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

A 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.
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