1965 Rat Islands earthquake
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| Date | February 4, 1965 UTC |
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| Magnitude | 8.7 Mw |
| Epicenter | 51°17′N 178°33′E / 51.29°N 178.55°ECoordinates: 51°17′N 178°33′E / 51.29°N 178.55°E |
| Areas affected | United States (Alaska) |
| Max. intensity | VI (Strong) |
| 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). It had a magnitude of 8.7 and triggered a tsunami of over 10 m on Shemya Island, but caused very little damage.
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.
The earthquake was associated with a 600 km long rupture along the plate boundary, based on the distribution of aftershocks. 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.
The main shock was followed by an earthquake of magnitude 7.6 nearly two months later, that triggered a small tsunami. This was not an aftershock, but a normal fault event within the outer rise of the subducting plate, triggered by the earlier event.
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.
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