How Fiber Optic Cables Could Warn You of an Earthquake
And last month in the journal Scientific Reports, a separate team of researchers described how they used undersea cables off the coasts of Chile, Greece, and France to detect earthquakes. They compared this data to seismometer data that monitored the same events, and they matched well. “We can, in real time while the earthquake is happening, analyze the signals recorded using optical fibers and estimate the magnitude of the earthquake,” says Itzhak Lior, a seismologist at Israel’s Hebrew University and lead author of the paper. “The game changer here is we can estimate the magnitude every 10 meters along the fiber.”
Because a traditional seismometer measures at a single point, it can get thrown off by localized data noise, like that caused by large vehicles rolling by. “If you have fibers, you can actually quite easily distinguish an earthquake from noise, because an earthquake is almost instantaneously recorded along hundreds of meters,” says Lior. “If it’s some local noise source, like a car or train or whatever, you only see it on a few tens of meters.”
Basically, DAS significantly bumps up the resolution of seismic data. That’s not to say that it would be a replacement for these highly accurate instruments—more of a complement to them. The overall idea is just to get more seismic detectors closer to earthquake epicenters, improving coverage. “In that sense, it doesn’t really matter if you have seismometers or DAS,” says Lior. “The closer you are to the earthquake, the better.”
And DAS research has a few challenges to contend with, notably that fiber optic cables weren’t designed to detect seismic activity—they were designed to shuttle information. “One of the issues with DAS cables is they’re not necessarily what we call ‘well coupled’ to the ground,” says Park, meaning the lines may just be laid loosely into piping, while a proper seismometer is finely tuned and situated to detect rumblings. Scientists are researching how a cable’s data-gathering might change depending on how it’s laid underground. But because there are so many miles of fiber optics out there, especially in urban areas, scientists have plenty of options. “Since it’s so dense, you have a lot of data to play with,” Park says.
Another obstacle, says geophysicist Ariel Lellouch, who studies DAS at Tel Aviv University, is that constantly firing laser pulses down fiber optics and analyzing what returns to interrogators creates an enormous amount of information to parse. “Just the sheer amount of data that you acquire, and the processing, means you’re going to need to do a lot of it probably on site,” says Lellouch. “Meaning, you cannot afford to upload all the data to the internet and then process it in some centralized location. Because by the time you upload, the earthquake would have been way, way past you.”
In the future, that processing might actually happen in the interrogators themselves—creating a network of continuously operating detectors. The same fiber optics that bring you the internet could well bring you precious seconds of extra warning to prepare for a quake.