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SH and Love waves have certain advantages over P-SV and Rayleigh waves when inverting shear-wave velocity (V S) profiles. They can also supplement Rayleigh waves to provide better model constraints on characterizing anisotropic media. Since the true 3D forward solution of full SH waves requires intensive computation, we propose, in this paper, a simple 2D wavefield solution and further modify it as an efficient pseudo-3D solution. This is achieved by applying an empirical amplitude correction function for geometric attenuation. In the transformed domain, this newly proposed pseudo-3D solution yields a dispersion image (frequency-velocity spectrum, FVS) practically equivalent to that of the true 3D solution which is also developed by the authors. Furthermore, this pseudo-3D solution is significantly more accurate than the modal summation method. Thanks to its fast computation speed and accuracy, the pseudo-3D algorithm is demonstrated to be an excellent surrogate for full wavefield inversion based on FVS. The FVS of SH waves is shown to be much more sensitive to embedded thin weak layers than that of P-SV waves. The superiority of FVS inversion over fundamental mode inversion is further demonstrated by examining their corresponding error functions, showing that FVS provides a much stronger constraint on the possible V S models. Examples demonstrate that the FVS inversion based on the pseudo-3D model outperforms the modal summation approach in both accuracy and generalization. The proposed pseudo-3D solution is quite general. It takes into account the source-to-receiver geometry and deals with special layer profiles where Love-type wave does not exist. • An efficient 2D model is developed and modified to approximate the true 3D dynamic response to a finite shear load. • Full waveform inversion based on the proposed pseudo-3D model in the transformed domain is presented. • The new model considers receiver locations and special conditions where the Love-wave dispersion curve does not exist. • Unique and advantageous characteristics of the transverse-loaded dynamic response are revealed. [ABSTRACT FROM AUTHOR]

Inversion of subsurface shear-wave velocity profile based on effective dispersion curve or full wavefield is still rare due to the lack of efficient forward computation kernel for the full wavefield in a layered medium. To facilitate exploiting the complete signal content in seismic testing, an efficient new computational framework for modeling synthetic full wavefields in horizontally layered systems is proposed. Dynamic response of an isotropic elastic layered system subjected to vertical loading is implemented and thoroughly validated. The new procedure is based the Fourier-Bessel series expansion (not the traditional Fourier-Bessel transform), and it is at least two-orders faster than the current full wavefield computation method based on integral transformation. It considers survey parameters and models all wave phenomena, including near-field effect and leaky waves, which cannot be captured by the modal summation method. Examples of full wavefield simulation are presented to demonstrate different levels of information provided by the experimentally available fundamental mode, broadband effective dispersion curve, and the full velocity spectrum. Different earth models may have similar fundamental modes or even effective dispersion curves; however, their difference manifests in different higher-mode contributions and can only be exploited by utilizing the entire velocity spectra including the vertical and radial components. The coupling between the vertical and radial components in terms of their spectral ratio and phase difference can provide additional constraints (data) in seismic testing. • Loading within a circle, instead of a point force, is used for better mimicking the surface testing load. • The computationally efficient finite Fourier-Bessel summation, instead of Hankel integral, is proposed. • Solution for vertical load using the stiffness matrix is presented, which can be easily extended to other loading conditions. • The full-wavefield solution reveals the important effects of near field, leaky and lateral waves, and radial-to-vertical characteristics. [ABSTRACT FROM AUTHOR]

Abstract: The surface wave (S-wave) method has gained popularity in engineering practice for determining S-wave velocity depth profiles. A growing trend is towards the application of S-wave testing for spatially 2-D S-wave velocity tomography, ignoring the assumption of horizontally layered medium. A fourth-order velocity-stress finite difference method is used to perform numerical simulations of S-wave testing in earth models with lateral variation. Results show that the lateral heterogeneity induces a non-stationary property in the space domain, resulting in false depth-related dispersion or higher modes if conventional approach based on stationary assumption is used for the dispersion analysis. Artifacts maybe introduced in spatially 2-D S-wave velocity imaging if the effect of lateral heterogeneity is not accounted for. As a potential countermeasure, a high-lateral-resolution S-wave method is proposed to reduce the effect of lateral heterogeneity while maintaining the resolution and depth range of dispersion analysis. It consists of a walk-away survey and a phase-seaming procedure when synthesizing seismograms with different nearest source-to-receiver offset, allowing wide-wavelength dispersion analysis within a small spatial range. The proof of concept is given with several numerical examples. They show that the high-resolution S-wave method can greatly alleviate the effect of lateral heterogeneity and increase spatial resolution. [Copyright &y& Elsevier]

Methods based on multi-station recordings are presented for constructing the experimental dispersion curve of Rayleigh waves. Multi-station recording permits a single survey of a broad depth range, high levels of redundancy with a single field configuration, and the ability to adjust the offset, effectively reducing near field and far field effects. A method based on the linear regression of phase angles measured at multiple stations is introduced for determining data quality and filtering criteria. This method becomes a powerful tool for on site quality control in real time. The effects of multiple modes and survey line parameters, such as near offset, receiver spacing, and offset range, are investigated. Parametric studies result in general guidelines for the field data acquisition. A case study demonstrates how to easily deploy commonplace seismic refraction equipment to simultaneously record data for P-wave tomographic interpretation and multi-station analysis of surface wave. [Copyright &y& Elsevier]

The multi-channel analysis of surface wave (MASW) method is a non-invasive method recently developed to estimate shear wave velocity profile from surface wave energy. Unlike conventional SASW method, multi-station recording permits a single survey of a broad depth range and high levels of redundancy with a single field configuration. An efficient and unified wavefield transform technique is introduced for dispersion analysis and on site data quality control. The technique was demonstrated in the assessment of soil liquefaction potential at a site in Yuan Lin, Taiwan. The shear wave velocity and liquefaction potential assessments based on MASW method compares favorable to that based on SCPT shear wave measurements. Two-dimensional shear wave velocity profiles were estimated by occupying successive geophone spreads at several sites in central western Taiwan, at some of which sand boils or ground cracks occurred during 1999 Chi Chi earthquake. Liquefaction potential analysis based on MASW imaging was shown to be effective for estimating the extent of potential liquefaction hazard. [Copyright &y& Elsevier]