Akhiok M5.3 | Alaska Earthquake Center

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. Recent examples include the M7.8 Simeonof earthquake in 2020 beneath the Shumagin Islands and the M8.2 Chignik earthquake in 2021 southwest of Kodiak Island. While these recent earthquakes did not produce damaging tsunamis, previous tsunamis have been documented in historical records of Russian communities and in recently discovered paleo-tsunami deposits. (2) Intermediate depth seismicity (below 20 miles/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 decreases at a depth of about 150 miles (241 km), reflecting the downdip extension of the Pacific Plate. The Aleutian-Alaska-Wadati-Benioff Zone produces thousands of earthquakes each year, most of which are too deep and small to be felt. The most notable examples of such earthquakes are the M7.0 events in 1999 and M6.9 on Kodiak Island in 2001. Both earthquakes caused damage and disruption in the town of Kodiak and other communities on the island. (3) Crustal seismicity in this region can be attributed to the Kodiak Shelf Fault Zone and the volcanic arc. In 1912, a series of M7+ earthquakes were associated with the Novarupta eruption, which was the world’s largest volcanic eruption of the 20th century.