How fiber optic cable can warn you of an earthquake

And last month in the magazine Scientific reportsa separate group of researchers describe how they used undersea cables off the coasts of Chile, Greece and France to detect earthquakes. They compared this data with seismometer data that track the same events, and they matched very well. “We were able, in real time when the earthquake was happening, to analyze the recorded signals,” said Itzhak Lior, a seismologist at the Hebrew University of Israel and lead author of the paper. optical fiber and estimate the magnitude of the earthquake”. “The game changer here is that we can estimate the magnitude every 10 meters along the fiber.”

Since a traditional seismometer measures at a single point, it can be subject to interference from local data noise, like noise caused by large vehicles. “If you have fiber, you can really easily distinguish an earthquake from noise, because an earthquake is almost instantaneously recorded along hundreds of meters,” says Lior. “If it’s some kind of local noise source, like a car, a train or whatever, you can only see it from a few tens of meters away.”

Essentially, DAS significantly increases the resolution of seismic data. That’s not to say it will be a replacement for these high-precision tools—but a complement to them. The overall idea is just to bring more seismographs closer to the epicenter of the earthquake, improving coverage. “In that sense, it doesn’t really matter whether you have a seismometer or a DAS,” says Lior. “The closer to the earthquake the better.”

And the DAS research has some challenges to deal with, notably that optical cables are not designed to detect seismic activity—they are designed to transport information. “One of the problems with DAS cables is that they are not necessarily what we would call ‘well-connected’ to ground, meaning lines can be loosely laid into the pipeline,” says Park. while the appropriate seismometer is fine-tuned and placed in the proper position. detect rumble. Scientists are studying how the cable’s data collection can change depending on how it is laid underground. But since there are so many miles of fiber optic cable out there, especially in urban areas, scientists have plenty of options. “Because it’s so dense, you have a lot of data to process,” says Park.

Geophysicist Ariel Lellouch, who studies DAS at Tel Aviv University, says another hurdle is repeatedly firing laser pulses down the fiber and analyzing what comes back to the interrogation devices. a huge amount of information to analyze. “Just the sheer amount of data you get and the processing means you’ll need to do a lot of it on-site,” says Lellouch. “Meaning you can’t 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 is already far away.”

In the future, that processing could actually happen in the detectors themselves—creating a network of continuously active detectors. The same fiber that gives you the internet can also give you those precious extra seconds of alert to prepare for an earthquake.


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