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Successful installation of the first connected underwater observatory in Guadeloupe

By recording its first earthquake on Sunday, June 20th, 2021, two days after its installation was completed, the new optical underwater observatory in Les Saintes quickly demonstrated its usefulness!

Successful installation of the first connected underwater observatory in Guadeloupe

This first recording marks the success of several years’ research and development on fibre-tip optical sensors, carried out by the IPGP, ESEO and ENS as part of the Interreg PREST project, with a view to closely monitoring the seismicity of the Saintes area, which was hit in 2004 by a magnitude 6.3 earthquake, the largest to hit the French West Indies for decades, and whose persistence is still debated.

Installed for the first time in real monitoring conditions, this innovative seismological station overcomes many of the problems associated with the usual deployment of electronics and energy on the seabed. The seismometer, which is purely mechanical, is installed at a depth of 40 m underwater and connected to land by a 5 km long optical cable, at the end of which a laser interrogator allows its movement to be measured remotely with a high degree of accuracy. This data is now transmitted in real time to the IPGP’s volcanological and seismological observatories in Guadeloupe and Martinique. In addition, thanks to an innovative approach to monitoring light signal disturbances linked to the passage of seismic waves, the fibre itself serves as a network of sensors (the equivalent of 500 seismometers!). This DAS (Distibuted Acoustic Sensing) method was set up as part of a PREST-Géoazur collaboration.

First regional earthquake detected by the underwater optical seismometer and measured on land by the Loki laser interrogator, developed by ESEO as part of the Interreg PREST project.
Installation of the various pieces of equipment on the seabed before burying the seismometer (foreground). The towers are used to store the excess lengths of fiber and the connection boxes.
Launching of the underwater observatory towers at Les Saintes (Guadeloupe) from the oceanographic vessel Antéa, with the divers in charge of installation in the Zodiac in the background.

To install this new device, the FibroSaintes oceanographic campaign led by Géoazur (CNRS, Université de la Côte d’Azur) required nearly 3 weeks of work at sea by experienced divers and engineers, as well as on land to connect and protect the fibres. This technical feat foreshadows the monitoring instruments of tomorrow, as more ambitious projects are due to be launched to study the source zones of major earthquakes in the Caribbean subduction zone in real time. Similar equipment will also soon be installed off Mayotte to complete the monitoring of the seismic-volcanic crisis currently underway.

Find out more about the PREST project (Regional Telluric Monitoring Platform), a project under the Interreg Caribbean V Programme 2014-2020 (European ERDF funds).

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