On July 15, 2023, a powerful earthquake measuring magnitude 7.2 struck the Alaska Peninsula region, occurring nearly three years after a magnitude 7.8 earthquake in the same area. The epicenter of the 7.2 event was located approximately 50 miles south of Sand Point, at a depth of around 20 miles. Immediately after the earthquake, a tsunami warning was issued, but it was later downgraded to an advisory level and eventually canceled before 1:00 a.m. Tsunami waves with a maximum height of 0.5 ft. were recorded in King Cove and Sand Point. The ground shaking was felt in various communities along the Alaska Peninsula and eastern Aleutian Islands, with a moderate intensity reaching level V.
This earthquake on July 15 took place within the aftershock zone of the M7.8 earthquake. While the activity of aftershocks from the M7.8 event had significantly decreased since its peak in the summer/fall of 2020, the Earthquake Center observed elevated seismic activity within the aftershock zone in 2023. Hence, the M7.2 earthquake can be considered a delayed aftershock of the M7.8 event. The source mechanism of the M7.2 earthquake is similar to the Simeonof event and indicates fault rupture along the Aleutian megathrust fault. It is anticipated that the M7.2 earthquake will generate its own sequence of aftershocks, similar to other moderate-sized earthquakes in the region. The largest aftershock so far, measuring M5.7, occurred three minutes after the mainshock.
Furthermore, another significant earthquake, a magnitude 8.2 event, took place on July 29, 2021, northeast of the epicenter of the Simeonof Earthquake. The rupture of the M8.2 earthquake propagated towards the northeast, away from the rupture zone of the M7.8 earthquake.
The M7.2 earthquake on July 15, 2023, adds to the series of major seismic events that have occurred within a span of three years, rupturing the subduction zone interface from the southwest Shumagin Islands to the northeast Kodiak Island. The Shumagin Island region had been identified as a seismic gap, an area where no significant earthquakes had occurred recently, prior to these three major events. The recent sequence of events has partially filled this gap.
Source – Earthquake.alaska
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