Nearly three years after the magnitude 7.8 Simeonof Earthquake, which also happened in the same area, a magnitude 7.2 earthquake of the Alaska Peninsula region struck at approximately noon Alaska time. About 100 miles southeast of the M7.8 event, at a depth of about 20 miles, was where the 7.2 earthquake occurred.
After the earthquake, a tsunami warning was immediately issued, but it was soon downgraded to an advisory level, then it was finally cancelled just before 1:00 a.m. King Cove and Sand Point both recorded tsunamis with waves as high as.5 feet. Several villages on the Alaska Peninsula and the eastern Aleutian Islands reported feeling ground shaking, with an intensity as high as V, moderate.
There was an earthquake in the M7.8 aftershock zone. The Earthquake Centre continued to detect high levels of seismic activity within the M7.8 aftershock zone in 2023, despite the M7.8 aftershock activity having significantly decreased from its peak in the summer/fall of 2020.
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So, it is possible to identify the M7.2 earthquake as a late aftershock of the M7.8 earthquake. Its origin mechanism resembles that of the Simeonof event and points to Aleutian megathrust fault fault rupture. Like the other moderate-sized earthquakes in the area, we anticipate that the M7.2 earthquake will produce its own aftershock series. The biggest aftershock to date, measuring M5.7, happened three minutes after the mainshock.
On July 29, 2021, a large earthquake with a magnitude of 8.2 occurred northeast of the Simeonof Earthquake epicentre. Away from the M7.8 rupture zone, the M8.2 rupture spread to the northeast.
The subduction zone contact between the Shumagin Islands in the southwest and Kodiak Island in the northeast was damaged by an earthquake, which occurred three years ago. Prior to these three significant earthquakes, the Shumagin Island region was known as a seismic gap, a place where there had been a long period without any significant earthquakes. The latest series of events helped to fill this vacuum in certain ways.