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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Subcoal seismic exploration in the Gippsland Basin (Australia) /

Dunne, Jarrod Craig. January 1996 (has links)
Thesis (Ph. D.)--University of Melbourne, 1996. / Includes bibliographical references.

A comparative study of the algebraic reconstruction technique and the constrained conjugate gradient method as applied to cross borehole geophysical tomography

Masuda, Ryuichi. January 1989 (has links)
Thesis (M.S.)--Ohio University, June, 1989. / Title from PDF t.p.

Subsurface electromagnetic sensing in the presence of the air-earth interface using a cross-borehole configuration /

Ellis, Grant Andrew. January 1995 (has links)
Thesis (Ph. D.)--University of Washington, 1995. / Vita. Includes bibliographical references (leaves [133]-138).

Wavelet estimation and debubbling using minimum entropy deconvolution and time domain linear inverse methods

Levy, Shlomo January 1979 (has links)
A new and different approach to the solution of the normal equations of minimum entropy deconvolution (MED) is developed. This approach which uses singular value decomposition in the iterative solution of the MED equations increases the signal-to-noise ratio of the deconvolved output and enhances the resolution of MEC. The problem of deconvolution, and in particular wavelet estimation, is formulated as a linear inverse problem. Both generalized linear inverse methods and Backus-Gilbert inversion are considered. The proposed wavelet estimation algorithm uses the MED output as a first approximation to the earth response. The approximated response and the observed seismograms serve as an input to the inversion schemes and the outputs are the estimated wavelets. The remarkable performance of the linear inverse schemes for cases of highly noisy data is demonstrated. A debubbling example is used to show the completeness of the linear inverse schemes. First the wavelet estimation part was carried out and then the debubbling problem was formulated as a generalized linear inverse problem which was solved using the estimated wavelet. This work demonstrates the power of the linear inverse schemes when dealing with highly noisy data. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Interferometric Imaging and its Application to 4D Imaging

Sinha, Mrinal 03 1900 (has links)
This thesis describes new interferometric imaging methods for migration and waveform inversion. The key idea is to use reflection events from a known reference reflector to ”naturally redatum” the receivers and sources to the reference reflector. Here, ”natural redatuming” is a data-driven process where the redatuming Green’s functions are obtained from the data. Interferometric imaging eliminates the statics associated with the noisy overburden above the reference reflector. To mitigate the defocussing caused by overburden errors I first propose the use of interferometric least-squares migration (ILSM) to estimate the migration image. Here, a known reflector is used as the reference interface for ILSM, and the data are naturally redatumed to this reference interface before imaging. Numerical results on synthetic and field data show that ILSM can significantly reduce the defocussing artifacts in the migration image. Next, I develop a waveform tomography approach for inverting the velocity model by mitigating the velocity errors in the overburden. Unresolved velocity errors in the overburden velocity model can cause conventional full-waveform inversion to get stuck in a local minimum. To resolve this problem, I present interferometric full-waveform inversion (IFWI), where conventional waveform tomography is reformulated so a velocity model is found that minimizes the objective function with an interferometric crosscorrelogram misfit. Numerical examples show that IFWI, compared to FWI, computes a significantly more accurate velocity model in the presence of a nearsurface with unknown velocity anomalies. I use IFWI and ILSM for 4D imaging where seismic data are recorded at different times over the same reservoir. To eliminate the time-varying effects of the near surface both data sets are virtually redatumed to a common reference interface before migration. This largely eliminates the overburden-induced statics errors in both data sets. Results with synthetic and field data show that ILSM and IFWI can suppress the artifacts caused by non-repeatability in time-lapse surveys. This can lead to a much more accurate characterization of the movement of fluids over time. In turn, this information can be used to optimize the extraction of resources in enhanced oil recovery (EOR) operations.

Residual migration velocity analysis in the plane wave domain theory and applications /

Jiao, Junru, January 2001 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Residual migration velocity analysis in the plane wave domain : theory and applications /

Jiao, Junru, January 2001 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references (leaves 181-185). Available also in a digital version from Dissertation Abstracts.

