Leveraging over 400 underwater cables for earthquake sensing, as revealed by expert

During an insightful Q&A session with Lavallée, we explored the complexity of this concept, aiming to uncover a clearer understanding of its potential and what could lie ahead for its future.

The following Q&A session has been lightly edited for flow. 

Please briefly introduce yourself/your company, and highlight the technology you use that underpins deep sea cable and satellite infrastructure.

My name is Brian Lavallée, and I'm a senior director at Ciena, a global networking systems, services, and software provider that builds networks that adapt to address ever-increasing bandwidth demands from humans and machines for richer, more connected digital experiences for users worldwide.

One of the goals of Ciena and me personally is to bridge the world's Digital Divide so that anyone in any country can benefit from high-speed internet. We're seeing a rise in Low-Earth Orbit (LEO) satellite services complementary to existing terrestrial and cellular networks, helping provide high-performance connectivity to traditionally underserved areas.

Our technology helps bridge the gap between satellites, undersea telecom cables, and earth-based Points of Presence (POP), where these technologies mesh together to form a global, holistic network. 

Based on your professional experience, how might undersea cables that sense seismic activity work, and what technology would be involved in their construction?

We already monitor the polarization states within fiber-optic cables to ensure error-free transmission, which can be used to monitor small undersea perturbations. 

Submarine cables use optical transmission technology to send information between endpoints, such as landing stations, central offices, and data centers. Data is transmitted down an optical fiber core using an electromagnetic transverse wave with an electric field and magnetic field tightly coupled and perpendicular to each other. 

The "polarization state" refers to the oscillation direction of the electric field. Under normal conditions, the polarization states are relatively stable. These states are detected by coherent optical modems using advanced Digital Signal Processing (DSP) algorithms and used to ensure data is properly decoded at receivers, resulting in errorless transmission between endpoints.

Being able to measure undersea perturbations without retrofitting existing submarine cables allows for possibly leveraging over 400 submarine cables crisscrossing our planet today. New submarine cables along new routes could also detect perturbations caused by undersea earthquakes, for example, without adding new wet plant sensors.

What are some advantages undersea cables offer over traditional seismometers?

With more than 70 percent of the globe covered by water, it is simply impractical to install and monitor undersea seismometers to keep track of the Earth's movements. As a result, most seismic stations are currently on land. 

Since submarine cables already traverse thousands of miles across the hard-to-reach ocean floor, they can potentially leverage existing infrastructure. 

Currently, when earthquakes occur miles offshore, it can take minutes for the seismic waves to reach land-based seismometers. Optical polarization-based seismic-sensing transoceanic telecom cables can detect earthquakes quicker, which could save lives by providing earlier tsunami warnings.

What kind of information can be gathered from undersea cables during an earthquake, and how could it be used to improve early warning systems?

Because earthquakes and tides can create tiny, detectable perturbations in State of Polarization (SOP) changes in the fiber-optic core of a submarine cable, the world's submarine cables could form a vast network for detecting earthquakes and tsunamis.

Scientists have deployed seismometers on land but relatively few on the seafloor, where the cost and complexity are challenging.

Cables, already on seabeds, could provide faster insights into tectonic movements than land-based sensors, resulting in earlier warnings and evacuation. They can also measure micro-movements of tectonic plates that could ultimately help predict where earthquakes may occur. 

What challenges will scientists face in using undersea cables for seismic detection? Do you know of any projects already working to progress this idea?

Ciena has worked with customers to understand and advance how undersea submarine cables can detect earthquakes based on ingenious machine-learning algorithms using streaming SOP tracking data provided by our WaveLogic 5 Extreme coherent modems. 

You can check out the earthquake detection results on the Curie submarine cable connecting Los Angeles, USA, to Valparaiso, Chile, along the southeast section of the Pacific Ring of Fire as an example of work in progress. However, there is still much more to be done. 

As more cable operators join this initiative, the accuracy and coverage for undersea earthquake detection will improve. Additionally, advancements in AI algorithms may further enhance earthquake detection accuracy and geolocation using multiple submarine cables. 

It should be noted that subsea cables are meant to complement and integrate with existing early warning systems and not replace them. 

Could undersea cables also be used to monitor other natural phenomena, such as ocean currents or marine life? Kindly highlight any other applications this 'double duty' could serve.

Submarine network cables equipped with additional sensors capable of measuring temperature, pressure, salinity, movement, and currents, among other things, are called Scientific Monitoring and Reliable Telecommunications (SMART) cables or green cables. They do exist, although few are deployed worldwide today. 

Sensors can theoretically be added to existing submarine cables, but this is extremely complex, costly, and risky since cables carry critical telecom traffic—and that's why this hasn't happened and likely won't happen. 

New installations are better candidates for SMART cables, as sensors can be installed before the cable is laid on the seabed. 

There are geopolitical concerns with sensors that can detect various undersea movements, hindering the widescale adoption of SMART cables.

Still, there's a lot that can be done with existing fiber-optic technology. For example, a team of Norwegian researchers has discovered a novel way to modify fiber-optic cables for tracking whales in the Arctic Ocean. 

Using a technique called Distributed Acoustic Sensing (DAS), they turned the cables into a kind of real-time hydrophone to track the whales' movements at sea. DAS is also being used to proactively monitor marine vessels and undersea activities in coastal regions where shallower water makes submarine telecom cables, even those buried, more vulnerable.