Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Microfiche copy available in Archives and Science. / Bibliography: leaves 65-66. / by Marc Allen Seltzer. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002. / Includes bibliographical references (p. 235-261). / In this thesis, I explore the geophysical structure and evolution of the Australian continental lithosphere. I combine insights from isotropic and anisotropic seismic surface-wave tomography with an analysis of the anisotropy in the mechanical properties of the lithosphere, inferred from the coherence between gravity anomalies and topography. With a new high-resolution waveform tomographic model of Australia, I demonstrate that the depth of continental high wave speed anomalies does not universally increase with age, but is dependent on the scale and the tectonic history of the region under consideration. I construct an azimuthally anisotropic three-dimensional model of the Australian upper mantle from Rayleigh-wave waveforms. I compare Bayesian inverse methods with discretely parameterized regularization methods, and explore the use of regular, tectonic and resolution-dependent tomographic grids. I advocate the use of multitaper spectral estimation techniques for coherence analysis of gravity and topography, applied to Australian isostasy. I investigate the importance of internal loading, the directional anisotropy of the gravitational response to loading, and the estimation bias affecting the long wavelengths of the coherence function. I develop a method for non-stationary coherence analysis which enables a complete characterization of continental strength by the dependency of gravity-topography coherence on wavelength, direction and geologic age. Combining high-resolution, depth-dependent anisotropy measurements from surface-wave tomography with the mechanical anisotropy from gravity/topography coherence, I assess the validity of two competing theories regarding the cause of continental anisotropy (vertically coherent deformation or simple asthenospheric flow) quantitatively for the very first time. / by Frederik Jozef Maurits Simons. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references. / In arid environments, near-surface complexity and surface topography present major challenges to land seismic data acquisition and processing. These challenges can severely affect data quality and introduce uncertainty into reservoir imaging and characterization. The primary objectives of this thesis are to model and study the contribution of near-surface heterogeneities on seismic wavefield scattering for better understanding of land seismic data, develop an effective approach to filter out the scattered noise from the seismic records to enhance the signal-to-noise ratio, and to accurately image and locate the near-surface heterogeneities. The first part of this thesis is concerned with simulating the effects of seismic wave scattering from buried, shallow, subsurface heterogeneities through finite difference numerical forward modeling. The near-surface scattered wavefield is modeled by separating the incident (i.e., in the absence of scatterers) from the total wavefield by means of a perturbation method. Wave propagation is simulated for several earth models with different near-surface characteristics to isolate and quantify the influence of scattering on the quality of the seismic signal. We show that the scattered field is equivalent to the radiation field of an equivalent elastic source excited at the scatterer locations. Moreover, the scattered waves consist mostly of body waves scattered to surface waves and are, generally, as large as, or larger than, the reflections. These scattered waves often obscure weak primary reflections and can severely degrade the image quality. The results indicate that the scattered energy depends strongly on the properties of the shallow scatterers and increases with increasing impedance contrast, increasing sizes of the scatterers, decreasing depth of the scatterers, and increasing the attenuation factor of the background medium. Also, sources deployed at depth generate weak surface waves, whereas deep receivers record weak scattered surface waves. The analysis and quantified results help in the understanding of the scattering mechanisms and, therefore, can lead to developing new acquisition and processing techniques to reduce the scattered surface waves and enhance the quality of the seismic image. The second part of this thesis develops an approach based on spatially varying local-slope estimation, aiming at alleviating the effects of scattered surface waves and enhancing the quality of the seismic signal. Understanding the mechanism and behavior of the simulated scattered surface waves in the first part of this thesis form the basis for designing the filtering scheme. The algorithm is based on predicting the spatially varying slope of the noise, using steerable filters, and separating the signal and noise components by applying a directional non-linear filter oriented toward the noise direction to predict the noise and then subtract it from the data. The slope estimation step using steerable filters is very efficient, as it requires only a linear combination of a set of basis filters at fixed orientation to synthesize an image filtered at an arbitrary orientation. We apply our filtering approach to simulated data as well as to seismic data recorded in the field to suppress the scattered surface waves from reflected body-waves, and demonstrate its superiority over conventional f - k techniques in signal preservation and noise suppression. The third part of this thesis presents an approach for prestack elastic reverse time migration (RTM) to locate and image near-surface heterogeneities using the near-surface scattered waves (e.g., body to P, S, and surface waves). The approach back-projects the scattered waves until they are in phase with the