<i>P</i>‐Delays from Floating Seismometers (MERMAID), Part I: Data Processing

Joubert, Cécile; Nolet, Guust; Bonnieux, S.; Deschamps, A.; Dessa, Jean‐Xavier; Hello, Y.

doi:10.1785/0220150111

Cited by 12 publications

(7 citation statements)

References 16 publications

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“…The correction for the total drift in the water column during ascent is typically less than 400 m. The equivalent time correction for a mantle P wave is less than 0.05 s, and the expected error even smaller. If the float did not rise immediately to the surface the error can be about three times as large 26 , but these cases are rare (most of the triggered signals that were stored without direct surfacing turned out to be false triggers). The depth of the float is accurately determined by the pressure sensor with an accuracy of a few meters and does not contribute to the over-all data error.…”

Section: Methodsmentioning

confidence: 99%

Imaging the Galápagos mantle plume with an unconventional application of floating seismometers

Nolet

Hello

Lee

et al. 2019

Sci Rep

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We launched an array of nine freely floating submarine seismometers near the Galápagos islands, which remained operational for about two years. P and PKP waves from regional and teleseismic earthquakes were observed for a range of magnitudes. The signal-to-noise ratio is strongly influenced by the weather conditions and this determines the lowest magnitudes that can be observed. Waves from deep earthquakes are easier to pick, but the S/N ratio can be enhanced through filtering and the data cover earthquakes from all depths. We measured 580 arrival times for different raypaths. We show that even such a limited number of data gives a significant increase in resolution for the oceanic upper mantle. This is the first time an array of floating seismometers is used in seismic tomography to improve the resolution significantly where otherwise no seismic information is available. We show that the Galápagos Archipelago is underlain by a deep (about 1900 km) 200–300 km wide plume of high temperature, with a heat flux very much larger than predicted from its swell bathymetry. The decrease of the plume temperature anomaly towards the surface indicates that the Earth’s mantle has a subadiabatic temperature gradient.

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Section: Methodsmentioning

confidence: 99%

Imaging the Galápagos mantle plume with an unconventional application of floating seismometers

Nolet

Hello

Lee

et al. 2019

Sci Rep

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“…It periodically surfaces at its own discretion to update its location and correct instrumental clock-drift errors via its built-in GPS receiver, and to transmit waveforms in near real-time via the commercial Iridium satellite constellation. MERMAID was designed to return teleseismic tomographic-quality ∼1 Hz P wave arrivals (Sukhovich et al 2011(Sukhovich et al , 2014, and the first-generation (Simons et al 2006(Simons et al , 2009 and second-generation floats (Hello et al 2011;Joubert et al 2016) have been shown to do this quite well (Sukhovich et al 2015;Nolet et al 2019;Simon et al 2020).…”

Section: Introductionmentioning

confidence: 99%

A MERMAID Miscellany: Seismoacoustic Signals beyond thePWave

Simon

Simons

Irving

2021

Seismological Research Letters

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Mobile Earthquake Recorder in Marine Areas by Independent Divers (MERMAID) is a passively drifting oceanic diving float that transmits acoustic pressure records from global earthquakes within hours or days of their rupture. The onboard algorithm used for the detection and identification of signals from the hydrophone prioritizes the recovery of ∼1 Hz teleseismic P waves, which are useful for seismic imaging of Earth’s mantle. Two years into a mission that launched 50 MERMAIDs to map 3D mantle wavespeed anomalies with high resolution under the Pacific in French Polynesia, it is clear that the data returned contain much information beyond the first-arriving seismic P phases. These include acoustic conversions from S waves, surface waves, T waves, and inner- and outer-core phases, generated by earthquakes heard across the globe—and sounds from otherwise unidentified events occurring in remote and uninstrumented parts of the world’s oceans. Our growing database of automatically accumulating ∼240 s long-triggered segments contains a treasure trove for geophysicists interested in seismology beyond P-wave tomography. Furthermore, equipped with two-way communication capabilities, MERMAID can entertain requests to deliver data from its 1 yr buffer. In this article, we highlight the data classes and categories in MERMAID’s “extended-utility” catalog.

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“…At the time of data transmission, Global Positioning System (GPS) location and time are obtained and bundled as metadata. The GPS time stamp is used to correct for instrument clock drift (Joubert et al 2016), typically by a fraction of a second (Simon et al 2021a). Over the course of the 11-month (about 336 d, or 8064 hr) period discussed here, MERMAID surfaced 44 times.…”

Section: Data a N D M E T H O D Smentioning

confidence: 99%

One year of sound recorded by a mermaid float in the Pacific: hydroacoustic earthquake signals and infrasonic ambient noise

Pipatprathanporn

Simons

2021

Geophysical Journal International

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Summary A fleet of autonomously drifting profiling floats equipped with hydrophones, known by their acronym mermaid, monitors worldwide seismic activity from inside the oceans. The instruments are programmed to detect and transmit acoustic pressure conversions from teleseismic P wave arrivals for use in mantle tomography. Reporting seismograms in near-real time, within hours or days after they were recorded, the instruments are not usually recovered, but if and when they are, their memory buffers can be read out. We present a unique one-year-long data set of sound recorded at frequencies between 0.1–20 Hz in the South Pacific around French Polynesia by a mermaid float that was, in fact, recovered. Using time-domain, frequency-domain, and time-frequency-domain techniques to comb through the time series, we identified signals from 213 global earthquakes known to published catalogs, with magnitudes 4.6–8.0, and at epicentral distances between 24○–168○. The observed signals contain seismoacoustic conversions of compressional and shear waves traveling through crust, mantle, and core, including P, S, Pdif, Sdif, PKIKP, SKIKS, surface waves, and hydroacoustic T phases. Only 10 earthquake records had been automatically reported by the instrument—the others were deemed low-priority by the onboard processing algorithm. After removing all seismic signals from the record, and also those from other transient, dominantly non-seismic, sources, we are left with the infrasonic ambient noise field recorded at 1500 m depth. We relate the temporally varying noise spectral density to a time-resolved ocean-wave model, WAVEWATCH III. The noise record is extremely well explained, both in spectral shape and in temporal variability, by the interaction of oceanic surface gravity waves. These produce secondary microseisms at acoustic frequencies between 0.1–1 Hz according to the well-known frequency-doubling mechanism.

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P‐Delays from Floating Seismometers (MERMAID), Part I: Data Processing

Cited by 12 publications

References 16 publications

Imaging the Galápagos mantle plume with an unconventional application of floating seismometers

Imaging the Galápagos mantle plume with an unconventional application of floating seismometers

A MERMAID Miscellany: Seismoacoustic Signals beyond thePWave

One year of sound recorded by a mermaid float in the Pacific: hydroacoustic earthquake signals and infrasonic ambient noise

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