Study shows potential for using fiber-optic networks to assess ground motions during earthquakes

Analysis of seismic wave velocities applying dispersed acoustic sensing method with fiber-optic cables. Credit history: Zack Spica

A new examine from a College of Michigan researcher and colleagues at three establishments demonstrates the prospective for applying existing networks of buried optical fibers as an cheap observatory for monitoring and studying earthquakes.

The study presents new evidence that the similar optical fibers that deliver substantial-pace internet and High definition movie to our homes could just one working day double as seismic sensors.

“Fiber-optic cables are the spine of modern telecommunications, and we have demonstrated that we can flip existing networks into considerable seismic arrays to assess ground motions through earthquakes,” said U-M seismologist Zack Spica, very first writer of a paper printed on the internet Feb. 12 in the journal JGR Stable Earth.

The review was performed employing a prototype array at Stanford College, wherever Spica was a postdoctoral fellow for various years just before a short while ago becoming a member of the U-M college as an assistant professor in the Section of Earth and Environmental Sciences. Co-authors involve scientists at Stanford and from Mexico and Virginia.

“This is the very first time that fiber-optic seismology has been used to derive a conventional evaluate of subsurface attributes that is utilized by earthquake engineers to anticipate the severity of shaking,” reported geophysicist Greg Beroza, a co-writer on the paper and the Wayne Loel Professor in Stanford’s University of Earth, Electrical power & Environmental Sciences.

To renovate a fiber-optic cable into a seismic sensor, the researchers hook up an instrument identified as a laser interrogator to a single close of the cable. It shoots pulses of laser light-weight down the fiber. The gentle bounces again when it encounters impurities together the fiber, building a “backscatter sign” that is analyzed by a system termed an interferometer.

Variations in the backscatter signal can reveal how the fiber stretches or compresses in response to passing disturbances, which includes seismic waves from earthquakes. The system is named distributed acoustic sensing, or DAS, and has been applied for several years to check the wellbeing of pipelines and wells in the oil and gas marketplace.

The new study in JGR Solid Earth extends prior work with the 3-mile Stanford exam loop by developing substantial-resolution maps of the shallow subsurface, which researchers can use to see which areas will endure the strongest shaking in potential earthquakes, Beroza said.

In addition, the examine demonstrates that optical fibers can be used to feeling seismic waves and receive velocity types and resonance frequencies of the ground—two parameters that are essential for ground-movement prediction and seismic-hazard assessment. Spica and his colleagues say their success are in fantastic settlement with an independent study that applied regular techniques, thus validating the methodology of fiber-optic seismology.

This solution seems to have terrific probable for use in large, earthquake-threatened towns this sort of as San Francisco, Los Angeles, Tokyo and Mexico Town, where by 1000’s of miles of optical cables are buried beneath the surface area.

“What’s great about employing fiber for this is that metropolitan areas presently have it as aspect of their infrastructure, so all we have to do is faucet into it,” Beroza said.

Numerous of these urban centers are developed atop gentle sediments that amplify and prolong earthquake shaking. The close to-area geology can differ noticeably from neighborhood to neighborhood, highlighting the require for specific, web page-unique facts.

Nevertheless having that variety of information can be a problem with standard techniques, which include the deployment of massive seismometer arrays—thousands of these types of instruments in the Los Angeles region, for case in point.

“In city locations, it is quite challenging to come across a area to put in seismic stations for the reason that asphalt is everywhere you go,” Spica claimed. “In addition, quite a few of these lands are personal and not accessible, and you cannot usually leave a seismic station standing by itself because of the hazard of theft.

“Fiber optics could sometime mark the conclude of this sort of substantial scale and pricey experiments. The cables are buried below the asphalt and crisscross the entire metropolis, with none of the shortcomings of surface seismic stations.”

The system would possible be fairly economical, as effectively, Spica mentioned. Ordinarily, commercial fiber-optic cables include unused fibers that can be leased for other purposes, which includes seismology.

For the minute, conventional seismometers present far better general performance than prototype techniques that use fiber-optic sensing. Also, seismometers sense floor movements in three directions, whilst optical fibers only feeling along the path of the fiber.

The 3-mile Stanford fiber-optic array and data acquisition had been made possible by a collective hard work from Stanford IT expert services, Stanford Geophysics, and OptaSense Ltd. Financial guidance was provided by the Stanford Exploration Challenge, the U.S. Department of Energy and the Schlumberger Fellowship.

The upcoming period of the task requires a significantly larger check array. A 27-mile loop was shaped just lately by linking optical fibers on Stanford’s historic campus with fibers at numerous other nearby places.

The other authors of the JGR Strong Earth paper are Biondo Biondi of Stanford, Mathieu Perton of Universidad Nacional Autónoma de México and Eileen Martin of Virginia Tech.

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