The 2011 Fox Islands Earthquake in the Aleutian Subduction Zone

The magnitude 7.3 earthquake that struck the Fox Islands region of the Aleutian Islands, Alaska, on 24 June 2011 at 03:09 UTC originated at a depth of 52 km. This event represents the sole strong earthquake recorded in the area since 1 January 2000. Its location within the tectonically active Aleutian arc underscores the persistent seismic hazards associated with plate boundary processes. The Fox Islands lie along the central portion of the Aleutian Islands, a volcanic arc extending westward from the Alaska Peninsula. This chain forms above the Aleutian subduction zone, where the Pacific Plate converges with and descends beneath the North American Plate at rates of approximately 6–7 cm per year. The 52 km focal depth places the rupture within the Wadati-Benioff zone of intermediate-depth seismicity, typical of the steeply dipping slab in this segment of the margin. Such earthquakes commonly result from internal deformation of the subducting slab rather than megathrust slip at the plate interface. Geologically, the Aleutian arc has developed over tens of millions of years through repeated subduction-related magmatism and crustal accretion. The Fox Islands segment features active volcanoes such as those on Unimak and Unalaska islands, built atop accreted oceanic and continental fragments. Regional stratigraphy includes Mesozoic to Cenozoic sedimentary and volcanic rocks deformed by ongoing convergence. The subduction zone’s geometry produces both shallow crustal events and deeper intraslab earthquakes, with the latter often exhibiting normal-faulting mechanisms due to slab bending or extension. Seismic history in the broader Aleutian region demonstrates recurrent large-magnitude activity driven by the subduction process. While the 2011 Fox Islands event stands as the only strong earthquake since 2000, earlier instrumentally recorded events illustrate the margin’s capacity for great earthquakes exceeding magnitude 8. The combination of high convergence rates and heterogeneous locking along the megathrust sustains elevated seismic potential throughout the arc. The 2011 earthquake produced no reported widespread damage or tsunami, consistent with its intermediate depth and moderate magnitude relative to historical Aleutian giants. Ground shaking was felt across parts of the Aleutian chain and mainland Alaska, prompting standard post-event monitoring by seismic networks. Ongoing GPS and seismic observations continue to refine models of slab geometry and strain accumulation in the region.

References

USGS Earthquake Hazards Program event page and catalog data for the 24 June 2011 Fox Islands earthquake. Alaska Earthquake Center regional seismicity summaries. Geological Society of America publications on Aleutian arc tectonics and volcanism.