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7.2 Magnitude Earthquake Strikes South of Sand Point

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Late in the evening on July 15, 2023, a significant earthquake measuring 7.2 on the Richter scale hit the Alaska Peninsula region, marking nearly three years since a previous 7.8 magnitude earthquake known as the Simeonof Earthquake occurred in the same area. The epicenter of the 7.2 event was approximately 50 miles south of Sand Point, situated at a depth of roughly 20 miles. Shortly after the earthquake, a tsunami warning was promptly issued. However, within an hour, it was downgraded to an advisory level and eventually cancelled entirely just before 1:00 a.m. Local measurements recorded tsunami waves peaking at 0.5 ft. in King Cove and Sand Point. Reports of ground shaking emerged from various communities along the Alaska Peninsula and eastern Aleutian Islands, reaching a maximum intensity of V, indicating moderate effects.

It is important to note that the July 15 earthquake occurred within the aftershock zone of the M7.8 event. Although the aftershock activity related to the M7.8 earthquake has significantly diminished since its peak in the summer/fall of 2020, the Earthquake Center has observed heightened levels of seismic activity in the same aftershock zone throughout 2023. Consequently, the M7.2 earthquake can be considered a late aftershock resulting from the M7.8 event. Its source mechanism closely resembles the Simeonof event, indicating fault rupture along the Aleutian megathrust fault. Anticipatedly, the M7.2 earthquake will generate its own sequence of aftershocks, similar to other moderate-sized earthquakes experienced in the region. As of now, the largest aftershock recorded was a magnitude 5.7, occurring three minutes after the mainshock.

It is worth mentioning that another major earthquake, measuring 8.2 in magnitude, transpired on July 29, 2021, northeast of the epicenter of the Simeonof Earthquake. The rupture associated with the M8.2 earthquake propagated in a northeastern direction, diverging from the rupture zone of the M7.8 event.

The occurrence of the M7.2 earthquake on July 15, 2023, represents yet another significant event within a three-year period, rupturing the subduction zone interface from the Shumagin Islands in the southwest to Kodiak Island in the northeast. Prior to these three substantial earthquakes, the Shumagin Island region had been identified as a seismic gap, denoting a stretch of land where major earthquakes had not recently occurred. The recent series of events has partially filled this seismic gap.

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