Magnitude 6.3 quake off Nikolski sets off dozens of Aleutian aftershocks

A magnitude 6.3 earthquake hit the seafloor south of Nikolski in the central Aleutians early Thursday, setting off dozens of aftershocks that rattled the area into Friday morning. No tsunami was triggered, and no damage was expected.

The quake struck offshore in a sparsely populated stretch of the island chain, at 3:17 a.m. Alaska time, deep beneath the seabed. Federal tsunami centers found no threat to Aleutian communities, and the U.S. Geological Survey put the quake at the lowest rung of its damage scale — no expected deaths and minimal economic loss, with only weak shaking reaching the few thousand people in range.

What followed was a busy sequence. The USGS logged more than 80 aftershocks through Friday morning, 15 of them magnitude 4 or larger, with 11 hitting in the first hour alone. The strongest aftershock reached magnitude 5.5. All of it clustered along the same offshore stretch of the Aleutian arc, the chain running west from the Alaska Peninsula.

Nikolski sits on Umnak Island, which has no active volcano nearby. Two Aleutian volcanoes are stirring elsewhere — Great Sitkin, slowly erupting lava, and Shishaldin — but both are hundreds of kilometers from this earthquake sequence.