A magnitude 7.5 earthquake struck north-eastern Japan on Monday, renewing fears about the potential arrival of the “Big One”—a catastrophic quake capable of causing widespread destruction.
Japan experiences around 1,500 earthquakes yearly due to its position on the Pacific “Ring of Fire.” Most are minor, but the 2011 Tōhoku earthquake, which measured magnitude 9.0 and triggered a deadly tsunami, remains a sobering reminder of the country’s vulnerability.
Experts have long warned about the Nankai Trough, a 600-kilometre fault line along Japan’s southern Pacific coast. Historical records show it releases “megathrust” earthquakes roughly every 100 years, often in pairs, with the last recorded in 1944 and 1946. Authorities estimate a 60 to 90% chance that a megaquake will strike here within 30 years.
In April, officials warned that such an earthquake could generate tsunamis over 20 metres high, threatening Tokyo and nearby prefectures, with a possible death toll of hundreds of thousands and economic damage reaching trillions of yen.
After Monday’s quake, residents in seven prefectures from Hokkaido to Chiba were urged to stay alert, review evacuation plans, and prepare emergency supplies. No evacuation orders were issued, with the Japan Meteorological Agency stating the chance of a larger quake remains a possibility, not a certainty—estimated at about one in 100.
Predicting earthquakes remains scientifically impossible. Robert Geller, emeritus professor of seismology at the University of Tokyo, described quake warnings as “not a useful piece of information,” explaining that it is impossible to distinguish foreshocks from aftershocks beforehand. Only 5% of earthquakes are foreshocks, although the 2011 disaster was preceded by a significant but largely ignored foreshock.
Japan’s early warning system, introduced after the 2011 catastrophe and first used in 2024, advises preparedness but does not predict exact events.