Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1999. / Includes bibliographical references (p. 87-92). / Current estimates of methyl bromide surface fluxes are inconsistent with the observed tropospheric mole fractions (9 to 10 ppt, globally averaged) and the calculated atmospheric lifetime (1.7 ± 0.2 years), with mid-range estimates of sinks exceeding sources by at least 50 Gg y-I. Given the uncertainties in process-specific surface flux estimates, we consider several distributions of terrestrial sources and sinks that satisfy the constraints on atmospheric abundance, Mole fractions corresponding to each distribution are simulated with a three-dimensional chemical transport model based on analyzed observed winds, coupled to a simple model of the ocean mixed layer. All of the resulting scenarios overestimate the observed zonal gradient, with interhemispheric ratios ranging from 1.39 to 1.60. In the absence of unknown sources, model results imply a biomass burning source near the upper limit of the range of present estimates (50 Gg y-1). Sensitivities to surface fluxes are also calculated to determine the extent to which uncertain terms in the methyl bromide budget can be better quantified using long-term measurements. Results show that a global network capable of accurately monitoring the monthly, zonal mean distribution of CH3Br would be able to distinguish between biomass burning fluxes and other known terrestrial sources and sinks. Modeled sensitivities to biomass burning emissions also highlight the importance of including tropical locations in any long-term monitoring network. However, technological sources and soil sinks have similar zonal patterns, and long-term, "background" mole fractions are relatively insensitive to zonal flux distributions. It is only when we examine the high frequency variability of the concentration that the effect of longitudinal gradients in the flux field becomes apparent. / by Christopher D. Jensen. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1999. / Includes bibliographical references (p. 62-64). / An experiment was designed to gain some insight into the phenomena of electrical charge in the uniaxially stressed environment of a sample of Westerly granite. Varying properties of size, shape, saturation, and stress rate of the Westerly granite, a tentative set of physical relationships were measured. For instance, there is a strong suggestion that the amount of acoustic energy released when the sample fractures is proportionately related to the amount of charge that moves into or out of the sample, the net charge, over the period of the experiment. Increasing the concentration of the saturating solution increased the amount of charge that moved into or out of the sample. With all the samples that were dry, more charge move in than out over the period of the experiment. The few samples that were alike in every way before and after they fractured had a difference in charge and acoustic energy by a magnitude of their measured net charge and acoustic energy. / by Elizabeth Annah Jensen. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1999. / Includes bibliographical references (p. 35-36). / A numerical simulation is presented for the generation and movement of petroleum in a single layer of source rock, a process also know as primary migration. The equations governing the system are derived from principles of mass and volume conservation and are then non-dimensionalized. The result of this formulation of the problem is an equation similar in form to a diffusion equation that describes the volume and flow of oil in the system. The linear form of this equation is solved using a Crank-Nicholson finite differencing scheme, and the form of the numerical solution is compared to a steady-state solution. The effects of two non-dimensional parameters are investigated. Based on these investigations, the compressibility of the fluid and the rate at which oil is generated appear to have significant roles in this model of primary migration. / by William R. Kahl. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1999. / Includes bibliographical references (p. 76-79). / A case study is performed to investigate the nature of tropical cyclogenesis in the eastern Pacific Ocean. Focus is given to the formation and development of the initial circulation which eventually intensified into Hurricane Fefa. Using satellite imagery, the author studies the development of convective activity in the genesis region. Gridded reanalysis data are used to document the synoptic-scale flow, with emphasis on tracing the easterly wave which is associated with the formation of Fefa. The data show that the easterly wave propagated across the Caribbean Sea and the Central American mountains, and the initial circulation developed while the wave had moved into the eastern Pacific. The wave is found to have moved through an unstable basic state while it was in the Caribbean, which is favorble for its growth and maintenance. Two phenomena are observed prior to the formation of the low-level circulation. These include an easterly jet in the eastern Pacific that may have been associated with the blocking effect of the Central American mountains, and a southerly wind surge into the monsoon trough region. In addition, aircraft observations collected during Tropical Experiment in Mexico are used to study the evolution of the mesoscale system. Initially, a circulation in the middle troposphere with a cold core in the boundary layer, and a shear line located to the west were found. One day later, a low-level warm core vortex had developed, and it was displaced from the mid-level vortex. It is suggested that the low-level vortex formed from the spin-up of the monsoon trough, independent of the mid-level vortex. / by Terence Kung. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1999. / Includes bibliographical references (p. 69-70). / We analyze atmospheric data in order to study the upper tropospheric dynamics in the area of the Asian summer monsoon. We look at summers of four years from 1987 to 1990. The divergent upper tropospheric circulation of the monsoon often adopts the form of a unified large-scale vortex. However, when the vortex becomes elongated enough, so that the flow in most of the area is close to zonal, the vortex usually sheds secondary, or daughter, vortices that then propagate away. Eddy shedding occurs in all four summers that we examined. We use the potential vorticity and Montgomery stream-function fields to document the characteristics of eddy shedding events. In most cases, the daughter cell propagates westward. In the vertical, eddy shedding is confined to the upper troposphere, between 300 and 100 mb. The relationship between lower convergent and upper divergent levels is strong. However, we have not found any simple relationship between eddy shedding and lower-level dynamics. / by Jelena M. Popovic. / S.M.