Aleutian Arc

[3][2] Unimak Pass at the southwestern end of the Alaska Peninsula (~165°W) marks the eastward transition from an intra-oceanic in the west to a continental arc in the east.

[2] Volcanic activity on the Aleutian Ridge extends from the Southwest corner of Alaska to around 175°E, west of Attu Island (~173°E).

[2] A forearc basin reaching depths of 7 km occupies the space between the trench and the island arc and leads up to the Aleutian Ridge, the north side of which being the area where the most volcanic activity occurs.

[3] Due to the arcuate geometry of the trench, the relative velocity vector changes from almost trench-normal in the Gulf of Alaska to almost trench-parallel in the west.

[2] The oblique direction of convergence in the western and central portions of the area is causing westward transportation of the arc.

[3][2] The boundaries of the 5 major blocks that have been identified form areas with cohesive movement that are often disrupted by strike-slip and normal faults.

[2] The majority of events have been noted as having a thrusting mechanism, which denotes them as earthquakes occurring from the interface of a plate.

Map showing the volcanoes and islands of the Aleutian Arc.
Diagram showing the process of subduction and the formation of volcanic arcs.
Image showing the Aleutian Island Arc, along with the trench. The trench is denoted by the dark blue line to the south running parallel with the island arc. The area between the trench and the ridge delineates the blocks of crust that cause much of the seismic activity in the region.