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Illuminating seafloor faults and ocean dynamics with dark fiber distributed acoustic sensing

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Science  29 Nov 2019:
Vol. 366, Issue 6469, pp. 1103-1107
DOI: 10.1126/science.aay5881

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Marine observations with optics

Placing sensors on the seafloor is difficult, but a sensor network has huge potential for observing processes occurring both below and above the seafloor. Lindsey et al. measured acoustic vibrations collected by attaching a laser to the Monterey Accelerated Research System's subsea optical fiber during a maintenance period (see the Perspective by Jousset). Acoustic waves were monitored by changes in laser light along the cable. The observations from just a few days allowed mapping of an unknown fault system and detection of several dynamic processes in the water column above.

Science, this issue p. 1103; see also p. 1076

Abstract

Distributed fiber-optic sensing technology coupled to existing subsea cables (dark fiber) allows observation of ocean and solid earth phenomena. We used an optical fiber from the cable supporting the Monterey Accelerated Research System during a 4-day maintenance period with a distributed acoustic sensing (DAS) instrument operating onshore, creating a ~10,000-component, 20-kilometer-long seismic array. Recordings of a minor earthquake wavefield identified multiple submarine fault zones. Ambient noise was dominated by shoaling ocean surface waves but also contained observations of in situ secondary microseism generation, post–low-tide bores, storm-induced sediment transport, infragravity waves, and breaking internal waves. DAS amplitudes in the microseism band tracked sea-state dynamics during a storm cycle in the northern Pacific. These observations highlight this method’s potential for marine geophysics.

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