The tectonic setting in Southern Alaska leads to a variety of earthquakes in Southcentral Alaska influenced by different geological features. The most powerful earthquakes in this region are associated with the megathrust fault that lies between the subducting Pacific Plate and the overriding North American Plate. Notably, the 1964 M9.2 Great Alaska Earthquake, recorded as the second most powerful earthquake globally, originated from the area under Prince William Sound.
Seismic activity at intermediate depths, specifically below 20 miles (32 km), occurs in the Wadati-Benioff Zone, where the Pacific Plate is descending towards the mantle beneath the North American Plate. This seismic zone runs along the Aleutian Arc, the Alaska Peninsula, and Cook Inlet, terminating beneath the northern foothills of the Alaska Range. In southern and central Alaska, this seismic activity decreases at about 140 miles (225 km) in depth, indicating the extension of the Pacific Plate. The 2016 M7.1 Iniskin and 2018 M7.1 Anchorage earthquakes are notable recent events from this zone, both causing significant ground shaking and damage to infrastructure.
Additionally, crustal seismicity in the region can be linked to three main sources: the faults and folds within the Cook Inlet basin, the Castle Mountain Fault, and a broad band of diffuse seismic activity stretching from northern Cook Inlet to the Denali Fault. Geological structures mapped in upper Cook Inlet have the potential to generate strong earthquakes, exemplified by the April 1933 M6.9 earthquake that caused severe damage in Anchorage, likely linked to such a structure. The Castle Mountain Fault, located 25 miles (40 km) north of Anchorage, shows evidence of geological shifts during the Holocene and was responsible for the 1984 M5.6 Sutton Earthquake. The diffuse seismic zone between Cook Inlet and the Denali Fault could represent a deformation area between the Bering microplate to the west and the southern Alaska block to the east, characterized by numerous thrust faults, with a significant 1943 M7.0 earthquake believed to have originated from this region.