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1999. / Includes bibliographical references (leaves 17-18). / We use nuclear magnetic resonance (NMR) imaging to obtain a three-dimensional image of the pore structure in a limestone core, 4.5 mm in diameter and 10 mm in length, with a resolution of 40 [mu]m. This image is converted into boundary conditions for simulation of fluid flow through the rock using the lattice gas method. The computed permeability is several orders of magnitude lower than the laboratory measured permeability, most likely a result of the image resolution being too coarse to resolve the smaller pore throats, which are believed to be significant for flow in this sample. / by Margaret Saxby Edie. / S.M.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1999. / Includes bibliographical references (p. 268-280). / Visible wavelength spectra have been obtained for 1189 main-belt asteroids during the second phase of the Small Main-belt Asteroid Spectroscopic Survey. These telescopic measurements were made using charge-coupled device (CCD) detectors, allowing for the targeting of smaller asteroids. A majority of the asteroids sampled have estimated diameters of 30 km or less. The SMASSII survey provides the largest internally-consistent sample of asteroid spectra ever obtained, and reveals a greater range of spectral diversity among asteroids than has been previously shown. This diversity may arise from a broad range of surface ages, where smaller (collisionally younger) asteroids may have less evolved or processed surfaces than do larger asteroids. Processes that affect the development of a regalia, and the distribution of regalia particle sizes may produce the observed variations in spectral features. The larger sample size, greater spectral resolution, and greater photometric precision of the SMASSII survey, compared with the most extensive previous survey, provide a basis for developing a new "feature-based" taxonomic classification system for asteroids. This new taxonomy builds on the robust, large-scale structure of existing taxonomies, and relies on the presence or absence of specific spectral features to define new class boundaries. The SMASSII measurements reveal that many of the previous taxonomic classes that appeared to be distinctly separate, are instead spanned by a nearly continuous transition of spectral properties. This continuum may be evidence of sampling a more complete range of mineralogies. This newly found continuum makes it difficult to define a unique taxonomic structure using classical multivariate techniques, requiring that subjective boundaries be defined in some cases. The scale-length in spectral variance observed in many dynamical asteroid families was used as a metric for constraining the class sizes in this new taxonomy. The resulting new taxonomy consists of twenty-six spectral classes. Members of the previously defined X-class (which could be subdivided only using albedo information) display sufficient variation in spectral features to allow subgroups to be distinguished without the use of albedo. A subset of 465 SMASSII asteroids were specifically targeted to test the genetic reality of small dynamical "families." These families likely result from the collisional disruption of larger parent asteroids, and are identified as clusters of objects having similar orbital parameters. The targeted region, encompassing the heliocentric distance range of 2.690 to 2.815 AU, contains 14 families that had been previously identified, based on numerous analyses of orbital distributions in this region of the;1 main belt. A newly developed multivariate technique that analyzes the combination of spectral characteristics and orbital parameters reveals that all 14 of these previously proposed families are distinct from the "background" population mt asteroids. This result implies that each of these families is likely to have been truly formed by a collisional event, providing strong evidence for an extensive collisional history within the asteroid belt. Cand S-type 2 asteroids appear equally capable of forming families. Each family is found to be relatively homogeneous in its spectral characteristics, allowing the boundaries of tile families, and potential interlopers, to be more precisely identified than was possible in previous dynamical analyses. The relative spectral homogeneity within each of these families provides little evidence for any to have been formed from a differentiated parent body. It remains a mystery as to why there is no clear evidence of a major family containing members from· different geologic units, derived from a differentiated parent asteroid. In addition to the 14 previously identified dynamical families, our analysis has revealed five additional associations of spectrally similar asteroids in this same small heliocentric range. These spectral clusters may represent the dispersed fragments of older collisionally derived families. / by Schelte John Bus. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1998. / Folded leaves in pocket on p. [3] of cover, v. 2. / Includes bibliographical references. / Recent studies of turbidite bed thickness distributions have demonstrated power law and other statistical distributions. Chapter 2 explores the different distributions which may express fan processes and may be used as a tool to classify environments. Chapter 3 illustrates a correlation between cumulative distributions of well known turbidite deposits and interpreted fan subenvironments. A power law distribution may be, for some systems, the primary input signal and a one dimensional model allows qualitative-quantitative characterization of the effects of different fan processes. Environments dominated by different fan processes may be characterized based on the degree to which processes have acted as a "filter", systematically modifying the assumed power law distribution. This model is used to help account for bed thickness distributions observed in several field sites. Turbidite sections are often characterized in terms of alternating packages of thinning- and thickening-upward intervals, which are interpreted to be representative of different subenvironments, including channel and levee environments. In Chapter 4, stratigraphic sections from several field sites are analyzed for dominance of asymmetrical bedding packages using runs analysis. Results indicate ( 1) a correlation between the number of beds in the dataset and the significance level of the results, with may relate to prevalence of progradational and lateral migration of deposits; (2) runs tests should be applied with caution to datasets containing significant levels of erosion and amalgamation; and (3) runs tests may be used to identify the presence of interlayered lithologies and perhaps flow types. In Chapter 5, the log-log cumulative distribution model and the runs test techniques are applied to turbidites of the Permian Skoorsteenberg Fonnation in the Tanqua-Karoo Basin, South Africa. Exceptional exposure permitted a number of lateral correlation studies over a range of scales. The cumulative distribution model is supported by the turbidite distributions broadly subdivided into fan and interfan environments. Runs analysis reveals that interfan environments are generally more ordered than fan environments. Chapter 6 illustrates the development of a dual-component heterogeneous sediment transport model. A grain-scale model is integrated with a large scale basin model to simulate transport and deposition of heterogeneous-sized sediment in a fluvial system. / by Jennifer Carlson. / Ph.D.

