Hidden Fibre-Optic Cables Illuminate the Earth’s Underground Secrets

The world’s 4 billion kilometres of buried fibre-optic cables are doing more than powering the internet—they’re giving scientists a new way to study the planet’s interior and detect seismic risks.

“These cables give us a new way to see the planet, revealing what lies beneath cities, volcanoes, and faultlines,” says Hilary Chang, a researcher who has tested this approach using MIT’s campus infrastructure.

Through a method called distributed acoustic sensing (DAS), dark fibre cables are repurposed as sensors to detect vibrations. In Istanbul, they tracked ground shifts linked to earthquakes; in London, they mapped the hum of urban life; in Iceland, they monitored volcanic rumblings. This low-cost approach, using existing infrastructure, could transform how we monitor hazards across both cities and oceans — protecting lives while unlocking new insights into the Earth’s hidden layers.