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In early May, over the span of two days, a swarm of more than 50 earthquakes occurred in the Fox Islands region in the Aleutians. Most of the earthquakes were small, with a few larger events measuring over magnitude 5 southwest of Umnak Island.
Similar earthquake swarms have periodically occurred in nearly the exact same location for the past 50 years, but scientists are still figuring out what causes them.
“This swarm, and the similar ones in previous decades, suggests that there’s just something interesting or different about the physics of the fault at that particular location,” said Stephen Holtkamp, a data analyst with the Alaska Earthquake Center.
The Alaska Earthquake Center shared a story in May showcasing the swarm. Scientists are theorizing what could be causing the swarms in this area, but Holtkamp said he doesn’t want to jump to conclusions just yet.
The Aleutian Islands are prone to earthquakes. Two of the earth’s tectonic plates collide in the area, creating the Alaska Aleutian megathrust fault, commonly known as the Aleutian Trench.
When plates slip, earthquakes typically have a mainshock followed by aftershocks. But swarms consist of a cluster of quakes with no distinct mainshock. There could be several reasons for why a mainshock is triggered, according to Holtkamp.
He said it can be particularly challenging to detect the cause of swarms in the Aleutians since the fault stretches over a thousand miles. One cause of swarms, for example, could be magma moving within a volcano, which could signal it’s active.
“Each time a swarm occurs, it’s a bit of a mystery to solve, you know,” he said. “Is it near a volcano? Is it related to slow slip? Is it some other process that we need to think about? But something is causing them.”
Holtkamp said the strength of the earthquakes can vary drastically in the region depending on how tightly locked the plates are. He said understanding the cause of these swarms could help improve knowledge of seismic hazards in the region.