LOS ANGELES, Dec. 18 (Xinhua) -- An international team of geoscientists has used fiber optic communications cables stationed at the bottom of the North Sea as a giant seismic network to track both earthquakes and ocean waves, according to a study published Wednesday in Nature Communications.
Oceans cover two-thirds of Earth's surface, but placing permanent seismometers under the sea is prohibitively expensive. The team, led by researchers from California Institute of Technology (Caltech), employed a 40,000-meter section of fiber optic cable that connects a North Sea wind farm to the shore, creating an array of more than 4,000 virtual sensors.
"With the flip of a switch, we have an array of 4,000 sensors that would've cost millions to place," said Ethan Williams, a Caltech graduate and the study's lead author.
Because of the network's fine degree of sensitivity, the North Sea array was able to track tiny, non-earthquake-related seismic noise and found evidence that supports a longstanding theory that the microseisms result from ocean waves, according to the study.
"Fiber optic communications cables are growing more and more common on the sea floor. Rather than place a whole new device, we can tap into some of this fiber and start observing seismicity immediately," said Williams.
The project relies on a technology called distributing acoustic sensing (DAS), which was developed for energy exploration but has been repurposed for seismology.
"Seafloor DAS is a new frontier of geophysics that may bring orders-of-magnitude more submarine seismic data and a new understanding of the deep Earth's interior and major faults," said Zhongwen Zhan, assistant professor of geophysics at Caltech and the study's co-author.