New technology will turn underwater cables into earthquake and tsunami detectors

As part of a project to speed up the detection of dangerous natural phenomena, seismologists from Caltech and optical cable experts from Google have developed a new method using cables already present on the ocean floor.

Earthquakes and tsunamis are some of the most dangerous and destructive natural phenomena we face, and more often than not, they are difficult to predict. With little or no warning, the ground begins to shake and huge waves flood vast residential areas, leaving residents no time to escape. It is for this reason that scientists and engineers are constantly working on more modern and effective ways to detect and give early warning of them. One of the newest, and to be implemented quickly, involves using underwater communication cables as a giant seismic network.

For although we live in a super-connected world, where many users seem to rely mostly on wireless or satellite technology, the truth is that 99% of international data transmission takes place over the cables that lie at the bottom of the oceans (except in the far polar regions, since our planet’s oceans are crisscrossed with wires). In comparison, land-based and ocean-based seismographic networks, such as the Deep-ocean Assessment and Reporting of Tsunamis (DART) system, do provide some data, but they are difficult to use in practice. Why? A tsunami can hit the seacoast 15-20 minutes after the main shock, meanwhile data from the system’s buoys can be used within 10-60 minutes of the shock, giving virtually no time to react.

However, if underwater cables could detect such phenomena, being much closer to their source, and warnings reached the coast at the speed of light, the situation could change a lot. And this is where the idea of using underwater cables comes in, which, while not new, dating back to the 1980s, previously required the installation of specialized equipment or the laying of all those cables, but now… the cables are already in place, as they also serve another purpose and are waiting to be used. As part of normal operation, the laser pulses used to transmit data are polarized and, when they reach the end of their journey, routinely monitored. If the equipment is working properly and the cable is undisturbed, the laser pulses are polarized correctly, and if there is any obstacle in the way, the polarization changes. This means that seismic events can be monitored on the wire without any additional equipment.

The team of scientists were able to analyze the polarization of pulses on the wire up to 20 times per second – most of the time it remained normal, but if there is an earthquake or huge ocean waves, it causes a sudden strong change in polarization, and the scientists can identify the source. Over nine months of testing, they detected 20 medium to large earthquakes, the largest of which had a magnitude of 7.7 on the Richter scale. Now all that remains is to develop a special algorithm to automatically monitor the cables while ignoring interference from ships or sea creatures moving along the wires. – We believe this is the first seismic monitoring solution for the ocean floor that can be easily deployed worldwide. It can complement existing networks and systems, in many cases detecting earthquakes and tsunamis much earlier, they explain.

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