July 16, 2025 Earthquake: Alaska, United States

Reference #13456:

Tectonic Summary

The July 16, 2025, M 7.3 earthquake southeast of Sand Point, Alaska (south of the Alaska Peninsula), occurred as the result of strike-slip faulting near the subduction zone interface between the Pacific and North America plates, either within the upper (North America) Plate or within the downgoing (Pacific) slab. The preliminary focal mechanism solution indicates rupture occurred on either a moderately dipping right-lateral strike-slip fault striking towards the NNW or on a steeply dipping left-lateral strike-slip fault striking towards the east, and therefore that this earthquake was not a thrust event on the plate interface itself. At the location of this event, the Pacific plate converges with North America to the northwest at a rate of about 65 mm/yr, subducting at the Alaska-Aleutian Trench 100 km to the southeast of the earthquake. The majority of large earthquakes in this area are thrust events on the plate interface, unlike the strike-slip event of July 16, 2025.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Strike slip faulting events of the size of the July 16, 2025, earthquake are typically about 90x15 km (length x width).

Large earthquakes are common in the Alaska-Aleutian subduction zone. Since 1900, 9 other earthquakes M7 and larger have occurred within 250 km of the July 16, 2025, event, including the October 19, 2020, M 7.6, which had a similar mechanism. The largest of these was a M8.6 earthquake on April 1, 1946, which generated a large tsunami that caused destruction and loss of life both locally on Unimak Island and more distantly at Hilo, Hawaii. The Alaska-Aleutian Trench also hosted the second largest earthquake recorded by modern seismic instrumentation, the M9.2 March 27, 1964, earthquake, which ruptured to within about 350 km of this event.