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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.

Parametric reconstruction of multidimensional seismic records

Naghizadeh, Mostafa. January 2009 (has links)
Thesis (Ph. D.)--University of Alberta, 2009. / Title from pdf file main screen (viewed on Dec. 1, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Geophysics, Department of Physics, University of Alberta." Includes bibliographical references.

Seismic behavior of structures with dampers made from ultra high damping natural rubber /

Lee, Kyung Sik, January 2003 (has links)
Thesis (Ph. D.)--Lehigh University, 2003. / Includes vita. In two parts. Includes bibliographical references (leaves 602-609).

Development of four-element end-fire array as seismo-acoustic sonar source /

Rumph, Steven E. January 2003 (has links) (PDF)
Thesis (M.S. in Engineering Acoustics)--Naval Postgraduate School, September 2003. / Thesis advisor(s): Steven R. Baker, Thomas G. Muir. Includes bibliographical references (p. 89-90). Also available online.

Total variation and adjoint state methods for seismic wavefield imaging

Anagaw, Amsalu Y. January 2009 (has links)
Thesis (M. Sc.)--University of Alberta, 2009. / Title from PDF file main screen (viewed on Feb. 19, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in Geophysics, Department of Physics, University of Alberta. Includes bibliographical references.

Convolutional perfectly matched layers for finite element modeling of wave propagation in unbounded domains

Xu, Boqing, 許博卿 January 2014 (has links)
A general convolutional version of perfectly matched layer (PML) formulation for second-order wave equations with displacement as the only unknown based on the coordinate stretching is proposed in this study, which overcomes the limitation of classical PML in splitting the displacement field and requires only minor modifications to existing finite element programs. The first contribution concerns the development of a robust and efficient finite element program QUAD-CPML based on QUAD4M capable of simulating wave propagation in an unbounded domain. The more efficient hybrid-stress finite element was incorporated into the program to reduce the number of iterations for the equivalent linear dynamic analysis and the total time for the direct time integration. The incorporation of new element types was verified with the QUAD4M solutions to problems of dynamic soil response and the efficiency of hybrid-stress finite element was demonstrated compared to the classical finite elements. The second development involves the implementation of a general convolutional perfectly matched layer (CPML) as an absorbing boundary condition for the modeling of the radiation of wave energy in an unbounded domain. The proposed non-split CPML formulation is displacement-based, which shows great compatibility with the direct time integration. This CPML formulation treats the convolutional terms as external forces and includes an updating scheme to calculate the temporal convolution terms arising from the Fourier transform. In addition, the performance of the CPML has been examined by various problems including a parametric study on a number of key coefficients that control the absorbing ability of the CPML boundary. The final task of this thesis is to apply the developed CPML models to the dynamic analyses of soil-structure interaction (SSI) problems. Typical loading conditions including external load on the structure and underground wave excitation on the medium has been considered. Practical applications of CPML models include the numerical study on the effectiveness of the rubber-soil mixture (RSM) as an earthquake protection material and the report of vibrations induced by the passage of a high-speed train. The former investigates the effectiveness of the CPML models for the evaluation of the performance of RSM subject to seismic excitation and the latter tests the boundary effects on the accuracy of the results for train induced vibrations. Both studies show that CPML as an absorbing boundary condition is theoretically sound and effective for the analysis of soil-structure dynamic response. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

The anisotropic seismic structure of the Earth's mantle : investigations using full waveform inversion

Matzel, Eric M. 28 August 2008 (has links)
I have developed a waveform inversion procedure to invert 3 component broadband seismic data for models of the anisotropic seismic structure of the Earth and applied the technique to an investigation of wave propagation through anisotropic media and earthquake data sampling the upper mantle beneath the East European platform. The procedure combines the conjugate-gradient and very fast simulated annealing methods and attempts to minimize a cross-correlation misfit function comparing data to synthetic seismograms. A series of inversion passes are performed over a range of frequency and time windows to progressively focus in on structural details. The intent is to obtain P and S velocity models that simultaneously match all components of the data (radial, vertical and tangential). The variables in the problem are the seismic velocities ([alpha] and [beta]) as a function of depth. When radial anisotropy is required this set is expanded to include the five variables that determine the seismic velocities in a radially anisotropic medium ([alpha subscript h, alpha subscript v, beta subscript h, beta subscript v, eta]). I investigate the propagation of seismic waves through radially anisotropic media, evaluate which elements of radial anisotropy are best resolved by seismic data and discuss strategies for identifying radial anisotropy in the Earth. S anisotropy, [beta]%, and the horizontal component of P velocity, [alpha subscript h], are typically well resolved by multicomponent seismic data. P anisotropy, [alpha]%, and [eta] are often poorly resolved and trade off with one another in terms of their effect on S[subscript V] arrivals. Erroneous structure will be mapped into models if anisotropy is neglected. The size of the erroneous structure will be proportional to the magnitude of anisotropy present and extend well below the anisotropic zone. The effects of anisotropy on P models produced with an isotropic assumption are most similar to the effects on isotropic S[subscript H] models. When comparing isotropic models, [alpha/beta subscript sh] is therefore often a better measure than [alpha/beta subscript sv] for characterizing mantle petrology. Isotropic S[subscript H], S[subscript V] and P models developed separately using the same data set can provide a good initial estimate of the presence, location and magnitude of anisotropy and those results can be used to create an initial model for an anisotropic inversion solving simultaneously for all 3 components of the data. Finally, I present models for the P and S velocity structure of the upper mantle beneath the East European platform including an analysis of radial anisotropy. The data are 3-component broadband seismograms from strike-slip earthquakes located near the edge of the platform and recorded in Russia and Europe. The timing, amplitude and interference characteristics of direct arrivals (S, P), multiply reflected arrivals (SS, PP), converted phases and surface waves provide very good radial resolution throughout the upper 400 km of the mantle. The platform is underlain by a radially anisotropic seismic mantle lid extending to a depth of 200 km with a largely isotropic mantle below. The model has a positive velocity gradient from 41 km to 100 km depth, and a relatively uniform velocity structure from 100 km to 200 km depth with high S[subscript H] and P[subscript H] velocities (4.77 km /s, 8.45 km/s). Shear anisotropy is uniform at 5% ([beta subscript H] > [beta subscript V]) from 41 to 200 km depth, drops to 2% from 200 to 250 km and is isotropic below that. The average shear velocity from 100 to 250 km is also uniform at 4.65 km/s and the drop in anisotropy is matched by a drop in [beta subscript H] to 4.70 km/s combined with an increase in [beta subscript V] to 4.60 km/s. Below 250 km there is a positive velocity gradient in both P and S velocity down to 410 km. P anisotropy is not well resolved, but P structure mimics the S[subscript H] velocity structure, suggesting that P is also anisotropic within the lid. / text

