Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 91-101). / Details of the biogeochemical cycles and the dominant mechanisms present in Precambrian remain heavily debated topics. The events of the Late Proterozoic onset to glaciations and what types of early life existed in the Archean are two of the many provoking topics within the Precambrian. We set out to improve the understanding of these geologic intervals by examining stable isotopic signatures and molecular fossils (biomarkers) in Late Proterozoic and Mesoarchean ages sedimentary rocks in Northwestern Territories, Canada and Pilbara, Western Australia, respectively. This thesis presents sulfur, carbon, oxygen and nitrogen stable isotopic data along with distribution of steranes and hopanes biomarkers. Geochemical data is analyzed in the context of elucidating the key biological and environmental factors involved in the Mesoarchean marine biosphere and the Late Proterozoic onset of glaciations. Stable isotopic analysis of the Gorge Creek Group in Pilbara, Western Australia reveals organisms capable of microbial sulfur disproportionation were likely the dominant biological players in Mesoarchean deep-ocean sulfur cycling. Biomarker and isotopic proxies of the Coppercap Formation reveal diverse biological activity directly prior to the Sturtian Glaciation with communities of green and purple sulfur bacteria as well as methanotrophs and cyanobacteria. Possible environmental implications of these communities co-existing are explained in context of changes in ocean chemistry and the diversification of eukaryotic life. / by Katherine S. Thomas. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1994. / Includes bibliographical references (leaves 69-70). / by Susan Aileen Evans. / M.S.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 37-40). / Escarpments are present on passive margins around the world, but their evolution is poorly understood. Some geologists interpret escarpments as stationary features, whereas others have argued that they are retreating inland faster than a kilometer per Myr. I investigate Brazilian escarpments by determining whether or not the river networks on either side of the escarpment are in erosional equilibrium with each other. My approach is based on the premise that rivers on opposite sides of a stationary escarpment would be eroding at the same rate (erosional equilibrium), whereas rivers on opposite sides of a mobile escarpment would be eroding at different rates (erosional disequilibrium). I use a recently developed technique called chi mapping to assess the erosional disequilibrium of river networks along the Brazilian escarpments. For comparison, I also compile erosion rates on either side of the escarpments from cosmogenic "Be measurements in the existing literature, and use these to calculate recent retreat rates of the escarpments, which fall between 4 and 40 m/Myr. I determine that chi mapping and cosmogenic erosion rates agree on the direction of escarpment movement, but disagree on the magnitudes of the retreat rates. I also estimate the percentage of drainage area exchanged by stream capture as the escarpment drainage divide moves across the landscape. Using two different estimation methods, I find that less than 40% of drainage area is exchanged by stream capture, making divide migration the dominant mechanism for drainage basin reorganization. If my estimates of recent escarpment retreat rates are representative of long-term rates, the Brazilian escarpments have retreated up to 5 km since their formation during the Cretaceous rifting event. My analysis shows that the topographic retreat of the Brazilian escarpments could have been driven by drainage basin disequilibrium resulting in divide migration. / by Madison M. Douglas. / S.B.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1998. / Includes bibliographical references (leaves 86-90). / by Carrie T. Friedman. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002. / Includes bibliographical references (p. 113-121). / It is suggested that orbital tuning casts a false light upon the chronology of glaciation and the understanding of the climatic response to orbital variations. By developing a new age-model, independent of orbital assumptions, a significant non-linear response to orbital forcing becomes evident in the [delta] 18 0 record. The new age-model also indicates glacial terminations two through eight are 8,000 years older than the orbitally based estimates. A simple obliquity threshold model is presented which reproduces the timing, amplitude, and observed non-linearities of the [delta] 18 0 record; and supports the plausibility of the new age-model and the inferred non-linear climatic response. / by Peter Huybers. / S.M.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1998. / Includes bibliographical references (leaves 163-173). / A Stoneley wave propagating in a borehole generates a flow of pore fluid in permeable zones intersected by the borehole. In turn, this flow of pore fluid induces a streaming electrical field. This thesis is an experimental and theoretical investigation of the electrical fields induced by Stoneley waves. The main emphasis of this thesis is to understand the electroseismic phenomena that are observed in the field. In the first experiment described in this thesis, we measured Stoneley-wave-induced electrical fields in a borehole drilled through fractured igneous rocks. Analysis of field data confirms that the electrical fields that we measured were induced by fluid flow in fractures. The normalized amplitude of these electrical fields correlated with the fracture density log. In the second experiment, we measured Stoneley-wave-induced electrical fields in several boreholes in vuggy dolomite. In dolomite, the normalized amplitude of the Stoneley-wave-induced electrical field correlates with the porosity of the formation around the borehole. Further, the Stoneley-wave-induced electrical fields have anomalously high amplitudes at an isolated fracture that intersected two boreholes. To explain the experimental results, we developed a theoretical model for the Stoneley-wave-induced electrical fields. According to the model, the normalized amplitude of the Stoneley-wave-induced electrical field is proportional to the porosity and inversely proportional to the pore space tortuosity of a formation around a borehole. Moreover, the amplitude-versus-frequency behavior of this electrical field depends on the permeability of the formation. To further test the theory's prediction, we measured electrical potentials induced by the borehole Stoneley wave in the frequency range from 100Hz to 4kHz. The normalized amplitudes of the Stoneley-wave-induced electrical potentials measured in the field were consistent with the amplitudes predicted by the theory. Also, the amplitude- versus-frequency dependence of the electroseismic signals recorded at the depth of the large fracture roughly followed the trend predicted by the theory. However, the general amplitude-versus-frequency dependence of the electroseismic signals recorded in the field is more complicated than that predicted by the theory. The main contributions of this thesis are: 1. This thesis develops a borehole electroseismic measurement technique and demonstrates that it works in the field. This technique can be used to make electroseismic logging measurements. 