Beginning in April, a series of earthquakes has rattled Port Heiden and surrounding areas more often than usual.

"If we look back over the past 15 years or so at earthquake activity in the area of Port Heiden that's shallow in the earth, what we can say is that the vast majority of those, meaning more than half of them, have occurred thus far in 2016," said Michael West, state seismologist with the Alaska Earthquake Center.

"Sometimes a fault will rupture in a single significant earthquake," West explained. "But other times faults will rupture in a lot of smaller earthquakes. And we call those earthquakes a swarm, or you can think of it as like a little cluster of earthquakes that, added together, might be sort of equivalent to a single, larger earthquake."

This swarm, West said, began abruptly on April 2 this year, with an earthquake that had a magnitude of 6.2.

"Following that, there was a rather normal, expected sequence of aftershocks. That is hundreds of smaller earthquakes, maybe magnitude-3s, a few magnitude-4s in response, in response to that earthquake. But the earthquakes in that area have continued over the recent months and kind of peaked again in the summer and are continuing on into today, though at a somewhat lesser rate than in the summer."

The area affected by the swarm includes the Aniakchak National Monument and Preserve, home to the Aniakchak Volcano, a stratovolcano that is seismically monitored by the Alaska Volcano Observatory.

Sometimes swarms stop abruptly, West noted, but more often they fade away.

And while the earthquakes in the Port Heiden area seem to have been decreasing since August, it's also possible that they could pick up again. Seismic activity is difficult to predict.