Evanescent wave coupling in a geophysical system: Airborne acoustic signals from the Mw 8.1 Macquarie Ridge earthquake

Evers, Läslo; Brown, David; Heaney, Kevin D.; Assink, Jelle; Smets, Pieter; Snellen, Mirjam

doi:10.1002/2013gl058801

Cited by 31 publications

(12 citation statements)

References 24 publications

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“…However, in cases where the acoustic wavelength significantly exceeds the in-water source depth (Godin, 2007), low-frequency underwater sound waves may transcend the anomalously transparent sea surface and propagate as atmospheric signals. This process is known as evanescent wave coupling and was first observed in a geophysical system by Evers et al (2014) for the 2004 M W 8.1 Macquarie Ridge earthquake. During times of activity at Monowai, no corresponding arrivals are registered in the IMS processing stream at the three closest infrasound stations, that is, IS22 at Port Laguerre (1,674-km source-receiver distance), IS36 at Chatham Islands (2,001 km), and IS24 at Tahiti (3,014 km), suggesting that an equivalent phenomenon is not present at Monowai and that the volcano probably failed to breach the sea surface during the time periods studied here.…”

Section: Discussionmentioning

confidence: 95%

Tracking Submarine Volcanic Activity at Monowai: Constraints From Long‐Range Hydroacoustic Measurements

et al. 2018

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Monowai is a submarine volcanic center in the Kermadec Arc, Southwest Pacific Ocean. In the past, activity at the volcano had been intermittently observed in the form of fallout at the sea surface, discolored water, changes in seafloor topography, and T phase seismicity, but there is no continuous record for more recent years. In this study, we investigated 3.5 years of recordings at a hydrophone array of the International Monitoring System, located near Juan Fernández Islands, for long‐range underwater sound waves from Monowai. Results from direction‐of‐arrival calculations and density‐based spatial clustering indicate that 82 discrete episodes of activity occurred between July 2003 and March 2004 and from April 2014 to January 2017. Volcanic episodes are typically spaced days to weeks apart, range from hours to days in length, and amount to a cumulative sum of 137 days of arrivals in total, making Monowai one of the most active submarine arc volcanoes on Earth. The resolution of the hydrophone recordings surpasses broadband network data by at least 1 order of magnitude, identifying seismic events as low as 2.2 mb in the Kermadec Arc region. Further observations suggest volcanic activity at a location approximately 400 km north of Monowai in the Tonga Arc and at Healy or Brothers volcano in the southern Kermadec Arc. Our findings are consistent with previous studies and highlight the exceptional capabilities of the International Monitoring System network for the scientific study of active volcanism in the global ocean.

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Section: Discussionmentioning

confidence: 95%

Tracking Submarine Volcanic Activity at Monowai: Constraints From Long‐Range Hydroacoustic Measurements

et al. 2018

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“…The SOFAR channel is a low-velocity layer in the deep ocean, that is, the average channel axis depth is 1.5 km, which allows low-frequency sound to be detected over long ranges (Munk & Forbes 1989). The efficiency of the SOFAR channel for sound propagation has already been used in studies related to earthquakes (Evers et al 2014;De Groot-Hedlin 2005;Guilbert et al 2005), icebergs (Chapp et al 2005;Talandier et al 2006;Evers et al 2013), explosions (Munk & Forbes 1989;Prior et al 2011), marine mammals ) and underwater volcanoes . Guided wave propagation contributes to the limited acoustical attenuation by the SOFAR channel.…”

Section: Introductionmentioning

confidence: 99%

Deep ocean sound speed characteristics passively derived from the ambient acoustic noise field

Evers

Wapenaar

Heaney

et al. 2017

Geophysical Journal International

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S U M M A R YThe propagation of acoustic waves in the ocean strongly depends on the temperature. Lowfrequency acoustic waves can penetrate the ocean down to depths where few in situ measurements are available. It is therefore attractive to obtain a measure of the deep ocean temperature from acoustic waves. The latter is especially true if the ambient acoustic noise field can be used instead of deterministic transient signals. In this study the acoustic velocity, and hence the temperature, is derived in an interferometric approach from hydrophone array recordings. The arrays were separated by over 125 km, near Ascension Island in the Atlantic Ocean, at a depth of 850 m. Furthermore, the dispersive characteristics of the deep ocean sound channel are resolved based on the retrieved lag times for different modes. In addition, it is shown how the resolution of the interferometric approach can be increased by cross correlating array beams rather than recordings from single-sensor pairs. The observed acoustic lag times between the arrays corresponds well to modelled values, based on full-wave modelling through best-known oceanic models.

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“…The high impedance contrast at the water-air interface inhibits sound transmission by reflecting sound downward. However, when the sound wavelength is much larger than the source depth a phenomenon known as "anomalous transparency" may occur where much of the sound energy incident upon the water/air interface is transmitted into the atmosphere (Godin 2006, Evers et al 2014. Infrasound from submarine volcanic sources has not been studied in great detail.…”

Section: Introductionmentioning

confidence: 99%

Seismo-acoustic evidence for vent drying during shallow submarine eruptions at Bogoslof volcano, Alaska

et al. 2019

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Characterizing the state of the volcanic vent is key for interpreting observational datasets and accurately assessing volcanic hazards. This is particularly true for remote, complex eruptions such as the 2016-2017 Bogoslof volcano, Alaska eruption sequence. Bogoslof's eruptions in this period were either shallow submarine or subaerial, or some combination of both. Our results demonstrate how low-frequency sound waves (infrasound), integrated with seismic and satellite data, can provide unique insight into shallow vent processes, otherwise not available. We use simple metrics, such as the infrasound frequency index (FI), event duration, and acoustic-seismic amplitude ratio, to look at changes in the elastic energy radiation and infer changes in seawater access to the vent. Satellite imagery before and after selected eruptions is used to ground-truth inferences on vent conditions. High FI and gradual increases in infrasound frequency content at Bogoslof correspond with transitions from submarine to subaerial vent conditions and a diminished or absent role of water, likely resulting in a drying out of the vent region. Event durations generally correlate with high FI and the range of FI values for each event, suggesting long duration events were more effective at drying out the vent region. A trend from low to high acoustic-seismic amplitude ratios for some long duration events also suggests an increase in acoustic efficiency as the vent dried out. We demonstrate that infrasound can serve as a robust indicator of seawater involvement for Bogoslof and other shallow submarine eruptions that may not be inferable from other datasets, particularly in near-real-time.

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Evanescent wave coupling in a geophysical system: Airborne acoustic signals from the M_w 8.1 Macquarie Ridge earthquake

Cited by 31 publications

References 24 publications

Tracking Submarine Volcanic Activity at Monowai: Constraints From Long‐Range Hydroacoustic Measurements

Tracking Submarine Volcanic Activity at Monowai: Constraints From Long‐Range Hydroacoustic Measurements

Deep ocean sound speed characteristics passively derived from the ambient acoustic noise field

Seismo-acoustic evidence for vent drying during shallow submarine eruptions at Bogoslof volcano, Alaska

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