To monitor seismic activity around the world scientists require equipment to be located at the site they want to monitor, but to monitor the seismic activity in the middle of the ocean is difficult and it always has been a drawback for researchers to understand the seismic movements in the oceans.
New research from the University of California, Berkeley, has created a new technique that could turn existing undersea fiber optic cables into a network of seismographs, creating an unprecedented global view of the Earth’s tectonic movements.
How does it work?
The undersea cables carry data over long distances, sometimes as part of the internet’s foundation, and sometimes as part of private networks. But one thing they all have in common is that they use light to do so — light that gets scattered and distorted if the cable shifts or changes orientation.
By carefully monitoring this “backscatter” phenomenon it can be seen exactly where the cable bends and to what extent — sometimes to within a few nanometers. That means that researchers can observe a cable to find out the source of seismic activity with an extraordinary level of precision.
The technique is called Distributed Acoustic Sensing, and it essentially treats the cable as if it were a series of thousands of individual motion sensors. The cable the team tested on is 20 kilometers worth of Monterey Bay Aquarium Research Institute’s underwater data infrastructure — which divided up into some ten thousand segments that can detect the slightest movement of the surface to which they’re attached.
“This is really a study on the frontier of seismology, the first time anyone has used offshore fiber-optic cables for looking at these types of oceanographic signals or for imaging fault structures,” said Berkeley National Lab’s Jonathan Ajo-Franklin.
After hooking up MBARI’s cable to the DAS system, the team collected a ton of verifiable information: movement from 3.4-magnitude quake miles inland, maps of known but unmapped faults in the bay, and water movement patterns that also hint at the seismic activity.