Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1986. / Microfiche copy available in Archives and Science. / Includes bibliographies. / by Kaye M. Shedlock. / Ph.D.

Thesis (S.M. in Planetary Science)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 67-78). / Other than Earth, Mars and Titan are the only bodies in our Solar System where we have observed widespread fluvial activity. In this thesis I present two approaches for constraining the extent of multiple resurfacing processes in order to gain insight into the early history of Mars and Titan. One of the most distinctive features of the Martian surface is the dichotomy between the heavily cratered southern highlands and the relatively smooth northern lowlands. The northern lowlands appear smooth because many of the craters in the north have been partially or completely buried beneath volcanic and sedimentary fill of unknown relative proportions. In Chapter 1, we use the Mars Orbiter Laser Altimeter (MOLA) topography data, the Mars Reconnaissance Orbiter (MRO) gravity model and a Wiener filter to map these buried craters and estimate minimum fill thickness and volume as well as maximum fill density. The overall trend observed for the northern lowlands is more sedimentation near the dichotomy and less sedimentation further north and near the Tharsis region, which is consistent with the geology of the region. Titan has few impact craters, suggesting that its surface is geologically young. In Chapter 2 we evaluate whether fluvial erosion has caused significant resurfacing by estimating the cumulative erosion around the margins of polar lakes. Images of drowned fluvial features around the lake margins, where elevated levels of hydrocarbon liquids appear to have partly flooded fluvial valleys, allow us to map topographic contours that trace the fluvially dissected topography. We then used a numerical landscape evolution model to calibrate a relationship between contour sinuosity, which reflects the extent of fluvial valley incision, and cumulative erosion. We find that cumulative fluvial erosion around the margins of Titan's polar lakes, including Ligeia Mare, Kraken Mare, and Punga Mare in the north and Ontario Lacus in the south, ranges from 4% to 31% of the initial relief. Additional model simulations show that this amount of fluvial erosion does not render craters invisible at the resolution of currently available imagery, suggesting that fluvial erosion is not the only major resurfacing mechanism operating in Titan's polar regions. / by Yodit Tewelde. / S.M.in Planetary Science

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1997. / Includes bibliographical references (leaves 176-180). / by Christopher A. Edwards. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989. / Includes bibliographical references (v. 2, leaves 314-331). / by Daniel Richard Tormey. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996. / Includes bibliographical references. / by Javier Esteban Escartín Guiral. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989. / Includes bibliographical references. / by Sarah Elizabeth Kruse. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1997. / Includes bibliographical references (leaves 119-121). / by Howard Fred Sklar. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2003. / Includes bibliographical references (leaves 168-174). / This thesis presents two innovations to geophysical inversion. The first provides a framework and an algorithm for combining linear deconvolution methods with geostatistical interpolation techniques. This allows for sparsely sampled data to aid in image deblurring problems, or, conversely, noisy and blurred data to aid in sample interpolation. In order to overcome difficulties arising from high dimensionality, the solution must be derived in the correct framework and the structure of the problem must be exploited by an iterative solution algorithm. The effectiveness of the method is demonstrated first on a synthetic problem involving satellite remotely sensed data, and then on a real 3-D seismic data set combined with well logs. The second innovation addresses how to use wavelets in a linear geophysical inverse problem. Wavelets have lead to great successes in image compression and denoising, so it is interesting to see what, if anything, they can do for a general linear inverse problem. It is shown that a simple nonlinear operation of weighting and thresholding wavelet coefficients can consistently outperform classical linear inverse methods in terms of mean-square error across a broad range of noise magnitude in the data. Wavelets allow for an adaptively smoothed solution: smoothed more in uninteresting regions, less at geologically important transitions. / (cont.) A third issue is also addressed, somewhat separate from the first two: the correct manipulation of discrete geophysical data. The theory of fractional splines is introduced, which allows for optimal approximation of real signals on a digital computer. Using splines, it can be shown that a linear operation on the spline can be equivalently represented by a matrix operating on the coefficients of a certain spline basis function. The form of the matrix, however, depends completely on the spline basis, and incorrect discretization of the operator into a matrix can lead to large errors in the resulting matrix/vector product. / by Jonathan A. Kane. / Ph.D.

Thesis: Ph. D. in Geophysics, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 127-134). / Faults are rough at all scales and can be described as self-affine fractals. This deviation from planarity results in geometric asperities and a locally heterogeneous stress field, which affect the nucleation and propagation of shear rupture. I study this effect numerically at the scale of small earthquakes, in which realistic geometry and friction law parameters can be incorporated in the model. The numerical approach developed in this thesis includes three main features. First, to enable slip that is large relative to the size of the elements near the fault, as well to capture accurately of the variation of normal stress during slip, I implement slip-weakening and rate and state friction laws into the Mortar Finite Element Method, in which non-matching meshes are allowed across the fault and the contacts are continuously updated. Second, the mesh near the fault is refined using hanging nodes to enable accurate representation of the fault geometry. Finally, to model the whole seismic cycle, including a completely spontaneous nucleation process, the method uses variable time stepping with quasi-static and fully dynamic implicit schemes. The developed methodology is used to study the response of rough faults governed by rate and state friction to slow tectonic loading, where, in each simulation, the earthquake sequence includes at least two seismic cycles. With increasing roughness, there is a transition from seismic to aseismic slip behavior, in which the load on the fault is released by more slip events but with lower slip rate, seismic moment, and average static stress drop. We analyze the nucleation process in the fast slip events and show that the roughness introduces local barriers that complicate the nucleation process and result in asymmetric expansions of the rupture, non-monotonic increases in the slip rates on the fault, and the generation of multiple slip pulses. In general, the nucleation length increases with increasing roughness amplitude. However, there are large differences between first slip events in the sequences, where the initial conditions are homogenous, and later events, where the initial stress field and friction conditions are determined by the rupture growth and arrest in previous slip events. / by Yuval Tal. / Ph. D. in Geophysics

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1990. / Includes bibliographical references (leaf 118). / by Philippe Guérendel. / M.S.