Stanford University: Fiber optic cable can be used to monitor earthquakes

Although current seismographs can accurately pick up slight tremors, their distance is relatively short. However, now, Stanford University research 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 acts by bounces the optical signal on a cable that is transparent like a glass plate, it is possible to measure the small interference of the signal. This technology, called Distributed Acoustic Sensing (DAS), has worked in the oil and gas industry.

Eileen Martin, co-author of the study, said: "The principle of DAS is that as light travels along the fiber, it encounters various impurities in the glass and bounces. If the fiber is completely still, then reverse The scatter signal always looks the same, but if the fiber starts to stretch in certain areas - the signal will change due to vibration or strain."

To test whether these cables can be used to monitor and measure earthquakes, Stanford University installed three miles (4.8 km) of fiber in the shape of Figure 8, with a laser interrogator for recording any motion.

The fiber-optic seismic observatory set up at Stanford University is said to be able to record more than 800 events in its first year of operation. This includes explosions from nearby quarries, small earthquakes, and even a massive 8.2-level incident on September 8 this year, which destroyed central Mexico and set about 2,000 miles (3,220 kilometers) from Stanford University. On one occasion, the sensor picked up two earthquakes from the same source with magnitudes of 1.6 and 1.8.

Lead researcher Biondo Biondi said: "As expected, the two earthquakes are all the same waveform or pattern because they originate in the same place, but the magnitude of the earthquake is larger. This shows that the fiber seismic station can correctly distinguish different magnitudes. ""

Similarly, the seismic observatory can also discern the difference between the S-wave and the P-wave, and the shock wave of the corrugated earthquake at different speeds. P waves are usually much earlier than S waves, but they are far weaker, so detecting them is the key to an effective early warning system.

Although their fiber optic seismic stations have shown some preliminary results, the researchers pointed out that traditional seismographs are still more sensitive to monitoring earthquakes, but fiber optic seismic observing systems have other advantages, such as economics and extensiveness.

Biondi said: "We can use the pre-existing fiber that has been deployed for telecommunications purposes to continuously listen and monitor the Earth. Every fiber in our network is like a sensor, costing less than a dollar, and traditional seismographs are created. The network cannot have this coverage density and cost advantage."