Two earthquakes of magnitude 7.0 or greater struck within days of each other in Alaska and Japan, raising concerns that another big quake could be on the way.
The first earthquake occurred in Alaska on December 6 with a magnitude of 7.0, a major earthquake capable of causing serious damage if it had not happened in such a remote area near the Canadian border. The second, a 7.6-magnitude earthquake, struck northern Japan on December 8, prompting tsunami warnings that were later lifted and injuring at least 30. Tens of thousands evacuated their homes.
Aftershocks were recorded for both earthquakes. On December 8, Japanese authorities warned that an even stronger earthquake could occur in the coming week and asked residents from the northernmost island of Hokkaido to Chiba prefecture, east of Tokyo, to be on high alert.
The earthquakes were notable for their power.
In an average year, the US Geological Survey says about 16 major earthquakes are expected worldwide, including 15 with a magnitude of 7.0 or greater and one of 8.0 or greater. This is based on records dating back to about 1900. In the past four to five decades, the long-term average number of major earthquakes in a year has been exceeded by about a dozen times.
But having two such earthquakes in a short period of time happens from time to time and does not necessarily signal another impending disaster.
“It’s not all the time, but it’s 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 disastrous earthquakes are coming, but they have no reliable way to predict when they’ll 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 might be,” the USGS said.
How strange is it for two large earthquakes to strike?
By “pure random chance,” it’s actually not unusual for two earthquakes of magnitude 7.0 or greater to strike so close together in time, according to CalTech seismologist Lucy Jones.
“We average about a magnitude-7.0 a month somewhere in the world,” Jones said.
The average of one per month is randomly distributed, Jones said. We might go a few months without one and then see more in a short span. Jones said he would estimate based on probabilities that earthquakes of magnitude 7 or greater are likely to occur within half a week of each other once every few years.
“It doesn’t happen all the time, but I looked and found no physical correlation,” she said.
A vehicle rests on the side of a collapsed road in the city of Tohoku in Aomori Prefecture on December 9, 2025, following a magnitude 7.5 earthquake off northern Japan. The Dec. 8 quake injured at least 30, authorities said, damaged roads and left thousands without power in freezing temperatures.
One earthquake can trigger another, as in an aftershock, but that’s not the relationship between the Alaska and Japan earthquakes, which appear to be unrelated, Schmandt said. Aftershocks tend to occur in the same geographic area as the main earthquake.
Jones said there is about a 5 percent chance after any earthquake that another earthquake of greater magnitude will strike nearby within days. While a 5 percent chance might not seem like much, it’s much higher than the baseline chance and is what prompts Japanese authorities to remain on high alert for now, she said.
A recent example happened in 2019 near Ridgecrest, California, Jones noted. A magnitude 6.4 shock on July 4th and less intense aftershocks followed. Then, a day later, a 7.1 earthquake became the largest to hit Southern California in 20 years.
Is the US at risk of devastating earthquakes? How 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 released a report last year that found hundreds of previously unidentified faults across the country.
People in 37 states have experienced earthquakes of magnitude 5.0 or greater in the past two centuries, according to the USGS.
The danger is most concentrated along the West Coast and southern Alaska, where the most active tectonic plate boundaries are found.
Concerns about a so-called “Big One” event, a massive earthquake that brought untold devastation, have long rattled residents of these areas. It could happen anytime, or not for long, experts say. And there could be more than one “Big One”.
The Great One: Is California ‘Overdue’ for a Major Devastating Earthquake?
Schmandt said the Cascadia Subduction Zone, which stretches from Northern California to Oregon and Washington and into Canada, has the potential for an 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.
“Scientists currently predict that there is about a 37 percent chance that a magnitude 7.1+ earthquake will occur on this fault zone in the next 50 years. This event will be felt in the Pacific Northwest,” the department said.
What does earthquake magnitude mean?
According to Michigan Technological University, earthquake magnitude can have the following effects:
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Under 2.5: In general, it is not felt
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2.5 to 5.4: Minor or no damage
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5.5 to 6.0: Light damage to buildings
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6.1 to 6.9: Serious damage
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7.0 to 7.9: Major earthquake. Serious damage
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8.0 or higher: 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 and Japan a warning?