Over the last year, researchers have been taking note of seismic disturbances in a 3-mile loop of optical fiber located underneath the university’s campus. These disturbances have been recorded with instruments called laser interrogators, which come from a company called OptaSense (OptaSense is assisting with the research).
“We can continuously listen to – and hear well – the Earth using preexisting optical fibers that have been deployed for telecom purposes,” Biondi noted. This would prove to be a far more cost-effective method than the current technique of using seismometers, which while more sensitive than fiber optic cables, are more expensive and more difficult to both install and maintain.
In contrast, Bondi pointed out, “Every meter of optical fiber in our network acts like a sensor and costs less than a dollar to install. You will never be able to create a network using conventional seismometers with that kind of coverage, density, and price.” If scientists are able to leverage fiber optic networks more broadly, they could study earthquakes more carefully and in more detail, and even detect the source of the tremor more efficiently than is possible today.
Stanford has maintained a fiber optic seismic observatory since September 2016, where it has recorded and catalogued more than 800 seismic events. Not only was the observatory able to detect disasters thousands of miles away, like the recent earthquakes in Mexico, but it was also able to pick up signals from minute local tremors, including a couple earthquakes with magnitudes of just 1.6 and 1.8.
“As expected, both earthquakes had the same waveform, or pattern, because they originated from the same place, but the amplitude of the bigger quake was larger,” Biondi said. “This demonstrates that fiber optic seismic observatory can correctly distinguish between different magnitude quakes.”
Biondi hopes that the array might soon operate throughout the Bay Area, though he still has to prove that the system works on a larger scale.
