1965 Rat Islands earthquake

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1965 Rat Islands earthquake
1965 Rat Islands earthquake is located in Alaska
1965 Rat Islands earthquake
Date February 4, 1965 (1965-02-04) UTC
Magnitude 8.7 Mw
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Areas affected United States (Alaska)
Tsunami 10.7 m (35 ft)

The 1965 Rat Islands earthquake occurred at 05:01 UTC, on 4 February (19:01, 3 February local time[1]). It had a magnitude of 8.7 and triggered a tsunami of over 10 m on Shemya Island,[2] but caused very little damage.

Tectonic setting

The Rat Islands form part of the Aleutian Islands, a chain of volcanic islands forming an island arc, that results from the subduction of the Pacific Plate beneath the North American Plate. This plate boundary, the Alaska-Aleutian megathrust, has been the location of many megathrust earthquakes.

Characteristics

Map showing the tectonics and seismicity of Alaska

Earthquake

The earthquake was associated with a 600 km long rupture along the plate boundary, based on the distribution of aftershocks.[3] The pattern of energy release suggest the presence of three asperities along the plate interface, each causing a pulse of moment release. Modelling of the tsunami supports the idea that the earthquake consisted of three sub-events, related to three structural 'blocks' within the overriding plate.[4]

The main shock was followed by an earthquake of magnitude 7.6 nearly two months later, that triggered a small tsunami.[1] This was not an aftershock, but a normal fault event within the outer rise of the subducting plate, triggered by the earlier event.[5]

Tsunami

The tsunami had a maximum run-up height of 10.7 m on Shemya Island, 2.0 m at Amchitka Island, 1.6 m at Attu Island and 1.1 m in northern Kauai, Hawaii. It was also observed in Peru, Ecuador, Mexico, California, Japan and eastern Russia.[1]

Damage

Flooding from the tsunami caused $10,000 worth of damage on Amchitka Island.[2] Minor damage from the earthquake was recorded on both Attu and Shemya islands in the form of cracks in runways.

See also

References

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