Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2007. / "Joint Program in Oceanography/Applied Ocean Science and Engineering"--Cover. Title from Web page (viewed on Mar. 24, 2008). "September 2007." Includes bibliographical references.

Sung, Siu Chung = 鎂矽酸鹽(MgSiO₃)在核幔邊界條件下的第一性原理研究 / 宋紹聰. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (p. 110-115). / Abstracts in English and Chinese. / Sung, Siu Chung = Mei xi suan yan (MgSiO₃) zai he man bian jie tiao jian xia de di yi xing yuan li yan jiu / Song Shaocong. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Review on MgSiO3 --- p.5 / Chapter 2.1 --- Interior of the Earth --- p.5 / Chapter 2.1.1 --- The importance of MgSiO3 in geosciences --- p.6 / Chapter 2.1.2 --- "Anomalies in lower mantle, D"" layer and the core-mantle boundary" --- p.7 / Chapter 2.2 --- Review on experimental and theoretical studies on MgSiO3 --- p.9 / Chapter 2.2.1 --- The perovskite structure --- p.9 / Chapter 2.2.2 --- MgSiO3 pv --- p.12 / Chapter 2.3 --- ppv structure --- p.14 / Chapter 2.3.1 --- MgSiO3 ppv --- p.15 / Chapter 2.3.2 --- MgSiO3 liquid --- p.18 / Chapter 3 --- Physical quantities in geoscience and molecular dynamics sim- ulations --- p.20 / Chapter 3.1 --- Equation of state --- p.21 / Chapter 3.2 --- Gruneisen parameter --- p.22 / Chapter 3.3 --- Thermoelasticity --- p.22 / Chapter 3.4 --- Phase transition --- p.24 / Chapter 3.5 --- Correlation function --- p.25 / Chapter 3.5.1 --- Pair Distribution function --- p.25 / Chapter 3.5.2 --- Coordination number --- p.27 / Chapter 3.5.3 --- Time correlation function and mean square displacement --- p.27 / Chapter 3.6 --- Seismic velocities --- p.28 / Chapter 4 --- Theoretical Methods --- p.30 / Chapter 4.1 --- Density Functional Theory --- p.30 / Chapter 4.2 --- Approximating exchange-correlation energy functional --- p.33 / Chapter 4.3 --- Car-Parrinello Molecular Dynamics --- p.34 / Chapter 4.4 --- Variable cell dynamics --- p.36 / Chapter 4.5 --- Nose-Hoover Thermostat --- p.37 / Chapter 5 --- Simulation method and details --- p.39 / Chapter 5.1 --- Structure at 0 K --- p.40 / Chapter 5.1.1 --- Initialization of simulation cells --- p.40 / Chapter 5.1.2 --- Convergence test --- p.41 / Chapter 5.1.3 --- "Electronic minimization, fictitious electronic mass and time step" --- p.42 / Chapter 5.2 --- Electronic and ionic minimization --- p.43 / Chapter 5.3 --- Cell optimization and structure at 0 K --- p.44 / Chapter 5.3.1 --- Optimized simulation cell of pv and ppv --- p.44 / Chapter 5.4 --- Equation of state and stability of solid --- p.46 / Chapter 5.5 --- Melting --- p.48 / Chapter 5.6 --- Statistical average --- p.50 / Chapter 6 --- MgSiO3 perovskite and post-perovskite at CMB conditions --- p.51 / Chapter 6.1 --- Equations of state of pv and ppv at 0 K --- p.51 / Chapter 6.2 --- Enthalpy of pv and ppv at 0 K --- p.54 / Chapter 6.3 --- Equations of state of pv and ppv at different temperatures --- p.55 / Chapter 6.4 --- Fluctuation of stress components of pv and ppv --- p.59 / Chapter 6.5 --- Pair distribution function of pv and ppv --- p.61 / Chapter 6.5.1 --- Pair distribution function at different temperatures with similar cell volume --- p.61 / Chapter 6.5.2 --- Pair distribution function at 4000 K and different volumes --- p.66 / Chapter 6.5.3 --- Pair distribution function at 6000 K and different volumes --- p.70 / Chapter 6.5.4 --- Coordination numbers --- p.74 / Chapter 7 --- Liquid structure at CMB conditions --- p.78 / Chapter 7.1 --- Equations of state of liquid --- p.78 / Chapter 7.2 --- Stress components of liquid --- p.80 / Chapter 7.3 --- Pair distribution function of liquid --- p.83 / Chapter 7.4 --- Coordination numbers of liquid --- p.88 / Chapter 7.4.1 --- Mean square displacement --- p.88 / Chapter 8 --- Phase diagram of MgSiO3 --- p.92 / Chapter 8.1 --- Pressure-temperature relations --- p.92 / Chapter 8.1.1 --- Enthalpy --- p.94 / Chapter 8.2 --- Internal energy --- p.96 / Chapter 8.3 --- Phase boundaries and phase diagram --- p.99 / Chapter 9 --- Discussions --- p.105 / Chapter 9.1 --- Phase diagram --- p.105 / Chapter 9.2 --- LDA vs GGA --- p.107 / Chapter 9.3 --- Pv and ppv at low pressure --- p.107 / Chapter 9.4 --- Two-phase method --- p.108 / Bibliography --- p.110 / Chapter A --- Rotation and shape optimization --- p.116

