New role of optical fiber and cable in earthquake

Although current seismometers can accurately pick up slight tremors, their distances are relatively short. However, now, research from Stanford University shows that a wide range of seismic detection networks can already exist at our feet: optical fiber and cable carrying high-speed Internet.

Because the optical fiber works by bouncing the optical signal on the optical cable similar to the transparent glass plate, the small interference of the signal can be measured. This technology, called distributed acoustic sensing (DAS), has been working in the oil and gas industry.

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

In order to test whether these optical cables can be used to monitor and measure earthquakes, Stanford University has installed a three-mile (4.8-kilometer) optical fiber in the shape of the number 8, equipped with a laser interrogator to record any movement.

It is said that the optical fiber seismic observatory set up by Stanford University can record more than 800 events in the year before its operation. This includes the sound of explosions from nearby quarries, small earthquakes, and even the massive 8.2 magnitude event on September 8 this year, which destroyed central Mexico, about 2000 miles (3220 kilometers) away 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, the two earthquakes are the same waveform or mode, because they originated from the same place, but the magnitude of the earthquake is larger. This shows that the optical fiber seismic observation station can correctly distinguish different magnitudes."

Similarly, the seismic observation station can also distinguish the difference between S wave and P wave, and wave the shock wave of earthquake with different velocities. 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 optical fiber seismic observation station has shown some preliminary results, the researchers pointed out that the traditional seismograph is still more sensitive to monitoring earthquakes, but the optical fiber seismic observation system has other advantages, such as economy, universality, etc