Seismic data processing in transversely isotropic media: a plane wave approach

Mukherjee, Anubrati 28 August 2008 (has links)
Not available / text

Mantle heterogeneity and flow from seismic and geodynamic constraints

Simmons, Nathan Alan 28 August 2008 (has links)
Not available / text

Characterizing Vs profiles by the SASW method and comparison with other seismic methods

Lin, Yin-Cheng 28 August 2008 (has links)
Not available / text

The effects of confining pressure, pore-fluid salinity and saturation on the acoustic properties of sandstones

Jones, Simon Mark January 1996 (has links)
Modern seismic data acquisition and processing methods now enable scientists to extract information on both the stratigraphy and the physical properties of subsurface rocks. Laboratory acoustic measurementsa llow the physical conditions to be precisely measured and controlled. In the present study, P- and S-wave velocities (Vs, VS) and attenuations (1000/Qp, 1000/Qs) were measured in a range of sandstones using the ultrasonic pulse-echo technique, at effective pressures of 5 MPa to 60 MPa. The measurement accuracy is ±0.3 % for velocity and ±0.1 dB/cm for attenuation using this method. Velocities and quality factors( Q) fall with decreasinge ffectivep ressure,a nd the relationships are described by the empirical equationsV =A+KP-B C71' and Q=A-B e7DP , where P is the effective pressure and A, K, B, and D are the regression coefficients (D=0.115±0.016 and 0.048±0.010 for V and Q, respectively). Velocity and Q can therefore be extrapolated to pressures beyond the experimental range. The Biot, Gassmann, and unrelaxed pore-fluid models of seismic wave propagation in porous media fail to explain the pressure-dependenceo f the velocities. The difference between the experimental and Biot model predictions of the rate of change in P-wave velocity with pore fluid salinity (dVýdM) increases with percentage clay content (C) of the rock at the approximately linear rate of 0.95 m/s/mol. There is no clear relationship for dVs/dM. In clean sandstones there is a close agreement between the experimental results and Biot model predictions for dVP/dM, but the agreement breaks down when C>5%. This suggests that changes in the pore-fluid salinity alter the frame bulk and shear moduli of sandstones. Attenuation is generally independent of pore-fluid salinity. Attenuation and velocity are often strongly dependent on the degree of pore-fluid saturation. A study of nine samples shows that 1000/Qp exhibits a resonance peak at midrange saturations (SW av 30 % to SW = 70 %) in most samples, and 1000/Qs shows similar behaviour in several of these. For porosities greater than 13%, the normalised amplitudes of the peaks in P-wave and bulk attenuation are correlated to porosity; the latter increases at a linear rate of 0.98 per percentage increase in porosity. These data suggest that attenuation reaches a maximum when the gas/water mixture is neither too compressible nor too incompressible. The Biot/squirt (BISQ) theory inadequately models the saturation dependence of 1000/Qp and Vp in a sample at low confining pressure. Vp falls with decreasing saturation between SW =100 % to SW - 50 %; below SW = 50 %, the behaviour of Vp is dependent on the confining pressure. Vs generally increases with decreasing saturation over the entire saturation range in all samples. The unrelaxed pore-fluid model of Mavko and Nolen-Hoeksema (1994) describes the Vp data reasonably well in most samples using low wetting fractions (< 15 %), which indicates that the pore fluid is unrelaxed at both the grain and sample scales. The wetting pore fluid becomes unrelaxed at high frequencies and/or low permeabilities. The V. data are poorly described by the model, possibly due to matrix softening by the wetting fluid. The experimental data have indicated significant shortcomings in the mathematical models of seismic wave propagation in reservoir rocks. The data highlight important aspects of wave propagation that must be addressed in revised theories.

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