Underwater fiber optic cables span the globe, providing telecommunication services in the blink of an eye. They transmit photons of light from one side to another, which are sometimes reflected back. Scientists have found that returning photons can be used to measure passing acoustic and seismic waves, as well as other small stresses, which can help provide a picture of earthquake activity
Through a process known as distributed acoustic sensing, scientists have experimented with optic cables to measure seismic activity for about a decade. Brad Lipovsky is an assistant professor at the University of Washington. He and a team of scientists began conducting research with Cook Inlet’s fiber optic cables last summer.
“We can observe marine mammals that make acoustic vocalizations, we can also observe the seismic waves of earthquakes that pass through the area,” Lipovsky said.
The team is sampling fibers from two cable routes belonging to telecommunications company GCI, one that stretches across Cook Inlet from Homer, and another that runs from Homer to Kenai. The company leased the team idle fibers within the cable network.
“They’re leasing us this cable just because they think it's going to be helpful that we can possibly use this to provide better warnings for earthquakes, or at the very least, better understand the hazard, to understand when and how and why the earthquakes happen and where they do,” Lipovsky said.
Lipovsky says the fiber optic cables have allowed the team to observe waves that echo off of converging seismic plates with higher precision. He says they can detect these waves at a distance of up to 200 kilometers, about 125 miles.
“Seismologists have known about these plates for a long time, they’re not particularly a new thing to science, however, when you see them with as much resolution as we have, you really can just see a lot more stuff going on,” Lipovsky said.
“If these cables can be used for scientific measurements and arrays, it’s just a massive amount of data that could be used by not only geophysicists but biologists picking up whales and other marine creatures,” said Bruce Rein, principal engineer at GCI. “It seems to be a technology that could be huge because of the massive amount of cables that are out in the ocean that could literally become scientific arrays for collecting data.”
While states like California have early warning systems when it comes to detecting earthquakes, Lipovsky says their biggest difficulty is recognizing seismic activity offshore. Currently, the most widely used technology to detect earthquakes is seismometers.
“With the fiber, we already have the sensors out there," Lipovsky said. "The fiber acts as a sensor itself, and so if we can use these systems, it would really help with the offshore seismicity.”
Lipovsky says distributed acoustic sensing can warn people roughly ten seconds before an earthquake hits. Because it’s a relatively new technology, no governments have implemented it into their current earthquake detection systems.
The University of Washington team plans to continue their research this spring.
