Seismologists Using Novel Fiber Optic Network to Monitor Aftershocks

Days after a 7.1 earthquake struck Searles Valley, California, a U.S Geological Survey crew scanning the area photographed huge swaths of surface rupture. (Ben Brooks / USGS)

PASADENA, Calif. (CN) – Weeks after California’s strongest earthquake in 20 years struck near the town of Ridgecrest, scientists have begun tracking aftershocks using a sophisticated network of fiber optic sensors.

The magnitude 7.1 quake struck July 5 in the Searles Valley, more than 150 miles from Los Angeles. The temblor and its magnitude 6.4 foreshock the day before caused damage to roads, buildings and highways.

The shaking – which caused tall buildings in downtown Los Angeles to sway – was felt as far north as the San Francisco Bay Area, as far east as Nevada and as far south as Mexico.

Tens of thousands of tiny aftershocks are occurring in the region everyday as a result of the quake – a number that is “unprecedented,” seismologists at the California Institute of Technology said in a statement Wednesday.

Using a new technology that involves shooting a beam of light down a dark fiber optic cable inserted in the ground where aftershocks are occurring, Caltech scientists hope to learn more about how seismic waves migrate and decay over time.

When an aftershock strikes and the soil is shifted, light is disrupted while traveling back through cables that have expanded or contracted. This allows scientists to register data points for the aftershock.

“These imperfections occur frequently enough that every few meters of fiber act like an individual seismometer,” study lead author Zhongwen Zhan said in a statement Wednesday. “For the 50 kilometers of fiber optic cable in three different locations we’ve tapped into for the project, it’s roughly akin to deploying over 6,000 seismometers in the area.”

Caltech seismologists were allowed to use fiber optic cables from the Inyokern Airport – located minutes from Ridgecrest – and a project that aims to build a 600-mile cable network along U.S. Route 395.

Zhan has previously tested his quake monitoring technology at the Mojave Desert-based Goldstone Deep Space Communications Complex, a NASA facility run by the Jet Propulsion Laboratory, which Caltech operates.

Immediately after the July 5 quake, the U.S Geological Survey set up a network of temporary seismology sensors around the epicenter region.

Zhan said in the statement that while his technology will complement, not duplicate, USGS’s monitoring, the cable system will provide data much quicker than remote, battery-operated sensors that are not tied to a network.

Caltech’s Michael Gurnis said in the statement that while Ridgecrest monitoring will be temporary, seismologists plan on setting up similar systems in key areas of Southern California, including a permanent system in Pasadena where JPL is located.

“They allow us to observe and understand how seismic waves reverberate through our complex mountains and basins following a major temblor,” Gurnis said.

Zhan said that processing the “dark” cable network’s data on aftershocks – estimated to be between 10 to 20 terabytes of data – will take months, even with automated processing.

“This will keep us busy for a while, but in the end we’ll have a clearer picture of how this sequence evolved than would otherwise be possible,” Zhan said.

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