Andreas Fichtner and Fabian Walter at the Swiss Federal Institute of Technology in Zurich (ETH) are “massively expanding the potential applications of optical fibers,” according to a press release from ETH Zurich.
In late June, a research team led by Fichtner and Walter laid a nine-kilometer-long cable across the surface of the Rhône Glacier and connected it to a measuring instrument. Laser pulses of a specific wavelength are directed through the optical fiber, and any pressure or tension on the cable changes the pattern of the light waves. The researchers then measure this interference to allow them to calculate where quakes occurred and how powerful they were.
“You’re basically replacing thousands of seismometers with a single cable,” said Fichtner, a professor of geophysics in the Department of Earth Sciences at ETH Zurich whose primary interest lies in the potential that fiber-optic cables offer in seismology. His colleague Walter, a professor at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) is particularly interested in “tiny earthquakes that originate in the glacier bed.”
The two researchers carried out their first tests with a short cable in 2019, which revealed that “glacier quakes primarily occur in clusters.” This implies that the ice does not slide smoothly but rather moves forward in a jerky manner.
“That’s not what you would expect based on current theories,” said Walter. “My hypothesis is that the sliding motion of glaciers is comparable to that of tectonic plates.”
Fichtner hopes that fiber-optic cables could one day be used in big cities to study the geological subsurface in an effort to better protect cities at high risk of earthquakes, such as Athens or San Francisco.
This was already demonstrated in a feasibility study in Bern, where Fitchner and his team, together with the internet service provider Switch, measured human-made seismic activity using a six-kilometer-long fiber-optic cable.
“That’s equivalent to about 3,000 small seismometers. Setting up that many devices so close together is simply impossible,” said Fichtner.
