Zhongwen Zhan met me at Caltech on a crisp December morning in December of 2022, the quiet hum of the Athenaeum’s halls a stark contrast to the work that occupied his mind. We made photographs beneath its grand arches before heading to his lab in Caltech’s Seismological Laboratory, a space where the earth’s tremors, usually imperceptible, were made visible.
There, surrounded by monitors pulsing with data, Zhan explained something remarkable: the wiring that already snakes beneath our cities, fiber-optic cables, power lines, communications networks, could be repurposed into a vast, untapped network of seismic sensors. Every vibration, every subtle shift in the ground, left a signature in these circuits, waiting to be decoded. With the right analysis, this infrastructure, built not for science but for utility, could be transformed into an immense listening device, capable of detecting earthquakes, landslides, even ocean waves crashing against the shore.
To demonstrate, he pulled up a live feed. The screen flickered, resolving into a slow, undulating pattern. At first glance, it was meaningless, just noise in the system. But Zhan pointed, tracing his finger along a particular rhythm, a spike here, a dip there. It wasn’t an earthquake, it was Pasadena’s morning traffic. The vibrations of cars, the low-frequency rumble of trucks, even the occasional weight of a pedestrian, all of it registered in the city’s electrical grid, like an invisible sonar of human movement.
It was an astonishing concept, the kind of insight that transforms an entire field. Traditional seismic monitoring depends on expensive, isolated stations placed in key locations, but Zhan’s work suggested that the world was already wired for observation, that our built environment could double as a planetary-scale sensor array. The implications stretched far beyond Pasadena: a system like this could revolutionize earthquake early warning, bringing real-time seismic monitoring to places that lacked conventional instruments.
Zhan’s eyes gleamed with quiet enthusiasm as he described the next steps, expanding the method, refining the models, uncovering what other hidden signals lay buried in the infrastructure we take for granted. It was a reminder that discovery is often not about building something new, but about seeing what has been there all along, unnoticed and waiting.
As we wrapped up, I glanced again at the screen, watching as a fresh wave of data rippled across it, cars passing unseen through the streets of Pasadena, their presence recorded in pulses of light and wire. The city was speaking. And in Zhan’s lab, for the first time, it was being heard.
