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Seismic observations have revealed two large low shear velocity provinces (LLSVPs) in the lowermost mantle beneath Pacific and Africa. One hypothesis for the origin of LLSVPs is that they are caused by accumulation of subducted oceanic crust on the core-mantle boundary (CMB). Here, I perform high resolution geodynamical calculations to test this hypothesis. The result shows that it is difficult for a thin (~ 6 km) subducted oceanic crust to accumulate on the CMB, and the major part of it is viscously stirred into the surrounding mantle. Another hypothesis for the origin of LLSVPs is that they are caused by thermochemical piles of more-primitive material which is remnant of Earth's early differentiation. In such case, a significant part of the subducted oceanic crust would enter the more-primitive reservoir, while other parts are either directly entrained into mantle plumes forming on top of the more-primitive reservoir or stirred into the background mantle. As a result, mantle plumes entrain a variable combination of compositional components including more-primitive material, old oceanic crust which first enters the more-primitive reservoir and is later entrained into mantle plumes with the more-primitive material, young oceanic crust which is directly entrained into mantle plumes without contacting the more-primitive reservoir, and depleted background mantle material. The result reconciles geochemical observation of multiple compositional components and varying ages of oceanic crust in the source of ocean-island basalts. Seismic studies have detected ultra-low velocity zones (ULVZs) in some localized regions on the CMB. Here, I present 3D thermochemical calculations to show that the distribution of ULVZs provides important information about their origin. ULVZs with a distinct composition tend to be located at the edges of LLSVPs, while ULVZs solely caused by partial melting tend to be located inboard from the edges of LLSVPs. This indicates that ULVZs at the edges of LLSVPs are best explained by distinct compositional heterogeneity, while ULVZs located insider of LLSVPs are better explained by partial melting. The results provide additional constraints for the origin of ULVZs.
ContributorsLi, Mingming (Author) / McNamara, Allen K (Thesis advisor) / Garnero, Edward J (Committee member) / Shim, Sang-Heon (Committee member) / Tyburczy, James (Committee member) / Clarke, Amanda (Committee member) / Arizona State University (Publisher)
Created2015
Description
The dynamic Earth involves feedbacks between the solid crust and both natural and anthropogenic fluid flows. Fluid-rock interactions drive many Earth phenomena, including volcanic unrest, seismic activities, and hydrological responses. Mitigating the hazards associated with these activities requires fundamental understanding of the underlying physical processes. Therefore, geophysical monitoring in combination with modeling provides valuable tools, suitable for hazard mitigation and risk management efforts. Magmatic activities and induced seismicity linked to fluid injection are two natural and anthropogenic processes discussed in this dissertation.
Successful forecasting of the timing, style, and intensity of a volcanic eruption is made possible by improved understanding of the volcano life cycle as well as building quantitative models incorporating the processes that govern rock melting, melt ascending, magma storage, eruption initiation, and interaction between magma and surrounding host rocks at different spatial extent and time scale. One key part of such models is the shallow magma chamber, which is generally directly linked to volcano’s eruptive behaviors. However, its actual shape, size, and temporal evolution are often not entirely known. To address this issue, I use space-based geodetic data with high spatiotemporal resolution to measure surface deformation at Kilauea volcano. The obtained maps of InSAR (Interferometric Synthetic Aperture Radar) deformation time series are exploited with two novel modeling schemes to investigate Kilauea’s shallow magmatic system. Both models can explain the same observation, leading to a new compartment model of magma chamber. Such models significantly advance the understanding of the physical processes associated with Kilauea’s summit plumbing system with potential applications for volcanoes around the world.
The unprecedented increase in the number of earthquakes in the Central and Eastern United States since 2008 is attributed to massive deep subsurface injection of saltwater. The elevated chance of moderate-large damaging earthquakes stemming from increased seismicity rate causes broad societal concerns among industry, regulators, and the public. Thus, quantifying the time-dependent seismic hazard associated with the fluid injection is of great importance. To this end, I investigate the large-scale seismic, hydrogeologic, and injection data in northern Texas for period of 2007-2015 and in northern-central Oklahoma for period of 1995-2017. An effective induced earthquake forecasting model is developed, considering a complex relationship between injection operations and consequent seismicity. I find that the timing and magnitude of regional induced earthquakes are fully controlled by the process of fluid diffusion in a poroelastic medium and thus can be successfully forecasted. The obtained time-dependent seismic hazard model is spatiotemporally heterogeneous and decreasing injection rates does not immediately reduce the probability of an earthquake. The presented framework can be used for operational induced earthquake forecasting. Information about the associated fundamental processes, inducing conditions, and probabilistic seismic hazards has broad benefits to the society.
