Fiber optic cables double as early quake detectors

Monday, 23 Oct, 2017

He points to the San Francisco Bay area where the current fibre optic setup can be used to setup a rather low-priced natural disaster monitoring system.

Biondo Biondi, a professor of geophysics at Stanford's School of Earth, Energy & Environmental Sciences, dreams of turning that dense network into an low-priced "billion sensors" observatory for continuously monitoring and studying earthquakes. Researchers have developed technology that detects seismic activity through jiggling in fiber optic lines. And the current proof of concept is a relatively modest 3-mile loop around Stanford University.

Researchers at Stanford's School of Earth, Energy and Environmental Sciences have successfully tested a mechanism which shall use fibre optic network to monitor seismic events. He calculates that for every meter of optical fibre you have to invest about a dollar and this is much less expensive than installing conventional seismometers over a large area.

Such a network would allow scientists to study earthquakes, especially smaller ones, in greater detail and pinpoint their sources more quickly than is now possible. They transmit digital data and Internet traffic at high speed to the students and faculty. "If the fiber were totally stationary, that "backscatter" signal would always look the same. But if the fiber starts to stretch in some areas - due to vibrations or strain - the signal changes".

Fiber-based detection isn't strictly new, but it previously centered around acoustic sensing that required wrapping them in cement, sticking them to a surface or otherwise making sure they contact the ground (to make it easier to spot impurities in the signal). It's optical fiber sitting inside a plastic cable under the ground, just like commercial cabling.

Last year, Prof. Biondi and graduate assistant Eileen Martin began experimenting with the fiber optic array and they have recorded about 800 seismic events since then. The fibre optic seismic observatory can also record the intensity of earthquakes because different intensity earthquakes result in different patterns and waveforms in the fibre optic network. Detecting P waves means knowing earlier that an natural disaster is imminent. "One of our goals is to contribute to an early quake warning system". P waves are particularly important to detect as they arrive before S waves and are typically the first waves felt from a seismic event.

Geophysics professor Biondo Biondi repurposed some of those cables, along with an existing underground network of sensors, to create a virtual three-mile-long, figure-eight-shape subterranean seismometer.