2. This thesis investigates an electrical field induced by a borehole Stoneley wave. This electroseismic phenomenon is explained, measured in the field and modeled theoretically. 3. This thesis derives from field data a parameter that describes local electroseismic coupling in a formation around a borehole. This parameter, the normalized amplitude of the Stoneley-wave-induced electrical field, is defined as the ratio of an electrical field amplitude to a pressure amplitude in the Stoneley wave at a certain depth. This thesis demonstrates that the normalized amplitude of the Stoneley-wave- induced electrical field can be used to identify permeable fractures in situ. 4. This thesis uses field electroseismic measurements to quantitatively characterize rock formations around a borehole. Using the theoretical model developed in this thesis, a porosity log for fractured granite is derived from electroseismic field data. / by Oleg Mikhailov. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2006. / Cataloged from PDF version of thesis. Some pages in the original thesis contain text that runs off the edge of the page. / Includes bibliographical references (pages 36-37). / This project explores whether cloud top altimetry can be used as an accurate and reliable means of estimating the intensity of tropical cyclones. Professor Kerry A. Emanuel developed the theory that is under investigation. His theory aims to calculate the peak surface wind speed in hurricanes using only three parameters, all of which can be collected from satellite imagery: cloud top height, sea surface temperature and cloud top temperature. Cloud top heights for selected hurricanes were obtained from the ICESat, and points were identified where the ICESat may have traversed the hurricanes. These points were compared with IR images to confirm the intersection of the ICESat track and the hurricane tracks. Out of 18 hurricanes examined, four provided feasible points to test this new technique. Two of these points were from hurricanes that were at the end stage of their life cycle; these two data points were discarded. Data from the two usable data points were compared to the recorded wind speeds from Unisys. It seems that the new method is overestimating the maximum surface wind speed by less than 10%. Two data points are insufficient for conclusively validating this technique. However, this project has established a viable method for gathering and analyzing altimetry data, providing a basis for further testing of the theory. / by Valerie Wong. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2008. / Includes bibliographical references. / This thesis presents methods of analysis and results from a petroleum reservoir monitoring application using induced seismicity data. The dissertation work is comprised of four major studies, each focusing on a different aspect of induced seismicity. First, methods and issues in location of induced seismicity are discussed, and strategies are proposed for determining accurate hypocenters of induced events. The importance of velocity model and how it impacts the depth determination of reservoir-induced events are demonstrated with real field data. A location method that is better-suited than other existing methods for this application is proposed. The accuracy and efficiency of this proposed location method is demonstrated with field data application.Secondly, event locations and interpretations are presented for about 1300 induced events recorded by a near-surface network over a seven year period at a petroleum field in Oman. The event hypocenters delineate two major northeast-southwest striking faults in the field, which are consistent with fault maps derived from reflection seismic interpretations. Spatiotemporal analysis of induced event locations reveals ongoing large scale fault reactivation in the field, and also suggests compaction of the gas reservoir as the major cause and water injection in the oil reservoir as the secondary cause for inducing seismicity in the field.Thirdly, event locations and interpretations are presented for a different set of induced seismicity data recorded by a deep-borehole network over an 11-month period at the same field. About 5400 events are located and analyzed, and detailed mapping of faults and fractures using the event hypocenters are presented. / (cont.) Patterns of seismicity also reveal faults and fracture systems previously unmapped by reflection seismic. While this dataset allows for much finer interpretation, the results between the two network data are found to be consistent and comparable.Finally, the double-difference relocation and tomography method is applied for event relocation and imaging of the reservoir. Better correlation of relocated events with faults is observed from application of this method to the surface-network events, and detailed velocity and structure images for the reservoir are obtained from application of tomography with the deep network events. / by Sudipta Sarkar. / Ph.D.

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 21-26). / Compositional analysis of atmospheric and laboratory aerosols is often conducted via single-particle mass spectrometry (SPMS), an in situ and real-time analytical technique that produces mass spectra on a single particle basis. In this study, machine learning classification algorithms are created using a dataset of SPMS spectra to automatically differentiate particles on the basis of chemistry and size. While clustering methods have been used to group aerosols into broad categories based on similarity, these models do not incorporate known aerosols labels and are not explicitly formulated for classification. Furthermore, traditional methods often rely on a smaller set of well-known, important variables whereas the proposed method is more general and flexible, allowing researchers to automatically quantify and select important variables from any aerosol subset. In this work, machine learning algorithms build a predictive model from a training set in which the aerosol type associated with each mass spectrum is known. Several such classification models were created to differentiate aerosol types in four broad categories: fertile soils, mineral/metallic particles, biological, and all other aerosols using -40 common positive and negative spectral features. For this broad categorization, machine learning resulted in a classification accuracy of -93%. More complex models were developed to classify aerosols into specific categories which resulted in a classification accuracy of -87%. The trained model was then applied to a 'blind' mixture of aerosols with model agreement on the presence of secondary organic aerosol, coated and uncoated mineral dust and fertile soil. Additionally, the model is used to characterize an ambient atmospheric dataset collected from the free troposphere. / by Costa Christopoulos. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1998. / Includes bibliographical references (p. 76-79). / by Barbara J. Souter. / Ph.D.