abstract: This research investigates Earth structure in the core-mantle boundary (CMB) region, where the solid rocky mantle meets the molten iron alloy core. At long wavelengths, the lower mantle is characterized by two nearly antipodal large low shear velocity provinces (LLSVPs), one beneath the Pacific Ocean the other beneath Africa and the southern Atlantic Ocean. However, fine-scale LLSVP structure as well as its relationship with plate tectonics, mantle convection, hotspot volcanism, and Earth's outer core remains poorly understood. The recent dramatic increase in seismic data coverage due to the EarthScope experiment presents an unprecedented opportunity to utilize large concentrated datasets of seismic data to improve resolution of lowermost mantle structures. I developed an algorithm that identifies anomalously broadened seismic waveforms to locate sharp contrasts in shear velocity properties across the margins of the LLSVP beneath the Pacific. The result suggests that a nearly vertical mantle plume underlies Hawaii that originates from a peak of a chemically distinct reservoir at the base of the mantle, some 600-900 km above the CMB. Additionally, acute horizontal Vs variations across and within the northern margin of the LLSVP beneath the central Pacific Ocean are inferred from forward modeling of differential travel times between S (and Sdiff) and SKS, and also between ScS and S. I developed a new approach to expand the geographic detection of ultra-low velocity zones (ULVZs) with a new ScS stacking approach that simultaneously utilizes the pre- and post-cursor wavefield.. Strong lateral variations in ULVZ thicknesses and properties are found across the LLSVP margins, where ULVZs are thicker and stronger within the LLSVP than outside of it, consistent with convection model predictions. Differential travel times, amplitude ratios, and waveshapes of core waves SKKS and SKS are used to investigate CMB topography and outermost core velocity structure. 1D and 2D wavefield simulations suggest that the complicated geographic distribution of observed SKKS waveform anomalies might be a result of CMB topography and a higher velocity outermost core. These combined analyses depict a lowermost mantle that is rich in fine-scale structural complexity, which advances our understanding of its integral role in mantle circulation, mixing, and evolution. / Dissertation/Thesis / Ph.D. Geological Sciences 2012

abstract: The interior of Earth is stratified due to gravity. Therefore, the lateral heterogeneities observed as seismic anomalies by seismologists are extremely interesting: they hold the key to understand the composition, thermal status and evolution of the Earth. This work investigates seismic anomalies inside Earth’s lowermost mantle and focuses on patch-like ultra-low velocity zones (ULVZs) found on Earth’s core-mantle boundary (CMB). Firstly, all previous ULVZ studies are compiled and ULVZ locations on the CMB are digitized. The result is a database, which is publicly available online. A key finding is that there is not a simple mapping between the locations of the observed ULVZs and the large low velocities provinces (LLVPs). Instead, ULVZs are more likely to occur near LLVP boundaries. This spatial correlation study supports a compositionally distinct origin for at least some ULVZs. Next, the seismic structure of the basal mantle beneath the Central America is investigated. This region hosts present and past subducted slabs, which could have brought compositionally distinct oceanic basalt all the way down to the CMB. The waveform distortions of a core-reflected seismic phase and a forward modeling method are used to constrain the causes of the CMB structures. In addition to ULVZ structures, isolated patches of thin zones with shear velocity increased by over 10% relative to background mantle are found for the first time. Ultra-high velocity zones (UHVZs) are interspersed with ULVZs and could be caused by subducted mid-ocean ridge basalt (MORB) that undergoes partial melting and melt segregation. Fe-rich partial melt of MORB can form ULVZs, and silica polymorphs (SiO2) and calcium-perovskite (CaPv) rich solid residue can explain the UHVZs. Finally, large-scale heterogeneities in the lowermost mantle are investigated using S waveform broadening observations. Several basal layer models are case-studied via synthetic calculations. S wave arrivals received at a distance larger than 80˚ in a global dataset from large earthquakes between the years 1994 and 2017 are examined and S waveform broadenings are documented. This approach exploits large distance data for the first time, and therefore is complementary to previous studies in terms of sampling locations. One possible explanation of S waveform broadening is velocity discontinuity inside the D″ layer due to the temperature controlled Bm-pPv phase transition. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2020

