Near-surface velocity modeling using a combined inversion of surface and refracted P-waves

Duret, F.; Bertin, Frederique; Garceran, K.; Sternfels, Raphael; Bardainne, T.; Deladerrière, N.; Meur, D. Le

doi:10.1190/tle35110946.1

“…Rector et al (2015) used surface wave tomography to image voids in an old mine working site in Nevada (USA). Duret et al (2016) combined standard P-wave refraction and SWT to compute primary statics for a 3-D narrow-azimuth land dataset. Krohn and Routh (2017a) and Krohn and Routh (2017b) developed a tomography method that evaluates the complex slowness distribution by fitting the trace transfer function, i.e.…”

Section: Introductionmentioning

confidence: 99%

Tackling Lateral Variability Using Surface Waves: A Tomography-Like Approach

Barone

¹

,

Boaga

²

,

Carrera

³

et al. 2021

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Lateral velocity variations in the near-surface reflect the presence of buried geological or anthropic structures, and their identification is of interest for many fields of application. Surface wave tomography (SWT) is a powerful technique for detecting both smooth and sharp lateral velocity variations at very different scales. A surface-wave inversion scheme derived from SWT is here applied to a 2-D active seismic dataset to characterize the shape of an urban waste deposit in an old landfill, located 15 km South of Vienna (Austria). First, the tomography-derived inverse problem for the 2-D case is defined: under the assumption of straight rays at the surface connecting sources and receivers, the forward problem for one frequency reduces to a linear relationship between observed phase differences at adjacent receivers and wavenumbers (from which phase velocities are straightforwardly derived). A norm damping regularization constraint is applied to ensure a smooth solution in space: the choice of the damping parameter is made through a minimization process, by which only phase variations of the order of the average wavelength are modelled. The inverse problem is solved for each frequency with a weighted least-squares approach, to take into account the data error variances. An independent multi-offset phase analysis (MOPA) is performed using the same dataset, for comparison: pseudo-sections from the tomography-derived linear inversion and MOPA are very consistent, with the former giving a more continuous result both in space and frequency and less artefacts. Local dispersion curves are finally depth inverted and a quasi-2-D shear wave velocity section is retrieved: we identify a well-defined low velocity zone and interpret it as the urban waste deposit body. Results are consistent with both electrical and electromagnetic measurements acquired on the same line.

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Near-surface Site Characterization Based on Joint Iterative Analysis of First-arrival and Surface-wave Data

Wang

¹

,

Sun

²

,

Wu

³

2022

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Near-surface site characterization is of great significance in the fields of geotechnical engineering and resource exploration. In this paper, we propose a near-surface site characterization method based on the joint iterative analysis of first-arrival and surface-wave data (JIAFS). The proposed method combines the advantages of first-arrival traveltime tomography (FATT) and multichannel analysis of surface waves (MASW). First, the 1D S-wave velocity ($$v_{{\text{S}}}$$ v S ) models obtained by MASW are interpolated to construct the pseudo-2D $$v_{{\text{S}}}$$ v S model. According to the available geological survey information and borehole data, the initial Poisson’s ratio ($$\sigma$$ σ ) model is estimated. Based on the estimated $$\sigma$$ σ model, the pseudo-2D $$v_{{\text{S}}}$$ v S model is converted to a referenced P-wave velocity ($$v_{{\text{P}}}$$ v P ) model which is utilized to constrain the progress of FATT. This helps FATT overcome the inherent defect that it cannot effectively identify velocity-inversion interfaces and low-velocity zones. On the other hand, the $$v_{{\text{P}}}$$ v P model obtained by FATT can provide a favorable priori information to improve the reliability of the results of MASW. Then, the $$v_{{\text{P}}}$$ v P and $$v_{{\text{S}}}$$ v S models obtained by constrained FATT and MASW are used to update the $$\sigma$$ σ model. In addition, the $$v_{{\text{P}}}$$ v P and $$v_{{\text{S}}}$$ v S models are also used as initial models in the next iterative analysis. Finally, through the iteration of this process, the two inversion methods can make use of their own advantages to improve each other, so we can establish accurate near-surface $$v_{{\text{P}}}$$ v P , $$v_{{\text{S}}}$$ v S and $$\sigma$$ σ models under complex geological conditions. A velocity model including low-velocity zone is established for synthetic model test to analyze and verify the advantage of JIAFS. The $$v_{{\text{P}}}$$ v P , $$v_{{\text{S}}}$$ v S and $$\sigma$$ σ models obtained by JIAFS can accurately identify the low-velocity zone and match the true models well. In addition, the proposed method is applied to the field seismic data acquired for oil and gas exploration in Northwest China. Compared with the results of individual inversions and borehole data, JIAFS can establish more reliable 3D $$v_{{\text{P}}}$$ v P , $$v_{{\text{S}}}$$ v S and $$\sigma$$ σ models by interpolating the 2D inversion results, which reveals further details and enhances the geological interpretation significantly.

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Surface wave tomography using dense 3D data around the Scrovegni Chapel in Padua, Italy

Barone

¹

,

Cassiani

²

,

Ourabah³

et al. 2022

Sci Rep

1

0

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A dense single-node 3D seismic survey has been carried out around the Scrovegni Chapel in Padua (Italy), in order to give new insights about the archaeological setting of the area. The survey made use of nearly 1500 vertical nodes deployed over two rectangular grids. 38 shot positions were fired all around the two receiver patches. The fundamental mode Rayleigh wave signal is here analysed: traveltimes are directly inferred from the signal phases, and phase velocity maps are obtained using Eikonal tomography. Also surface wave amplitudes are used, to produce autospectrum gradient maps. The joint analysis of phase velocity and autospectrum gradient allowed the identification of several buried features, among which possible remains of radial walls of the adjacent Roman amphitheater, structures belonging to a medieval convent, and the root area of an eradicated tree. Finally, depth inversion of 1D dispersion curves allowed the reconstruction of a quasi-3D shear-wave velocity model.

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Near-surface velocity modeling using a combined inversion of surface and refracted P-waves

Cited by 8 publications

References 19 publications

Tackling Lateral Variability Using Surface Waves: A Tomography-Like Approach

Tackling Lateral Variability Using Surface Waves: A Tomography-Like Approach

Near-surface Site Characterization Based on Joint Iterative Analysis of First-arrival and Surface-wave Data

Surface wave tomography using dense 3D data around the Scrovegni Chapel in Padua, Italy

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