy of the present method are demonstrated on different soil profiles adopted from literature, including normally dispersive media, irregularly dispersive media with high-velocity contrast, and a crustal level model. Results indicate the proposed approach can clearly distinguish the relative spectral amplitude of each mode and dominant dispersion trend. Calculated seismograms and dispersion images are compared with the existing 2D staggered grid finite difference method. Although both methods yield similar results, the current method is at least two orders (x102) faster than the staggered grid finite difference method. Unlike numerical approaches, the proposed method does not require additional computational resources to model materials with a high Poisson's ratio. Furthermore, it minimizes the contamination of leaky waves in the dispersion spectrum when modeling a high Poisson's ratio. The proposed method does not produce any numerical artifacts and can be used to generate accurate synthetic seismograms as well as dispersion spectra. In addition, the proposed wavefield modeling approach can be effectively used to develop an accurate and faster inversion scheme by including the entire dispersion spectrum.