Earthquakes are some of our planet's most devastating natural disasters. With almost no warning, an earthquake can level entire cities in a matter of minutes. For the millions of people living on or near fault lines, a few extra minutes of warning can mean the difference between life and death, so it's crucial that we're able to see major earthquakes coming as soon as possible.

Mostly, that requires building sensitive earthquake detectors that can measure the smallest of quakes, which can signal that a larger one is on the way. But standard earthquake detectors can only get us so far, which is why a group of Stanford researchers is turning to a different solution: fiber optic networks.

Fiber optic cables transmit information at nearly the speed of light, and are used by telecommunications companies around the world. But they're also used by oil and gas companies to monitor small quakes caused by drilling equipment. These companies exploit a property of the cables called 'backscatter' to track movement of the cables and record seismic events.

At one end of the cable is a laser, that shines light into the cable. Some of that light hits impurities in the glass walls of the cable and bounces back; this is the 'backscatter' referred to earlier. The signal that comes back down the cable can change depending on whether the part of the cable that caused the backscatter was still or moving, and recording those backscatter signals can give scientists a map of seismic activity across a large area.

Typically, these fiber optic detectors are mounted to the sides of pipelines and other equipment, to monitor them for damage. But to monitor earthquakes, the Stanford researchers needed to use unattached cables, which most people believed was impossible.

A map of the researchers' fiber optic network on the Stanford campus. Stamen Design and the Victoria and Albert Museum

"People didn't believe this would work," said researcher Eileen Martin. "They always assumed that an uncoupled optical fiber would generate too much signal noise to be useful."

But using a 3-mile fiber loop on the Stanford campus, the researchers demonstrated that using optical fibers in this way is entirely possible. Using their fiber network, they've been able to detect around 800 seismic events, including the recent earthquake in Mexico and two small, local earthquakes measuring at 1.6 and 1.8 magnitude.

This means that scientists can detect earthquakes using the existing fiber optic cables that telecom companies have already laid down across the country. While these cables will never be able to match the sensitivity of traditional seismometers, they are significantly cheaper and can give a broader detection network.

"Every meter of optical fiber in our network acts like a sensor and costs less than a dollar to install," said researcher Biondo Biondi. "You will never be able to create a network using conventional seismometers with that kind of coverage, density and price."

Source: Stanford University

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