Japan Wires the Ocean with an Earthquake-Sensing ‘Nervous System’
Japan’s new earthquake-detection network lengthens warning times, and researchers in Wales have harnessed nuclear blast detectors to gauge tsunami risks. But the U.S. lags in monitoring the massive Cascadia megathrust fault
Aerial view of the devastated along the north eastern coast of Japan following a massive earthquake and tsunami March 25, 2011.
If the ocean floor had a nervous system, it might look something like this: thousands of miles of fiber-optic cables connected to sensors set atop the fault lines where Japan’s earthquakes begin. Completed in June, this system aims to stave off devastation like that of 2011—when a relentless six-minute-long temblor was followed by a 130-foot tsunami that reached speeds of 435 miles per hour and pounded cities into rubble. Delayed alerts gave some communities less than 10 minutes to evacuate and only warned of much smaller waves, based on inaccurate earthquake readings. Nearly 20,000 people died, with thousands more injured or missing. Reactor meltdowns at the flooded Fukushima Daiichi nuclear power plant irradiated the surrounding land and spilled radioactive water into the ocean.
The undersea, magnitude 9.0 “megathrust” earthquake—the worst in Japan’s recorded history—began in the Pacific seafloor 45 miles off the country’s eastern coast. Land-based sensors detected its first shock waves but couldn’t immediately provide clear readings of its magnitude or that of the tsunami it created. Mere months later, Japan began expanding its earthquake-detection system to cover the ocean floor. With the system’s completion last month, Japan has become the first country to achieve direct, real-time monitoring of entire subduction zones—adding minutes and seconds to evacuate people and brace crucial infrastructure for impact.
If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
Within months of the 2011 earthquake, the Japanese government began to build S-net (Seafloor Observation Network for Earthquakes and Tsunamis). S-net wired the nation’s earthquake-detection network to the Japan Trench, the seismologically active offshore region where the 2011 earthquake began. Roughly 3,540 miles of cable now zigzag across 116,000 square miles of ocean to connect 150 observatories on the ocean floor. Each contains 14 distinct sensing channels, including seismometers and accelerometers, as well as pressure gauges to measure waves passing overhead. This network—the first part of the larger network that was completed in June 2025—was finished in 2017. When a magnitude 6.0 quake struck the following year, alerts reached the cities before the first jolt hit—a full 20 seconds before the nearest land seismometer rang its alarm—allowing precious time to slow bullet trains and broadcast warnings.
N-net technicians will spend the coming months calibrating instruments and folding their feeds into a single monitoring backbone that includes Japan’s approximately 6,000 land-based sensors. But the hardest part is done: installing armored fiber-optic cables and observatories along the abyssal plain from ships and “plowing” shallow seabed areas to bury cables and protect them from anchors and fishing gear. Underwater robots helped out in deeper waters and will now service the observatories and replace parts.
The completion of Japan’s network coincides with that of another tsunami-detection program at Cardiff University in Wales. GREAT (Global Real-Time Early Assessment of Tsunamis) came online in June and streams data from four of the 11 hydroacoustic ocean stations created for the Comprehensive Nuclear-Test-Ban Treaty Organization. Built to listen for clandestine nuclear bomb blasts, the globe-spanning system detects low-frequency acoustic-gravity waves. These pressure pulses sprint through seawater at roughly 3,355 miles per hour—more than 10 times faster than a tsunami’s leading edge. Researchers at Cardiff University use machine-learning algorithms to interpret the hydrophone signals. Within seconds, the system estimates earthquake magnitude, fault slip type, and tsunami potential and sends out alerts, though researchers estimate that a total of two dozen hydrophone sites would be required to make coverage global.
Deni Ellis Béchard is Scientific American’s senior tech reporter. He is author of 10 books and has received a Commonwealth Writers’ Prize, a Midwest Book Award and a Nautilus Book Award for investigative journalism. He holds two master’s degrees in literature, as well as a master’s degree in biology from Harvard University. His most recent novel, We Are Dreams in the Eternal Machine, explores the ways that artificial intelligence could transform humanity. You can follow him on X, Instagram and Bluesky @denibechard.
Source: www.scientificamerican.com