Thesis (Ph. D.)--Joint Program in Marine Geology and Geophysics (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2007. / 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. 167-196). / This thesis presents three studies which apply geophysical tools to the task of better understanding mantle melting phenomena at the upper and lower boundaries of the mantle. The first study uses seafloor bathymetry and small variations in the gravitational acceleration over the Hawaii-Emperor seamount chain to constrain the changes in the igneous production of the hot spot melting in the mantle which has created these structures over the past 80 My. The second study uses multichannel seismic reflection data to constrain the location and depth of axial magma chambers at the Endeavour Segment of the Juan de Fuca spreading ridge, and then correlates these magma chamber locations with features of the hydrothermal heat extraction system in the upper crust such as microseismicity caused by thermal cracking and high temperature hydrothermal vent systems observed on the seafloor. The third study uses two-dimensional global pseudospectral seismic wave propagation modeling to characterize the sensitivity of the SPdKS seismic phase to two-dimensional, finite-width ultra-low velocity zones (ULVZs) at the core-mantle boundary. Together these three studies highlight the dynamic complexities of melting in the mantle while offering new tools to understand that complexity. / by Emily Mary Van Ark. / Ph.D.

Thesis (Ph. D.)--Joint Program in Marine Geology and Geophysics (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2007. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references. / I provide constraints on mantle convection through observations of the rheology and composition of the oceanic upper mantle. Convection cannot be directly observed, yet is a fundamental part of the plate tectonic cycle. Relative motion among plates is accommodated by localized deformation at their boundaries. I demonstrate that in the ductile regime, strain localization occurs when different mineral phases are mixed together, limiting grain annealing. Upper mantle flow is by dislocation creep, resulting in seismic anisotropy due to mineral alignment. I use a shear zone in the Josephine Peridotite to quantify the relationship between mineral orientation and shear strain, providing an improved framework for the interpretation of seismic anisotropy. The upper mantle is generally assumed to be homogeneous in composition. From detailed isotopic and chemical analyses of abyssal peridotites from the Southwest Indian Ridge, I show that the mantle is heterogeneous at a range of length-scales. Abyssal peridotites recovered at ocean ridges are generally interpreted as the depleted residues of melt extraction. I find that melt-rock reaction is a significant part of the melt extraction process, modifying the composition of the lithospheric mantle. The generation of heterogeneous lithosphere provides a source for asthenospheric heterogeneity, via subduction and mantle convection. / by Jessica Mendelsohn Warren. / Ph.D.

Assuming that liquid iron alloy from the outer core interacts with the solid silicate-rich lower mantle the influence on the core-mantle reflected phase PcP is studied. If the core-mantle boundary is not a sharp discontinuity, this becomes apparent in the waveform and amplitude of PcP. Iron-silicate mixing would lead to regions of partial melting with higher density which in turn reduces the velocity of seismic waves. On the basis of the calculation and interpretation of short-period synthetic seismograms, using the reflectivity and Gauss Beam method, a model space is evaluated for these ultra-low velocity zones (ULVZs). The aim of this thesis is to analyse the behaviour of PcP between 10° and 40° source distance for such models using different velocity and density configurations. Furthermore, the resolution limits of seismic data are discussed. The influence of the assumed layer thickness, dominant source frequency and ULVZ topography are analysed. The Gräfenberg and NORSAR arrays are then used to investigate PcP from deep earthquakes and nuclear explosions. The seismic resolution of an ULVZ is limited both for velocity and density contrasts and layer thicknesses. Even a very thin global core-mantle transition zone (CMTZ), rather than a discrete boundary and also with strong impedance contrasts, seems possible: If no precursor is observable but the PcP_model /PcP_smooth amplitude reduction amounts to more than 10%, a very thin ULVZ of 5 km with a first-order discontinuity may exist. Otherwise, if amplitude reductions of less than 