Spectral Element Modeling of Acoustic to Seismic Coupling Over Topography

Journal Article · 22 December 2021 · Journal of Geophysical Research. Solid Earth

DOI: https://doi.org/10.1029/2021jb023142 · OSTI ID:1855139

Bishop, Jordan W.  ^[1]; Fee, David  ^[2]; Modrak, Ryan  ^[3]; Tape, Carl  ^[2]; Kim, Keehoon  ^[4]

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1. Univ. of Alaska, Fairbanks, AK (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2. Univ. of Alaska, Fairbanks, AK (United States)
3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Acoustic waves in the atmosphere are commonly recorded on seismometers as they couple into the ground. These signals, here called ground coupled airwaves, are not commonly considered in numerical modeling of infrasound propagation, which often assumes a rigid unmeshed boundary. Starting from an analytically-tractable spherical wave model, we analyze how the coupling of an acoustic wave into a planar elastic halfspace changes over a wide range of scenarios. We use energy admittance to quantify acoustic to seismic coupling over both a planar elastic halfspace and meshed topography. Our spectral element and analytic calculations have different maxima as a function of incidence angle, with very high admittance values for near-vertical incidence (maximum ≈78%). Energy admittance calculations at shallow incidence angles are much smaller (less than 1%). In simulations over the complex topography of Sakurajima Volcano, we attribute the variable spatial pattern of energy admittance to changes in earth parameters between each model. The observed pressure difference over the simulated 15 km region appears to be < 2%. While this value is relatively small, the cumulative addition over 100s of km and multiple acoustic bounce points may be significant. Acoustic to seismic coupling along the propagation path may bias long distance yield estimates, particularly when infrasound propagates over regions with steep topography or particularly slow seismic velocities, such as alluvial planes.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: Defense Threat Reduction Agency (DTRA); National Science Foundation (NSF); USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: 89233218CNA000001; AC52-07NA27344
• OSTI ID: 1855139
• Report Number(s): LA-UR-21-28604; LLNL-JRNL-832763
• Journal Information: Journal of Geophysical Research. Solid Earth, Journal Name: Journal of Geophysical Research. Solid Earth Journal Issue: 1 Vol. 127; ISSN 2169-9313
• Publisher: American Geophysical UnionCopyright Statement
• Country of Publication: United States
• Language: English