Seismologists are monitoring an earthquake swarm that continues to develop off Alaska’s Aleutian island chain and includes several stronger quakes.

According to the US Geological Survey (USGS), the first magnitude 6.3 earthquake struck just before 11 a.m. local time on Sunday in the Pacific Ocean about 70 miles southwest of Adak, Alaska, at a depth of about 11 miles. At least six aftershocks with a maximum magnitude of 5.8 were recorded within an hour.

Then, a few hours later, two more major quakes of magnitude 6 or higher occurred within 20 minutes. According to the Alaska Earthquake Center at the University of Alaska Fairbanks, this is not a typical aftershock sequence after a mainshock, but rather a swarm or collection of earthquakes close to the same magnitude.

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“Swarms of moderate earthquakes are common in the Aleutian Islands and do not necessarily indicate anything more significant,” said Michael West, director of the Alaska Earthquake Center and state seismologist. “Because this area has been affected by or has been on the verge of numerous large historic earthquakes, we are keeping a close eye on it.”

This map from the Alaska Earthquake Center shows earthquakes recorded between December 4 and 8, 2024, including the swarm southwest of Adak Island on December 8 in red.

(Alaska Earthquake Center)

The earthquake center said its seismologists are continuing to monitor the region due to the “unusually high number” of moderate earthquakes. Additional aftershocks of magnitude 5 and below are forecast to occur in the coming weeks.

On Monday, the USGS recorded several more quakes off the coast of Adak.

No tsunami warnings or warnings were issued due to the weekend earthquakes.

In the Aleutian Islands, the Pacific Plate is subducting into the Earth’s mantle beneath the North American Plate. This region is considered seismically active and thousands of earthquakes occur every year.