Forward modeling of multichannel Rayleigh wave dispersion curve in laterally inhomogeneous media

Multichannel analysis of surface wave (MASW) method has been one of the effective tools for retrieving near-surface shear-wave velocity. As with other geophysical methods, its forward problem is of great importance to the design of the field survey and the solution of the inversion. Currently, the forward algorithms of surface wave dispersion curve are generally classified into two categories: solution of surface wave eigenproblems in a horizontally layered model, which is time-efficient but difficult to consider lateral variations; and wave equation-based full wavefield simulation, which can theoretically deal with any complicated geological model but requires high computational costs. In this paper, we present a forward algorithm of multichannel Rayleigh wave dispersion curves in laterally inhomogeneous media based on amplitude-normalized beamforming. By analyzing the formula of beamforming, the relationship between the local phase velocity and the phase velocity in the power spectrum estimated by the amplitude-normalized beamforming is derived, and then the theoretical dispersion curve of multichannel Rayleigh wave data is calculated by utilizing the Golden Section search method. Numerical results show that the proposed algorithm can quickly and efficiently calculate the theoretical dispersion curve of multichannel Rayleigh waves in laterally inhomogeneous media. The difference between dispersion curves calculated by the proposed algorithm and produced by the 2D elastic wave finite-difference time-domain algorithm is small, which indicates the reliability of the proposed algorithm. The proposed forward algorithm can provide a theoretical foundation for the inversion of dispersion curves in laterally inhomogeneous media and an efficient tool for the optimization design of the MASW acquisition system. © 2021, Science Press. All right reserved.