Government or official record

M9.2 Alaska Earthquake and Tsunami of March 27, 1964

U.S. Geological Survey

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Where this source supports the record

Each entry separates the File’s editorial relevance note from its exact, section-level claims. A bibliography link without a direct claim is labeled plainly.

Natural disasters · 27 March 1964
The 1964 Great Alaska Earthquake and Tsunami

Prince William Sound rupture zone and south-central Alaska · United States

Open File evidence →

Why editors use it here
Authoritative event overview, tectonic explanation, timing, and geographic effects.
1. Quick read
  A magnitude 9.2 earthquake ruptured the Alaska–Aleutian subduction zone for roughly four and a half minutes, making it the most powerful earthquake recorded in United States history.
  Reviewed 24 July 2026
2. Trigger and conditions
  The Pacific Plate thrust beneath the North American Plate, abruptly displacing an immense section of the seafloor and coastline.
  Reviewed 24 July 2026
3. Uncertainty
  Fatality totals vary slightly by source depending on whether indirect deaths and distant tsunami losses are included.
  Reviewed 24 July 2026
4. Why it matters
  The event made cascading coastal risk visible at continental scale.
  Reviewed 24 July 2026