Residual migration velocity analysis in the plane wave domain : theory and applications

Jiao, Junru, 1959- 21 March 2011 (has links)
Not available / text

A discreet-scatterer model of the seismic P coda

Craig, Mitchell Scott 05 1900 (has links)
No description available.

Structure-Specific Probabilistic Seismic Risk Assessment

Bradley, Brendon Archie January 2009 (has links)
This thesis addresses a diverse range of topics in the area of probabilistic seismic risk analysis of engineering facilities. This intentional path of diversity has been followed primarily because of the relatively new and rapid development of this facet of earthquake engineering. As such this thesis focuses on the rigorous scrutinization of current, and in particular, simplified methods of seismic risk assessment; the development of novel aspects of a risk assessment methodology which provides easily communicated performance measures and explicit consideration for the many uncertainties in the entire earthquake problem; and the application of this methodology to case-study examples including structures supported on pile foundations embedded in liquefiable soils. The state-of-the-art in seismic risk and loss assessment is discussed via the case study of a 10 storey New Zealand office building. Particular attention is given to the quality and quantity of information that such assessment methodologies provide to engineers and stakeholders for rational decision-making. Two chapters are devoted to the investigation of the power-law model for representing the ground motion hazard. Based on the inaccuracy of the power-law model at representing the seismic hazard over a wide range of exceedance rates, an alternative, more accurate, parametric hazard model based on a hyperbola in log-log space is developed and applied to New Zealand peak ground acceleration and spectral acceleration hazard data. A semianalytical closed-form solution for the demand hazard is also developed using the hyperbolic hazard model and applied for a case-study performance assessment. The power-law hazard model is also commonly used to obtain a closed-form solution for the annual rate of structural collapse (collapse hazard). The magnitude of the error in this closed-form solution due to errors in the necessary functional forms of its constitutive relations is examined via a parametric study. A series of seven chapters are devoted to the further development of various aspects of a seismic risk assessment methodology. Intensity measures for use in the estimation of spatially distributed seismic demands and seismic risk assessment which are: easily predicted; can predict seismic response with little uncertainty; and are unbiased regarding additional properties of the input ground motions are examined. An efficient numerical integration algorithm which is specifically tailored for the solution of the governing risk assessment equations is developed and compared against other common methods of numerical integration. The efficacy of approximate uncertainty propagation in seismic risk assessment using the so-called First-Order Second-Moment method is investigated. Particular attention is given to the locations at which the approximate uncertainty propagation is used, the possible errors for various computed seismic risk measures, and the reductions in computational demands. Component correlations have to date been not rigorously considered in seismic loss assessments due to complications in their estimation and tractable methodologies to account for them. Rigorous and computationally efficient algorithms to account for component correlations are presented. Particular attention is also given to the determination of correlations in the case of limited empirical data, and the errors which may occur in seismic loss assessment computations neglecting proper treatment of correlations are examined. Trends in magnitude, distribution, and correlation of epistemic uncertainties in seismic hazard analyses for sites in the San Francisco bay area are examined. The characteristics of these epistemic uncertainties are then used to compare and contrast three methods which can be used to propagate such uncertainties to other seismic risk measures. Causes of epistemic uncertainties in component fragility functions, their evaluation, and combination are also examined. A series of three chapters address details regarding the seismic risk assessment of structures supported on pile foundations embedded in liquefiable soils. A ground motion prediction equation for spectrum intensity (found to be a desirable intensity measure for seismic response analysis in liquefiable soils) is developed based on ground motion prediction equations for spectral accelerations, which are available in abundance in literature. Determination of intensity measures for the seismic response of pile foundations, which are invariably located in soil deposits susceptible to liquefaction, is examined. Finally, a rigorous seismic performance and loss assessment of a case-study bridge structure is examined using rigorous ground motion selection, seismic effective stress analyses, and professional cost estimates. Both direct repair and loss of functionality consequences for the bridge structure are examined.

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