The 1946 Aleutian Islands earthquake occurred near the Aleutian Islands, Alaska on April 1, 1946. The shock had a moment magnitude () of 8.6, a tsunami magnitude of 9.3, and a surface-wave magnitude () of only 7.4, and a maximum Mercalli intensity of VI (Strong). It resulted in 165–173 casualties and over $26 million in damage. The seafloor along the fault was elevated, triggering a Pacific-wide tsunami with multiple destructive waves at heights ranging from . The tsunami obliterated the Scotch Cap Lighthouse on Unimak Island, Alaska among others, and killed all five lighthouse keepers. Despite the destruction to the Aleutian Island Unimak, the tsunami had almost an imperceptible effect on the Alaskan mainland. Tectonic setting The Aleutian Islands are a group of 14 large and 55 smaller volcanic islands situated between mainland Alaska and Kamchatka. They are situated along the Aleutian Trench as they were formed by the active subduction of the oceanic Pacific plate underneath the continental crust of the North American plate. The western portion of the trench becomes more and more oblique until near the Commander Islands where faulting becomes nearly exclusively strike-slip and causes earthquakes such as the 2017 Komandorski Islands earthquake. The trench ends where the Kuril-Kamchatka Trench begins in the west. In the east, the trench extends for a couple thousand miles before reaching the transition zone near Yakataga responsible for creating earthquakes such as the 1899 Yakutat Bay earthquakes. The collision totally ends slightly further east, where the Queen Charlotte Fault becomes the dominant fault of the tectonic regime. This specific area of the Aleutian Islands is thought to have ruptured in the 1585 Aleutian Islands earthquake. Earthquake The earthquake struck at 2:29 am local time on April 1, 1946, at a shallow depth of . The earthquake was very large, but the maximum felt intensity was only a VI. The earthquake was originally thought to be a rather smaller earthquake of 7.4, however further research uncovered that this was truly a much larger event, but with a hidden seismic signature. A size of 8.6 fits this event best, with an estimated slip between and . This event shows the classic signs of a tsunami earthquake as the surface-wave magnitude was very low compared to the moment and tsunami magnitudes, and the tsunami height was far larger than expected for the surface wave magnitude. The very high tsunami magnitude value is due