The ocean is a mysterious, fascinating place, that is constantly studied by scientists to learn more about the environment and the creatures that live in there. On the ocean’s seabed lies more than 1.2 million kilometers of cable. In recent years, researchers are developing a new way to monitor the ocean: use of undersea cables to detect earthquakes causing tsunamis. Their method doesn’t require any new tech or modification to the cables, so the coverage of sensors for detecting danger is already very large.
There are many seismometers on land but not that much on the seabed. The main cause of it is the cost of installation the devices underwater. Zhongwen Zhan, a professor of geophysics at the California Institute of Technology said „We suspect that earthquakes in the ocean are fundamentally different from the ones we have on land”. Earthquakes beneath the water, causing tsunamis are very destructive and deadly, and yet we still don’t have wide, precise detection system.
Research
Giuseppe Marra is a research scientist at the National Physical Laboratory in Teddington, England. In 2021, Google allowed Marra to conduct his research on their 5800-meters cable starting in Southport, England stretching to Halifax, Canada. Marra’s team drove to the station in Southport to install customized lasers and detectors connected to remote access computers. Their devices were able to detect phase shifts beneath the water, but they still had to determine the exact location of seabed movements. To solve this problem, Marra with his team divided the cable into segments. Undersea cables have signal repeaters with built-in tiny mirrors, which normally allow technicians diagnose problems along specific sections. Each repeater is supposed to boost the signal making sure it reaches next one without loosing speed. The team sent their own signal and analyzed the frequency at every repeater. „In the case of no perturbation, we get stable signals: The frequency that we receive is the same that we sent,” says Marra. Between Southport and Halifax there are 128 repeaters, allowing the team to turn the cable into 128 vibrational sensors.
Marra’s team managed to successfully detect two tremors. Furthermore, in November, they noticed a phase change in the cable section beneath the Irish Sea. The signal was something that they hadn’t seen before. It turned out that a cyclone was passing through the area. Next day, Marra confirmed the that the phase change was related to wave height by checking the data recorded by a nearby buoy.
The future
„The whole point of this is transforming the underwater infrastructure into a giant detector for earthquakes and more,” says Marra. Marra with his team developed a method that could help to detect earthquakes in real time, but also how the pressure of tides travel along the seabed. This new method covers a widespread area of the seabed as opposed to regular seismometers. „It becomes an incredibly powerful tool.” Marra said that there is still a lot to improve. They have to analyze the data and separate phase changes caused by waves, earthquakes, and other factors in order to avoid misleading signals. But Marra predicts a future in which cables could provide data and warnings to authorities about the exact location and height of tsunamis.
https://www.science.org/doi/10.1126/science.abo1939
https://www.submarinenetworks.com/images/figures/submarine-repeater.jpg
