Date of Award

2020

Document Type

Dissertation - Open Access

Degree Name

Doctor of Philosophy in Engineering Physics

Department

College of Arts & Sciences

Committee Chair

Dr. Jonathan B. Snively, Ph.D.

First Committee Member

Dr. Michael P. Hickey, Ph.D.

Second Committee Member

Dr. Matthew D. Zettergren, Ph.D.

Third Committee Member

Dr. Attila Komjathy, Ph.D.

Abstract

Natural hazards (NHs) are causes for significant concern due to their potentially catastrophic impacts on society. The study of their effects on the upper atmosphere can provide significant insight into the coupled nature of geophysical processes, and drives important applications for radio communication and navigation, leading potentially to the development of NH early-warning systems. Although general concepts underlying their coupling mechanisms are well understood, recent computational capabilities, supported by high temporal and spatial density of observations, have reached the level where such processes can be modeled with unprecedented realism for detailed case studies. The studies provided in this thesis are aimed to advance the understanding of the mechanisms of the generation and propagation of acoustic and gravity waves (AGWs) triggered by earthquakes and tsunamis, and their effects on mesopause airglow and ionospheric plasma.

First, we examine coupling mechanisms based on case studies for two inland earthquakes. We demonstrate that the incorporation of near-epicentral seismic wave dynamics, based on earthquake finite-fault models, provides marked improvement for the simulation of realistic AGWs and coseismic ionospheric disturbances (CIDs). Particularly, earthquake rupture propagation (and its direction) plays important role in AGW and CID asymmetries. The regime of propagation of the AGWs, driven by large earthquakes, can be weakly to strongly nonlinear, leading to substantially different dynamics in comparison with linear assumptions. Global Navigation Satellite System signals’ derived total electron content (TEC) observations may supplement seismological studies through the investigation of finite-fault models and their ability to reproduce detected ionospheric perturbations. In this case, numerical simulations are the most comprehensive way to resolve AGW propagation through the whole range of altitudes and to subsequently reproduce CIDs accurately. Electron density depletion processes and resonance of AGWs between thermosphere and ground, leaking energy into upper atmospheric layers, can contribute to long-lived CIDs that remain observable in TEC after the event.

This thesis also investigates the characteristics and propagation regimes of AGWs driven by tsunamis, based on realistic and parametric case studies with demonstrative and simplified bathymetry variations and sources. We show that AGW propagation is markedly affected by variations in atmospheric state, as well as nonlinear effects. Substantial amplification of AGWs reaching thermosphere may lead to their self-acceleration and breaking that, along with dissipative mechanisms, leads to the excitation of secondary AGWs of a broad range of periods. Bathymetry variations, resulting in focusing, reflection and refraction of ocean waves, play a crucial role on AGW characteristics, dispersion, and amplitudes.

Finally, we demonstrate that AGWs from large earthquakes and tsunamis can be sufficiently intense to drive strong perturbations in mesospheric nighttime airglow emissions, readily measurable from ground or space by contemporary imagers. New targeted observations above regions at high risk of seismic hazards have the potential to provide an additional source of data for tsunami early-warning systems, as well as new diagnostics of surface displacements for seismological studies.

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