Magnitude 4.3 - 31 miles SE of Nikolski

September 23, 2021 14:41:08 AKDT (September 23, 2021 22:41:08 UTC)
52.6858°N 168.2654°W Depth 13.5 miles (21 km)

No reports of this event being felt have been received at this time.

This event has been reviewed by a seismologist

34 miles (55 km) S of Mt. Recheshnoi
35 miles (56 km) SE of Mt. Vsevidof
52 miles (84 km) S of Okmok Caldera
64 miles (103 km) E of Kagamil Island
68 miles (110 km) E of Uliaga Island
71 miles (115 km) E of Mt. Cleveland
76 miles (123 km) E of Carlisle Island
78 miles (126 km) E of Herbert Island
87 miles (141 km) S of Bogoslof Island
100 miles (162 km) SW of Makushin Volcano
102 miles (165 km) E of Yunaska Island
110 miles (178 km) SW of Dutch

Magnitude type: M_l²
Event type: earthquake

Tectonic Setting of the Aleutian Islands

The world's largest earthquakes originate along convergent plate boundaries such as the Aleutian megathrust. Starting in 1938, a series of three great earthquakes ruptured the subduction zone along its entire length from the Alaska Peninsula to the western Aleutians with the exception of a small gap near the Shumagin Islands. The sequence began with a M8.2 earthquake southwest of Kodiak Island. A M8.6 in the Andreanof Islands followed in 1957, and the sequence concluded with the Rat Islands M8.7 in 1965. The Shumagin Gap still has not ruptured, but GPS observations suggest that little strain has built up in this region.

Another notable source of seismicity in the arc are the intermediate depth earthquakes within the subducting Pacific Plate, known as the Wadati-Benioff zone. The largest recorded earthquake of this kind was the 2014 M7.9 Little Sitkin event. Shallow earthquakes associated with volcano processes and crustal faults within the overriding North American plate occur regularly and may produce vigorous aftershock or swarm-like sequences.