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Abstract AbyssalT‐waves are seismo‐acoustic waves originating from abyssal oceans. Unlike subduction‐zone‐generated slopeT‐waves which are generated through multiple reflections between the sea surface and the gently dipping seafloor, the genesis of abyssalT‐waves cannot be explained by the same theory. Several hypotheses, including seafloor scattering, sea surface scattering, and internal‐wave‐induced volumetric scattering, have been proposed to elucidate their genesis and propagation. The elusive mechanism of abyssalT‐waves, particularly at low‐frequencies, hinders their use to quantify ocean temperatures through seismic ocean thermometry (SOT) and estimate oceanic earthquake parameters. Here, using realistic geophysical and oceanographic data, we first conduct numerical simulations to compare synthetic low‐frequency abyssalT‐waves under different hypotheses. Our simulations for the Romanche and Blanco transform faults suggest seafloor scattering as the dominant mechanism, with sea surface and internal waves contributing marginally. Short‐scale bathymetry can significantly enhance abyssalT‐waves across a broad frequency range. Also, observedT‐waves from repeating earthquakes in the Romanche, Chain, and Blanco transform faults exhibit remarkably high repeatability. Given the dynamic nature of sea surface roughness and internal waves, the highly repeatableT‐wave arrivals further support the seafloor scattering as the primary mechanism. The dominance of seafloor scattering makes abyssalT‐waves useable for constraining ocean temperature changes, thereby greatly expanding the data spectrum of SOT. Our observations of repeating abyssalT‐waves in the Romanche and Chain transform faults could provide a valuable data set for understanding Equatorial Atlantic warming. Still, further investigations incorporating high‐resolution bathymetry are warranted to better model abyssalT‐waves for earthquake parameter estimation.
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Seismic Detection of Oceanic Internal Gravity Waves from Terrestrial Observations
Oceanic internal gravity waves propagate along density stratification within the water column and are ubiquitous. They can propagate thousands of kilometers before breaking in shoaling bathymetry and the ensuing turbulent mixing affects coastal processes and climate feedbacks. Despite their importance, internal waves are intrinsically difficult to detect as they result in only minor amplitude deflection of the sea surface; the need for global detection and long time series of internal waves motivates a search for geophysical detection methods. The pressure coupling of a propagating internal wave with the sloping seafloor provides a potential mechanism to generate seismically observable signals. We use data from the South China Sea where exceptional oceanographic and satellite time series are available for comparison to identify internal wave signals in an onshore passive seismic data set for the first time. We analyze potential seismic signals on broadband seismometers in the context of corroborating oceanographic and satellite data available near Dongsha Atoll in May–June 2019 and find a promising correlation between transient seismic tilt signals and internal wave arrivals and collisions in oceanic and satellite data. It appears that we have successfully detected oceanic internal waves using a subaerial seismometer. This initial detection suggests that the onshore seismic detection and amplitude determination of oceanic internal waves is possible and can potentially be used to expand the historical record by capitalizing on existing island and coastal seismic stations.
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- Award ID(s):
- 1753317
- PAR ID:
- 10318390
- Date Published:
- Journal Name:
- AGU advances
- Volume:
- 2
- ISSN:
- 2576-604X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1002/essoar.10507103.1
