Four quakes off Nikolski, largest magnitude 5.3; no tsunami danger

Four earthquakes were recorded offshore southwest of Nikolski late Monday, the largest at magnitude 5.3, and the National Tsunami Warning Center said there was no tsunami danger. No one has reported feeling them.

The warning center issued an information statement eight minutes after the largest quake, giving its preliminary magnitude as 5.1 and its location as 45 miles southwest of Nikolski. "There is NO tsunami danger from this earthquake," the statement said.

The Alaska Earthquake Center said it reviewed the largest event, which it put at magnitude 5.2 and which occurred at 10:44 p.m. AK time Monday, 58 miles south-southwest of Nikolski. "No felt reports have been received at this time," the center said in a post on its official account. The U.S. Geological Survey's reviewed catalog lists the same event at magnitude 5.3 and a depth of 26 kilometers, under the identifier us7000tdab.

The three other events came within an hour of the largest. The reviewed catalog lists a magnitude 3.7 at 10:52 p.m., a 4.5 at 11:05 p.m. and a 4.5 at 11:45 p.m., at depths of 26, 42 and 38 kilometers. Automated USGS and EMSC feeds published before seismologists reviewed the events carried different figures.

Nikolski sits on Umnak Island, in the Fox Islands group of the Aleutian chain. The offshore ground under it moves often. The cause is the same one that built the islands. The Pacific plate is grinding beneath the North American plate along the Aleutian arc, a 3,000-kilometer boundary the USGS says produces both the Aleutian Islands and the deep offshore trench. Frequent quakes there do not automatically mean a tsunami threat.

Reviewed magnitudes and depths are posted at earthquake.alaska.edu, and residents who feel shaking can file a report through the USGS "Did You Feel It?" page.