Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1992. / Includes bibliographical references (p. 277-292). / by Carolyn Denise Ruppel. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989. / Includes bibliographical references (leaves 145-148). / by Stephen Michael Slivan. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1997. / Includes bibliographical references (leaves 39-40). / by Xiang Zhu. / M.S.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2000. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 70-71). / There are numerous models for convection of the Earth's mantle, the end cases of which are whole-mantle convection and layered convection. Heat flow is an important consideration in the evalution of these models. Simple thermal evolution models based on boundary layer theory have in the past been used to look at these models. However, insufficient attention has been paid to how well the theory applies. This was particularly uncertain for the case of layered convection with a radiogenically enriched lower mantle. I modified the finite-element code ConMan to include exponentially decaying internal heating so that the radiogenic isotopes in the lower layer would be accurately represented, and compared the experimental results of a one-layer case and a two-layer case to the theoretical solutions for those cases from boundary layer theory. It turns out that boundary layer theory does indeed seem to be accurate for the case of a two-layered convecting system with a radiogenic lower layer that produces exponentially decaying internal heating. / by Jenwa Hsung. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2001. / Includes bibliographical references (p. 144-151). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / This thesis discusses the interaction of atmosphere and ocean in midlatitudes on interannual and decadal timescales. We investigate the extent to which mutuallycoupled atmosphere-ocean feedback can explain the observed coupled variability on these timescales, and look for preferred modes of atmospheric response to forcing by sea-surface temperature anomalies. First, we formulate and study a very simple analytical model of the mutual interaction of the middle-latitude atmosphere and ocean. The model is found to support coupled modes in which oceanic baroclinic Rossby waves of decadal period grow through positive coupled feedback between the thermal forcing of the atmosphere induced by associated SST anomalies and the resulting windstress forcing of the ocean. Growth only occurs if the atmospheric response to thermal forcing is equivalent barotropic, with a particular phase relationship with the underlying SST anomalies. The dependence of the growth rate and structure of the modes on the nature of the assumed physics of air-sea interaction is explored, and their possible relation to observed phenomena discussed. We then construct a numerical model with the same physics; this enables us to consider the effects of nontrivial boundary conditions and background flows within the model. We find that the finite fetch of a closed ocean basin reduces growth rate and can lead to decay. However, the coupled mode described above remains the least-damped, and is thus the pattern most easily energized by stochastic forcing. Using a non-uniform atmospheric background flow focuses perturbation energy into particular areas, so that the coupled mode's expression in the atmosphere becomes fixed in space, rather than propagating. This improves the mode's resemblance to observed patterns of variability, such as the North Atlantic Oscillation, which are generally stationary patterns which fluctuate in intensity. The atmospheric component of the coupled mode exists in a balance between Rossby-wave propagation and vorticity advection. This is the same balance as the "neutral vectors" described by Marshall and Molteni (1993). Neutral vectors are the right singular vectors of the linearized atmospheric model's tendency matrix that have the smallest eigenvalues; they are also the patterns that exhibit the largest response to forcing perturbations in the linear model. We explain how the coupled mode arises as the ocean excites atmospheric neutral vectors. Neutral vectors act as pattern-specific amplifiers of ocean SST anomalies. We then proceed to study the neutral vectors of a quasigeostrophic model with realistic mean flow. We find a striking similarity between these patterns and the dominant patterns of variability observed in both the full nonlinear model and in the real world. We provide a mathematical explanation for this connection. Investigation of the "optimal forcing patterns" - the left singular vectors - proves to be less fruitful. The neutral modes have equivalent barotropic vertical structure, but their optimal forcing patterns are baroclinic and seem to be associated with low level heating. But the horizontal patterns of the forcing patterns are not robust, and are sensitive to the form of the inner product used in the SVD analysis. Additionally, applying "optimal" forcing patterns as perturbations to the full nonlinear model does not generate the response suggested by the linear model. / by Jason Goodman. