Scientists harness 'thunderquakes' and fiber-optic cables for subsurface seismic imaging

A lightning bolt strikes the ground during a summer storm, and the earth trembles. For decades, seismologists have known that thunder produces vibrations in the soil—what researchers now call thunderquakes. But until recently, capturing and interpreting those signals required specialized equipment buried in the earth, expensive arrays of sensors, or controlled explosions. A new study shows that the fiber-optic cables already threaded beneath city streets and connecting telecommunications networks can do the job just as well.

The discovery emerged from a straightforward insight: the same cables that carry internet traffic and phone signals are sensitive enough to detect the faint seismic waves generated when lightning strikes the ground. Researchers realized they could repurpose this existing infrastructure—miles of it already installed in urban areas—to map what lies beneath the surface without laying a single new wire or detonating anything.

The technique works because fiber-optic cables respond to physical strain and vibration. When a thunderquake sends waves through the soil, those waves compress and stretch the cables, causing measurable changes in the light traveling through them. By analyzing these changes, scientists can reconstruct a detailed picture of the subsurface geology—the layers of rock, soil, and water that lie hidden below. The resolution and depth of imaging rival what traditional seismic surveys produce, but at a fraction of the cost and without the disruption of installing dedicated equipment.

This matters most in cities, where conventional seismic surveys are expensive, logistically difficult, and often impossible. Urban areas are dense with infrastructure—buildings, utilities, traffic—that makes it hard to place sensors or conduct controlled explosions. Fiber-optic cables, by contrast, are already there. They run under streets, along utility corridors, through neighborhoods. They are invisible and in place. Using them for seismic imaging transforms a communication network into a geological sensing tool.

The implications ripple outward. Cities could monitor ground stability and detect geological hazards—subsidence, groundwater changes, fault movements—continuously and at minimal cost. Engineers planning construction projects could map subsurface conditions before breaking ground. Researchers studying urban geology and earthquake risk could gather data that was previously too expensive or impractical to collect. The technique also works in places where traditional seismic surveys are simply not feasible: beneath dense urban cores, in developing regions with limited resources, in areas where environmental or safety concerns rule out explosives.

Thunderquakes themselves are not rare. Lightning strikes Earth roughly 100 times per second, and each one sends seismic energy into the ground. The challenge has always been detecting and interpreting that signal. Fiber-optic cables solve both problems at once. They are sensitive, they are ubiquitous, and they are already paid for.

The research opens a new frontier in what scientists call distributed acoustic sensing—using long cables as networks of sensors rather than as conduits for data. Telecommunications companies, which own and operate these cables, now have a reason to think of them as dual-use infrastructure. The same fiber that carries your email can also tell geologists what the earth looks like a hundred meters down. As cities grow and climate change intensifies storm activity, the ability to understand and monitor subsurface conditions becomes more valuable. Thunderquakes, it turns out, are not just a curiosity of physics. They are a tool waiting to be used.