Abstract

Over the past few decades, the world has been wired together by millions of kilometers of fiber-optic cables, carrying the high-speed internet we all rely on. But these cables can do much more than just transmit data. With the right technology, they can be turned into powerful environmental sensors, opening up an entirely new way to observe our planet. In this talk, I’ll share two recent examples from Iceland that show how fiber-optic sensing is being used in innovative ways.

The first example comes from the Reykjanes Peninsula, which has been restless since 2019. Since late 2023, a series of magma intrusions and eruptions have taken place along the Sundhnúksgígur fissure swarm — just north of the town of Grindavík and only 2 km from the Svartsengi geothermal power plant and the famous Blue Lagoon spa. In some cases, evacuations were ordered with less than 30 minutes’ notice.

From November 2023 to November 2024, a distributed acoustic sensing (DAS) interrogator operated on the peninsula, converting a 100-km-long telecommunication fiber crossing Grindavík into a dense array of 10,000 strain-rate sensors. Remarkably, we found that the cable picked up clear low-frequency signals more than 30 minutes before each eruption. Building on this, we developed a simple but robust warning system using these signals — one that was so effective it was quickly adopted into the official monitoring protocols of the Icelandic Meteorological Office.

1. The second example shifts to the oceans. About 70% of the Earth’s surface is covered by water, making it extremely difficult and expensive to record seismic signals beneath the sea. But recently, researchers have shown that existing subsea telecom cables — the same ones that carry internet traffic across oceans — can also detect seismic waves., existing commercial systems are limited to short ranges with high resolution or integrated measurements over the whole length of the cable.

In our work, we tested a prototype distributed fiber-optic sensing (DFOS) system on the IRIS subsea cable between Iceland and Ireland. This system measures strain along each segment between repeaters, essentially turning every 100-km span of the cable into its own sensor. This allows us to separate signals, reduce noise, and get much clearer earthquake records over the full length of the cable. Using this setup, we were able to detect several large earthquakes across 17 different cable segments.  

Equipping subsea cables worldwide with similar systems could extend current seismic monitoring networks to the oceans, offering a transformative step toward truly global earthquake observation

Biography

Vala Hjörleifsdóttir is a seismologist and Associate Professor at Reykjavík University, Iceland. Her research centers on advancing methods for geothermal exploration and natural hazard monitoring, with a particular emphasis on fiber-optic sensing. Before joining RU, she served as Head of Innovation and Strategic Planning at Reykjavík Energy, one of the world’s largest geothermal operators, where she oversaw innovation initiatives and long-term resource management for the company and its subsidiaries. Earlier in her career, she was a Research Professor in Seismology at the Institute of Geophysics at UNAM in Mexico City, where her work focused on observational constraints on the frictional behavior of the Mexican subduction zone megathrust.