Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1985. / Microfiche copy available in Archives and Science. / Bibliography: leaves 80-81. / by Haim Nelken. / M.S.

Thesis: Ph. D. in Geophysics, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references. / The aim of seismic tomography is to determine a model of Earth properties that best explain observed seismic data. In practice, the limitations placed on our observations and computational capabilities force us to make a number of decisions about the scales and parameterizations of models, the nature of the data considered, and the approximations to wave propagation that connect the two. This thesis will consider three divergent approaches to seismic tomography spanning different representations of Earth structure at different scales, using different parts of the teleseismic wavefield, and solving the inverse problem with different approximations to the wave equation and different optimization methods. In choosing each of these approaches, we address two major decisions that influence the tomographic process: First, what relative value do we place on an less approximate treatment of wave physics versus the ability to incorporate as much information as possible in our inversion? Second, how can we use novel data to better constrain smooth seismic structure in regions that were previously unresolved? The first project presents a global ray-theoretical P-wave model that encompasses millions of traveltime picks. In this inversion, the addition of data from the dense USArray Transportable Array to global catalog data allows us to image the structure of the Eastern United States with unprecedented resolution and make a robust evaluation of the spatial scales of the heterogeneity. The second project develops a finite frequency approach to turning wave transmission tomography using a computationally efficient one-way wave propagation on curvilinear coordinates. The use of overturning coordinate systems allows for the application of wave equation tomography to phases previously unused in other oneway schemes. The final project presents a novel approach to wave-equation teleseismic reflection tomography using free surface multiples. The use of these multiply reflected phases helps to localize heterogeneity in the model to within layers of Earth structure. This project spans the final two chapters and includes the theoretical developments and an inaugural application to SsPmp data from the Hi-CLIMB array in Tibet. / by Scott A. Burdick. / Ph. D. in Geophysics

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1997. / Includes bibliographical references (p. 127-130). / by Albert S. Fischer. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1994. / Includes bibliographical references (leaves 50-63). / by Alberto Edgardo Saal. / M.S.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 151-162. / by Stephen Hilary Richardson. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Microfiche copy available in Archives and Science. / Bibliography: leaves 40-41. / by Pamela A. Melroy. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, February 2001. / Includes bibliographical references (p. 67-74). / We reexamine the longstanding hypothesis that lunar contraction is constrained by the lack of a visible global system of compressive faults. We model the lunar lithosphere as a layered elastic medium that fails according to a Mohr-Coulomb criterion. We use elastic constants inferred from lunar seismic profiles, and use a finite element code to model the response of this lithosphere to contraction. We find that fault localization and propagation are strongly affected by the thickness of the lithosphere. A thin lithosphere promotes fault localization by extending through the entire lithosphere and thus enabling large stress relief and large displacements. For a thick elastic lithosphere the mode of faulting is less localized and many faults form in the upper part of the lithosphere, each with small displacements. Furthermore, localization in a thin lithosphere enables fault propagation through a compliant layer, such as a 1-3 km megaregolith layer, while for a thick lithosphere faults cannot penetrate this layer. Thus, the lack of an observed global system of compressive faults, similar to the locate scarps observed on the surface of Mercury, may not be due to the absence of an episode of global contraction on the moon, but rather due to the thickness of the lithosphere at that time. / by Ori Weisberg. