Magnitude 1.1 - 5 miles N of Mt. Ugashik

Tectonic Setting of the Alaska Peninsula

Seismicity in the Alaska Peninsula region is produced by different tectonic features: (1) The Aleutian megathrust is the source of the strongest earthquakes in the region, such as the 1938 M8.3 earthquake southwest of Kodiak Island. These earthquakes are capable of producing damaging tsunamis, as was documented in historical records of Russian settlers and in recently discovered paleo-tsunami deposits. (2) Intermediate depth seismicity (below 20 miles) occurs in the so-called Wadati-Benioff Zone, where the subducting Pacific Plate descends towards the mantle beneath the North American Plate. This zone extends along Aleutian Arc, Alaska Peninsula and Cook Inlet. In the Alaska Peninsula region, the seismicity abates at approximately 150 miles depth, reflecting the down-dip extension of the Pacific Plate. The Aleutian-Alaska Benioff zone produces thousands of earthquakes each year, most of which are too deep and too small to be felt. The most notable examples of such earthquakes are the 1999 M7.0 and 2001 M6.9 Kodiak Island events. Both events caused damage and disruption to the City of Kodiak and other communities on the island. (3) Crustal seismicity in this region can be attributed to the Kodiak Shelf Fault Zone and to the volcanic arc. In 1912, a series of M7+ earthquakes was associated with the Novarupta eruption, which was the largest eruption of the 20th Century worldwide.