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- All Subjects: Geophysics
- Creators: School of Earth and Space Exploration
- Status: Published
In this dissertation, I measure the decades-long time evolution of fault-related crustal deformation along the San Andrea Fault in California and the northeast Japan subduction zone using space-borne geodetic techniques, such as Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR). The surface observation of deformation combined with seismic data set allow constraining the time series of creep distribution on the fault surface at seismogenic depth. The obtained time-dependent kinematic models reveal that creep in both study areas evolves through a series of SSEs, each lasting for several months. Using physics-based models informed by laboratory experiments, I show that the transient elevation of pore fluid pressure is the driving mechanism of SSEs. I further investigate the link between SSEs and evolution of seismicity on neighboring locked segments, which has implications for seismic hazard models and also provides insights into the pattern of microstructure on the fault surface. I conclude that while creeping segments act as seismic rupture barriers, SSEs on these zones might promote seismicity on adjacent seismogenic segments, thus change the short-term earthquake forecast.
Although nitrogen is the dominant element in Earth’s atmosphere, it is depleted in the bulk silicate Earth (relative to expected volatile abundances established by carbonaceous chondrites). To resolve this inconsistency, it has been hypothesized that this “missing nitrogen” may actually be stored within the Earth’s deep interior. In this work, we use multi-anvil press experiments to synthesize solid solution mixtures of the mantle transition zone mineral wadsleyite (Mg2SiO4) and silicon nitride (Si3N4). Successful synthesis of a 90% Si3N4, 10% Mg2SiO4 solid solution implies that nitrogen may not be sequestered within the most abundant mineral phases in the Earth’s mantle. Instead, nitrogen-rich accessory phases may hold the key to studying nitrogen storage within the deep interior. Ultimately, quantifying the amount of nitrogen within the mantle will further our understanding of the N cycle, which is vital to maintaining planetary habitability. Similar N cycling processes may be occurring on other rocky bodies; therefore, studying nitrogen storage may be an important part of determining habitability conditions on other worlds, both within in our solar system and beyond.