A magnitude 6.3 earthquake occurred in Alaska yesterday (7/28/15) at 6:35 pm local time 143 miles (230 km) southwest of Anchorage. The earthquake occurred 70 miles below the surface. Shaking was felt as far away as Fairbanks, about 383 miles (616 km) away. No injuries or deaths were reported.
The earthquake was caused by the subduction of the Pacific tectonic plate under the North American plates. This subduction formed the Aleutian Islands and the adjacent Aleutian Trench. The Pacific plate moves at a varied rate along the Aleutian Islands at 60 mm/yr at the eastern edge and 76 mm/yr along the western edge. The eastern and western margins of this subduction zone behave very differently. In the eastern portion of the Aleutian Islands, the Pacific plate is subducting perpendicular (head on) to the arc. In the western portion, the movement changes to a translational motion (side-to-side motion), parallel and to the east of the arc.
This area is extremely prone to earthquakes. The second largest earthquake ever record occurred within this area. The Prince William Sound earthquake occurred on March 28, 1964 and had a magnitude of 9.2.