Today, surface-wave analysis is widely adopted for building near-surface S-wave velocity models. The surface-wave method is under continuous and rapid evolution, also thanks to the lively scientific debate among different disciplines, and interest in the technique has increased significantly during the last decade. A comprehensive review of the literature in the main scientific journals provides historical perspective, methodological issues, applications, and most-promising recent approaches. Higher modes in the inversion and retrieval of lateral variations are dealt with in great detail, and the current scientific debate on these topics is reported. A best-practices guideline is also outlined.

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Surface-wave analysis for building near-surface velocity models — Established approaches and new perspectives

SUMMARY

I calculate Fourier–Bessel expansion coefficients for recorded shallow-seismic wavefields using a discrete approximation to the Bessel transformation. This is the first stage of a full-wavefield inversion. The transform is a complete representation of the data, recorded waveforms can be reconstructed from the expansion coefficients obtained. In a second stage (described in a companion paper) I infer a 1-D model of the subsurface from these transforms and P-wave arrival times by fitting them with their synthetic counterpart. The whole procedure avoids dealing with dispersion in terms of normal modes, but exploits the full signal-content, including the dispersion of higher modes, leaky modes and their true amplitudes. It is robust even in the absence of a priori information. I successfully apply it to the near field of the source. And it is more efficient than direct inversion of seismograms. I have developed this new approach because the inversion of shallow-seismic Rayleigh waves suffers from the interference of multiple modes that are present in the majority of our field data sets. Since even the fundamental-mode signal cannot be isolated in the time domain, conventional phase-difference techniques are not applicable.



The potential to reconstruct the full waveform from the transform is confirmed by two field-data examples, which are recorded with 10 Hz geophones at effective intervals of about 1 m and spreads of less than 70 m length and are excited by a hammer source. Their transforms are discussed in detail, regarding aliasing and resolution. They reveal typical properties of shallow surface waves that are at variance with assumptions inherent to conventional inversion techniques: multiple modes contribute to the wavefield and overtones may dominate over the fundamental mode. The total wavefield may bear the signature of inverse or anomalous dispersion, although the excited modes have regular and normal dispersion. The resolution at long wavelengths (and thus the penetration depth of the survey) is limited by the length of the profile rather than by the signal-to-noise ratio at low frequencies.



Finally, this approach is compared with conventional techniques of dispersion analysis. This illustrates the advantage of conserving the full wavefield in contrast to the reduction to one dispersion curve.

/pdf/inversion-of-shallow-seismic-wavefields-i-wavefield-3kez87lfmv.pdf

Inversion of shallow-seismic wavefields: I. Wavefield transformation

Grey Wolf Optimizer for parameter estimation in surface waves

Surface-wave dispersion analysis is widely used in geophysics to infer a shear wave velocity model of the subsoil for a wide variety of applications. A shear-wave velocity model is obtained from the solution of an inverse problem based on the surface wave dispersive propagation in vertically heterogeneous media. The analysis can be based either on active source measurements or on seismic noise recordings. This paper discusses the most typical choices for collection and interpretation of experimental data, providing a state of the art on the different steps involved in surface wave surveys. In particular, the different strategies for processing experimental data and to solve the inverse problem are presented, along with their advantages and disadvantages. Also, some issues related to the characteristics of passive surface wave data and their use in H/V spectral ratio technique are discussed as additional information to be used independently or in conjunction with dispersion analysis. Finally, some recommendations for the use of surface wave methods are presented, while also outlining future trends in the research of this topic.

/pdf/application-of-surface-wave-methods-for-seismic-site-3j7j41wf74.pdf

Application of Surface-Wave Methods for Seismic Site Characterization

A multimodal approach to nondestructive seismic pavement testing is described The presented approach is based on multichannel analysis of all types of seismic waves propagating along the surface o

https://parkseismic.com/files/RydenEtAl2004.pdf

Multimodal approach to seismic pavement testing

SUMMARY
The theory of Love- and Rayleigh-wave dispersion for plane-layered earth models has undergone a number of developments since the initial work of Thomson and Haskell. Most of these were concerned with computational difficulties associated with numerical overflow and loss of precision at high frequencies in the original Thomson-Haskell formalism. Several seemingly distinct approaches have been followed, including the delta matrix, reduced delta matrix, Schwab-Knopoff, fast Schwab-Knopoff, Kennett's Reflection-Transmission Matrix and Abo-Zena methods. This paper analyses all these methods in detail and finds explicit transformations connecting them. It is shown that they are essentially equivalent and, contrary to some claims made, each solves the loss of precision problem equally well. This is demonstrated both theoretically and computationally. By extracting the best computational features of the various methods, we develop a new algorithm (sec Appendix A5), called the fast delta matrix algorithm. To date, this is the simplest and most efficient algorithm for surface-wave dispersion computations (see Fig. 4).

The theory given in this paper provides a complete review of the principal methods developed for Love- and Rayleigh-wave dispersion of free modes in plane-layered perfectly elastic, isotropic earth models and puts to rest controversies that have arisen with regard to computational stability.

/pdf/free-mode-surface-wave-computations-45mzs5wvst.pdf

Free-mode surface-wave computations

SUMMARY This paper is concerned with the dispersion of Love and Rayleigh waves in multilayered models with smooth and weakly non-parallel boundaries. Perturbation formulae for the phase, frequency, wavenumber, phase velocity, group velocity and amplitude are derived from ¢rst-order perturbation theory of Whitham’s equation for dispersive waves in non-uniform media. Derivation of the average Lagrangian for Love and Rayleigh waves is obtained as required by the perturbation formulae. Explicit formulae are given for Love waves in the long-wavelength limit and comparisons with related studies are made. In order to demonstrate the results, numerical calculations for the perturbation in frequency, wavenumber, amplitude and phase are performed. The models consist of non-uniform media of one and two layers over a half-space. The perturbed parameter is the layer depth, sampled at diierent locations.

/pdf/love-and-rayleigh-waves-in-non-uniform-media-1l53o6gx4y.pdf

Ronen Ben-Hador

Papers

Free-mode surface-wave computations

Love and Rayleigh waves in non-uniform media

Perturbation formulas for linear dispersive waves in weak spatially non-uniform media

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