1946 Aleutian Islands earthquake
UTC time | 1946-04-01 12:29:01 |
---|---|
ISC event | 898313 |
USGS-ANSS | ComCat |
Local date | April 1, 1946 |
Local time | 02:29 |
Magnitude | 7.4 Ms, 8.6 Mw, 9.3 Mt |
Depth | 15 km (9.3 mi)[1] |
Epicenter | 53°29′N 162°50′W / 53.49°N 162.83°W[1] |
Type | Megathrust |
Areas affected | Hawaii, Alaska United States |
Max. intensity | MMI VI (Strong) |
Tsunami | Up to 42 m (138 ft) at Unimak Island |
Casualties | 165–173[2] |
The 1946 Aleutian Islands earthquake occurred near the
Tectonic setting
The Aleutian Islands are a group of 14 large and 55 smaller volcanic islands situated between mainland Alaska and
Earthquake
The earthquake struck at 02:29 local time on April 1, 1946, at a shallow depth of 15 km (9.3 mi). The earthquake was very large, but the maximum felt intensity was only a VI.[1] The earthquake was originally thought to be a rather smaller earthquake of Ms 7.4, however further research uncovered that this was truly a much larger event, but with a hidden seismic signature.[3] A size of Mw 8.6 fits this event best, with an estimated slip between 9 m (30 ft) and 12.7 m (42 ft).[3][11] 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.[3] The very high tsunami magnitude value is due to the sheer strength of the waves. It was calculated by using tsunami run up from Honolulu, Hilo, and the average of stations in California. Even excluding the values given by Hilo (the highest Mt ), the tsunami magnitude is at least 9.1.[4] The earthquake was originally thought to be a strike-slip earthquake, and later a strike slip earthquake with a normal faulting component. These erroneous focal mechanisms were due to a lack of stations recording the earthquake. However, modeling of the S wave, rather than the P wave helped to uncover both the true magnitude of the earthquake, as well as the widely accepted thrusting mechanism. This thrust mechanism is consistent with a subduction earthquake helping to relieve stress on the Aleutian Trench.[3]
Tsunami
At Unimak Island, tsunami run-up reached 42 m (138 ft). The tsunami earthquake aspect of this event helps to explain a portion of this massive height; however, the rest must be attributed to a local submarine landslide.[3] Waves reportedly traveled across the ocean at 500 miles per hour (430 kn; 800 km/h) and measured 55 feet (17 m) high, crest to trough. The wave reached Kauai, Hawaii 4.5 hours after the quake, and Hilo, Hawaii 4.9 hours later. In the Hawaiian Islands 159 people died.[12] In Hilo alone, 96 people died,[12] 163 were injured, 488 buildings were demolished and 936 more were damaged. On Kauai the McKee sugar mill and buildings were demolished, and the archives of the Kauai newspaper were a loss. Witnesses told of waves inundating streets, homes, and storefronts. Many victims were swept out to sea by receding water. The tsunami caused much damage in Maui as well. Waves there demolished 77 homes and many other buildings.[13] The residents of these islands were caught off-guard by the onset of the tsunami due to the inability to transmit warnings from the destroyed posts at Scotch Cap, and the tsunami is known as the April Fools' Day Tsunami in Hawaii because it happened on April 1. The effects of the tsunami also reached Washington, Oregon, and California.[5]
The tsunami was unusually powerful for the size of the earthquake. The event was classified as a tsunami earthquake due to the discrepancy between the size of the tsunami and the relatively low surface-wave magnitude.[14] The large-scale destruction prompted the creation of the Seismic Sea Wave Warning System, which became known as the Pacific Tsunami Warning Center in 1965.[15]
See also
References
- ^ a b c National Geophysical Data Center. "Comments for the Significant Earthquake". Archived from the original on August 7, 2022. Retrieved September 10, 2011.
- ^ USGS (September 4, 2009), PAGER-CAT Earthquake Catalog, Version 2008_06.1, United States Geological Survey, archived from the original on July 17, 2020, retrieved August 3, 2018
- ^ .
- ^ . Retrieved August 8, 2022.
- ^ a b "1946 Aleutian Tsunami". www.usc.edu. Archived from the original on January 12, 2016. Retrieved February 2, 2016.
- ^ "Aleutian Islands". Britannica. Archived from the original on September 12, 2019. Retrieved August 7, 2022.
- ^ "Aleutian Trench". Archived from the original on February 25, 2014. Retrieved August 7, 2022.
- ^ S2CID 55917937.
- ^ from the original on July 3, 2022. Retrieved July 3, 2022.
- S2CID 32932011. Retrieved August 8, 2022.
- S2CID 249857173.
- ^ S2CID 259868444.
- ^ "A History of Tsunamis in Hawaii". March 11, 2011. Archived from the original on September 29, 2018. Retrieved September 29, 2018.
- doi:10.1016/0031-9201(72)90058-1. Archived from the original(PDF) on February 22, 2016. Retrieved February 15, 2016.
- ^ The April 1, 1946 Earthquake and Tsunami in the Aleutian Islands, George Pararas-Carayannis, archived from the original on January 19, 2019, retrieved February 9, 2007
External links
- Tsunami 1946 – Hilo on YouTube
- Tsunami Animation: Unimak Island, Aleutian Islands, 1946 – Pacific Tsunami Warning Center
- 1946 Aleutians Tsunami – Western States Seismic Policy Council
- Mystery of Deadly 1946 Tsunami Deepens – LiveScience
- The International Seismological Centre has a bibliography and/or authoritative data for this event.
- Survivor audio interview transcript