Curved ray seismic tomography: application to the Grand Etang Dam (Reunion Island)

Cottin, J.F.; Deletie, P.; Jacquet-Francillon, H.; Lakshmanan, J.; Lemoine, Y.; Sánchez, Manuel

doi:10.3997/1365-2397.1986015

Cited by 11 publications

(5 citation statements)

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“…the unknowns). The non-linearity of the equation system must be approached by relaxation, solving iteratively in turn for the ray paths and for the velocities (Cottin et al 1986;Bregman et ul. 1989a).…”

Section: Introductionmentioning

confidence: 99%

Traveltime tomography in anisotropic media-II. Application

Pratt

Chapman

1992

Geophysical Journal International

144

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S U M M A R YCross-borehole seismic data have traditionally been analysed by inverting the arrival times for velocity structure (traveltime tomography). The presence of anisotropy requires that tomographic methods be generalized to account for anisotropy. This generalization allows geological structure to be correctly imaged and allows the anisotropy to be evaluated. In a companion paper we developed linear systems for 2-D traveltime tomography in anisotropic media. In this paper we analyse the properties of the linear system for quasi-compressional waves and invert both synthetic and real data. Solutions to the linear systems consist of estimates of the spatial distributions of five parameters, each corresponding to a linear combination of a small subset of the 21 elastic, anisotropic velocity parameters. The parameters describe the arrival times in the presence of weak anisotropy with arbitrary symmetries. However, these parameters do not, in general, describe the full nature of the anisotropy. The parameters must be further interpreted using additional information on the symmetry system. In the examples in this paper we assume transverse isotropy (TI) in order to interpret our inversions, but it should be noted that this final interpretation could be reformulated in more general terms.The singular value decomposition of the linear system for traveltime tomography in anisotropic media reveals the (expected) ill-conditioning of these systems. As in isotropic tomography, ill-conditioning arises due to the limited directional coverage that can be achieved when sources and receivers are located in vertical boreholes. In contrast to isotropic tomography, the scalelength of the parametrization controls the nature of the parameter space eigenvectors: with a coarse grid all five parameters are required to model the data; with a fine grid some of the parameters appear only in the null space.The linear systems must be regularized using external, a priori information. An important regularization is the expectation that the elastic properties vary smoothly (an ad hoc recognition of the insensitivity of the arrival times to the fine-grained properties of the medium). The expectation of smoothness is incorporated by using a regularization matrix that penalizes rough solutions using finite difference penalty terms. The roughness penalty sufficiently constrains the solutions to allow the smooth eigenvectors in the null space of the unconstrained problem to contribute to the solutions. Hence, the spatial distribution of all five parameters is recovered. The level of regularization required is difficult to estimate; we advocate the analysis of a suite of solutions. Plots of the solution roughness against the data residuals can be used to find 'knee points', but for the fine tuning of the regularization one has little recourse but to examine a suite of images and use geological plausibility as an additional criterion.The application of the regularized numerical scheme to the synthetic data reveals that the roughness penalty shoul...

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Section: Introductionmentioning

confidence: 99%

Traveltime tomography in anisotropic media-II. Application

Pratt

Chapman

1992

Geophysical Journal International

144

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“…The assumption is often made that the P-and S-wave events recorded have travelled directly from source to receiver in each case and a straight-line tomography programme is used. However, curved ray path tomography is preferred to allow for velocity anisotropy (Cottin et al 1986 andBertrand et al 1987b). Inadequate coupling will result in inaccurate travel times being recorded, which might produce spurious velocity and modulus values.…”

Section: Acoustic Tomographymentioning

confidence: 99%

The determination of the dynamic elastic moduli of rock masses by geophysical methods

