Two earthquakes of magnitude 7.0 or greater struck within days of each other in Alaska and Japan, raising concerns that another big one could be on the way.
The first earthquake occurred in Alaska on December 6 with a magnitude of 7.0, a large earthquake capable of producing serious damage if it did not occur in such a remote area near the Canadian border. The second, a 7.6 mega-earthquake, struck northern Japan on December 8, prompting tsunami warnings that were later lifted and causing at least 30 injuries. Tens of thousands evacuated their homes.
Aftershocks were recorded for both earthquakes. On December 8, Japanese authorities warned that an even stronger earthquake could strike in the next week and asked residents from the northernmost island of Hokkaido to Chiba prefecture, east of Tokyo, to be on high alert.
The earthquakes were remarkable for their strength.
In an average year, the US Geological Survey says about 16 major earthquakes are expected around the world, including 15 with a magnitude of 7.0 or higher and one 8.0 or higher. That’s based on records going back to about 1900. For the last four to five decades, the long-term average number of large earthquakes in a year has been surpassed about a dozen times.
But having two such earthquakes in a short period of time happens from time to time and does not necessarily indicate another impending disaster.
“Not all the time, but not that crazy,” said Brandon Schmandt, a Rice University professor and seismology expert.
It’s a reminder of an uncomfortable truth in earthquake science: Scientists know that disastrous earthquakes are imminent, but they have no reliable way to predict when they will strike.
“No one can predict earthquakes. However, by investigating past faults and earthquakes, scientists can better assess the likelihood of future earthquakes and how intense their shaking may be,” said the USGS.
How strange is it that two big earthquakes hit?
By “pure random chance,” it’s actually not uncommon for two earthquakes with a magnitude of 7.0 or higher to strike this close together in time, according to CalTech seismologist Lucy Jones.
“We average about one magnitude-7.0 a month somewhere in the world,” Jones said.
The average of one a month is randomly distributed, Jones said. We can go several months without one, and then see multiples at close range. Jones said she would estimate based on probabilities that earthquakes of magnitude 7 or higher are likely to occur within half a week of each other once every few years.
“It’s not like it happens all the time, but we’ve looked and we can’t find any physical correlation,” she said.
A vehicle rests at the end of a collapsed road in Tohoku city in Aomori Prefecture on December 9, 2025, following a magnitude 7.5 earthquake in northern Japan. The Dec. 8 earthquake left at least 30 injured, authorities said, damaged roads and left thousands without power in freezing temperatures.
One earthquake can cause another, as in an aftershock, but that is not the relationship between the Alaska and Japan earthquakes, which appear to be completely unrelated, Schmandt said. An aftershock tends to occur in the same geographic area as the main earthquake.
Jones said there is about a 5% chance after any earthquake that another will follow nearby within a few days that is larger in magnitude. Although a 5% chance may not seem like much, it is far greater than the baseline chances, and is what is prompting Japanese authorities to remain on high alert for now, she said.
A recent example happened in 2019 near Ridgecrest, California, Jones noted. A 6.4 hit on the Fourth of July, 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 United States in danger of devastating earthquakes? What about ‘the Big One?’
Most of the United States is at risk of damaging earthquakes in the next century, according to the US Geological Survey, which published a report last year that found hundreds of previously unidentified faults across the country.
People in 37 states have experienced earthquakes with a magnitude of 5.0 or greater in the past two centuries, according to the USGS.
The danger is most concentrated along the West Coast and the southern part of Alaska, where the most active tectonic plate boundaries are found.
Concerns about the so-called “Big One” event, a large earthquake that would cause untold devastation, have been perplexing residents in these areas. It can happen at any time, or not for a long time, experts say. And there may be more than one “Big One.”
The Great: Is California ‘overdue’ for a major devastating earthquake?
Schmandt said the Cascadia Subduction Zone that stretches from northern California up through Oregon and Washington and into Canada has the potential for a lurking event that could be considered “the Big One.” The last known earthquake on this 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 that a 7.1+ magnitude megathrust earthquake in this fault zone will occur in the next 50 years. This event will be felt across the Pacific Northwest,” the department said.
What does the magnitude of earthquakes mean?
According to the Michigan Technological University, the magnitude of earthquakes can have the following effects:
-
Under 2.5: It is usually not felt
-
2.5 to 5.4: Little or no damage
-
5.5 to 6.0: Minor building damage
-
6.1 to 6.9: Serious damage
-
7.0 to 7.9: A big earthquake. Serious damage
-
8.0 or greater: Massive damage, can destroy communities
Contributing: Elizabeth Weise and Terry Collins, USA TODAY; Reuters
This article originally appeared on USA TODAY: Are earthquakes in Alaska, Japan a warning?