Geophysical applications of sound : volcano infrasound and marine seismic sources
Abstract/Contents
- Abstract
- Acoustic waves are generated by a wide range of natural and artificial geophysical phenomena. By studying the acoustic signals, insight can be gained about the fundamental processes governing these phenomena. In this thesis I examine acoustic signals from two different sources; volcanic eruptions and pneumatic marine seismic sources. In Part I of this thesis I consider acoustic waves generated by volcanic activity. Volcanoes are prodigious sources of low frequency acoustic waves, which are termed infrasound as the signals are predominantly at frequencies below human hearing. Harmonic infrasound signals are observed at open-vent volcanoes and in Chapter 2 I develop a numerical model to demonstrate that these signals can be explained by acoustic resonance of the crater. In Chapter 3 I apply this model to the 2015 eruption of Villarrica (Chile) and show that the lava lake rose in the crater prior to the paroxysmal eruption. These two chapters illustrate the utility of monitoring infrasound resonant modes at open vent volcanoes and may aid in forecasting future eruptive activity. The majority of volcano infrasound studies assume linear wave propagation. However, volcanic eruptions are violent phenomena and there is increasing evidence of nonlinear wave phenomena, such as shock waves, during eruptive activity. In Chapter 4 I perform nonlinear computational aeroacoustic simulations of volcanic eruptions to explore the effect of nonlinear wave propagation and demonstrate that assuming linearity can result in overestimation of erupted fluxes for eruptions with high (supersonic) exit velocities. In Part II of this thesis I study pneumatic marine seismic sources, which are the predominant source used in marine seismic surveys. Pneumatic seismic sources are broadband sources that generate both geophysically useful low frequencies and high frequency noise that is harmful to marine life. In Chapter 5 I explore controls on the initial peak of a pneumatic seismic source signature. The initial peak is generated by the initial release of highly pressurized air into the water and is responsible for generating high frequency noise that can be environmentally damaging. In Chapter 6 I present numerical simulations of a novel pneumatic seismic source, called the Tuned Pulse Source, and demonstrate that this source will generate increased low frequency content. In Chapter 7 I digress slightly to compare marine seismic signals with the low frequency calls of fin whales and speculate on possible mechanisms of low frequency sound generation in whales
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2020; ©2020 |
| Publication date | 2020; 2020 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Watson, Leighton Myles |
|---|---|
| Degree supervisor | Dunham, Eric |
| Thesis advisor | Dunham, Eric |
| Thesis advisor | Segall, Paul, 1954- |
| Thesis advisor | Suckale, Jenny |
| Degree committee member | Segall, Paul, 1954- |
| Degree committee member | Suckale, Jenny |
| Associated with | Stanford University, Department of Geophysics. |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Leighton Myles Watson |
|---|---|
| Note | Submitted to the Department of Geophysics |
| Thesis | Thesis Ph.D. Stanford University 2020 |
| Location | electronic resource |
Access conditions
- Copyright
- © 2020 by Leighton Myles Watson
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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