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

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