Spectral Element Modeling of Acoustic to Seismic Coupling Over Topography

Bishop, Jordan W.; Fee, David; Modrak, Ryan; Tape, Carl; Kim, Kee Hoon

doi:10.1029/2021jb023142

Cited by 18 publications

(7 citation statements)

References 90 publications

(226 reference statements)

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“…In our forward modeling, we assume the boundary between the atmosphere and the ground to be flat. However, the ground surface topography affects the compliance (e.g., Bishop et al., 2021) by altering the guided infrasound horizontal wavenumber relative to the ground surface. To incorporate the topography into the compliance computation, we can compute the spatial wavenumber of the topography and combine the wavenumber with the one of guided infrasound, similar to the microseism studies which consider ocean waves coupling with topographic seafloors (e.g., Ardhuin et al., 2015).…”

Section: Discussionmentioning

confidence: 99%

Modeling Seismic Recordings of High‐Frequency Guided Infrasound on Mars

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Garcia

et al. 2022

JGR Planets

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IntroductionNASA's InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed on the Martian surface in November 2018 and has since been conducting geophysical and meteorological observation (Banerdt et al., 2020). To achieve its objectives, InSight is equipped with a Very Broad Band (VBB) and a Short Period (SP) seismometer, which together constitute the SEIS (Seismic Experiment for Internal Structure) instrument (Lognonné et al., 2019). SEIS is operated in combination with a weather station, Auxiliary Payload Sensor Suite (APSS) including an atmospheric pressure sensor and wind and temperature sensors, to perform meteorological observation (Banfield et al., 2019). Due to power issues appearing in the second Martian year of the mission, SP and APSS have become temporarily unavailable, and VBB has been kept on most of the time. Thus only the VBB seismic data is available for analyzing the seismic events in this study.The ground motion recorded by InSight originates from different types of sources, most of which are marsquakes (e.g., Giardini et al., 2020) or atmospheric seismic events like pressure drops (e.g., Lognonné et al., 2020). The recent seismic recordings provides a new type of seismic events, a dispersive wave train following a typical very-high-frequency marsquake (Clinton et al., 2021), where a dispersive wave train means that the wave velocity, Abstract NASA's Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) mission records several high-frequency (>0.5 Hz) dispersive seismic signals on Mars. These signals are due to the acoustic-to-seismic coupling of infrasound generated by the entry and impact of meteorites. This dispersion property is due to infrasound propagating in a structured atmosphere, and we refer to this dispersive infrasound as guided infrasound. We propose to model the propagation of guided infrasound and the seismic coupling to the ground analytically; we use a 1D layered atmosphere on a three-layer solid subsurface medium. The synthetic ground movements fit the observed dispersive seismic signals well and the fitting indicates that the regolith beneath InSight is about 40-m in thickness. We also examine and validate the previously-published subsurface models derived from InSight ambient seismic vibration data.Plain Language Summary Under particular weather conditions, the Martian atmosphere displays a special sound-wave velocity profile, where the wave velocity becomes larger with increasing altitude within a few hundred meters. When an infrasound signal-a low-frequency (<20 Hz) sound wave inaudible to humanspropagates through such a structure, the infrasound exhibits dispersion: its propagation velocity depends on its frequency. We refer to such infrasound as guided infrasound. Guided infrasound can deform the ground, and have been recorded by the seismometer of NASA's Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) mission on the Martian surface. We propose to mo...

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Section: Discussionmentioning

confidence: 99%

Modeling Seismic Recordings of High‐Frequency Guided Infrasound on Mars

Froment

Garcia

et al. 2022

JGR Planets

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“…In addition to the accuracy of the DEM impacting the resultant numerical Green's functions, the FDTD method used here assumes a rigid boundary which may not 10.1029/2021JB023223 28 of 30 always be a good assumption (e.g. Bishop et al, 2021;Matoza et al, 2009). Numerical models that represent a smoothly varying topographic surface using stairstep boundaries may introduce spurious scattering into the modeled Green's functions (e.g., de Groot-Hedlin, 2004).…”

Section: Limitations Of the Studymentioning

confidence: 99%

Synthetic Evaluation of Infrasonic Multipole Waveform Inversion

et al. 2022

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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.

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“…Topographic features are known to diffract infrasonic waves and change the waveform significantly (e.g., Kim and Lees, 2011;Kim et al, 2015;Lacanna and Ripepe, 2020;Bishop et al, 2022). We conduct a first order analysis of topographic diffraction and propagation effects using the Finite Difference Time Domain code infraFDTD by Kim and Lees (2011).…”

Section: Topographic Effectsmentioning

confidence: 99%

Lava fountain jet noise during the 2018 eruption of fissure 8 of Kīlauea volcano

et al. 2022

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Real-time monitoring is crucial to assess hazards and mitigate risks of sustained volcanic eruptions that last hours to months or more. Sustained eruptions have been shown to produce a low frequency (infrasonic) form of jet noise. We analyze the lava fountaining at fissure 8 during the 2018 Lower East Rift Zone eruption of Kīlauea volcano, Hawaii, and connect changes in fountain properties with recorded infrasound signals from an array about 500 m from the fountain using jet noise scaling laws and visual imagery. Video footage from the eruption reveals a change in lava fountain dynamics from a tall, distinct fountain at the beginning of June to a low fountain with a turbulent, out-pouring lava pond surrounded by a tephra cone by mid-June. During mid-June, the sound pressure level reaches a maximum, and peak frequency drops. We develop a model that uses jet noise scaling relationships to estimate changes in volcanic jet diameter and jet velocity from infrasound sound pressure levels and peak frequencies. The results of this model indicate a decrease in velocity in mid-June which coincides with the decrease in fountain height. Furthermore, the model results suggest an increase in jet diameter, which can be explained by the larger width of the fountain that resembles a turbulent lava pond compared to the distinct fountain at the beginning of June. The agreement between the infrasound-derived and visually observed changes in fountain dynamics suggests that jet noise scaling relationships can be used to monitor lava fountain dynamics using infrasound recordings.

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Spectral Element Modeling of Acoustic to Seismic Coupling Over Topography

Cited by 18 publications

References 90 publications

Modeling Seismic Recordings of High‐Frequency Guided Infrasound on Mars

Modeling Seismic Recordings of High‐Frequency Guided Infrasound on Mars

Synthetic Evaluation of Infrasonic Multipole Waveform Inversion

Lava fountain jet noise during the 2018 eruption of fissure 8 of Kīlauea volcano

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