Viewpoint
By Geoff Bennett, Director of Solutions and Technology at Infinera
The thousands of kilometres of fibre deployed beneath the waves could be the key to better understanding our oceans – and detecting deadly tsunamis.
A 2015 United Nations report estimated that, every year, an average of 60,000 people and $4 billion in assets are exposed to the global tsunami hazard, which can be triggered by certain types of undersea earthquakes or volcanic eruptions.
Fortunately, there is a way to provide early warning of an impending tsunami – and the way it works is similar to thunder and lightning.
In a storm we see the lightning first and, by counting the seconds until we hear the thunder, we know how far away the storm is. We can do this because light from the lightning travels to us much faster than the sound of the thunder. In a similar way, the seismic vibrations that travel through the Earth’s crust move 20 times faster than the tsunami does on the surface of the ocean – so, if scientists can detect the initial earthquake, they can provide a warning of the subsequent tsunami that allows people to evacuate vulnerable areas. And every minute of additional warning is vital.
Most seismic sensors today are located on land, but undersea earthquakes can take place many kilometres from the nearest land-based detector. For every 200km increase in distance from the earthquake’s epicentre to the detector, we lose about one minute of warning time. Ocean-based measurement buoys – such as DART buoys – somewhat alleviate this issue, but they themselves are exposed to extreme weather, often used as unofficial moorings, and are even vandalized to the point where up to 60% of them are offline at any one time.
Submarine cables, on the other hand, are safely located on the seabed and stand a good chance of being closer to an earthquake than a land-based detector.
So, do existing submarine cables include earthquake detectors? The simple answer is no – but a lot of people think they should. In fact, there’s an initiative to add vibration, temperature, and pressure sensors to a new type of cable called SMART (Science Monitoring And Reliable Telecommunications). SMART cables will one day be the gold standard for ocean monitoring but the first such cable is not expected to be deployed until 2025, and it’s not clear what percentage of new submarine cables will be SMART in the future.
There are currently over 500 submarine communication cables deployed around the world providing high-capacity communications for the internet. Many of these cables run across the most seismically active regions of the world; for example, in just one month (August 26th to September 25th in 2023) there were 142 earthquakes of magnitude 4.0 or higher in the Indian Ocean region. Existing cables in this region would be ideal candidates for subsea earthquake detection if only they were equipped with the right kind of sensors.
There is a considerable interest in enhancing cables in this way, but previous efforts have either failed to offer accurate location measurements for the earthquake epicentre or require complex and expensive equipment to be installed in the landing stations where the cables come ashore.
In our webinar, we explain how Infinera has pioneered the research and development needed to enhance existing submarine cables so they can be used as seismic detection systems while addressing both of the issues I described above – i.e., localisation and specialised equipment. Using some clever mathematics, the Infinera gear can localise the event to within a few tens of kilometres, despite some of these cables being over 10,000km long. And the equipment used is based on their existing commercial offering, meaning that the cable operators’ engineers have already been trained on it.
Seismic detection using existing submarine cables is an area of rapid technological development and we are looking forward to a year of progress in this area throughout 2024.
Want to learn more? Check out Infinera’s webinar on seismic detection techniques for subsea cables on-demand here!
What does the future hold for SMART submarine cables? Join Infinera and the submarine connectivity ecosystem at Submarine Networks EMEA, the world’s largest subsea cable conference
