Tectonic position of the Alaska Peninsula

Seismicity in the Alaska Peninsula region is caused by several tectonic features: (1) The Aleutian megathrust is the source of the strongest earthquakes in the region. The most recent examples are the 2020 magnitude 7.8 Simeonof earthquake beneath the Shumagin Islands and the 2021 magnitude 8.2 Chignik earthquake southwest of Kodiak Island. While these recent earthquakes did not produce destructive tsunamis, previous tsunamis have been documented in historical records from Russian communities and in recently discovered paleotsunami deposits. (2) Intermediate depth seismicity (below 32 km) occurs in the Wadati-Benioff zone, where the subducting Pacific Plate is sinking toward the mantle beneath the North American Plate. This zone extends along the Aleutian Arc, the Alaska Peninsula, and Cook Inlet. In the Alaska Peninsula region, seismicity subsides at a depth of about 241 km, reflecting the downward extension of the Pacific Plate. The Wadati-Benioff Zone between the Aleutian Islands and Alaska experiences thousands of earthquakes each year, most of which are too deep and weak to be felt. The best-known examples of such earthquakes are the magnitude 7.0 earthquakes in 1999 and the magnitude 6.9 on Kodiak Island in 2001. Both earthquakes caused damage and disruption to the city of Kodiak and other communities on the island. (3) Seismic activity in the Earth's crust in this region can be attributed to the Kodiak Shelf Fault Zone and the volcanic arc. In 1912, a series of magnitude 7+ earthquakes were associated with the eruption of Novarupta, the world's largest volcanic eruption of the 20th century.