Vertical‐Slice Ocean Tomography With Seismic Waves

Callies, Jörn; Wu, Wenbo; Peng, Shirui; Zhan, Zhongwen

doi:10.1029/2023gl102881

Cited by 6 publications

(34 citation statements)

References 41 publications

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“…For example, the seasonal variations line up reasonably well. Both ECCO and Argo, however, tend to underestimate the variations, as already seen in Wu et al (2020) and discussed more quantitatively in Callies et al (2023). The improved time resolution at H08 helps us better capture some signals, especially those with sub-seasonal time scales.…”

Section: Comparison Between Dgar and H08mentioning

confidence: 78%

“…The global network of CTBTO stations is too sparse to achieve such a dense sampling. Frequency-dependent T-wave travel time changes can constrain the depth distribution of a temperature anomaly, albeit coarsely (see Callies et al, 2023). Argo or ship-based point measurements, in contrast, are well localized and have excellent depth resolution but suffer from insufficient coverage in time and space and therefore alias mesoscale eddies and other oceanic transients.…”

Section: Discussionmentioning

confidence: 99%

“…Signals likely attributable to biweekly equatorial waves, for example, can be seen throughout the time series at H08 but are poorly resolved at DGAR except for the few months following the M 8.6 event in March 2005, when aftershocks are abundant. A decadal warming trend is apparent in both H08 and DGAR time series (see quantification in Callies et al (2023)).…”

Section: Comparison Between Dgar and H08mentioning

confidence: 96%

“…The temperature effects can be isolated by subtracting the origin time errors from the T-wave arrival time anomalies. In an accompanying manuscript (Callies et al, 2023), we describe how to set up a system of linear equation, impose priors, and use a Gauss-Markov estimator to invert for the time series of T-wave arrival time anomalies and origin time corrections. The T-wave arrival time offset measurement and inversion are similar to those described in Wu et al (2020) but constitute a somewhat more systematic approach.…”

Section: Inversion For Time Seriesmentioning

confidence: 99%

“…These corrections are now part of the inversion. We here briefly introduce the inversion framework and refer to Callies et al (2023) for a more detailed discussion.…”

Section: Inversion For Time Seriesmentioning

confidence: 99%

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Seismic Ocean Thermometry Using CTBTO Hydrophones

Wu,

Shen,

Peng

et al. 2023

JGR Solid Earth

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Due to limited observational coverage, monitoring the warming of the global ocean, especially the deep ocean, remains a challenging sampling problem. Seismic ocean thermometry (SOT) complements existing point measurements by inferring large‐scale averaged ocean temperature changes using the sound waves generated by submarine earthquakes, called T waves. We demonstrate here that Comprehensive Nuclear‐Test‐Ban Treaty Organization (CTBTO) hydrophones can record T waves with a higher signal‐to‐noise ratio compared to a previously used land‐based T‐wave station. This allows us to use small earthquakes (magnitude <4.0), which occur much more frequently than large events, dramatically improving the resulting temporal resolution of SOT. We also find that the travel time changes of T waves at the land‐based T‐wave station and the CTBTO hydrophone show small but systematic differences, although the two stations are only about 20 km apart. We attribute this feature to their different acoustic mode components sampling different parts of the ocean. Applying SOT to two CTBTO hydrophones in the East Indian Ocean reveals signals from decadal warming, seasonal variations, and mesoscale eddies, some of which are missing or underestimated in previously available temperature reconstructions. This application demonstrates the great advantage of hydrophone stations for global SOT, especially in regions with a low seismicity level.

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Section: Comparison Between Dgar and H08mentioning

confidence: 78%

Section: Discussionmentioning

confidence: 99%

Section: Comparison Between Dgar and H08mentioning

confidence: 96%

Section: Inversion For Time Seriesmentioning

confidence: 99%

“…These corrections are now part of the inversion. We here briefly introduce the inversion framework and refer to Callies et al (2023) for a more detailed discussion.…”

Section: Inversion For Time Seriesmentioning

confidence: 99%

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Seismic Ocean Thermometry Using CTBTO Hydrophones

Wu,

Shen,

Peng

et al. 2023

JGR Solid Earth

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Ocean Bottom Distributed Acoustic Sensing for Oceanic Seismicity Detection and Seismic Ocean Thermometry

Shen,

2024

JGR Solid Earth

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A T‐wave is a seismo‐acoustic wave that can travel a long distance in the ocean with little attenuation, making it valuable for monitoring remote tectonic activity and changes in ocean temperature using seismic ocean thermometry (SOT). However, current high‐quality T‐wave stations are sparsely distributed, limiting the detectability of oceanic seismicity and the spatial resolution of global SOT. The use of ocean bottom distributed acoustic sensing (OBDAS), through the conversion of telecommunication cables into dense seismic arrays, is a cost‐effective and scalable means to complement existing seismic stations. Here, we systematically investigate the performance of OBDAS for oceanic seismicity detection and SOT using a 4‐day Ocean Observatories Initiative community experiment offshore Oregon. We first present T‐wave observations from distant and regional earthquakes and develop a curvelet denoising scheme to enhance T‐wave signals on OBDAS. After denoising, we show that OBDAS can detect and locate more and smaller T‐wave events than regional OBS network. During the 4‐day experiment, we detect 92 oceanic earthquakes, most of which are missing from existing catalogs. Leveraging the sensor density and cable directionality, we demonstrate the feasibility of source azimuth estimation for regional Blanco earthquakes. We also evaluate the SOT performance of OBDAS using pseudo‐repeating earthquake T‐waves. Our results show that OBDAS can utilize repeating earthquakes as small as M3.5 for SOT, outperforming ocean bottom seismometers. However, ocean ambient natural and instrumental noise strongly affects the performance of OBDAS for oceanic seismicity detection and SOT, requiring further investigation.

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Seismic Ocean Thermometry of the Kuroshio Extension Region

Peng,

Callies,

et al. 2024

JGR Oceans

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Seismic ocean thermometry uses sound waves generated by repeating earthquakes to measure temperature change in the deep ocean. In this study, waves generated by earthquakes along the Japan Trench and received at Wake Island are used to constrain temperature variations in the Kuroshio Extension region. This region is characterized by energetic mesoscale eddies and large decadal variability, posing a challenging sampling problem for conventional ocean observations. The seismic measurements are obtained from a hydrophone station off and a seismic station on Wake Island, with the seismic station's digital record reaching back to 1997. These measurements are combined in an inversion for the time and azimuth dependence of the range‐averaged deep temperatures, revealing lateral and temporal variations due to Kuroshio Extension meanders, mesoscale eddies, and decadal water mass displacements. These results highlight the potential of seismic ocean thermometry for better constraining the variability and trends in deep‐ocean temperatures. By overcoming the aliasing problem of point measurements, these measurements complement existing ship‐ and float‐based hydrographic measurements.

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Vertical‐Slice Ocean Tomography With Seismic Waves

Cited by 6 publications

References 41 publications

Seismic Ocean Thermometry Using CTBTO Hydrophones

Seismic Ocean Thermometry Using CTBTO Hydrophones

Ocean Bottom Distributed Acoustic Sensing for Oceanic Seismicity Detection and Seismic Ocean Thermometry

Seismic Ocean Thermometry of the Kuroshio Extension Region

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