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Session: Filling the Data Gap: Ocean-bottom Sensing with Fiber-optic Cables [Poster]

Type: Poster

Date: 10/9/2024

Time: 07:00 AM

Room: Stanley Park Ballroom

Seismological sensors are predominantly found on the 30% of the Earth’s surface that is on-land. Distributed Fibre Optic Sensing (DFOS) using submarine telecom cables offers a means to bridge this observational gap. Cables come in different designs, where fibers sit in gel (loose fibers) or are layered with an acrylate coating (tight fibers). The design can change the energy transfer from the surface of the cable to the fibers, impacting the measurements. We examine this effect using the 6 km-long FOCUS cable located 29 km offshore Catania in 2 km water depth. This prototype cable contains three tight fibers at its center and two loose fibers coiled around them. One loose and two tight fibers are connected in series and loop in the cable allowing one interrogator to sample the same location using the different fiber configurations. We compare the performance of the loose and tight fibers as a strain rate sensor using DAS data collected in November 2023. With a local ML 3.3 earthquake we show that, on average, the energy transfer is greater on the tight fiber and is frequency dependent: 25% more energy is transferred to the tight fiber compared to the loose fiber in the 0.1-2.5 Hz range, but this decreases to 13% in the 10-12.5 Hz range. This previously unreported result shows how cable structure affects DAS records. We perform a similar analysis for static strain using a BOTDR interrogator on the same cable, recording since October 2020. We have observed one natural deformation (causing ~40 με), bag drops on the cable (~200 με), and an abrupt pulling of the cable end (~400 με). Strain measured along the tight fibers was two to ten times larger than that measured on the loose fiber. Controlled loading experiments in a laboratory on the FOCUS cable confirm these observations as the tight fiber consistently deforms 200% more than the loose fiber. In tight fibers, amplitude loss is 0.26 db/km vs the 0.19 db/km in loose fibers, reducing the coverage of DFOS by 40 km. However, better energy transfer favors tight fibers over loose fibers for sensing both strain and strain rate.

Presenting Author: Giuseppe

Additional Authors

Giuseppe Cappelli

Presenting Author Corresponding Author

giuseppe.cappelli@idil.fr

IDIL Fibres Optiques, Perros-Guirec, , France

Stephan Ker

stephan.ker@ifremer.fr

Institut Français de Recherche pour l'Exploitation de la Mer, Plouzané, , France

Shane Murphy

shane.murphy@ifremer.fr

Institut Français de Recherche pour l'Exploitation de la Mer, Plouzané, , France

Mael Arhant

Mael.Arhant@ifremer.fr

Institut Français de Recherche pour l'Exploitation de la Mer, Plouzané, , France

Pascal Casari

Pascal.Casari@univ-nantes.fr

Institut Universitaire de Technologie de Nantes, Nantes, , France

Lionel Quetel

lionel.quetel@idil.fr

IDIL Fibres Optiques, Lannion, , France

Peter Davies

Peter.Davies@ifremer.fr

Institut Français de Recherche pour l'Exploitation de la Mer, Plouzané, , France

Marco Terzariol

Marco.Terzariol@ifremer.fr

Institut Français de Recherche pour l'Exploitation de la Mer, Plouzané, , France

Marc-André Gutscher

gutscher@univ-brest.fr

Laboratoire Géosciences Océan, Plouzané, , France

Giorgio Riccobene

riccobene@lns.infn.it

Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, Catania, , Italy

Salvatore Aurnia

aurnia@lns.infn.it

Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, Catania, , Italy

Salvatore Viola

sviola@lns.infn.it

Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, Catania, , Italy

Sara Pulvirenti

spulvirenti@lns.infn.it

Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, Catania, , Italy

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