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- Title
Synthetic Evaluation of Infrasonic Multipole Waveform Inversion.
- Authors
Iezzi, Alexandra M.; Matoza, Robin S.; Fee, David; Kim, Keehoon; Jolly, Arthur D.
- Abstract
Acoustic source inversions estimate the mass flow rate of volcanic explosions or yield of chemical explosions and provide insight into potential source directionality. However, the limitations of applying these methods to complex sources and their ability to resolve a stable solution have not been investigated in detail. We perform synthetic infrasound waveform inversions that use 3‐D Green's functions for a variety of idealized and realistic deployment scenarios using both a flat plane and Yasur volcano, Vanuatu as examples. We investigate the ability of various scenarios to retrieve the input source functions and relative amplitudes for monopole and multipole (monopole and dipole) inversions. Infrasound waveform inversions appear to be a robust method to quantify mass flow rates from simple sources (monopole) using deployments of infrasound sensors placed around a source, but care should be taken when analyzing and interpreting results from more complex acoustic sources (multipole) that have significant directional components. In the examples we consider the solution is stable for monopole inversions with a signal‐to‐noise ratio greater than five and the dipole component is small. For most scenarios investigated, the vertical dipole component of the multipole explosion source is poorly constrained and can impact the ability to recover the other source term components. Because multipole inversions are ill‐posed for many deployments, a low residual does not necessarily mean the proper source vector has been recovered. Synthetic studies can help investigate the limitations and place bounds on information that may be missing using monopole and multipole inversions for potentially directional sources. Plain Language Summary: Explosions such as those from volcanoes create low‐frequency sound below the threshold of human hearing (infrasound) that can be recorded at a variety of distances. Infrasound can be used to calculate the amount of material being ejected from a volcano and if the sound waves are preferentially emitted in a certain direction. However, this directionality can be difficult to determine because infrasound sensors are often placed on the ground surface, which makes determining the vertical directionality of an explosion source difficult. We use numerical model examples of infrasound deployments around a volcanic source and vary parameters including the station locations, noise level, strength of directionality, and impact of wind to investigate the ability to recover the input source parameters. We find that assuming an infrasound source radiates equally in all directions is good enough even for directional sources if the directional component is small and the signal is five times higher in amplitude than the noise. However, caution should be used for sources that are directional for many infrasound sensor deployments. Key Points: We investigate the ability to resolve multipole acoustic sources using infrasound waveform inversion methods for a variety of scenariosA monopole inversion yields results that may be sufficient for practical purposes, even for multipole sources with a small dipole componentSynthetic inversion studies can increase understanding of the limitations of multipole infrasound inversions based on deployment scenarios
- Subjects
INVERSIONS (Geology); COMPUTER simulation; INFRASONIC waves; DETECTORS; MAGNETIC monopoles
- Publication
Journal of Geophysical Research. Solid Earth, 2022, Vol 127, Issue 1, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2021JB023223