The makings of a sophisticated earthquake detection system may already exist under our feet. Researchers at Stanford University have shown that the existing fiber optic cables that provide high-speed internet could be harnessed as sensors for detecting the magnitude and direction of seismic events.

In a project dubbed the “fiber optic seismic observatory,” scientists at Stanford’s School of Earth, Energy & Environmental Sciences installed a 3-mile loop of optical fiber underneath the university. Since September 2016 the system has recorded more than 800 earthquakes, from small, man-made temblors to the deadly quake that struck Mexico earlier this year.

The system uses a technology called distributed acoustic sensing, in which laser light is sent down the optical fiber bundle: During an earthquake, a detector measures the amount of light that bounces back due to vibrations or strain in the fiber.

While seismometers are currently more sensitive than the proposed fiber optic array, their coverage is sparse and they are expensive to install and maintain. The Stanford researchers believe a seismic observatory based on telecom cable would be relatively inexpensive to operate.

“Every meter of optical fiber in our network acts like a sensor and costs less than a dollar to install,” Biondo Biondi, a professor of geophysics at Stanford, said in a statement.

The researchers hope to develop a seismic network across the Bay Area to demonstrate that such an array can operate on a citywide scale.