Here’s What to Know About Japan’s Mega Quake Advisory

Japan’s government says that the chances of a magnitude 8 earthquake have increased. Scientists can’t predict when one will strike, but it represents a meaningful jump over typical odds.A vehicle teetered on a collapsed road in Tohoku Town off the coast of northern Japan.Credit...Jiji Press, via Agence France-Presse — Getty ImagesDec. 11, 2025Updated 3:27 p.m. ETA powerful earthquake that jolted Japan’s northern coast on Monday prompted the government to issue a rare advisory that the chance of a far larger and more destructive earthquake in the next week had increased.While scientists can’t predict when, or whether, one will strike, the chance of a so-called mega quake occurring in the following week rose to 1 percent. That may seem small, but it represents a meaningful jump over typical odds.The government uses the term to refer to any quake stronger than 8 on the Richter scale. To put that number into perspective, an earthquake that powerful is about 32 times stronger than a 7.That’s why officials treat even a 1 percent chance very seriously.Here’s what the advisory means:The advisory indicates an increase in the chance of a larger quake.Scientists review historical data any time an earthquake stronger than a 7 strikes. That’s what happened on Monday, when a magnitude 7.6 rattled the area near Aomori Prefecture in northern Japan on Monday.The government issued the advisory because there is a “more likely than normal” chance for a magnitude 8 to strike in the next week, said Fumiaki Tomita, a professor at the International Research Institute of Disaster Science at Tohoku University.The chance of that happening in the following seven days is now 1 in 100, based on historical global earthquake data, according to the meteorological agency. The agency issued its first mega quake advisory in 2024, which expired seven days after without a more powerful quake having occurred.The government points to a series of quakes in March 2011 and other historical data, as evidence that powerful ones can follow each other. On March 11 of that year, a 9.1 magnitude earthquake devastated the country’s northeast coast, triggering a tsunami that killed more than 19,000 people. Two days earlier, a less powerful quake had rocked the region.While 1 percent is low, it is roughly 10 times higher than the usual likelihood of a magnitude 8 earthquake in the region, said Takuya Nishimura, a professor at Kyoto University’s Disaster Prevention Research Institute. The advisory covers an area from northern Japan all the way down to near Tokyo.The advisory neither restricts daily activities nor requires people to evacuate, but urges people to be prepared.Monday’s quake caused buildings and bridges to sway and injured more than 30 people, according to local media. There were no reports of deaths or major damage.Japan’s geology makes major earthquakes inevitable.Japan’s location along the Pacific “Ring of Fire,” a chain of seismologically active faults encircling the Pacific Ocean, makes it one of the world’s most earthquake-prone countries. The nation experiences around 1,500 earthquakes a year, or up to three a day, according to the University of Tokyo.Japan has a long history of devastating mega quakes, including the one in March 2011, which was the strongest in the nation’s history. In 2003, an 8-magnitude earthquake struck about 50 miles off the southeastern coast of Hokkaido, Japan’s northernmost main island, cutting power to tens of thousands.“The fear of large earthquakes in Japan is a reality,” says Meghan S. Miller, a professor at the Research School of Earth Sciences at Australian National University.The megaquake advisory system was introduced in 2022, according to experts and local media.Japan is a global leader in earthquake warnings.Although scientists cannot precisely predict the time, location and magnitude of an earthquake, Japan has one of the world’s most advanced early warning systems, Professor Miller said.The government operates hundreds of seismometers across land and water. When an earthquake occurs, instruments detect its primary wave within seconds, allowing the authorities to issue alerts quickly.If the instruments record shaking at a seismic intensity of 3 or higher on Japan’s 10-level scale, the meteorological agency releases a Seismic Intensity Information report within 90 seconds.Other nations with advanced earthquake-preparedness systems include Chile, which revised its building codes after a the 7.8-magnitude earthquake in Valparaíso in 1985, and Mexico, which has repeatedly strengthened its codes in recent decades and is now considered among the world’s most advanced. In Japan, building codes were tightened in 1981 and in 2000 to increase safety and increase responsibility for builders.Jin Yu Young is a reporter and researcher for The Times, based in Seoul, covering South Korea and international breaking news.SKIP