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2008. / Includes bibliographical references. / The Colca-Majes and Cotahuasi-Ocona rivers in southwest Peru that cut through the western margin of the Andean plateau en route to the Pacific Ocean incised canyons over 3 km deep in response to late Cenozoic surface uplift. This latest uplift represents a fundamental shift in the style and magnitude of surface deformation that had been ongoing since at least late Cretaceous time, but only relatively recently created what represents the only major barrier to atmospheric circulation in the Southern Hemisphere. Studying canyon incision history as a proxy for surface uplift offers a promising route to understanding how climate and tectonics have interacted throughout the evolution of the Central Andean plateau. In this thesis, a combination of bedrock low-temperature thermochronology (apatite and zircon (UTh)/He techniques), 40Ar/39Ar dating of valley-filling volcanic flows, and three-dimensional thermal modeling using a modified version of Pecube were applied to investigate the incision history of the rivers. Results suggested between 2.6 and 3.0 km of incision occurred in the deepest reaches of the canyons starting at ca. 10 to 11 Ma and ending between 2.3 and 3.5 Ma. The onset of surface uplift that is likely to have driven incision probably did not precede incision by more than one million years, although incision may have continued long after surface uplift ceased. The magnitude and timing of uplift that we infer is in broad agreement with uplift documented along the western margin in northern Chile, in the interior of the Andean plateau, and the eastern margin. Additional work on the style of structural accommodation of this uplift provide important context for interpreting what potential geodynamic mechanisms may have been responsible for this latest tectonic activity. Structural mapping revealed an early history of predominantly reverse fault activity that probably generated the first significant topography in the Central Andes. This compressional period was succeeded by a phase of longwavelenth warping deformation and normal kinematic movement on high-angle faults. / (cont.) This later activity appears to have continued through the latest phase of uplift documented through river incision history, hence was likely responsible for accommodating uplift. Given the broadly synchronous timing of late Cenozoic uplift across the Andean plateau and the style of structural accommodation documented on the western margin, two possible geodynamic mechanisms appear most feasible for generating this latest phase of uplift: lithospheric delamination, and redistribution of ductile material through mid- to lower-crustal flow. Our initial studies of coastal uplift suggest that each is likely to have played a role, although additional work is required to understand how important each may have been in generating uplift. / by Taylor F. Schildgen. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2008. / Page 248 blank. / Includes bibliographical references (p. 237-247). / The objective of this thesis is to investigate the applications of Time Reversed Acoustics (TRA) to locate seismic sources and image subsurface structures. The back-propagation process of the TRA experiment can be divided into the acausal and causal time domain. Studying the acausal process of TRA enables us to locate the source, such as an earthquake, inside a medium. The causal domain allows us to create a new datum through the TRA-based redatuming operators and then image the subsurface structures. The source location application directly uses the retro-focusing feature of the TRA technique. An earthquake is traditionally located using the arrival times of individual phases, such as P and S. As a supplementary tool, TRA provides an opportunity to locate earthquakes using whole waveforms. In this TRA technique, we first record the full seismograms due to an earthquake at an array of stations. The traces are then time-reversed and numerically sent back into the medium at those station locations using an a priori model of the medium. The wavefield of the back-propagation is tracked and in the end energy will concentrate at a focal spot which gives the original earthquake location. Both synthetic and field experiments show the capability of the TRA technique to locate the source. TRA, combined with the idea of empirical Green's function, also provides an alternative approach to quickly estimating the focal depth for shallow events. In several field studies, solutions from other independent methodologies confirm the validity of the results. The subsurface imaging application extends the TRA principle into a redatuming method, which allows us to image the target more effectively by bypassing the overburden - which could potentially be very complicated in certain situations - between the sources and receivers. / (cont.) An accurate subsurface model required by conventional imaging techniques, which can be difficult and time-consuming to obtain, is no longer the prerequisite with this data-driven, TRA-based redatuming technique. Meanwhile, by imaging from a new datum that is closer to the target, the uncertainty of the imaging operator is dramatically reduced. The applicability of imaging the salt flank with the presence of a salt canopy is investigated in both acoustic and elastic scenarios with synthetic examples. Resulting images show very good delineation of the salt edge and dipping sediments abutting the salt dome. Then with the theoretical knowledge of the technique, we apply it to a 3D field experiment. In this complex field problem, with its challenge of the 3D geometry of the salt and acquisition, together with the limitation of the single well imaging, we propose a new directional imaging approach to implementing the TRA-based redatuming algorithm. The result is consistent with previous studies in this field, given the uncertainties on positioning of steep events from surface seismic data. / by Rongrong Lu. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1998. / Vita. / Includes bibliographical references. / by Jess F. Adins. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996. / Includes bibliographical references (leaves 57-58). / by William James Williams. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmosphere and Planetary Sciences, 1988. / Includes bibliographical references. / by Jeffrey William Campbell. / M.S.