The Aleutian Trench (or Aleutian Trough) is an oceanic trench along a convergent plate boundary which runs along the southern coastline of Alaska and the Aleutian islands. The trench extends for 3400 km from a triple junction in the west with the Ulakhan Fault and the northern end of the Kuril–Kamchatka Trench, to a junction with the northern end of the Queen Charlotte Fault system in the east. It is classified as a "marginal trench" in the east as it runs along the margin of the continent. The subduction along the trench gives rise to the Aleutian Arc, a volcanic island arc, where it runs through the open sea west of the Alaska Peninsula. As a convergent plate boundary, the trench forms part of the boundary between two tectonic plates. Here, the Pacific plate is being subducted under the North American plate at a dip angle of nearly 45°. The rate of closure is 7.5 cm per year. The Pacific plate subducting under the North American plate, leads to increased faulting. This subduction began in the Early Cretaceous and continues into the present day. Within and near the Aleutian Island arc and depending on the location, there is thrust faulting, strike-slip faulting, and normal faulting. These result in an increased amount of seismic activity. Earthquakes can reach magnitudes between 7–8.5.

Trench morphology

The north side of the trench slopes 3°–4° and the south side 1°–4°. The deepest part of the Aleutian trench has been measured at 7822 m at 51.21°N, 174.83°E., located about 145 km SSW of Buldir Island. Center pressure: 10762 psi. Variations in total magnetic intensity (residual) of more than 600 γ (600 nanoteslas) were found in the center of the trench and more than 1100 γ on the southern flank.

Associated seismicity

The subduction of the Pacific plate below the North American plate along the Aleutian Trench is associated with numerous earthquakes. Several of these earthquakes are notable for their size and/or associated tsunamis.