One of the largest recorded earthquakes in the Aleutian Islands, generating a basin-wide Pacific tsunami and causing roughly $5 million in total losses.
Key Facts
- Moment Magnitude
- 8.6 Mw
- Date
- March 9, 1957
- Max Mercalli Intensity
- VIII (Severe)
- Total Losses
- ~$5 million (1957) USD
- Tsunami Reach
- Alaska, Hawaii, and Pacific rim
By the Numbers
Location
Cause → Event → Consequence
The earthquake resulted from convergent plate boundary activity along the Aleutian Trench, where the Pacific Plate subducts beneath the North American Plate. The sudden rupture at depth south of the Andreanof Islands released enormous energy, a process characteristic of megathrust events along this highly active seismic zone in the southwestern Alaska region.
On March 9, 1957, at 04:22 local time, an earthquake of moment magnitude 8.6 struck south of the Andreanof Islands in the Aleutian chain. It registered a maximum Modified Mercalli intensity of VIII (Severe). The violent seabed displacement immediately generated a large tsunami that spread across the Pacific Ocean basin.
The resulting tsunami produced strong waves felt across the Pacific rim, with notable effects recorded in Alaska and Hawaii. Total property and infrastructure losses amounted to approximately $5 million, equivalent to over $57 million in 2025 dollars. The event highlighted the tsunami hazard posed by major Aleutian subduction earthquakes to distant coastlines.