Although current seismometers can pick up mild tremor accurately, their distance is relatively short. However, research by Stanford University now shows that a wide range of seismic detection networks can already exist at our feet: fiber-optic cables that carry high-speed Internet.
Since the fiber functions by bouncing the optical signal over a glass-like transparent cable, the signal's slight interference can be measured. This technology, known as Distributed Acoustic Sensing (DAS), has been working in the oil and gas industry.
Eileen Martin, co-author of the study, said: "DAS works by moving the light along the fiber as it encounters various kinds of impurities in the glass and rebounding. If the fiber is completely at rest, the reverse Scattering signals always look the same, but if the fiber begins to stretch in some areas - the signal changes due to vibration or strain. "
To test whether these cables can be used to monitor and measure earthquakes, Stanford installed three miles (4.8 km) of fiber in the shape of a number eight with a laser interrogator to record any movement.
The Fiber Optic Earthquake Observatory set up by Stanford University is said to record more than 800 events in its first year of operation. These include explosions from nearby quarries, small earthquakes and even a massive 8.2-magnitude event on September 8, this year that destroyed central Mexico and about 2,000 miles (3,220 kilometers) from Stanford University. Once, the sensor picked up two earthquakes from the same source with magnitudes of 1.6 and 1.8.
Biondo Biondi, Principal Researcher, said: "As expected, both earthquakes were the same waveform or pattern because they originated in the same place but with a greater magnitude of the earthquakes, suggesting that fiber optic seismic stations correctly distinguish between different magnitude "
Similarly, seismic stations can also distinguish between S wave and P wave to shock waves of ripple at different velocities. P waves are generally much earlier than S waves, but far weaker, so detecting them is the key to an effective early warning system.
Although their fiber optic seismic observatories have shown some initial results, the researchers point out that while traditional seismometers are still more sensitive to monitoring earthquakes, fiber optic seismic observing systems have other advantages such as economics and breadth.
Biondi said: "We can continually listen to and monitor the Earth using preexisting optical fibers that have been deployed for telecommunications purposes, and every meter of fiber in our network costs less than a dollar like a sensor, and traditional seismometers create Of the network can not have this coverage density and cost advantages. "