Thesis: Ph. D. in Geophysics, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2019 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 185-205). / Hydraulic fracturing is an essential tool used to enhance connectivity in shale gas reservoirs by maximizing the intersection between the hydraulic fracture (HF) and pre-existing natural fractures (NF) or faults. The technique is most effective when the hydraulic fracture crosses natural fractures rather than arresting on them. Experiments conducted to examine the interaction between HF and artificial pre-existing faults suggest that the coupling of diffusivity and fault slip is an important element of the HF-fault interaction problem. Fault slip, once activated is associated with an apparent increase in diffusivity. Whether the hydrofracture crosses or arrests on the pre-existing fault is also affected by surface roughness, differential stresses, and fault slip mode (i.e., stable or stick-slip sliding). Calibrated piezoelectric transducers were used to measure acoustic emissions (AE) generated during HF and fault slip. / Moment tensor analysis of these events was used to distinguish pure tensile, shear, and possibly closure events during the experiments. Seismic moment magnitudes were approximately -7 for events during the initiation of the HF and about -5 for events during fault slip. Such a low ratio of seismic moments for tensile and slip events may explain the small numbers of tensile events recorded during reservoir stimulations. I also studied the time-dependent behavior in shales to gain insight into the post-stimulation efficiency of exploitations. Shale experiences strain hardening and compaction during loading by both isostatic (pressure-driven) and differential stress (shear-driven). Transient creep strain increased linearly with log(time), possibly transitioning to constant rate in timescale of several days. Motivated by the multi-scale nature of heterogeneities in shales, I examined the micromechanics of deformation using the nano-indentation technique. / Elastic and creep moduli found in nano-indentation and triaxial tests agreed within a factor of 2, but within that factor, the creep strength may depend on spatial scale. / by Saied Mighani. / Ph. D. in Geophysics / Ph.D.inGeophysics Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2019 / Cataloged from PDF version of thesis. / Includes bibliographical references. / This thesis contains four chapters that together investigate the igneous history of the Earth and the Moon. Each chapter explores new quantitative methods for combining experiments in igneous petrology with observed local and global major and trace element compositional variations and geophysical constraints. Integrating all types of geochemical fingerprints and geophysical observations allows us to solve complex natural processes where several interdependent variables are always at play. Chapter 1 investigates the timing and trace element partition coefficient conditions under which the Earth could have crystallized a magma ocean that then overturned and remixed to form an Early Enriched Reservoir and a complementary Early Depleted Reservoir consistent with isotopic measurements of Archean rocks. This study found that Earth most likely last differentiated a highly heterogenous mantle ~40 Ma after Solar System formation. / Chapter 2 is an experimental study of the multiple saturation point of the ultramafic Apollo 14 volcanic yellow glasses and their genesis via mixing melts of different lunar magma ocean cumulates. In finding successful mixing scenarios, this study highlighted the importance and possibility of internally consistent petrologic models. Chapters 3 and 4 shift in time from the Hadean and the Archean to the present by focusing on the generation and evolution of mid-ocean ridge basalts. Chapter 3 answers the question "What is the source of the garnet signature in MORB?" by quantifying the permissible range of mantle potential temperatures, mantle compositions, spreading rates, and mantle flow regimes that give rise to recognizable garnet-lherzolite field melting. Chapter 4 applies garnet melting systematics (Chapter 3) and consistency in petrologic models (Chapter 2) to the slow to ultraslow spreading 9-25°E Southwest Indian Ridge. / This study found that plagioclase peridotite melting, and not garnet peridotite or pyroxenite melting, of compositionally variable peridotite explains all observed compositional and geophysical variations. / by Stephanie M. Brown. / Ph. D. / Ph.D. Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences