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In a few days, 2 big earthquakes happened. Is this a warning?

Two earthquakes of magnitude 7.0 or greater struck in Alaska and Japan within days of each other, raising concerns that another big one could be on the way.

The first earthquake hit Alaska on December 6 with a magnitude of 7.0, a major earthquake capable of producing severe damage if it had not occurred in a remote area near the Canadian border. A second, 7.6 mega-earthquake struck northern Japan on December 8, prompting a tsunami warning that was later lifted and injuring at least 30 people. Tens of thousands have left their homes.

Aftershocks from both earthquakes have been recorded. On December 8, Japanese authorities warned of more powerful earthquakes within the next week and called on residents of Chiba Prefecture, east of Tokyo from the northern island of Hokkaido, to be on high alert.

Earthquakes were notable for their power.

In an average year, the U.S. Geological Survey expects about 16 major earthquakes worldwide, including 15 of magnitude 7.0 or greater and one of magnitude 8.0 or greater. That’s based on records from about 1900 years ago. Over the last four to five decades, the long-term average number of major earthquakes in a year has exceeded a dozen times.

But two such earthquakes occur from time to time within a short period and do not signal another impending disaster.

“It’s not all the time, but it’s not crazy,” said Rice University professor and seismologist Brandon Schmand.

It’s a reminder of an uncomfortable truth in seismology: Scientists know catastrophic earthquakes are coming, but they have no reliable way to predict when they’ll hit.

“No one can predict earthquakes. However, by researching faults and past earthquakes, scientists can better assess the likelihood of future earthquakes and how intense their tremors may be,” the USGS said.

How strange is it to have two major earthquakes?

By “pure random chance,” according to CalTech seismologist Lucy Jones, it’s not uncommon for two earthquakes of magnitude 7.0 or greater to occur together in time.

“We’re averaging about a magnitude-7.0 per month somewhere in the world,” Jones said.

An average of one per month is randomly distributed, Jones said. We may go several months without one, and then see more within the near term. Jones said she would estimate based on probability that a pair of magnitude-7 or higher earthquakes would occur within half a week of each other about once every few years.

“It’s not always the case, but we looked and couldn’t find any physical connection,” she said.

A vehicle sits on the side of a damaged road in Tohoku city, Aomori Prefecture on December 9, 2025, after a magnitude 7.5 earthquake hit northern Japan. Officials said at least 30 people were injured in the Dec. 8 quake, which damaged roads and left thousands without power in frigid temperatures.

One earthquake can trigger another, as in an aftershock, but that’s not the connection between the Alaska and Japan earthquakes, which appear to be completely unrelated, Schmand said. Aftershocks occur in the same geographical area as the main earthquake.

Jones said that after any earthquake there is a 5% chance that another one that is larger in magnitude will follow within a few days. While a 5% chance may not seem like much, it’s much larger than the baseline odds, and it’s prompting Japanese officials to remain on high alert for now, she said.

A recent example occurred in 2019 near Ridgecrest, California, Jones noted. A magnitude 6.4 shock struck on the Fourth of July and was followed by less intense aftershocks. Then, a day later, a 7.1 earthquake became the largest to hit Southern California in 20 years.

Is the US at risk of catastrophic earthquakes? What about the ‘big one’?

Much of the United States is at risk of earthquake damage within the next century, according to the US Geological Survey, which published a report last year that found hundreds of previously unknown faults around the country.

According to the USGS, people in 37 states have experienced earthquakes of magnitude 5.0 or greater in the past two centuries.

The threat is most concentrated on the West Coast and southern Alaska, where the most active tectonic plate boundaries are found.

Concerns of a so-called “Big One” event, a large earthquake that would cause untold destruction, have long haunted residents of these regions. It can happen at any time, or for a long time, experts say. And there can be more than one “big one”.

The big one: Is California ‘Overdue’ for a Destructive Major Earthquake?

Schmandt said the Cascadia subduction zone, which stretches from northern California through Oregon and Washington to Canada, has the potential for a subduction event that could be considered a “big one.” The last known earthquake on the fault occurred in January 1700, with an estimated magnitude of 9.0, according to the Oregon Department of Emergency Management.

“Currently, scientists are predicting that there is about a 37% chance of a 7.1+ magnitude megathrust earthquake occurring on this fault zone within 50 years. This event will be felt in the Pacific Northwest,” the department said.