January 14 -PARIS, FRANCE: Orange and members of the FLY-LION3 consortium (Lower Indian Ocean Network) - the Société Réunionnaise du Radiotéléphone and Comores Câbles - have announced the signing of an agreement with the Institut de Physique du Globe de Paris (IPGP) to provide the IPGP’s Mayotte volcano and earthquake monitoring network with a pair of optical fibres. This will allow it to experiment with a new technique to listen to the region’s seismic activity. The scientists involved hope to get a better understanding of major geological structures linked to current seismo-volcanic activity.

Commissioned on 10 October and measuring 400 km in length, the FLY-LION3 ultra-high-speed cable improves connectivity in the Indian Ocean, with a new route linking Mayotte to the global internet. This submarine fibre optic cable links Moroni (Grande Comore) and Mamoudzou (Mayotte), a seismically active zone which scientists are aiming to better understand. As part of the agreement, this cable will allow the IPGP to listen to seismic activity in the region, particularly volcanoes in this part of the Indian Ocean. Seismic measurements (ground vibration) will be recorded along the FLY-LION3 cable from Kaweni for a distance of around 50 km in a south-easterly direction from Mayotte.

For the IPGP, it is a unique observation task involving a major submarine cable. This full-scale experiment will help test new types of measurement equipment. Like terrestrial fibre, submarine cables can be used not only for communications, but also to identify vibrations in the ground where fibre is laid. Equipment placed at the end of the pair of fibre cables will allow it to be used as an antenna to better locate the region’s seismic signals.

18 months ago, an initial long sequence of earthquake swarms was felt by the Mayotte people and recorded by regional earthquake stations. In order to shine a light on the mechanisms underlying this activity, observation and research operations involving various French research organisations (CNRS, IPGP, BRGM, Ifremer, etc.) were launched in autumn 2018 by the authorities. These operations helped discover a new active underwater volcano off the coast of Mayotte in late May 2019. Following this discovery, and to organise the scientific and operational response to this major geological phenomenon near to Mayotte, the “Mayotte volcano and earthquake monitoring network” (REVOSIMA) was established in summer 2019. But analysis of the crisis and its real-time monitoring are limited by the low density of land measurements (Mayotte and the Glorieuses). Sea data is currently recorded for several weeks but it is only processed in retrospect once the instruments are retrieved. It is therefore very important to have sea measurements which can acquire real-time data and whose accuracy and resolution are adapted to current issues.

Whilst the use of optical fibre to monitor infrastructure has been common for around twenty years, with sensors located on portions of fibre, scientists are looking to exploit the different intrinsic backscatter of fibre as sensors to acquire information on its environment (temperature, pressure, stress, vibration, etc.). Optical fibres themselves can be used as a sensor, known as “Fibre Optic Sensors” (FOS).

For vibration measurements, current query systems (DAS system, for Distributed Acoustic Sensor) provide the equivalent of thousands of seismometers distributed along the fibre, and over tens of kilometres. This equipment has been acquired as part of a FEDER project involving the ESEO Group in Angers, the University of Le Mans Acoustics Laboratory (LAUM UMR CNRS 6613) and the IPGP. The DAS will be connected to the end of one of the available fibres in the FLY-LION3 cable in Mayotte to test its capacity to measure seismic signals from the active zone.

This agreement between the FLY-LION3 consortium and the IPGP allows us to consider various uses of submarine cables beyond connectivity.

About the Institut de Physique du Globe de Paris (Paris Institute of Earth Physics)

The IPGP is a major higher education and research institute. It is also part of the University of Paris. An internationally renowned geosciences research organisation, the IPGP studies the Earth and the planets from the core through to the most superficial liquid layers, via observation, experimentation and modelling, in association with the CNRS, the Universities of Paris and Reunion Island and the IGN and CNES. The IPGP provides certified observation services in volcanology, seismology, magnetism, gravimetry and erosion. It specifically monitors active volcanoes in France and overseas departments (La Soufrière in Guadeloupe, Mount Pelée in Martinique, Piton de la Fournaise on Reunion Island and now the volcano east of Mayotte) as well as regional earthquake activity. The IPGP’s permanent volcanology and seismology observatories and networks (OVSG, OVSM, OVPF and REVOSIMA) aim to collect geological, geophysical and geochemical data in the long-term to feed research on how volcanoes work and their geological context. Through education from bachelor’s degree to PhD level, the IPGP offers its students training in geosciences which combines observation, quantitative analysis and modelling, reflecting the quality, breadth and diversity of the themed research conducted by the IPGP teams.

For more information: www.ipgp.fr