At 9:43 p.m. AST (06:43 11/17 UTC) on Sunday evening, November 16, 2003, a major earthquake occurred in the Rat Islands region of the Aleutian Islands. This earthquake was situated 95 kilometers (59 miles) south-southwest of Amchitka. The epicenter (red star) was located at 50.7487N and 178.4427E, the estimated moment magnitude is 7.7. This earthquake is the largest to occur in North America since the magnitude 7.9 Denali Fault, Alaska earthquake of November 3, 2002, and the largest in the Aleutian Islands since the June 1996 magnitude 7.9 Adak earthquake. The AEIC located 182 aftershocks (open circles) in the 17.5 hours after the main shock. This page will be updated as more aftershocks are located. The largest aftershock occurred at 10:50 p.m. AST on November 17 (7:50 UTC, 11/18) and had a moment magnitude of 5.7. The main shock generated a small tsunami of about 50 cm (1.64 ft) at Shemya and 12 cm (0.39 ft) at Adak (Alaska Tsunami Warning Center).

The M 7.7 earthquake occurred on the convergent boundary between the subducting Pacific and overriding North American crustal plates. This region, where the two plates are being forced directly into one another, is one of the world's most active seismic zones. Over one hundred earthquakes of magnitude seven or larger have occurred along this boundary in the past hundred years. A separate map illustrates the recent earthquakes as circles, superimposed on stippled areas illustrating the rupture zones of major earthquakes. Generally speaking, the magnitude of an earthquake is roughly proportional to the area involved in its faulting. Each major rupture is labelled with the earthquake's year and a black dot indicating the epicenter for the associated earthquake. With the exception of the Unalaska and Shumagin seismic gaps, all portions of this plate boundary have ruptured within the past hundred years.

The 1965 Mw 8.7 Rat Islands earthquake ruptured an ~600 km-long portion of the plate boundary. In November 17, 2003 M7.7 earthquake, the easternmost part of the 1965 zone failed again.