Successful forecasting of the timing, style, and intensity of a volcanic eruption is made possible by improved understanding of the volcano life cycle as well as building quantitative models incorporating the processes that govern rock melting, melt ascending, magma storage, eruption initiation, and interaction between magma and surrounding host rocks at different spatial extent and time scale. One key part of such models is the shallow magma chamber, which is generally directly linked to volcano’s eruptive behaviors. However, its actual shape, size, and temporal evolution are often not entirely known. To address this issue, I use space-based geodetic data with high spatiotemporal resolution to measure surface deformation at Kilauea volcano. The obtained maps of InSAR (Interferometric Synthetic Aperture Radar) deformation time series are exploited with two novel modeling schemes to investigate Kilauea’s shallow magmatic system. Both models can explain the same observation, leading to a new compartment model of magma chamber. Such models significantly advance the understanding of the physical processes associated with Kilauea’s summit plumbing system with potential applications for volcanoes around the world.
The unprecedented increase in the number of earthquakes in the Central and Eastern United States since 2008 is attributed to massive deep subsurface injection of saltwater. The elevated chance of moderate-large damaging earthquakes stemming from increased seismicity rate causes broad societal concerns among industry, regulators, and the public. Thus, quantifying the time-dependent seismic hazard associated with the fluid injection is of great importance. To this end, I investigate the large-scale seismic, hydrogeologic, and injection data in northern Texas for period of 2007-2015 and in northern-central Oklahoma for period of 1995-2017. An effective induced earthquake forecasting model is developed, considering a complex relationship between injection operations and consequent seismicity. I find that the timing and magnitude of regional induced earthquakes are fully controlled by the process of fluid diffusion in a poroelastic medium and thus can be successfully forecasted. The obtained time-dependent seismic hazard model is spatiotemporally heterogeneous and decreasing injection rates does not immediately reduce the probability of an earthquake. The presented framework can be used for operational induced earthquake forecasting. Information about the associated fundamental processes, inducing conditions, and probabilistic seismic hazards has broad benefits to the society.
ContributorsZhai, Guang (Author) / Shirzaei, Manoochehr (Thesis advisor) / Garnero, Edward (Committee member) / Clarke, Amanda (Committee member) / Tyburczy, James (Committee member) / Li, Mingming (Committee member) / Arizona State University (Publisher)
Created2018
Description
The transport of hydrogen to the Earth’s deep interior remains uncertain. The upper mantle minerals have very low hydrogen solubilities (hundreds of ppm). The hydrogen storage capability in the transition zone minerals (2 wt%) is high compared to those of the upper mantle. The hydrogen storage in the lower mantle is not well known. The main minerals in the lower mantle bridgmanite and ferropericlase have very low hydrogen storage capacities (less than 20 ppm). In order to further understand the hydrogen storage in the lower mantle, a series of experiments had been conducted to simulate the environment similar to the Earth’s mantle. The experiments with hydrous Mg2SiO4 ringwoodite (Rw) show that it converts to crystalline dense hydrous silica, stishovite (Stv) or CaCl2-type SiO2(mStv), containing ∼1 wt% H2O together with bridgmanite (Brd) and MgO at the pressure-temperature conditions expected for lower mantle depths between approximately 660 to 1600 km. Brd would break down partially to dense hydrous silica (6–25 mol%) and(Mg,Fe)O in mid-mantle regions with 0.05–0.27 wt% H2O. The hydrous stishovite has a CaCl2 structure, which is common among hydrous minerals in the lower mantle. Based on this observation, I hypothesize the existence of hydrous phases in the lower mantle. The experiments found a new hexagonal iron hydroxide (η-Fe12O18+x/2Hx) between the stability fields of the epsilon and pyrite-type FeOOH at 60–80 GPa and high temperature. The new phase contains less H2O, limiting the H2O transport from the shallow to the deep mantle in the Fe–O–H system. Possible hydrogen storage in Ca-perovskite was studied. CaPv could contain 0.5–1 wt% water and the water in CaPv could distort the crystal structure of CaPv from cubic to tetragonal structure. In conclusion, hydrogen can be stored in hydrous stishovite in the shallower depth of the lower mantle. At greater depth, the new η phase and pyrite-type phase would take over the hydrogen storage. The role of CaPv in deep water storage needs to be considered in future studies.
ContributorsChen, Huawei (Author) / Shim, Sang-Heon (Thesis advisor) / Garnero, Edward (Committee member) / Bose, Maitrayee (Committee member) / Li, Mingming (Committee member) / Leinenweber, Kurt (Committee member) / Arizona State University (Publisher)
Created2019