A little over three years ago, a group of researchers from the United States decided take extra advantage of a stretch of about twenty kilometers of fiber optic cable that had been submerged for a decade at the bottom of Monterey Bay, California. In addition to its usual function as a data transmitter – specifically, it linked an information collection node and a Californian laboratory – they decided to use it as a high-sensitivity seismometer.
For four days they took advantage of the line and its enormous susceptibility to what was happening around it to create the equivalent – they assured from the University of Berkeley – around 10,000 virtual motion sensors. Result: They detected a 3.4 magnitude earthquake near Gilroy, California, and increased their knowledge of the earthquake system. the Falla de San Gregorio.
From volcanoes to permafrost
The Monte Rey experience is not unique. Not even an isolated case. In 2015 another team of German scientists, del GFZ Potsdam, also made use of underused optical fibers in a 15-kilometer cable linking two geothermal power plants in Iceland to “hunt” distant earthquakes. Shortly after, around 2016, another California researcher verified how a 2.5 km stretch spread through the Stanford tunnels collected both earthquakes and traffic vibrations, the footsteps of passersby or even the waves of the oceans.
The Monterrey experience, that of the GFZ Postdam and that developed in the Stanford tunnels are part of a common trend: the increasing profit and more and more interesting that scientists are pulling from fiber cables to create sensor networks that allow them to probe the dynamics that lurk underground. Magazine Science explore its possibilities in an article which highlights how, over the last few years, cables have gone only from carrying data to becoming valuable themselves. And with two added advantages: its cost, reduced, and the possibilities of creating a dense network of indicators to “comb” the terrain.
How do they do it?
The cables are bundles of fine glass fibers, not much thicker than a human hair, through which information encoded in the form of light travels. As detailed ScienceThey are often endowed by operating companies with greater capacity than they later use, creating an untapped “dark” fiber that researchers can inexpensively and securely draw on without cutting off the flow of data. The fibers also include random “defects”, which act like mirrors. Every time the light hits them, it bounces off and scatters. When an external wave, such as that associated with an earthquake, passes through the fiber segment, those same “defects” are altered. It’s very little, nanometers, but enough to affect the light.
Researchers take advantage of these slight alterations – measured in detail – for their studies. They are dedicated to launch laser pulses along an unused fiber, then record the changes. With the data on the table, scientists can monitor and read a surprising variety of phenomena: earthquakes, the tremors that accompany volcanic eruptions, movements in glaciers and avalanches, the melting of permafrost, storms, acoustic waves that probe the temperature of the deep ocean… Or even changes in vehicle and pedestrian flows in a city, which could have commercial applications.
It is not just theory. Science pick up an extensive list of applications of fiber optics from which different research areas are already benefiting. In Iceland they are taking advantage of it to “take the pulse” of a volcano located a short distance from Reyjavik; It has also been used to analyze movements in the Rhone glacier, in the Swiss Alps; snow avalanches in southwestern Switzerland; permafrost thawing in Alaska or earthquakes in California. In May a Cambridge team explained how it even uses it to map the Greenland ice.
Optical fiber has obvious advantages. Thanks to its handling, for example, scientists have a deployment difficult to imagine decades ago with traditional seismometers, devices that sometimes had to be installed kilometers apart. Its characteristics allow it to be adapted to different scenarios and its cost, to make matters worse, is relatively low. There are buts, of course. The main one, perhaps, the enormous amount of data it generates, which makes it very difficult to store them.
What is clear is that the times when fiber optic cables were used only to transmit information are long gone. Today they seem, at least, just as important to generate it.
Via | Science