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. / Since the discovery of plate tectonics, geophysicists have sought to understand the dynamic system driving the evolution of the earth, both at the surface and in the deep interior. While the deep earth contains far fewer phases than the crust, the inaccessibility of the mantle and core present a different challenge: unraveling the physical behavior of materials at conditions beyond our intuitive, observational, and experimental grasp. Among the most persistent of problems has been determining the influence of pressure on the mechanical behavior of deep rocks. Deformation experiments have typically been limited by equipment capabilities to only a tiny fraction of the pressure of the deep mantle, and thus our understanding pressure effect on rock strength has remained insufficient to precisely model the convection of the mantle at large scales in time and space. In the last decade, a promising new campaign in mantle rheology has been waged with two powerful emerging technologies: synchrotron x-ray diffraction, and complementary multi-anvil deformation machines. These advancements have allowed precisely controlled deformation experiments at conditions representative of the deep upper mantle, with unprecedented measurement precision. Here I present a detailed experimental study of the behavior of olivine at upper mantle conditions. Among the results is evidence of a significant pressure effect on the strength of olivine (an activation volume of 14 ± 3 cm3/mol), as well as pioneering in situ measurements of fabric development, slip system transitions, and stress heterogeneity. / by Nathaniel Adams Dixon. / Ph. D. in Geophysics

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984. / Microfiche copy available in Archives and Science. / Bibliography: leaves 48-49. / by Michael E. Rocha. / M.S.

Thesis: S.M. in Geophysics, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 34-39). / We apply a generalized Radon transform (GRT) to SKKS data to obtain a large-scale high-resolution image of the lowermost mantle (400 kilometers above the core-mantle boundary) beneath the Pacific Ocean (125° E-75°W, 45° S-65°N in this work). More than 4,000,000 radial teleseismic traces from about 8,000 events (mb >= 5.8) between 1990 and 2015, globally recorded by one or more of a total ~27,000 receivers, were collected from IRIS-DMC. All of the traces were automatically band-pass filtered (10s to 50s), rotated, clustered, deconvoluted, and finally migrated to structural reflectivity profiles using reference wavespeeds according to the iasp91 model. We compare the 2D and 3D imaging results beneath the Pacific subduction zones and the non-subducting regions, including the southeastern Pacific and Hawaii, focusing on the positive velocity contrast above the CMB that might delineate the D" discontinuity. We observe broad zones of scatter surfaces, which may indicate multiple-interface post-perovskite phase transitions caused by compositionally differentiated subducted lithosphere. Furthermore, we observe a sharp change in the proposed multiple-interface structure regarding the total number of positive interfaces, the intervals, and the overall pattern of the anomalies from the subduction zones to the non-subducting regions. Such structural complexity implies: (1) the presence of old (at least 180 Ma) subducted material layer of either continental or oceanic lithosphere under the whole Pacific Ocean; and (2) spatial variations in iron, magnesium, and silica components in the subducted lithosphere. Understanding the possible relationship between observed complexity and composition requires further interdisciplinary research. / by Zhulin Yu. / S.M. in Geophysics

