Optical fibers in seismology

A team of researchers from the USA presents the potential for applying current networks of buried optical fibers as a cheap observatory for controlling and studying earthquakes. The researchers demonstrate new evidence that these optical fibers that transmit high-speed internet and HD video to homes allow doubling as seismic sensors.

High power fiber cables are considered to be the basis of modern telecommunications, therefore, it is possible to convert current networks into extensive seismic arrays to estimate ground movements during earthquakes. The fiber optic technology has been already tested by researchers that employed a prototype array.

It should be noted that it is the first time when seismology based on fiber optic cables is employed to obtain a conventional measurement of subsurface features that are applied by earthquake engineers to forecast the severity of shaking. To be more precise, to convert a high power fiber cable into a seismic sensor, the team links a laser beam interrogator to one end of the fiber cable and short pulses of laser light down the optical fiber.

The operating principle is based on the light that reflects back when it faces impurities along with the optical fiber, generating a backscatter signal analyzed by an interferometer device. Shifts in the backscatter signal demonstrate how the optical fiber stretches or compresses in response to passing disturbances as well as seismic waves evoked by earthquakes.

These optical fibers allow creating high-resolution maps of the shallow subsurface, which researchers can apply to see which areas will be exposed to the strongest shaking in future earthquakes. Moreover, these fiber optic cables enable to sense seismic waves and get velocity models and resonance frequencies of the ground. Herewith, the results provided by fiber cables are the same as used conventional methods.

The most important thing in fiber optic technology is that most cities already have optical fibers as part of their infrastructure, so all it is necessary to do is tap into it.

The thing is that “many urban centers are built atop soft sediments that amplify and extend earthquake shaking, the near-surface geology can vary considerably from neighborhood to neighborhood, highlighting the need for detailed, site-specific information.” Nevertheless, it remains difficult to deploy thousands of seismometer arrays across these urban landscapes.

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