Description
- Abstract:
- To image Earth structure and dynamics, seismologists employ measurements of the frequency-dependent propagation speeds of surface waves generated by earthquakes, which provide unique and critical constraints on the structure of the upper mantle. However, measurements of surface wave propagation are impeded by overtones, which act as a source of both random and systematic error. The thesis develops a new understanding of the phenomenon of overtone interference and generates new, improved images of the Earth’s interior. The second chapter of this thesis shows the first observations of overtone interference in Rayleigh wave phase, amplitude, and array-based phase velocities. In this study, we categorically prove, using synthetic seismograms, that the origin of the oscillatory interference phenomena we observe is major-arc overtone interference, which results in an increase in measurement error at large epicentral distances. Chapter three presents an analysis of overtone interference in Rayleigh and Love waves using synthetic seismograms and real data. We develop a framework to estimate overtone contamination in any Love and Rayleigh wave measurement, explaining the characteristic dependence of errors in array-based Rayleigh wave phase velocity measurements as a function of epicentral distance. Chapter four develops an approach to isolate relatively uncontaminated Love wave measurements and presents the first Love wave phase velocity maps for USArray. These maps are consistent with a previous high-resolution study of radial anisotropy in the crust of the western U.S. and suggest changes in radial anisotropy between the crust and upper mantle. We also discuss geographic and frequency-dependent variations in the availability of high-quality Love wave measurements globally. Chapter five uses the new Love wave maps to solve for a 3D model of radial anisotropy. At crustal depths, our preferred model features distinctive radial anisotropy in the Western and Easternmost U.S. that aligns well with physiographic provinces and regions of Cenozoic extension. At greater depth, the model features strong anisotropic heterogeneity in the uppermost mantle. In the sixth chapter, we discuss overtone interference in other surface-wave observables, explore the likelihood of overtone interference on other planets, and present progress towards a tool for calculating mode and frequency-dependent surface-wave excitation.
- Notes:
- Thesis (Ph. D.)--Brown University, 2023
Citation
Hariharan, Anant,
"Understanding Overtone Interference in Surface wave Measurements: Application to Anisotropic Imaging of the Uppermost Mantle Beneath North America"
(2023).
Earth, Environmental and Planetary Sciences Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://repository.library.brown.edu/studio/item/bdr:bw6vrewg/
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Earth, Environmental and Planetary Sciences Theses and Dissertations
Theses and Dissertations for the Earth, Environmental and Planetary Sciences department....