Thesis: Ph. D. in Planetary Science, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 236-262). / The shape and gravity field are fundamental properties of a planetary body. Combining gravity and topography data sets is, arguably, the most powerful tool to study planetary interiors from orbit. However, even when gravity and topography data are in hand, typically, a wide range of possible geophysical structures is possible. The reader will find that this problem of non-unique solutions permeates all chapters of this thesis. The general strategy to reduce non-uniqueness is to find ways to use additional observations that are sensitive to the interior structure but are not degenerate with gravity and/or topography. In this work, we study three Solar System bodies: asteroid Vesta, dwarf planet Ceres and the Earth's Moon. Using the data from the Dawn spacecraft, we find that once hot and hydrostatic, Vesta is no longer either. It was despun by two giant collisions. We use the Dawn gravity/topography data along with meteoritic data to provide constraints on Vesta's internal structure. Unlike Vesta, Ceres is close to hydrostatic equilibrium. Based on Ceres' topographic spectrum, we conclude that it has experienced limited viscous relaxation. Contrary to the pre-Dawn expectations, we find that the cerean crust is mechanically rock-like. We provide constraints on Ceres' rheology and density structure by combining gravity/topography data with finite-element modeling of lithospheric relaxation. Additionally, we find that Ceres' obliquity undergoes large oscillations, which has important implications for volatile transport. The GRAIL mission has produced gravity models of the Moon with an unprecedented accuracy. We study the spectral content of gravity models and characterize their effective resolution to provide users of these models with the information necessary to understand the model limitations. / by Anton Ermakov. / Ph. D. in Planetary Science

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 18-19). / The ratio of 238U/ 235U has long been assumed to be constant and equal to 137.88. However, recent research has found that uranium fractionation occurs in a variety of environments, especially reducing environments. Fractionation in metal/silicate systems could be a contributor to Earth's geodynamo heating and affect Pb-Pb geochronology. Sixteen experimental iron/silicate samples were separated magnetically into iron and silicate fractions. Each fraction was leached with 2.5 M HCl, 10 M HCl, 10 M HCl at a higher temperature, and HF and the uranium released in each step was measured by mass spectrometry. The depleted nature of the uranium used to create the samples precludes high-precision isotope fractionation assessments. However, the effectiveness of the leaching procedure was examined for potential use on future samples. The U release pattern in silicate fractions was not consistent between all of the samples, and major element concentration measurements will allow identification of the phase being digested in each step. The contamination from silicate and graphite in the metal fractions prevents uranium from being accurately measured. / by Mary C. Spanjers. / S.B.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 111-122). / Shear-wave splitting measurements of teleseismic shear waves, such as SKS, have been used to estimate the amount and direction of upper-mantle anisotropy worldwide. One of the basic assumptions in making these measurements is that the anisotropy is confined to a single, homogeneous layer. In this thesis, I use both numerical and analytical modeling to examine the validity of this assumption. I find that variability in the orientation of anisotropy with depth causes observable effects, such as frequency dependence in the apparent splitting parameters, and that the measured fast-axis direction is consistently different than the average of the medium. A separate focus of this thesis is how spatial associations between minerals in a thin-section can be used to infer the evolutionary pressure-temperature history of a rock. I present a new method for textural analysis that uses digital images obtained with the electron microprobe. This method is used to characterize nine mantle xenoliths erupted from kimberlite pipes in South Africa and to test whether the pyroxenes are spatially correlated with the garnets. The observed associations can be explained by a model in which harzburgitic residues are produced