Using Fiber Optics For High-Speed Internet, Remote Sensing, And … Detecting Icequakes?

By John Oncea, Editor

Fiber optics have been used in many ways by many industries. Now, the technology is being used to help detect earthquake’s little brother, icequakes.

Fiber optics are used in telecommunications to transmit data signals for high-speed internet, telephones, and cable television, offering higher bandwidth and lower interference than copper wires. They’re commonly integrated into medical instruments to provide precise illumination to the human body during surgery and other minimally invasive procedures, such as endoscopy. Museums and retailers use fiber optics to light exhibits and illuminate showcases, respectively.

Now, according to the Seismological Society of America, fiber optics are being used to detect crevasse icequakes on a Swiss glacier.

What Is An Icequake?

An icequake, also known as a frost quake or cryoseism, is a phenomenon where sudden, loud cracking or booming sounds are produced by the rapid freezing of water that has infiltrated and saturated the ground, according to Britannica. This rapid expansion of freezing water creates stress, causing the ground or rock to fracture suddenly, producing the seismic-like noises and shaking. These events typically occur on cold, clear nights with little snow cover.

Icequakes occur under specific conditions that involve the saturation of the ground, a rapid drop in temperature, and a lack of snow cover. For an icequake to happen, water must be present in the soil, penetrating deeply into cracks and open spaces.

When a sudden and significant temperature drop occurs, from above freezing to below zero, this water can freeze quickly, contributing to the phenomenon. Additionally, a minimal snow cover is essential; while some snow can provide insulation, a thick blanket can inhibit the rapid freezing process that triggers these seismic events. Timing also plays a crucial role, as icequakes typically manifest between midnight and dawn, the coldest parts of the night, and can persist for hours or even days.

When an icequake occurs, residents may experience some dramatic effects. Loud booms or crackling sounds akin to an earthquake are often reported, catching people off guard. The rapid cracking of the ground can lead to shaking, which might result in minor damage or vibrations felt within homes.

As the ground contracts and fractures, visible fissures may appear on the surface, highlighting the disturbance. In rare instances, distant flashing lights have been observed, possibly due to electrical changes associated with the stress and compressions occurring during these events. Such phenomena remind us of the dynamic interactions between weather conditions and the earth beneath our feet.

While they do not cause widespread destruction like earthquakes, their concentrated surface effects can be significant enough to jar people awake and, in rare instances, lead to minor property damage, writes Carrier Management. Examples of their effects include cracked foundations or fractured drainage pipes, though they are rarely reported due to their localized nature and low energy release.

How Fiber Optics Detects Icequakes

At the Seismological Society of America’s Annual Meeting this past April, researchers reported that fiber optic cables installed on a Swiss glacier successfully recorded the seismic activity caused by the opening of ice crevasses. The results highlight the potential of this technology for tracking icequakes in challenging environments where traditional instruments are difficult to deploy.

Crevasse formation plays a critical role in glacier dynamics. These fractures not only compromise the structural stability of the ice but also provide channels for meltwater to reach the glacier bed, ultimately accelerating both ice movement and melting. However, installing conventional seismic sensors in heavily fractured glacier zones is often unsafe and technically impractical.

Tom Hudson of ETH Zürich explained that seismic signals from icequakes differ from those generated by tectonic earthquakes or explosions. Unlike earthquakes driven by shear forces or blasts produced by a sudden release of energy, icequakes represent a straightforward cracking event – a fracture opens in one direction, producing a characteristic seismic signature.

Hudson, along with ETH Zürich colleague Andreas Fichtner and their team, used fiber optics as a dense seismic network across the Gornergletscher (Gorner Glacier), Switzerland’s second-largest glacier. “This work is essentially a real-world demonstration of detecting crack-type seismicity directly adjacent to the source,” Hudson noted, pointing out that some crevasse events occurred less than 10 meters from the cable. He also emphasized that this proximity to the fracture source is exceptionally rare in seismology.

The team benefitted from optimal installation conditions at the transition between summer and winter, when the absence of snow made crevasse fields more navigable. Moreover, the natural environment improved coupling between the fiber cable and ice. During daylight, the black-coated fiber absorbed heat and melted slightly into the ice surface. At night, freezing temperatures secured the cable in place, creating near-ideal contact for seismic measurement.

Over the monitoring period, the researchers documented 951 distinct icequakes. Many seismic traces displayed pronounced oscillations following the surface-wave arrivals. While such patterns can sometimes be linked to water resonances inside crevasses, the group’s analysis suggests the signals instead arose from seismic waves reverberating between multiple fractures in the crevassed field.

To validate their results, the team compared the fiber optic system to an array of conventional seismic nodes. The comparison revealed a significant advantage: the fiber optic setup produced nearly 20 times more data, offering a detailed view of the entire seismic wavefield. Fiber cables also detect a much broader frequency range, including low-frequency signals persisting for hours to days, enabling long-term tracking of glacier flexure and structural changes.

Hudson emphasized that the simplicity of seismic wave propagation in glacial ice, compared to rock, makes glaciers an excellent testbed for developing new methods. Insights gained here could later be applied to more complex systems, such as monitoring rock fracturing around geothermal plants or carbon storage reservoirs.

Looking ahead, the team hopes to expand their fiber-based imaging experiments on Gornergletscher. Future work will focus on constructing 3D models of the glacier’s internal fractures, quantifying crack sizes and densities, and better understanding the conditions that trigger icequakes.