incident waves at the scatterer locations. The P wave components (divergence of the wavefield) are derived from the spatial derivatives of the measured wavefields. Imaging the near-surface heterogeneities is important for planning seismic surveys or explaining nearsurface related anomalies in the data. The scattered body-to-surface waves travel horizontally along the free surface, and, therefore, they provide optimal illumination of the near-surface compared to scattered body-to-body waves. Additionally, the elastic RTM scheme preserves the relative amplitude because all wave propagation losses, including mode conversions, are properly taken into account. We demonstrate, using synthetic data, that elastic RTM of near-surface scattered waves constructs an accurate and reliable depth image of near-surface scatterers. / by Abdulaziz M. Almuhaidib. / Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2008. / Includes bibliographical references. / This thesis addresses processes associated with the uplift, deformation, and erosion of orogenic plateaus. The timing and mechanisms of uplift of the Tibetan Plateau and the Altiplano are the subject of ongoing debate. Central issues include the strength of the lower crust and the role of lower crustal flow, the relative importance of continuous deformation versus block deformation, and the possibility of lithospheric delamination. The goal of this thesis is to further explore several of these issues using a combination of numerical modeling, field observations, and thermochronology. I investigate controls on the large-scale evolution of the Tibetan Plateau and the Altiplano using a new quasithree-dimensional viscous flow model that allows for both the development of a weak lower crust and lateral and temporal viscosity variations. Modeling motivated by the Tibetan Plateau shows that lateral variations in crustal strength can have a significant effect on surface velocities throughout the plateau, as well as on the location, shape, and slope of plateau margins and the overall plateau morphology. Model results suggest that crustal strength heterogeneities may be responsible for a number of seemingly unrelated aspects of Tibetan Plateau morphology and deformation. Modeling motivated by the Altiplano explores the relationship between subduction angle, the strength of the lower crust, crustal thickening, and surface shortening in the Central Andes. Model results illustrate that lower crustal flow above regions of steep-slab subduction can redistribute material along strike and can explain discrepancies between surface shortening and crustal thickness in the northern and southern Altiplano. I address the distribution of Middle Cenozoic deformation on the eastern margin of the Tibetan Plateau by using field observations and thermochronology to document an episode of extension and constrain its timing to the Oligocene. Finally, I examine the response of a major river system to flow over an abrupt plateau margin by using topographic data, cosmogenic nuclide dating, and numerical modeling to describe the incision history of the Colorado River into the southwestern Colorado Plateau. / by Kristen Lee Cook. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1991. / Title as it appears in the M.I.T. Graduate List, Sept. 1991: Analysis of the Titus Canyon Formation, evidence for Early Oligocene extension in the Death Valley Area, California. / Includes bibliographical references (leaves 48-50). / by Beverly Z. Saylor. / M.S.

Thesis (S.M. in Geophysics)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 63-64). / Although the surface deformation resulting from the opening of a single fracture in a layered elastic half-space resembles the observed deformation at the InSalah site, it seems unlikely that only a single fracture is involved. This raises the question of how interaction among multiple fractures affects surface deformation. Finite element modeling is used to build a 3D model of a reservoir with multiple fractures. The interacting cracks and fractures give this model a more complicated stress state, and so any surface deformation would be different from that of a model with a single fracture. Geodetic monitoring of large-scale CO 2 sequestration provides a potentially powerful and cost-effective tool for interrogating reservoir structure and processes. For example, InSAR observations at the InSalah, Algeria sequestration site have mapped the surface deformation above an active reservoir, and helped delineate the effects of CO2 storage. The impact of interactions on individual fractures and the qualitative changes in the surface displacement and stress fields are considered and the importance of orientation, position and fracture area is investigated. It was found that when the crack locations are biased towards stacked parallel arrangements, then the shielding effect of interactions dominates, meaning that the overall stiffness of a representative volume increases. When collinear interactions dominate then the overall stiffness is reduced. These effects are then used to find a volume average and a continuum description of a solid with effective elastic properties. In this way a volume of fractured rock can be replaced with a representative volume with elastic properties that approximate the interaction effects. / by Ruel Jerry. / S.M.in Geophysics

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1995. / Includes bibliographical references (leaves 209-216). / by Sarah Tragler Gille. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996. / Includes bibliographical references (leaves 31-32). / by Janice A. Vatland. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989. / Includes bibliographical references (leaves 89-93). / by David Brian Chester. / M.S.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Microfiche copy available in Archives and Science. / Bibliography: leaves 214-230. / by Levent Gulen. / Ph.D.