Wires Can Save Thousands of Lives—Impossible!

Many students traveling to school often look up at the electricity wires in the street and ruminate on their detrimental effects. Can electric wires be harmful to birds? Can power outages stop a city? However, a special type of wire created by Narinder Singh Kapany in 1952 can help save many lives by detecting earthquakes. These are called fiber optic cables, and they are cooler than they seem. 

The first notion regarding fiber optic cables started with French inventors Daniel Colladon and Jacques Babinet, who discovered this concept in the early 1840s. They thought of these cables as pathways guiding light through refraction, or the bending of it. Then, this Irish inventor John Tyndall in the mid-1850s studied it further. Tyndall’s demonstrations using water fountains to describe refraction influenced Scottish inventor John Logie Baird’s invention of the television. Afterward, Kapany invented fiber optic cables. Since then, scientists have been researching fiber optic cables and their ability to detect earthquakes. 

An earthquake is the shaking of the Earth’s surface. The Earth is composed of four main layers: the crust, the mantle, a liquid outer core, and a solid inner core. The shaking occurs on the outermost layer, the lithosphere, which is made up of the crust and the top part of the mantle. The lithosphere can be thought of as the “eggshell” of our planet since it encompasses Earth’s outer surface. Tectonic plates are the pieces of the lithosphere that shift around. Many believe that the mere movement of tectonic plates is what causes earthquakes; however, the real cause of earthquakes is when the tectonic plates suddenly move near a fault line, a crack created in the surface due to the stress put on the Earth’s crust. This stress stems from the constant movement of the tectonic plates. 

Currently, one of the main ways earthquakes are measured is through seismic waves, which quantify the energy from an earthquake in the form of vibrations. Using a seismometer, scientists can determine many characteristics of earthquakes, such as the time at which they occurred or the location. Although it is useful to be able to determine the characteristics of earthquakes after they occur, the time it happens is still important; scientists are still developing technology to detect earthquakes more efficiently. While a seismometer measures the features of an earthquake after it occurs, fiber optic cables are able to actually predict earthquakes before they happen.

Fiber optic cables are network cables made up of strands of glass fibers. These fibers are packed inside an insulated casing. Each glass fiber has a core surrounded by a large layer of glass called the cladding, which helps retain the signal by reflecting light inward, allowing light to pass through the bends of the cable. The main cable type that allows for communication and signal transferring is single-mode optic fiber networks using wave division multiplexing techniques. This allows light at multiple wavelengths to combine (multiplexed) and separate (de-multiplexed), leading to the effective transmission of signals throughout the cable. Fiber optic cables are mainly used for communication, and they provide reliable, long-distance data connections. They are the backbones of our telephone systems, television, and the entire internet.

Fiber optic cables can be used for earthquake detection if they are set up as such: at one end of the cable, laser emitters pass beams of light all the way through the long, thin glass of the cable. Light passes through because the thin glass in the core has imperfections that reflect a small amount of light back on the laser emitters. The reflected light is then recorded through a sensor at the beginning of where the light was emitted. Because seismic waves are vibrations, they cause the cable to move. This movement interferes with the travel time from and to the laser emitter. With these recordings, it is as if the little imperfections within the fiber optic cable are many seismometers within the cable.

A study run by Caltech Geophysics professor Zhongwen Zhan describes the ability of these cables to detect earthquakes and their future potential. In a 2021 experiment, they examined the light passing through the cables in Eastern Sierra Nevada during the 2021 Antelope Valley magnitude six earthquake. For clarity, a magnitude six earthquake is considered strong; magnitudes range from one (weak) to around 9.5-10 (very strong and destructive). Due to the many imperfections, the cable was equal to about 10,000 seismometers. This cable was able to detect four small ruptures within the earthquake. Conventional seismometers and seismic networks would not be able to detect these smaller events, but scientists can predict earthquakes right before they strike. 

As scientists learn more about earthquakes and fiber optic cables, scientists will become more efficient at detecting earthquakes. The ability of one cable to have the strength of thousands of conventional seismometers illustrates the immense potential of fiber optic cables. Imagine thousands of cables wired around the surface of the earth. As research develops these cables, when an earthquake strikes, we will be able to detect it in no time.