Stanford University: Fiber optic cables can be used for earthquake monitoring

Due to the fact that optical fibers work by bouncing light signals on transparent cables similar to glass plates, it is possible to measure small interferences in the signal. This technology, known as Distributed Acoustic Sensing (DAS), has been working in the oil and gas industry.

The co-author of the study, Eileen Martin, said: 'The working principle of DAS is that as light propagates along fibers, it encounters various impurities in the glass.'. If the fiber optic cable is stationary, the backscatter signal will always look the same, but if the fiber optic cable starts to stretch in certain areas - due to vibration or strain, the signal will change. ”

To test whether these cables can be used for monitoring and measuring earthquakes, Stanford University installed three miles (4.8 kilometers) of fiber optic cables in the shape of the number 8, equipped with laser interrogators to record any motion.

It is said that the fiber optic seismic observatory set up by Stanford University can record more than 800 events in its operating year. This includes explosions from nearby quarries, small earthquakes, and even a massive 8.2 magnitude event on September 8th this year, located about 2000 miles (3220 kilometers) from Stanford University. Once, the sensor picked up two earthquakes from the same source, with magnitudes of 1.6 and 1.8.

Researcher Biondo Biondi said, "As expected, both earthquakes had the same waveform or pattern because they originated from the same place, but with larger amplitudes. This indicates that fiber optic seismic observation stations can correctly distinguish between different magnitudes

Similarly, earthquake observation stations can also distinguish the differences between S-waves and P-waves, as well as the shock waves of seismic waves with different velocities. P-waves are usually much earlier than S-waves, but much weaker, so detecting them is key to an effective warning system.

　

(Original title: Stanford University: Fiber optic cables can be used for earthquake monitoring)
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