Ph.D. Dissertation Defense

Understanding earthquake triggering and fault slip behavior based on complete earthquake catalogs

Large mainshocks can alter stress field on subsurface asperities across broad spatial and temporal windows, which would promote or inhibit fault motion. Beyond rapid rupture during earthquakes, fault can also slip at a steady rate without seismic radiation. In between these two end members, slow slip events have been documented within the conditionally stable transition zone.

Wildfires in Earth System: The Driver, Transport, and Feedback

Wildfires release large amounts of greenhouse gases, carbonaceous aerosols, and other pollutants, therefore having complex impacts on the earth climate, local weather, and air quality. To study the transport of the wildfire emissions, a plume height dataset has been developed. The resulting dataset from 2002 to 2010 captured well the observed MISR plume height distribution. By adding the plume height dataset in the climate model, the plume-rise enhanced AOD downstream of the wildfire spots by 20 to 50%.

Effects of metal impurity on the structure and reactivity of manganese oxides

Mn oxides are among the most ubiquitous and reactive mineral phases in natural environments and significantly influence the cycles of essential elements such as C and N, as well as the transport and fate of a wide range of metals. The structure and reactivity of Mn oxides were extensively studied but most of these studies used pure Mn oxide minerals, which are barely found in real geological or engineering settings.

Geochemical controls of the microbially mediated redox cycling of uranium and iron

Mining and processing of uranium ore, followed by improper disposal and aging nuclear waste infrastructure, have left behind a legacy of uranium contamination across the United States. Uranium bioreduction, an in situ bioremediation strategy which promotes microbial reduction of aqueous U(VI) to insoluble U(IV) solids, has proven successful at decreasing groundwater uranium concentrations below regulatory limits. However, iron 

Improved understanding of extent and size of tsunamigenic earthquakes through geodetic and tsunami datasets

Some of the largest earthquakes yet observed occur along the broad interface between two converging tectonic plates called the megathrust. The extent of the megathrust and its associated seismicity differs with each subduction zone, but typically crustal deformation related to the rupture extends both in submarine and terrestrial environments. On land, this coseismic deformation is common observed with stationary instruments such as Global Navigational Satellite Systems (GNSS) or through satellite imagery using Interferometric Synthetic Aperture Radar (InSAR).

Oceanographic controls of hydrocarbon degradation in the Gulf of Mexico

The risk of an oil spill accident is increasing in pristine regions of the world’s oceans due
to the development and transport of crude oil resources. The ability to predict the trajectory of
spilled oil is critical for the improvement of emergency response strategies. Although the controls of
petroleum hydrocarbon biodegradation have been studied in the ocean for years, there is as yet no
consensus on the results for predictive modeling. One of the reasons is the complexity of the

Hydrocarbon degradation by bacteria in coastal environment of northern Gulf of Mexico sediment after the Deepwater Horizon oil spill

The objective of this dissertation research was to characterize sedimentary microbial populations that are active in degrading petroleum hydrocarbons that reach the seafloor during accidental oil spills. Whereas most previous work has investigated hydrocarbon-degrading microbial communities in sediments from seep environments that are regularly exposed to high levels of oil, the focus of this study was on non-seep sediments that are not pre-exposed to high levels of petroleum.

Exploiting Subsurface Ocean Dynamics for Decadal Predictability in the Upwelling Systems of the Eastern North Pacific

Given the strong recent interest in the decadal timescale variability and the potential for its predictability, it is critical to identify dynamics that carry inherent decadal-scale predictability. This work enhances our understanding and prediction capability of the subsurface signature of the decadal variability in the eastern North Pacific upwelling systems using reanalysis products and a set of eddy-resolving ocean model simulations.

Tropospheric O3 modeling study: Contributions of anthropogenic and biogenic sources to O3-CO and O3-CH2O correlations

This dissertation employs DISCOVER-AQ aircraft experiments and 3-D chemical and transport model to study the contributions of different sources to the  correlation of O3-CO and O3-CH2O on different scales, and the implements of O3 estimation using the correlations and concentrations of CO and CH2O.

Applications of satellite retrievals in deriving pollutant emissions and trends

This dissertation employs various satellite retrievals and the 3-D Regional chEmical trAnsport Model (REAM) to (1) identify and quantify the emission sources, and (2) derive pollutant trends.

First, we use short-lived reactive aromatics as proxies to diagnose transport of pollutants through the Himalayas to Tibet. We find enhancements of reactive aromatics over Tibet by a factor of 6 on average due to rapid transport from India and nearby regions during the presence of a high-altitude cut-off low system.

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