Over the last year, earthquakes wreaked havoc on various parts of the world. Central and Southwest Mexico experienced a devastating natural disaster when an earthquake reaching a magnitude of 7.1 that pummelled Mexico City and killed hundreds of people.
As the quakes are growing in strength, scientists rush to find innovative ways to sense the earliest rumbles of a giant earthquake. Recently, researchers at Stanford University are using optical fibers that generally transmit data, such as high-speed internet and HD video, to also observe what is happening around them, including seismic activity.
Biondo Biondi, a professor of geophysics at Stanford’s School of Earth, Energy & Environmental Sciences, has been working with a 4.8 kilometer (or 3-mile) test loop of optical fibers installed on the University campus to record vibrations caused by earthquakes in the area.
Optical fibers are human hair sized strands of pure glass which are normally bundled together to create cables which transmit data signals over long distances, which convert these electronic signals into light.
So far, Biondo and his team have recorder 800 seismic events using this fiber optic system with instruments called laser interrogators provided by the company OptaSense, which is a co-author on publications about the research. Since September 2016; they've noted signals from the Mexican earthquake and vibrations from quarry blasts in the area.
"As expected, both earthquakes had the same waveform, or pattern, because they originated from the same place, but the amplitude of the bigger quake was larger," Biondi said. "This demonstrates that fiber optic seismic observatory can correctly distinguish between different magnitude quakes."
The fibers can distinguish between two types of earthquake waves by classifying them as P waves and S waves. P waves travel faster, and S waves cause more damage.
A Fiber optic sensory system isn’t a new technology; many oil and gas companies use it as a standard operating procedure, called DAS or distributed acoustic sensing.
"How DAS works is that as the light travels along the fiber, it encounters various impurities in the glass and bounces back," said Eileen Martin, a graduate student on the project in a statement. "If the fiber were totally stationary, that ‘backscatter’ signal would always look the same. But if the fiber starts to stretch in some areas — due to vibrations or strain — the signal changes."
Though, the difference between the energy sector’s process and Biondi’s involves stabilization. Oil and gas usually attach fibers to a surface area of a pipeline or by solidifying them in cement. Biondi however, used free-floating fiber optic cables laying inside plastic piping, similar to a standard optical communications installation.
Both stabilized, and free systems work by taking advantage of these innate impurities in optical fibers.
Dubbed the fiber optic seismic observatory, researchers claim the system is also cheaper to run. Currently, the only equipment used to monitor earthquakes are seismometers, while they are more sensitive than Biondi’s telecom array, their coverage is sparse and can be expensive to both install and maintain.
"Every meter of optical fiber in our network acts as a sensor and costs less than a dollar to install," Biondi said. "You will never be able to create a network using conventional seismometers with that kind of coverage, density, and price."
The observatory is still a long way from developing a city-wide seismic network, as there are still bureaucratic hurdles to overcome, such as proving the array can operate within a cities infrastructure.