Seismic Wave Studies Over a High‐speed Surface Layer

Press, Frank; Dobrin, Milton B.

doi:10.1190/1.1438227

Cited by 15 publications

(10 citation statements)

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“…pavement profile. However, at this point there were some speculations regarding the nature of surface wave propagation in this type of layered system (Press and Dobrin, 1956). was first to acknowledge that phase velocities greater than the shear wave velocity of the subgrade represent leaky waves and must be calculated with a complex wave number.…”

Section: The Steady State Vibration Methodsmentioning

confidence: 99%

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Surface wave testing of pavements.

Rydén

2009

The Journal of the Acoustical Society of America

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Pavements are constructed using several layers of materials, and their durability depends on the quality of all of these strata. It is, therefore, valuable to be able to determine the properties of the layers nondestructively. A method is presented for evaluating the thickness and stiffness of multilayered pavement structures from guided waves measured at the surface. In this type of layered structure, the interaction of leaky Lamb waves in the embedded layers generates surface waves corresponding only to certain portions of the guided wave dispersion curves and branches measurable at the pavement surface. To resolve the different mode branches, the wavefield is measured at the surface by using a light hammer as the source and an accelerometer as receiver, generating a synthetic receiver array. The recorded data are transformed to a phase velocity spectrum, which is then inverted to give the layer properties using a global inversion algorithm. The theoretical background along with experimental results of the application to nondestructive testing of pavements will be presented. Ongoing research on noncontact air-coupled measurements is also demonstrated. This opens up the possibility for faster on-the-fly surface wave testing of pavement layers, since surface contact is no longer required.

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Section: The Steady State Vibration Methodsmentioning

confidence: 99%

“…Related studies have dealt with the case of one stiff ͑fast͒ layer on a lower velocity half-space ͑Press and Dobrin, 1956;Lefeuvre et al, 1998;Cheng et al, 2001;. Yapura and Kinra ͑1995͒ investigated dispersion curves and mode shapes for a fluid-solid bilayer.…”

Section: Introductionmentioning

confidence: 99%

Surface wave testing of pavements.

Rydén

2009

The Journal of the Acoustical Society of America

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“…Studies over these years remained mainly at the level of rather qualitative discussions (Howell 1949; Dobrin et al 1954; Press & Dobrin 1956). However, Evison (1956) had already published a comparison between field data and synthetic waveforms.…”

Section: Introductionmentioning

confidence: 99%

Inversion of shallow-seismic wavefields: I. Wavefield transformation

Forbriger

2003

Geophysical Journal International

199

134

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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.

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“…Press and Dobrin 1956;Mooney et al 1970;Whiteley and Greenhalgh 1979;Tewari, Dixit and Murty 1995). Press and Dobrin 1956;Mooney et al 1970;Whiteley and Greenhalgh 1979;Tewari, Dixit and Murty 1995).…”

Section: Introductionmentioning

confidence: 99%

The problem of velocity inversion in refraction seismics: some observations from modelling results

Krishna

Rao

Sarkar

1999

Geophysical Prospecting

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The applicability of seismic refraction profiling for the detection of velocity inversion, which is also known as a low‐velocity layer (LVL), is investigated with the aid of synthetic seismogram computations for a range of models. Our computational models focus on the inherent ambiguities in the interpretation of first‐arrival time delays or ‘skips’ in terms of LVL model parameters. The present modelling results reveal that neither the measure nor even the existence of a shadow zone and/or a time shift (skip) in first arrivals is necessarily indicative of an LVL. Besides attenuation effects, the cap‐layer velocity gradient is a critical parameter, determining the termination point of the cap‐layer diving wave and thus the time skip. We suggest that shallow LVLs can be delineated more reliably by traveltime and amplitude modelling of coherent phases reflected from their top and bottom boundaries, often clearly observed in the pre‐ and near‐critical ranges in seismogram sections of refraction profiling experiments with a close receiver spacing. We demonstrate the applicability of this approach for a field data set of a refraction profile in the West Bengal Basin, India. The inferred LVL corresponds to the Gondwana sediments underlying the higher‐velocity layer of the Rajmahal Traps. This interpretation is consistent with the data from a nearby well in the region.

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Seismic Wave Studies Over a High‐speed Surface Layer

Cited by 15 publications

References 0 publications

Surface wave testing of pavements.

Surface wave testing of pavements.

Inversion of shallow-seismic wavefields: I. Wavefield transformation

The problem of velocity inversion in refraction seismics: some observations from modelling results

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