The 1964 Alaska Earthquake: North America's Largest

History

June 2026 · 6 min read · By Tremr

At 5:36 p.m. on Good Friday, March 27, 1964, the ground beneath Alaska's Prince William Sound began to rupture. What followed was four to five minutes of continuous shaking — an almost incomprehensible duration for an earthquake. The magnitude was 9.2. It is the most powerful earthquake ever recorded in North America, and the second most powerful ever recorded anywhere on Earth, exceeded only by the 1960 Valdivia earthquake in Chile.

The rupture zone stretched approximately 800 kilometres along the Aleutian Megathrust — the subduction zone where the Pacific Plate drives beneath the North American Plate at roughly 5–7 centimetres per year. In some areas, the ground uplifted by as much as 9 metres. In others, it subsided by 2 metres. Coastlines were permanently reshaped. Forests were killed by saltwater intrusion as land sank into tidal zones. The shaking was felt across the entire state of Alaska and in parts of Canada and the Pacific Northwest.

Downtown Anchorage, Alaska showing the dramatic effects of the 1964 Good Friday earthquake, with streets collapsed into sinkholes — 4th Avenue in downtown Anchorage after the 1964 Good Friday earthquake — the street dropped by several metres as the soil gave way. Image: USGS / Wikimedia Commons

The Scale of Physical Destruction

In Anchorage — then a city of about 80,000 — the shaking lasted nearly five minutes, long enough for people to flee buildings, realise they had nowhere safe to go, and wait for it to stop. The Turnagain Heights neighbourhood slid into Cook Inlet as the bluff beneath it liquefied and failed — about 130 homes were destroyed in that single landslide. Downtown's Fourth Avenue dropped by as much as 3 metres as soil beneath the street collapsed.

The port towns of Valdez, Seward, and Kodiak were devastated. In Valdez, a submarine landslide triggered a local tsunami that struck the waterfront almost immediately, killing 32 people who had gathered to watch a cargo ship unload. The town was subsequently relocated to higher ground — the original site was abandoned entirely. In Seward, the waterfront slid into Resurrection Bay, taking rail lines, fuel storage tanks, and dock facilities with it. Fuel fires burned on the water for hours.

Prince William Sound, Alaska — the epicentre of the 1964 earthquake and the centre of the 800 km rupture zone along the Aleutian Megathrust

Tsunamis Across the Pacific

The megathrust rupture generated one of the most powerful tsunamis of the 20th century. The uplift of the seafloor in Prince William Sound displaced a massive volume of water. Within minutes, local tsunamis up to 20 metres high struck the Alaskan coast. But the tsunami also propagated across the entire Pacific Ocean at jet-plane speeds.

Crescent City, California — over 3,000 kilometres from the epicentre — was struck by waves that caused $7.5 million in damage (1964 dollars) and killed 12 people. Hilo, Hawaii received a significant wave. Japan recorded tsunami waves along its Pacific coast. The tsunami was detected as far away as Antarctica.

Despite lasting nearly five minutes, the 1964 Alaska earthquake killed only 139 people. The low death toll — remarkable for an M9.2 event — reflects Alaska's sparse population. The tsunami killed more people than the shaking. In a densely populated area like Tokyo or Los Angeles, an equivalent event would be incomparably more catastrophic. Population density, not magnitude alone, determines death tolls.

What It Taught Science

The 1964 Alaska earthquake transformed earthquake science in several fundamental ways. It provided the most complete set of seismic recordings ever gathered for an earthquake of that size, and the data were used to refine understanding of how megathrust faults rupture and how seismic waves propagate through the Earth.

The earthquake was also pivotal in the acceptance of plate tectonics theory. At the time of the quake, plate tectonics was still a controversial hypothesis — it had been proposed but not yet universally accepted by the geological community. The pattern of uplift and subsidence observed in Alaska matched precisely what subduction zone mechanics would predict. The evidence was so clear and so large-scale that it contributed significantly to the consolidation of the theory in the following years.

The 1964 earthquake also prompted a major revision of building codes in Alaska and contributed to the development of better seismic-resistant construction nationwide. The failure modes observed — landslides triggered by liquefaction, soil amplification in soft sediment areas, tsunami generation from megathrust ruptures — became fundamental case studies in geotechnical and structural earthquake engineering.

It also directly led to improvements in the Pacific Tsunami Warning System. Before 1964, tsunami warnings were poorly coordinated and slow to reach threatened coastlines. The deaths in Crescent City — people who had been warned but returned to watch the waves — prompted both improved warning protocols and public education programmes about tsunami behaviour.

Alaska Today

Alaska remains one of the most seismically active regions on Earth. The state experiences more earthquakes each year than any other US state, accounting for roughly 75% of all US earthquakes and 11% of the world's largest earthquakes. The Aleutian Arc — the chain of volcanic islands extending southwest from the Alaskan mainland — is one of the most geologically active regions on the planet.

A similar magnitude event to 1964 is considered not just possible but geologically inevitable along the same Aleutian Megathrust. Anchorage has grown significantly — its population is now over 300,000 — and has substantially improved its seismic building codes since 1964. But the region's tsunami vulnerability extends far beyond Alaska: a megathrust rupture in the eastern Aleutians could threaten Hawaii and the Pacific coast of North America within hours. The 1964 earthquake remains the calibration event against which Pacific Rim tsunami preparedness is measured.