The internet makes it possible to connect worldwide around the clock. But where does the data we access actually come from? We often only ask this question when our internet connection isn’t working smoothly. The global digital infrastructure, also referred to as the “digital nervous system” or “backbone of the internet,” is a network of approximately 1.4 million kilometres of undersea cables that spans the globe. Around 99 percent of global data transfer runs through these cables on the seabed.
As part of the EU project FOCUS, Marc-André Gutscher and a team of scientists have been researching how to expand the applications of this gigantic cable network. The project is part of the growing field of research known as ‘fibre-optic seafloor sensing’, which involves using submarine cables as sensors. The results show success: the technology was able to register the smallest movements on the seabed and measure temperature changes. This proves that submarine cables could serve as an early warning system for earthquakes, tsunamis and other environmental hazards.
In the future, these cables could not only secure data transfer on the seabed, but also increase safety on land. By recording natural events immediately as they occur, we save time when reacting to disasters. Local authorities and warning systems can kickstart more quickly, leading to better protection for affected regions.
Your smartphone as an important earthquake sensor
Earthquake mapping from your pocket? Accelerometers in mobile phones provide data to help us understand earthquakes and make our cities safer.
Around the world in 600 cables
Submarine cables are becoming critical infrastructure for more and more countries. There is currently no alternative way to transfer data between continents. While some countries are investing in satellite systems, these are more expensive, slower and more prone to disruption.
There are more than 600 active or planned submarine cables worldwide. Online maps such as Submarinecablemap keep track of many of the connections. The cables contain sensitive fibre optics that transmit digital information using light pulses. Layers of steel, polyethylene and waterproof materials protect them from deep-sea conditions. However, it’s hard to avoid damage completely. The International Telecommunication Union (ITU) reports 150 to 200 incidents of damage annually.
The natural enemies of undersea cables are fishing and ship anchors, especially in areas where the cables are in shallower waters. When damage occurs, it’s often impossible to conclude whether it was an accident or sabotage. A specific case occurred in September 2025, when a severed fibre optic cable in the Red Sea disrupted data transfer for Microsoft’s Azure cloud service. Whether this was sabotage by Houthi rebels (as in 2024) or simply an accident caused by the anchor of a cargo ship remains unclear.
Submarine cables as environmental sensors: “We are effectively transforming the world’s digital nervous system into an ecological nervous system”
With a few technical adjustments, the global network of undersea cables has the potential to serve as an environmental monitoring system. Marc-André Gutscher, head of the FOCUS project, believes that “The novel secondary use of fibre optic cables could represent an enormous breakthrough in seismology and hazard warning. We are effectively transforming the world’s digital nervous system into an ecological nervous system.”
Gutscher’s research group uses two complementary techniques for this purpose: Distributed Acoustic Sensing (DAS) and Brillouin Optical Time Domain Reflectometry (BOTDR). In both methods, a laser sends light through the fibre optic cable. This detects the smallest changes in how light travels through the fibre, registering activity and temperature changes on the sea floor.
DAS uses Rayleigh scattering to detect acoustic signals along fibre optic cables. A laser pulse travels through the cable and movements or vibrations alter the backscattered light. These changes can be used in real time to determine where something is happening along the fibre. The technology allows vibrations, sound waves and other movements along the fibre to be measured. Seismic waves are detected within seconds. This enables immediate early warnings for earthquakes and tsunamis. DAS can also be used to observe ship movements, detect whale calls and even track individual whales.
BOTDR (Brillouin Optical Time Domain Reflectometry) is based on Brillouin scattering and measures mechanical strain and temperature changes. Here, too, a laser is sent through the fibre. The light hits the crystal lattice of the glass fibre. Changes in tension or temperature lead to a change in Brillouin scattering, which is measured along the fibre. This allows temperature and tension curves to be recorded over distances of several kilometres. BOTDR is particularly suitable for the long-term monitoring of underwater deformations and contributes to the analysis and prediction of earthquake risks.
Both technologies enable the detection of even the smallest deformations in the cable, effectively monitoring activity on the seabed. “If anything disturbs the cable—pulls on it, moves it or causes it to heat up or cool down—we’ll notice,” says Gutscher.
FOCUS technology in use
A prototype cable developed by the research group is located off the coast of Sicily, near Mount Etna. In 1908, a severe earthquake hit the region, closely followed by a tsunami wave. More than 80,000 people died. In this seismically active region, the FOCUS cable now plays a part in protecting the population.
At first glance, the prototype looks like a conventional telecommunications cable. However, it contains highly sensitive sensor fibres that detect the slightest mechanical disturbances on the seabed. With the help of BODTR, the researchers measure minimal changes in length that indicate seismic activity. In 2020, this method detected a massive undersea current: a type of underwater avalanche that can trigger tsunamis.
Off the Caribbean island of Guadeloupe, Gutscher’s team is also using undersea cables to monitor environmental conditions. They supplement satellite technology, which records data from the ocean’s surface, with their cables’ real-time data from the depths. In addition to temperature developments, they also record changes in the deep sea. For example, their technology detected severe coral bleaching, which leads to the death of 30 percent of coral within two years. The reason for this was a 1.5-degree rise in water temperature between 2022 and 2024.