by large extents of partial melting at shallow depths (-60-90 km) and high temperatures (1300-1400ʻ C) and are then subsequently dragged down to greater depths where garnet and clinopyroxene exsolve, perhaps in an Archean subduction zone. The third focus of this thesis is on the seismological evidence for compositional heterogeneity in the lower mantle. Using reprocessed ISC data, I compare P and S wave tomographic models and find systematic differences between regions that have undergone subduction in the last 120 million years and those that have not below -1500 km. / (cont.) This global study is followed up with a regional study using higher-quality P and S wave differential traveltimes. Beginning at depths of -1000 km down and continuing down to the core-mantle boundary I find variability in Poisson's ratio that is greater than what would be expected by temperature variations alone. A simple explanation is that the variability includes a contribution from compositional effects, such as 2% variability in iron from one region to another. / by Rebecca Lee Saltzer. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1995. / Includes bibliographical references (leaves 42-45). / by Tiepeng Zhou. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2009. / Includes bibliographical references (leaves 76-78). / Determining the focal mechanism of an earthquake helps us to better characterize reservoirs, define faults, and understand the stress and strain regime. The objective of this thesis is to find the focal mechanism and depth of earthquakes. This objective is met using a full waveform modeling method in which we generate synthetic seismograms using a discrete wavenumber code to match the observed seismograms. We first calculate Green's functions given an initial estimate of the earthquake's hypocenter, the locations of the seismic recording stations, and the velocity model of the region for a series of depths with intervals of 1 km. Then, we calculate the moment tensor for 6840 different combinations of strikes, dips, and rakes for each of those depths. These are convolved with Green's function and with an assumed smooth ramp source time function to produce the different synthetic seismograms corresponding to the different strikes, dips, rakes, and depths. / We use a grid search in order to find the synthetic seismogram, with the combination of depth, strike, dip, and rake, that best fits the observed seismogram. These parameters will be the focal mechanism solution of an earthquake. The whole procedure is repeated for a reduced number of recording stations in order to determine a minimum number of recording stations that is needed for a reliable source mechanism and depth solution. We tested the method using two earthquakes in Southern California. Their locations, depths, and source mechanisms were determined using data from a multitude of stations. Southern California Seismic Network's real-time solution of earthquake 9718013 puts the earthquake at a depth of 15.22 km. The moment tensor inversion method determines the depth of the earthquake to be 8 km with a strike, dip, and rake of 318, 33, -180, respectively. The same network determines the depth of earthquake 14408052 to be 7.3 km. / The moment tensor solution determines the strike, dip, rake, and depth of earthquake 14408052 to be 162, 82, -167, and 5 km, respectively. In this study, we wanted to test our method using seismograms from a relatively few stations. We used five stations for each earthquake, then 3 stations for earthquake 9718013, and two stations for earthquake 14408052. When using five recording stations, the strike, dip, rake, and depth of earthquake 9718013 are 300, 60, -170, and 15 km, respectively. When using three recording stations for the same earthquake, the strike, dip, rake, and depth are 300, 60, -180, and 14 km, respectively. For earthquake 14408052, the strike, dip, rake, and depth are 160, 80, -170, and 7 km, respectively, when using five recording stations. The strike, dip, rake, and depth for this same earthquake are 160, 80, -160, and 8 km, respectively, when using only two stations. / The results show that the ten best solutions for each earthquake are very similar, and identical in many cases, indicating that the method is robust and the solution is unique. This assures us that the full waveform modeling method is a fast and reliable way to find the focal mechanisms and depths of earthquakes using seismograms from a few stations when the velocity structure is known. / by Hussam A. Busfar. / S.M.