A Mysterious Earthquake Sequence Near Buldir Island

March 11, 2026

Heather McFarlin

On March 4 at 8:54 a.m., a magnitude 6.4 earthquake struck the western Aleutian Islands, about 42 miles south of Buldir Island (Figure 1). No one felt it, and there were no reports of damage, landslides, or a tsunami.

But the earthquake still caught our attention.

That’s because it wasn’t the only one.

Since March 1, this remote stretch of the Aleutians has produced a total of 48 earthquakes (Figure 2), with five magnitude 5 earthquakes and 28 magnitude 4 earthquakes (Figure 3). There were almost certainly many more smaller ones that we simply couldn’t detect because of the distance to our nearest stations.

Even more intriguing, three of the magnitude 5 earthquakes happened before the magnitude 6.4 event. That means this isn’t the classic pattern in which a large earthquake happens first, and smaller aftershocks follow.

So what exactly is going on in this not-so-quiet corner of Alaska?

One of the Most Remote Places in the Aleutians

Part of the mystery comes from just how remote this area is. Buldir Island sits between the Rat Islands and the Near Islands, and it is one of the most isolated islands in the entire Aleutian chain (Figure 1). In fact, it is described as being farther from the nearest land than any other Aleutian island. The island itself is tiny, only about 7.5 square miles, and completely uninhabited.

The nearest seismic monitoring equipment isn’t on Buldir at all. Instead, the closest stations are about 100 miles away from this sequence, on Shemya Island, operated by the National Tsunami Warning Center, and on Little Sitkin Island, run by the Alaska Volcano Observatory (Figure 1).

Because there are so few instruments nearby, our view of what’s happening underground is limited. We can confidently detect earthquakes larger than about magnitude 4.0 in this area, but smaller earthquakes may go unnoticed or be difficult to locate precisely.

That means there could be dozens or even hundreds of smaller earthquakes occurring that never make it into the catalog. Without those smaller events, we are missing important pieces of the puzzle.

A Different Kind of Fault Motion

Even with limited data, we do know a few important things.

The earthquakes are shallow, occurring within about the upper 25 miles of the Earth’s crust. They also show strike-slip motion, where blocks of crust slide horizontally past one another, similar to the motion along Alaska’s Denali Fault.

That might sound surprising, because these earthquakes occur near the Alaska–Aleutian megathrust, where the Pacific Plate normally dives beneath the North American Plate.

But in the far western Aleutians, the motion between the plates begins to change direction. Instead of pushing directly beneath North America, the Pacific Plate moves more parallel to it. As a result, the stress in the crust shifts from mostly squeezing to more sideways sliding, producing the strike-slip earthquakes we’re seeing here.

Foreshocks Before the Main Event?

Another interesting clue is the timing of the earthquakes. Several magnitude 5 events happened before the magnitude 6.4 earthquake. That pattern suggests they may have been foreshocks, followed by the larger mainshock and the aftershocks that continue today.

However, because so many smaller earthquakes likely went undetected, we can’t say exactly when the sequence began or how large the aftershock zone might be. Those smaller earthquakes normally help outline the edges of the fault that slipped during a sequence, but here, much of that information is missing.

Watching From Afar

For now, we will continue monitoring the activity around Buldir Island. The earthquakes pose little risk to people because of the area’s extreme isolation.

Still, the sequence offers a reminder that even in the most remote parts of Alaska, the Earth is constantly moving, and sometimes the most interesting earthquake stories happen where almost no one is around to feel them.

Map of western Aleutian Islands, showing earthquakes as yellow circles, seismic stations as red triangles. The recent earthquakes clustered near Buldir Island are circled in red.

Figure 1. Location of the events in the Buldir Island sequence from the Alaska Earthquake Center interactive map. Buldir Island is labeled. The Rat Islands are to the east, and the Near Islands are to the west. The yellow dots are earthquakes in the last 2 weeks. Red dots are within the last 24 hours (as of March 11, 11:50 am). The dots are sized by magnitude. The red circle surrounds the earthquakes that we consider as part of the Buldir Island sequence. The red triangles represent the nearest seismic stations. To the west is SMY, operated by the National Tsunami Warning Center, and to the right is the Little Sitkin network, a collection of stations on Little Sitkin Island operated by the Alaska Volcano Observatory.

Graph of cumulative number of earthquakes between February 2 and March 11, with a steep increase on March 2. The largest, a magnitude 6.4 is shown as a yellow star, several days after activity increased.

Figure 2. The total number of events so far since March 2. The large yellow star is the largest event, a M6.4 earthquake.

Graph showing earthquake magnitudes (for earthquakes mainly magnitude 3 or above) over time. Activity dramatically increased between March 2 through March 11.

Figure 3. Magnitude-time plot of the earthquakes in this region, south of Buldir Island in the far west Aleutian Islands. The smallest event is a magnitude 2.8. These smaller events cannot be reliably detected, however. The major factor for locating smaller events is the distance of an event from the closest seismic stations in the area.

Map of Alaska showing historical earthquake activity in Alaska. The plate boundary is shown as a black line, Buldir Island is circled in white, and white arrows show the direction of Pacific Plate motion.

Figure 4. How the Pacific Plate interacts with the North American plate depends on the location along the plate boundary. The white arrows show the direction the Pacific Plate is moving. In the central Aleutian Islands, the Pacific Plate moves nearly directly at the North American Plate, so it is forced underneath, causing subduction zone earthquakes. Near Buldir Island, however, the Pacific Plate moves horizontally past the North American Plate, causing strike-slip earthquakes.