Limits of cable usage
In addition to accident risks and possible acts of sabotage, access to submarine cables is a particularly critical factor. Ownership structures in the global data network are complex. In the past, submarine cables were largely operated by a group of telecommunications providers and, in some cases, by governments. Today, data control by Big Tech companies such as Alphabet, Apple, Amazon, Google, Microsoft and Meta is growing massively. These companies are continuing to develop their AI systems and need to connect their ever-growing global networks of data centres. Against this backdrop, planned investments in new submarine projects between 2025 and 2027 are estimated at around 13 billion US dollars. In addition, China’s influence is also growing steadily.
Beneath the surface: undersea cables follow colonial patterns
Artist Esther Mwema reveals the hidden architecture of the internet and uses submarine cables as an example to show how global Big Tech players reproduce colonial power structures.
Marc-André Gutscher points out that cable access poses a significant challenge. Until now, the use of active submarine cables has only been possible in exceptional cases. Among other things, cable operators are concerned that the sensor technology used could interfere with data transfer. Gutscher and his team haven’t yet completely dispelled this concern.
Gutscher’s research team and similar projects use interrogators that send laser pulses into the fibre optic cable. They then analyse the backscattered light to detect vibrations, strain or temperature along the cable. Many of the interrogators operate in the same wavelength range as data transfer. This can lead to interference, occupy transmission capacity and pose a risk to cable operators. However, technical alternatives are now available. “There is now a new generation of interrogators that operate in a different optical band,” says Gutscher. “This means we can use these interrogators on active telecommunications fibres without disrupting data traffic. This is much more attractive for cable operators because they won’t lose any transmission bandwidth.”
A positive example of the use of active cables is a research project led by scientist Zhongwen Zhan. For his research on earthquake warning systems, he and his team had access to Google’s ‘Curie Cable,’ which connects the United States with Chile and Panama.
Researchers can’t make use of decommissioned submarine cables because of environmental regulations, which state they must be removed from the ocean when not in use. Other problems include complex approval procedures (especially in sensitive maritime zones) and high costs for measuring equipment and cable operation, as well as legal issues regarding ownership, liability and data use.
According to Gutscher, the limited range of the interrogators is also a technical challenge. This is currently a maximum of 150 km for DAS interrogators and a maximum of 70 km for BOTDR interrogators. At present, it’s not yet possible to perform queries beyond the first repeater unit (at approximately 70 km) in a commercial submarine cable. This limits observations to the first section of cable near the coast. There are new developments that could enable interrogation across ocean boundaries using specialised repeater units. However, these are not yet fully feasible from a technical standpoint. The repeaters amplify the light for transmission over long distances, but weaken the reflections travelling back along the fibre.
The enormous amounts of data produced by technologies such as DAS are also a hurdle. “Due to the high resolution, a typical 50 to 100 kilometre long cable can generate around 1 terabyte of data per day. That’s too much to easily manage, and we have to find suitable solutions depending on the application,” says Gutscher. One possible solution could be the selective storage of relevant events.
What happens after the FOCUS project?
The FOCUS project officially ended in September 2025. What happens next is still unclear. However, in conversation with Gutscher, he told us that he will pursue his research approach despite the existing challenges. He is currently working on a new research proposal for 2026. Although he hasn’t yet fully developed the cable technology and there is still a long way to go before establishing a global sensor network, recent technical advances and the fact that his topic is currently the subject of heated debate make the researcher confident.
A lot is going on in the field of fibre-optic seafloor sensing. In mid-December 2025, a team led by Nokia Bell Labs, Nokia’s research and development division, presented its approach to overcoming range limitations caused by repeaters without disrupting ongoing data transfer. To this end, a 4,400-kilometre telecommunications cable between Hawaii and California was extended to 44,000 seismic stations, each 100 metres apart. The research team’s approach makes use of the repeaters. These have a so-called “loop-back function” that monitors the fibres for functionality. This function allows the reflected light signals to be sent back and amplified, so even the most remote cable sections can be monitored. With the help of DAS, the cable registered an earthquake measuring 8.8 on the Richter scale, which struck the Kamchatka Peninsula in Russia at the end of July 2025. It also registered signs of a subsequent tsunami wave.
In Germany, too, the GFZ Helmholtz Centre for Geosciences in Potsdam and the GEOMAR Helmholtz Centre for Ocean Research in Kiel have been focusing on the use of submarine cables as sensors for environmental monitoring since March 2025. 30 million euros are being invested in a five-year project to bring the SAFAtor (SMART Cables And Fibre-optic Sensing Amphibious Demonstrator) to life. For this purpose, a submarine cable will also be equipped with special sensor technology. This will be supplemented by coastal monitoring at various observatories. The aim is to create a permanent monitoring infrastructure and, in the long term, to close the ‘ocean data gap’. It remains to be seen whether SAFAtor will live up to its name.