10% are obtained, this could indicate either a moderate, thin ULVZ or a gradient mantle-side CMTZ. Synthetic computations reveal notable amplitude variations as function of the distance and the impedance contrasts. Thereby a primary density effect in the very steep-angle range and a pronounced velocity dependency in the wide-angle region can be predicted. In view of the modelled findings, there is evidence for a 10 to 13.5 km thick ULVZ 600 km south-eastern of Moscow with a NW-SE extension of about 450 km. Here a single specific assumption about the velocity and density anomaly is not possible. This is in agreement with the synthetic results in which several models create similar amplitude-waveform characteristics. For example, a ULVZ model with contrasts of -5% VP / -15% VS and +5% density explain the measured PcP amplitudes. Moreover, below SW Finland and NNW of the Caspian Sea a CMB topography can be assumed. The amplitude measurements indicate a wavelength of 200 km and a height of 1 km topography, previously also shown in the study by Kampfmann and Müller (1989). Better constraints might be provided by a joined analysis of seismological data, mineralogical experiments and geodynamic modelling. / Unter der Annahme, dass flüssiges Eisen aus dem äußeren Erdkern mit dem festen, silikat-reichen Unteren Mantel reagiert, wird eine Einflussnahme auf die Kern-Mantel Reflexionsphase PcP erwartet. Ist die Kern-Mantel Grenze aufgeweicht, und nicht wie bislang angenommen ein diskreter Übergang, so zeichnet sich dies in der Wellenform und Amplitude von PcP ab. Die Interaktion mit Eisen führt zu teilweise aufgeschmolzenen Bereichen höherer Dichte, welche die seismischen Wellengeschwindigkeiten herabsetzen. Basierend auf den Berechnungen von kurzperiodischen synthetischen Seismogrammen, mittels der Reflektivitäts- und Gauss Beam Methode, soll ein möglicher Modellraum dieser Niedriggeschwindigkeitszonen ermittelt werden. Das Ziel dieser Arbeit ist es das Verhalten von PcP im Distanzbereich von 10° bis 40° unter dem Einfluss dieser Modelle mit diversen Geschwindigkeits- und Dichtekontrasten zu untersuchen. Ferner wird das Auflösungsvermögen hinsichtlich seismischer Daten diskutiert. Entscheidende Parameter wie Anomaliedicke, Quellfrequenz und Topographie werden hierbei analysiert. Tiefe Erdbeben und Kernexplosionen, die sich im entsprechenden Entfernungsbereich zum Gräfenberg und NORSAR Array befinden, werden anschließend im Hinblick auf PcP ausgewertet. Das seismische Auflösungsvermögen von Niedriggeschwindigkeitszonen ist stark begrenzt sowohl in Bezug auf Geschwindigkeits- und Dichtekontraste als auch hinsichtlich der Mächtigkeit. Es besteht sogar die Möglichkeit einer dünnen, globalen Kern-Mantel Übergangszone, selbst mit großen Impedanzkontrasten, ohne dass dies mit seismologischen Methoden detektiert werden könnte: Wird kein precursor zu PcP beobachtet aber das PcPmodel /PcPsmooth Amplitudenverhältnis zeigt gleichzeitig eine Reduktion von mehr als 10%, dann könnte eine sehr dünne Niedriggeschwindigkeitszone von ca. 5 km Mächtigkeit und einer Diskontinuität erster Ordnung vorliegen. Andererseits, ist PcP um weniger als 10% reduziert, könnte dies entweder auf eine dünne, moderate Niedriggeschwindigkeitszone oder einen graduellen Kern-Mantel Übergang hindeuten. Die synthetischen Berechnungen ergeben starke Amplitudenvariationen als Funktion der Distanz, welche auf den Impedanzkontrast zurückzuführen sind. Dabei ergibt sich ein primärer Dichteeffekt im extremen Steilwinkelbereich und ein maßgeblicher Geschwindigkeitseinfluss im Weitwinkelbereich. Im Hinblick auf die modellierten Resultate lässt sich eine 10 - 13.5 km mächtige Niedriggeschwindigkeitszone 600 km südöstlich von Moskau mit einer NW-SE Ausdehnung von mindestens 450 km folgern, wobei eine exakte Aussage über Geschwindigkeiten und Dichte nicht möglich ist. Dies ist im Konsens mit den synthetischen Berechnungen, wonach viele unterschiedliche Modelle ähnliche Amplituden- und Wellenformcharakteristiken erzeugen. Zum Beispiel erklärt ein Modell mit Kontrasten von -5% VP / -15% VS and +5% Dichte die gemessenen PcP Amplituden. Darüber hinaus können unterhalb des südwestlichen Finnlands und nord-nordwestlich des Kaspischen Meeres Undulationen an der Kern-Mantel Grenze selbst vermutet werden. Unter Berücksichtigung früherer Studien, z. B. von Kampfmann and Müller (1989), deuten die Messergebnisse auf eine laterale Topographie von 200 km und eine Höhe von 1 km hin. Eine Eingrenzung der potentiellen Anomaliemodelle kann nur durch eine gemeinsame Auswertung mit mineralogischen Experimenten und geodynamischen Modellierungen erfolgen.