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007. / Includes bibliographical references (leaves [34]-38). / New reconnaissance data for a poorly characterized area in the western Bhutan Himalaya show distinction between the 40Ar/39Ar cooling age distributions of detrital minerals in the two river catchments of the Punatsang chu and the Wang chu. Muscovites from five samples of Wang chu river sands yield ages (corresponding roughly to the time of bedrock cooling through a temperature of ca.350°C) between 9.37± 0.08 Ma and 13.98 ± 0.08 Ma. The majority of ages are less than 13 Ma, and the data for all samples have a unimodal distribution with an average age of ca. 11.4 ± 1.5 Ma. In contrast, muscovites from 14 Punatsang chu samples yield ages with nearly the same total range but with a distinctively multi-modal distribution. Two modes predominate in the Punatsang chu data: one at ca. 11.4 Ma, which is statistically indistinguishable from the single mode of the Wang chu data, and one at ca. 14.5 Ma. The full explanation for this distribution must await further bedrock and detrital dating studies, but one hypothesis is that the out-of-sequence Kakhtang thrust fault system - which is thought to transect the upper reaches of the river catchments - has juxtaposed two bedrock terrains with different cooling histories. / (cont.) A second possibility is that the younger mode of cooling ages is related to uplift of the footwall of the Chomolhari fault system, which includes the major bounding structures of the Yadong-Gulu rift northwest of the catchments. Exactly why the older mode of ages is not found in the Wang chu dataset is unclear. If the first of the above hypotheses is correct, the lack of an older mode in the Wang chu dataset may mean that the muscovites in the Wang chu fluvial sediments were derived exclusively from the Kakhtang thrust system hanging wall. If the second hypothesis is correct, the muscovites may have been derived exclusively from the Chomolhari fault system footwall. However, since we do not know the actual distribution of muscovites in the Wang chu catchment and we do not know that modern erosion is uniform in the catchment, it is also possible that the older mode is simply missing as an artifact not-uniform sampling. Again, more studies are needed to evaluate these alternative explanations. / by Peldon Tshering. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002. / Includes bibliographical references (p. 34). / With millimeter-level positioning capabilities, annual fluctuations in GPS height estimates can now be resolved. A likely explanation for these height variations is loading of the Earth's surface. We examine the relative contribution of atmospheric pressure loading to the total signal by modeling loads utilizing Farrell's elastic Green's functions. A focus on four permanent GPS sites provided insight on coastal and seasonal differences as well as the relative impact of atmospheric pressure loading on annual vertical displacements. Our findings suggest that accounting for the inverted barometer response [Farrell, 1972] of the ocean at coastal sites provides a better fit to GPS data. However, near restricted bodies of water we find that the non-inverted barometer fits better. We also found lower closer fits of the modeled pressure load to the GPS data during winter months than during the summer possibly due to larger pressure variations during the winter and/or mismodeling of tropospheric delay during summer months [Herring, 1990]. As for the contribution due to multiple sources of loading, in most cases, by adding an expected water load (from upper 2 meters of soil) to the atmospheric pressure load, a closer agreement to the GPS signal was found. / y Jennifer L. Alltop. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002. / Includes bibliographical references (p. 97-98). / The MIT general circulation model is used with simplified setup to study steady zonally averaged monsoon circulations. Two dimensional model runs are made with a zonally symmetric continent north of 15N and a slab ocean of uniform sea surface temperature to study the applicability of axisymmetric theory. Forcing to drive the monsoon is applied by heating the subtropical land surface. The dynamical constraints of axisymmetry prevent low-level cross-equatorial flow and inhibit the northward transport of moisture onto the continent when there is no temperature gradient across the equator. The ocean cannot supply adequate moisture to feed the monsoon, and the ground hydrology strictly controls the behavior of the monsoon. A second set of two dimensional runs with similar continent, but with an SST gradient across the equator, result in a viable steady monsoon with low-level cross-equatorial flow providing moisture to the monsoon. The surface forcing required to induce a monsoon is reasonable given the constraints of the axisymmetric model setup. A series of three dimensional model runs with a zonally symmetric continent are made to study the role of zonally asymmetric flow on the zonal mean monsoon. It is found that greater land surface forcing is required to induce a zonally averaged monsoon circulation in the three dimensional runs than in similar axisymmetric runs. The behavior of the monsoon disturbances in the three dimensional runs is similar to the observed Asian monsoon in that there is low-level cross-equatorial flow which is southwesterly along the coastline, and in that a large-scale angular momentum conserving meridional circulation develops with ascent over the continent and subsidence in the opposite hemisphere. Moisture transport is found to play a very strong role in the monsoon dynamics in all of the model runs. / by Nikki C. Privé. / S.M.