Near-offset effects on Rayleigh-wave dispersion measurements: Physical modeling

Bodet, Ludovic; Abraham, Odile; Clorennec, Dominique

doi:10.1016/j.jappgeo.2009.02.012

Cited by 56 publications

(30 citation statements)

References 28 publications

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“…When the source-receiver distance is small, effective dispersion curve is determined by the amplitudes of multiple dispersion modes. While for small spread length or low frequency, the phase slowness resolution becomes unstable (Bodet et al, 2009). This effect is called "spread length effect".…”

Section: Effective Dispersion Curvementioning

confidence: 99%

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Effective dispersion curve and pseudo multimode dispersion curves for Rayleigh wave

Zhang

2011

J. Earth Sci.

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The hi-energy bands in the dispersion image are usually interpreted as the true dispersion phase velocities. However, the multiple dispersion modes of Rayleigh wave in layered media stack in space, producing the effective dispersion curve and the pseudo multimode dispersion curves in dispersion image. The effective dispersion curve has the maximum energy with lower phase velocities than pseudo dispersion phase velocities, and thus is often misunderstood as the fundamental mode. Within the tolerable misfit, the effective dispersion curve can approach the true fundamental mode. Different from the true multimode dispersion curves, the pseudo multimode dispersion curves are related to the effective dispersion curve. A numerical model is adapted to simulate the true dispersion curves, effective dispersion curve, and pseudo multimode dispersion curves. Their differences and mutual relations are demonstrated. KEY WORDS: Rayleigh wave, pseudo multimode dispersion curves, effective dispersion curve, numerical simulation, layered media.

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Section: Effective Dispersion Curvementioning

confidence: 99%

“…Next, it improved the S/N ratio in dispersion data construction. Last, it may avoid the unwrapping effect at low frequency by selecting reasonable spread length (Bodet et al, 2009).…”

Section: Effective Dispersion Curvementioning

confidence: 99%

Effective dispersion curve and pseudo multimode dispersion curves for Rayleigh wave

Zhang

2011

J. Earth Sci.

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“…For θ=0° and θ=15°, the three curves matched well at most frequencies except for the extremely low frequencies. Such mismatch at extremely low frequencies is mainly caused by near-field effects (Bodet et al, 2009;Rix, 2006, 2004;Lin and Chang, 2004). Their composed dispersion curve can be understood as the ground truth.…”

Section: Raw Data and Dispersion Featuresmentioning

confidence: 99%

“…"Near-field effects" and "spreading length effects" are therefore the major effects concluded by some research works. For the near-field effects, the near-offset of the spread may affect the phase unwrapping at the extremely low frequencies of the dispersion curve (Bodet et al, 2009;Rix, 2006, 2004;Lin and Chang, 2004). For the spreading length effects, the resolution of phase velocity is naturally determined by the spread length (Bodet et al, 2009(Bodet et al, , 2005Forbriger, 2003;O'Neill, 2003); long spreading length is beneficial for obtaining high-resolution dispersion data of surface waves.…”

Section: Introductionmentioning

confidence: 99%

Influence of uneven trace spacing on Rayleigh wave dispersion

Zhang

2011

J. Earth Sci.

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Rayleigh wave dispersion signals are significant to underground investigation. Traditionally, uniformed trace spacing is employed in surface wave surveys. In some cases, however, uneven trace spacing is often encountered because of the limitations of the site condition. In order to study the influence of uneven trace spacing on the dispersion data construction of Rayleigh waves, data acquisition is performed based on a 2.5D field layout with a linear array of geophones fixed and a mobile source. The observation direction controls the trace spacing of the measurement. The final results demonstrate that the trace nonuniformity has significant influence on the Rayleigh wave dispersion feature constructed. When the observation angle is over 45º, the dispersion image will be too distorted to extract dispersion data correctly. KEY WORDS: Rayleigh wave, uneven trace spacing, 2.5D data acquisition layout, observation angle, dispersion curve.

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“…Tokimatsu et al (1992a,b) and Lai and Rix (1999) have proposed the expressions of the effective phase velocity, which take into account the higher modes but ignore the near-field effects. The near-field effect can be investigated via analytical methods, numerical methods, physical modeling and field testing (Zywicki and Rix, 2005;Strobbia and Foti, 2006;Bodet et al, 2009;Yoon and Rix, 2009). It has been recognized that the near-field effect can be mitigated by using the cylindrical beamformer and multi-offset phase analyses, or by increasing the total number of receivers and the array center distance in an array-based testing (Zywicki and Rix, 2005;Strobbia and Foti, 2006;Yoon and Rix, 2009).…”

Section: Introductionmentioning

confidence: 99%