And last month in a magazine Scientific reportsa separate group of researchers described how they used submarine cables off the coast of Chile, Greece and France to detect earthquakes. They compared this data with data from seismometers that tracked the same events, and they matched well. “We can, in real time, when an earthquake occurs, analyze the signals recorded with optical fibers and estimate the magnitude of the earthquake,” says Yitzhak Lior, a seismologist at the Hebrew University of Israel and lead author of the paper. “The game changer here is that we can estimate the magnitude every 10 meters along the fiber.”
Because a traditional seismometer measures at a single point, it can be distorted by local data noise, such as that caused by large vehicles passing by. “If you have fibers, you can quite easily distinguish an earthquake from noise, because an earthquake registers almost instantly at a distance of hundreds of meters,” says Lior. “If it’s some kind of local noise source, like a car, a train, or whatever, you only see it from a few tens of meters away.”
In essence, DAS greatly increases the resolution of seismic data. This does not mean that it will become a replacement for these high-precision devices – rather, an addition to them. The general idea is simply to place 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 an earthquake, the better.”
And DAS research has several problems to contend with, in particular the fact that fiber optic cables were not designed to detect seismic activity – they were designed to transmit information. “One of the problems with DAS cables is that they are not necessarily what we call “well-connected” to the ground,” Park says, meaning the lines can just be laid freely in the pipeline while how the right seismometer is finely tuned and positioned to detect rumbling. Scientists are investigating how data collection over a cable can change depending on how it is laid underground. But because there are so many miles of fiber optics, especially in urban areas, scientists have plenty of options. “Because it’s so dense, you have a lot of data to work with,” says Park.
Another hurdle, says geophysicist Ariel Lelouch, who studies DAS at Tel Aviv University, is that constantly firing laser pulses down the fiber and analyzing what comes back to investigators creates a huge amount of information to analyze. “The sheer volume of data you receive and process means you will probably have to do most of it in-house,” says Lelouch. “This means that you cannot afford to upload all the data to the Internet and then process it in some centralized place. Because by the time you upload, the quake will be far behind you.”
In the future, this processing may actually take place within the interrogators themselves, creating a network of constantly running detectors. The same fiber optics that gives you the internet could very well give you precious seconds of extra warning to prepare for an earthquake.