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In traditional seismology, researchers studying how the earth moves in the moments before, during, and after an earthquake rely on sensors that cost tens of thousands of dollars to make and install underground. And because of the expense and labor involved, only a few seismic sensors have been installed throughout remote areas of California, making it hard to understand the impacts of future earthquakes as well as small earthquakes occurring on unmapped faults.
Now researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have figured out a way to overcome these hurdles by turning parts of a 13,000-mile-long testbed of "dark fiber," unused fiber-optic cable owned by the DOE Energy Sciences Network (ESnet), into a highly sensitive seismic activity sensor that could potentially augment the performance of earthquake early warning systems currently being developed in the western United States. The study detailing the work—the first to employ a large regional network as an earthquake sensor—was published this week in Nature's Scientific Reports.
Jonathan - Ajo-Franklin - Staff - Scientist - Berkeley
According to Jonathan Ajo-Franklin, a staff scientist in Berkeley Lab's Earth and Environmental Sciences Area who led the study, there are approximately 10 million kilometers of fiber-optic cable around the world, and about 10 percent of that consists of dark fiber.
The Ajo-Franklin group has been working toward this type of experiment for several years. In a 2017 study, they installed a fiber-optic cable in a shallow trench in Richmond, California, and demonstrated that a new sensing technology called distributed acoustic sensing (DAS) could be used for imaging of the shallow subsurface. DAS is a technology that measures seismic wavefields by shooting short laser pulses across the length of the fiber. In a follow-up study, they and a group of collaborators demonstrated for the first time that fiber-optic cables could be used as sensors for detecting earthquakes.
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