A magnitude-6.2 earthquake struck Wednesday night about 50 miles from Adak.
"To give you an idea of how large that is, you get only about 100 magnitude-6 earthquakes on the globe annually," said seismologist Ken MacPherson of the Alaska Earthquake Center. "So that's a fairly significant earthquake."
Adak residents felt the shallow earthquake, which followed a series of smaller quakes in the same area.
MacPherson also said there have been dozens of aftershocks.