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, February 2001. / Includes bibliographical references. / Tectonically active for the past ~160 million years, the igneous basement of the Indian Ocean basin has formed due to complex interactions between mid-ocean ridges and mantle plumes. Plateaus, ridges and islands associated with the Kerguelen hotspot, the world's second largest, oceanic igneous province, dominate the bathymetry of the southeastern Indian Ocean. Lavas erupted by the Kerguelen plume range in age from the -119 million year old basalts of the southern Kerguelen Plateau to the recent eruptions at Kerguelen, Heard, and McDonald Islands. This dissertation presents: 1) the Pb geochronology of the oldest rocks recovered from the Kerguelen Plateau, 2) the geochronology and Sr-Nd-Pb-He isotopic characteristics of the olivinerich lavas of the Kerguelen Archipelago, and 3) Sr-Nd-Pb isotopic evidence for contamination of Southeast Indian Ridge basalts with melts from the Amsterdam-St. Paul and Kerguelen plumes. At Elan Bank of the Kerguelen Plateau, Leg 183 of the Ocean Drilling Program recovered basalt, trachyte, and garnet-biotite gneiss clasts from a 26 m thick fluvial conglomerate which is intercalated with Kerguelen Plateau basalts. Zircons and monazites obtained from the gneiss clasts yield a range of Proterozoic Pb-Pb dates when examined by conventional mass spectrometric and electron microprobe techniques. The deposition of the gneiss clasts, slow seismic velocities in the crust of Elan Bank, and anomalous isotopic compositions of basalts above and below the conglomerate suggest that some part of the crust of Elan Bank is a continental fragment formed during the rifting of East Gondwana. Cenozoic eruptions from the Kerguelen plume constructed the primarily basaltic Kerguelen Archipelago (6500 km 2) on the northern Kerguelen Plateau. "Ar/ 39Ar geochronology of 15 basalts from five stratigraphic sections yields isochron ages ranging from 29.26±0.87 to 24.53±0.29 Ma. The oldest dated basalt from the archipelago (-29 Ma) is much younger than the -40 Ma conjunction between the hotspot and the Southeast Indian Ridge. Basalt eruption seems to have ceased shortly after -24 Ma although small volume lava flows and plutonic intrusions continued to form in the archipelago. The basalt age data suggest an average lava accumulation rate of -1.6 0.9 km/my during the Oligocene. The archipelago's volumetric eruption rate (0.009 km3/y) is lower than estimates made for the Cretaceous Kerguelen Plateau (1.7 k 3/y) and the Ninetyeast Ridge hotspot track (0.18 km3 /y), suggesting that the late Cenozoic extrusive activity of the Kerguelen plume is waning. Cenozoic volcanism attributed to the Kerguelen plume occurs over a diffuse area with Quaternary eruptions at Heard and McDonald Islands and within the Kerguelen Archipelago. The lithosphere of the Cretaceous Kerguelen Plateau overriding and insulating the plume. Although the volcanic activity of the Kerguelen plume spans 119 million years, the helium isotopic signature of Kerguelen lavas has never been documented. The isotopically-enriched mantle source of the Kerguelen plume has been attributed to either subducted sediments or delaminated sub-continental lithosphere. * Ar/ 3 9Ar dating of the archipelago samples shows that the three northern samples are ~28 Ma whereas the samples from the southeastern peninsulas fall into two distinct age groups: 10 Ma and 24-25 Ma. The basanite dike is 9 Ma and probably fed the lower Miocene basalts of the southeastern peninsulas. The helium isotopic signature of eight of these basalts was examined by analyzing olivine and pyroxene separates. Multiple analyses of olivine separates reveal 3He/ 4He from 7.43 ±0.17 to 10.40±0.06 R/RA. Analyses of pyroxene separates reveal lower ratios in general (6.53±0.33 to 9.64±0.25 R/RA) although they overlap with the olivine data. The lower 3He/ 4He ratios of the pyroxenes may reflect radiogenic ingrowth of 'He since eruption. Between 36°S and -45°S, two volcanic hotspots, Kerguelen and Amsterdam-St. Paul (ASP), affect the physical structure of the Southeast Indian Ridge which is the longest spreading center in the Indian Ocean. Presently the thickened platform of the Amsterdam-St. Paul hotspot is bisected by the Southeast Indian Ridge and approximately 40 million years ago the ridge intersected the Kerguelen hotspot. Lavas derived from the