Master of Science (MS), Bowling Green State University, 2017, Geology

The length of a day on Earth (abbreviated LOD) is not exactly 24 hours. There is a small excess LOD that varies on timescales ranging from a few days to thousands of years, generally on the order of milliseconds. One characteristic of LOD variations is a sinusoidal component with a period of ~6 years. The cause of the ~6-year signal is unknown, but is generally suspected to be exchanges of angular momentum between the mantle and the core. This study aimed to test the hypothesis that the ~6-year LOD signal is due to coupling between the mantle and fluid outer core. The flow of the core's fluid deforms the base of the mantle, leading to redistribution of Earth's mass (causing changes in the gravitational field) and deformation of the overlying crust. Surface deformation data from a global network of high-precision Global Positioning System (GPS) stations was analyzed, and the component that acts on the ~6-year timescale was isolated and inverted for the core's flow. Resulting angular momentum changes were computed for the outer core and compared to the LOD signal to search for evidence of core-mantle coupling. Outer core angular momentum changes obtained from GPS deformation data exhibit evidence of the suspected core-mantle coupling, but this result is sensitive to inversion parameters. Changes in the gravitational field were also modeled and found to be smaller than the errors in the currently available data.

Committee: Yuning Fu PhD (Advisor); Richard Gross PhD (Committee Member); Marco Nardone PhD (Committee Member); Margaret Yacobucci PhD (Committee Member) Subjects: Geology; Geophysics