Just four seconds after an earthquake starts, scientists may now know how big it will grow — and the secret lies in the same cables that bring high-speed internet into homes and schools.
Researchers from the U.S. Geological Survey (USGS) and Cal Poly Humboldt have developed a new way to estimate earthquake size using fiber-optic cables, the thin glass threads that transmit data across the internet. Their findings, published in the journal Nature Communications, show that the first few seconds of an earthquake's vibrations contain telltale patterns that reveal whether a quake will stay small or grow into something more dangerous.
The work focuses on Northern California's coast, where the continental United States shakes most frequently. The team tested their approach on real earthquake data — ranging from magnitude 3.5 to magnitude 7.1 — and applied it to fiber-optic cables running through Arcata and Eureka. By training a machine-learning system to recognize the differences between smaller and larger earthquake signatures, they achieved accurate size estimates within just four seconds.
"One of the biggest challenges in earthquake early warning is determining how large an earthquake has become as quickly as possible," said USGS geophysicist Theresa Sawi, a coauthor of the study. "This study shows that fiber-optic sensing may help answer that question within seconds."
Traditional earthquake monitoring requires specialized instruments placed at specific locations. Fiber-optic sensing works differently — when seismic waves ripple through the ground, they slightly stretch or compress the cables buried underground, changing how light travels through them. Scientists can measure those tiny changes and detect earthquakes without installing new hardware.
The implications stretch far beyond land. Because fiber-optic cables already snake across the seafloor, connecting continents, this technology could bring earthquake and tsunami warnings to coastal communities that are currently hard to monitor. Offshore sensors are expensive and difficult to maintain, but existing underwater cables could serve double duty.
For Connie Stewart, study coauthor and executive director of University Initiatives at Cal Poly Humboldt, the research highlights an unexpected benefit of public infrastructure investment. "Expanding broadband infrastructure creates opportunities far beyond internet access," Stewart said. "This study demonstrates how investments in fiber-optic networks can also advance scientific discovery and, ultimately, help build safer, more resilient communities."
Earthquake early warning systems already send alerts to phones and apps, giving people seconds to drop, cover, and hold on. Faster, more accurate size estimates would help emergency managers decide whether to slow trains, shut off gas lines, or warn communities about potential tsunamis — actions that could save lives when seconds matter most.