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017. / Page 376 blank. Cataloged from PDF version of thesis. / Includes bibliographical references. / This thesis examines critical aspects of the terrestrial environment that have resulted in a habitable planetary surface: the establishment of the continental crust and the progressive rise of an oxygenated atmosphere. The volume of continental crust on the earliest Earth is a critical parameter for constraining the chemical evolution of major terrestrial reservoirs, and radiogenic isotope signatures document this varying geochemical character. Chapter 1 presents a Lu-Hf and U-Pb isotopic characterization of zircons from the 4.0-2.9 Ga Acasta Gneiss Complex (AGC) and documents the magmatic extraction history of this domain, including changes in source compositions. These results are compared with a complementary dataset obtained using solution methods in Chapter 2. The integration of these results demonstrates the utility of performing coupled solution- and laser-based analyses on the same zircon populations to parse out U-Pb and Lu-Hf systematics. Zircons from many of these orthogneisses exhibit isotopic complexity due to the combined effects of accumulated radiation damage and repeated metamorphic episodes. For this reason, it is best to subsample zircon grains to isolate domains of distinct age and isotopic composition. In order to obtain suitable precision for subsampled domains, it was necessary to develop analytical techniques (Chapter 3) suited to small-volume analysis of the U-Pb and Lu-Hf isotope systems in zircon (via both laser ablation and solution analysis). In contrast to the whole rock Nd isotopic record of the AGC, the zircon Hf isotopic record does not indicate that rocks within the AGC were derived from a strongly depleted mantle. In order to evaluate the polymetamorphic evolution of these rocks, in Chapter 4 1 present a combined U-Pb and Sm-Nd isotope and trace element study of MREE-rich accessory minerals. In Chapter 5, I investigate sedimentary pyrite formation pathways and the oxygenation history of the late Archean atmosphere using combined sulfur and iron isotope signals as recorded in distinct morphologies of pyrite. This work represents a critical step in deconstructing the pathways of S-MIF production, transfer and preservation in the sedimentary record. Collectively, these studies contribute to our understanding of the establishment and evolution of the early continental crust and an oxygenated atmosphere. / by Ann M. Bauer. / Ph. D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2008. / Includes bibliographical references (p. 55-57). / The goal of this Masters project is to implement the WRF model with 3D variational assimilation (3DVAR) at MIT. A working version of WRF extends the scope of experimentation to mesoscale problems in both real and idealized scenarios. A state-of-the-art model and assimilation package can now be used to conduct science or as a benchmark to compare new methods with.The second goal of this project is to demonstrate MIT's WRF implementation in an ongoing study of the impact of position errors on contemporary data assimilation (DA) methods [21]. In weather forecasting, accurately predicting the position and shape of small scale features can be as important as predicting their strength. Position errors are unfortunately common in operational forecasts [2, 14, 21, 27] and arise for a number of reasons. It is difficult to factor error into its constituent sources [21].Traditional data assimilation methods are amplitude adjustment methods, which do not deal with position errors well [4, 21]. In this project, we configured the WRF-Var system for use at MIT to extend experimentation on data assimilation to mesoscale problems. We experiment on position errors with the WRF-Var system by using a standard WRF test; a tropical cyclone. The results for this identical twin experiment show the common distorted analysis from 3DVAR in dealing with position errors. A field alignment solution proposed by Ravela et al. [21] explicitly represents and minimizes position errors. We achieve promising results in testing this algorithm with WRF-Var by aligning WRF fields from the identical twin. / by John K. Williams. / S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 21-24). / To quantify the effects of the NO, SIP call in urban and rural locales, surface ozone data from the Air Quality System is analyzed. Methods from extreme value theory are applied to calculate and compare 20-year return levels at 5 urban and 17 rural/suburban sites in Illinois based upon maximum daily 8-. hour average ozone concentrations from summer (JJA) for two periods (1992- 2002 and 2003-2013) and a threshold of 70 (ppb). Between the two periods, 21 out of 22 sites experienced a decrease in 20-year return levels. The magnitude of these decreases does not indicate a strong correlation between population density and air quality improvements, however, further analysis is required. / by Elizabeth Ndayu Rider. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989. / Includes bibliographical references (leaf 148). / by Peter Neil Schweitzer. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1992. / Maps in box, 23 cm. / Includes bibliographical references (leaves 222-233). / by Allison Margaret Macfarlane. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2014. / 55 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 28-33). / A machine-learning model was created to predict air pollution at high spatial resolution in Manhattan, New York using taxi trip data. Urban air pollution increases morbidity and mortality through respiratory and cardiovascular impacts, and understanding and predicting it is a significant public health challenge. A neural network NARX model was created in MATLAB for each cell on a 250m square grid laid over Manhattan, for a total of 907 individual models across the city, for PM2 .5 , CO, NO2 , 03, and SO 2. In addition to standard meteorological inputs, data describing the distance and time traveled by taxis within each grid cell was used in the models. The models generally performed well, with mean R2 values between .62 (SO 2) and .86 (03), comparable to or better than previous models at this spatial scale. The model is computationally efficient enough to be run in real-time to aid citizens' and public health officials' decisions, and its efficacy suggests that taxi data is a valuable additional input to previous neural network pollution models. / by Rachel H. Keeler. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1985. / Vita. / Includes bibliographies. / by Steven Richard Bratt. / Ph.D.