Tectonic position of the Aleutian Islands

The Aleutian Arc marks the region where the Pacific Plate subducts into the mantle beneath the North American Plate. It is a seismically active region, as evidenced by thousands of earthquakes each year. Since 1900, this region has experienced several large megathrust earthquakes, including the 1957 M8.6 Andreanof Islands earthquake, the 1965 M8.7 Rat Islands earthquake, the 1986 and 1996 M7.9 Andreanof Islands earthquake, and the 2003 M7.8 Rat Islands earthquake. Together, they have ruptured the entire length of the megathrust boundary in this region. Another notable seismic source in the arc is the 10–15 km wide zone of intermediate-depth earthquakes within the subducting Pacific Plate known as the Wadati-Benioff Zone. The largest recorded intermediate-depth earthquake in this region was the magnitude 7.9 Little Sitkin event in 2014. A third source of seismic activity in this region is shallow earthquakes associated with volcanic processes and crustal ruptures within the overlying North American Plate. They occur regularly and can produce violent aftershocks or swarm-like sequences.