McDowell

1990

EGSP

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Dynamic moduli values for rock masses are calculated from corresponding compressional and shear wave velocities and in situ bulk densities using standard equations based on elastic theory. These moduli values can be used for the design of foundations for vibrating machines to avoid resonance during operation. Static moduli values can be assessed from the dynamic moduli values if the rock mass quality has been determined either directly or from the ratio of vfie~a to Via b. Where possible, the results of these procedures should be correlated with the results of in situ static tests, such as large scale plate bearing tests.Geophysical surveys need to be carefully designed to ensure that the correct seismic event is being recorded and wave velocities are being measured accurately. There are several field techniques in common usage, which include seismic refraction surveying, cross-hole shooting and a variety of along-hole methods. In each case, careful consideration should be given to timing errors resulting from inadequate coupling of energy sources and receivers. Enhancement of shear-wave events is usually required to avoid ambiguity and misinterpretation, particularly in layered ground. For fractured rock masses the wavelength of the seismic events may also be significant for both compressional and shear wave events.The results of ground investigations at the proposed sites of generators for the Akjoujt Power Station in Mauritania, West Africa, are presented to illustrate the advantages and limitations of geophysical techniques for assessing rock mass deformation moduli. Compressional and shear wave velocities were determined by cross-hole, along-hole and surface seismic refraction surveying techniques for the very weathered metamorphic rocks. Dynamic values of Young's modulus were obtained for 1 m intervals to a depth of 15 m.The results of this investigation are reviewed in the light of recent developments in equipment, field procedures and data processing techniques.In the design of the foundations for many engineering structures, the engineer requires values of the dynamic moduli, as well as the static moduli, of the rock mass.

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“…Tomography has been used to solve many subsurface problems (Peterson et al, 1985;Cottin, et al, 1986;Lytle and Dines, 1980;Kilty and Lange, 1990). A tomographic technique (Joint Analysis of Surface Waves and Refraction [JASR]) incorporating inversion of first arrivals with an initial model from S-wave velocity profiles from surface wave data (Ivanov, et al, 2000) provided 2-D V p sections consistent with borehole measurements.…”

Section: Refraction/tomographymentioning

confidence: 99%

3‐D characterization of seismic properties at the smart weapons test range, YPG

Miller

Anderson

Davis

et al. 2003

SEG Technical Program Expanded Abstracts 2003

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The Smart Weapons Test Range (SWTR) lies within the Yuma Proving Ground (YPG), Arizona. SWTR is a new facility constructed specifically for the development and testing of futuristic intelligent battlefield sensor networks. In this paper, results are presented for an extensive high-resolution geophysical characterization study at the SWTR site along with validation using 3-D modeling. In this study, several shallow seismic methods and novel processing techniques were used to generate a 3-D grid of earth seismic properties, including compressional (P) and shear (S) body-wave speeds (V p and V s ), and their associated body-wave attenuation parameters (Q p , and Q s ). These experiments covered a volume of earth measuring 1500 m by 300 m by 25 m deep (11 million cubic meters), centered on the vehicle test track at the SWTR site. The study has resulted in detailed characterizations of key geophysical properties. To our knowledge, results of this kind have not been previously achieved, nor have the innovative methods developed for this effort been reported elsewhere. In addition to supporting materiel developers with important geophysical information at this test range, the data from this study will be used to validate sophisticated 3-D seismic signature models for moving vehicles.Each of the four material-property volumes (V p , V s , Q p , and Q s ) was constructed by interpolating 2-D seismic measurements made along survey lines optimized for the physical properties at the SWTR site. The geostatistical properties of the data guided the interpolation of data points between survey lines and established confidence limits around each interpolated value. Ground truth was accomplished through cross-hole seismic measurements and borehole logs. Surface wave and refraction acquisition methods were used to acquire most raw data for this study. In addition to standard reflection and refraction data analysis procedures, we also applied turning ray tomography and surface wave analysis. A variety of seismic energy sources (including vibroseis, accelerated weight drop, and high frequency impulses from projectile and explosive shots) and recording array configurations were considered for optimizing the quality of each analysis.Inversion of the specific portions of the seismic wavefield was key to the success of the characterization effort. Tomographic inversion produced P-wave velocity matrices with the greatest resolution and finest sampling without the necessity for assumptions about layer properties. Standard refraction analysis was used to confirm the tomographically defined P-wave velocities and to map prominent layers. Inversion of surface-wave dispersion curves from multichannel data resulted in optimal estimates of the S-wave velocity field. Prior to this study, no numerically rigorous methods had been documented for estimating Q for near-surface materials. Geophysical properties at the site appear to be anisotropic, reflecting local trends in near-surface geology. For example, spatial continuity in V s can be env...

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Curved ray seismic tomography: application to the Grand Etang Dam (Reunion Island)

Cited by 11 publications

References 0 publications

Traveltime tomography in anisotropic media-II. Application

Traveltime tomography in anisotropic media-II. Application

The determination of the dynamic elastic moduli of rock masses by geophysical methods

3‐D characterization of seismic properties at the smart weapons test range, YPG

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