Kerguelen and Amsterdam-St. Paul hotspots have distinctly higher Sr and Pb isotopic ratios than mid-ocean ridge basalts, and the hotspots differ in that the Kerguelen basalts have higher 87Sr/16Sr and lower Nd and Pb isotopic composition compared to basalts from the ASP hotspot. New Sr, Nd and Pb isotopic data for 46 samples from the Southeast Indian Ridge, nearby islands and seamounts in the region of 77-88'E show that the Amsterdam-St. Paul hotspot (1 7Sr/ 86Sr>0.7035, 1 43Nd / 14 4Nd<0.5128, 206Pb/ 204Pb~19.2, 207 Pb/ 204Pb~15.62, 2 0sPb/ 2 04Pb-39.45) influences basalt compositions of three ridge segments located on the hotspot platform. Additionally, basalts from the ridge segment just north of the hotspot platform have isotopic compositions, that fall on mixing lines between ASP and normal mid-ocean ridge basalts suggesting that material from the Amsterdam-St. Paul hotspot flows northward beneath the ridge. The HIMU-like isotopic and trace element composition of the ASP hotspot requires partial melting of recycled oceanic crust in the mantle source. The low La/Nb of the ASP hotspot basalts suggests that processing during subduction stripped the recycled oceanic crust of highly incompatible elements. In contrast, some basalts from ridge segments have enriched isotopic ratios (8 7Sr / 86Sr>0.7044, 14 3Nd/l"Nd<0.51275, 2 06Pb/ 21Pb-18.1, 207Pb/ 20 Pb-15.54, 20 8Pb/ 20 4Pb~38.6) characteristic of the Kerguelen hotspot. The distribution of these Kerguelen-influenced basalts suggests that metasomatism associated with the early impact of the Kerguelen plume may have contaminated much of the upper mantle beneath the eastern Indian Ocean basin. Additionally, the Kerguelen isotopic signature of basalts from one ridge segment may reflect an active mantle conduit between the Kerguelen plume and the Southeast Indian Ridge. / by Kirsten E. Nicolaysen. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 229-243). / Continuously operating Global Positioning System (GPS) networks record station position changes with millimeter-level accuracy and have revealed transient deformations on various spatial and temporal scales. However, the transient deformation may not be easily identified from the position time series because of low signal-to-noise ratios (SNR), correlated noise in space and time and large number of sites in a network. As a systematic detection method, we use state estimation based on Kalman filtering and principal component analysis (PCA). State estimation improves the SNR in the time domain by estimating secular and transient motions and reducing the level of both white and colored noise. PCA improves the SNR in space domain by accounting for the coherence of transient motions between nearby sites. Synthetic tests show that the method is capable of detecting transient signals embedded in noisy data but complex signals (e.g., large-scale signals in space and time, multiple and/or propagating signals) are difficult to detect and interpret. We demonstrate the detection capability with two known signals in the Los Angeles basin, California: far-field coseismic offsets associated with the 1999 Hector Mine earthquake and locally-observed hydrologic deformation due to heavy rainfall in winter 2004-2005 in San Gabriel Valley. We applied the method to the daily GPS data from the Plate Boundary Observatory (PBO) network in Alaska and in the Washington State section of the Cascadia subduction zone. We have detected a transient signal whose maximum displacement is -9 mm in the horizontal and -41 mm in the vertical at Akutan volcano, Alaska, during the first half of 2008 and two previously unrecognized small slow slip events with average surface displacements less than 2 mm, which was thought to be below current GPS resolution. The detection method improves the SNR and therefore provides higher resolution for detecting weak transient signals, and it can be used as a routine monitoring system. / by Kang Hyeun Ji. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1987. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN. MIT's copy accompanied by maps in separate folder. / Bibliography: leaves 256-268. / by David Walter Klepacki. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1985. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN. / Bibliography: leaves 230-234. / Stephen Emil Zebiak. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1995. / Includes bibliographical references (p. 171-180). / by James B. Gaherty. / Ph.D.