1964 Great Alaska Earthquake: The Good Friday Earthquake That Reshaped Seismology

Key Takeaways

• The 1964 Great Alaska Earthquake struck at 5:36 PM local time on March 27 (03:36 UTC March 28), registering magnitude 9.2 — the second-largest earthquake ever instrumentally recorded, after the 1960 Chile M9.5 event.
• Of the 131 confirmed deaths, 119 were caused by tsunamis — including local waves that obliterated coastal villages and a transpacific tsunami that killed 11 people in Crescent City, California.
• The earthquake deformed an area of approximately 250,000 km², with tectonic uplift reaching up to 11.5 meters on Montague Island and subsidence of up to 2.3 meters in other areas — permanently reshaping Alaska's coastline.
• The disaster directly led to the expansion of the Pacific Tsunami Warning Center (PTWC) and the creation of the National Tsunami Warning Center in Palmer, Alaska.
• The earthquake provided critical early evidence confirming plate tectonics theory and the mechanics of subduction zone megathrust earthquakes.

Introduction

At 5:36 PM Alaska Standard Time on Good Friday, March 27, 1964, the ground beneath Prince William Sound began to shake. For the next four to five minutes — an almost incomprehensible duration for an earthquake — the Pacific plate lurched beneath the North American plate along a rupture zone stretching roughly 800 kilometers from Prince William Sound southwest past Kodiak Island.

The resulting magnitude 9.2 earthquake was the most powerful ever recorded in North American history and the second-largest instrumentally recorded worldwide. It released approximately twice the energy of the 2004 Indian Ocean earthquake and roughly 1,000 times the energy of the 1811 New Madrid earthquakes that terrified the young United States.

What happened over the following hours — massive tsunamis, submarine landslides, ground failures, and permanent coastal deformation — would reshape not only Alaska's geography but humanity's understanding of how the Earth works. The 1964 earthquake arrived at a pivotal moment in geoscience: the theory of plate tectonics was still debated, and the mechanics of subduction zones were poorly understood. The sheer scale of deformation forced the scientific community to confront evidence that would help confirm the revolutionary theory within just a few years.

This article examines the earthquake's causes, its devastating effects, the tsunamis it generated, and its lasting scientific and policy legacy.

Tectonic Setting: The Alaska-Aleutian Subduction Zone

Alaska sits atop one of the most seismically active convergent plate boundaries on Earth. The Pacific plate subducts beneath the North American plate along the Alaska-Aleutian megathrust at a rate of approximately 55–65 mm per year — slightly faster than the global average for such boundaries and faster than the ~50 mm/year total Pacific-North American plate motion measured further south.

The Ring of Fire wraps along Alaska's southern coast, and the Alaska-Aleutian subduction zone has produced more large earthquakes than nearly any other fault system in the modern instrumental record. Before 1964, the region had experienced significant earthquakes in 1899 (Yakutat Bay, approximately M8.0) and 1957 (Andreanof Islands, M9.1), but the Prince William Sound segment had been notably quiet — what seismologists now recognize as a classic "seismic gap" where stress was accumulating.

The 1964 rupture initiated at a depth of approximately 25 km beneath northern Prince William Sound and propagated primarily to the southwest. The fault plane dipped at a shallow angle of about 9–12 degrees, meaning the rupture extended far inland beneath the continent. The area of significant slip covered roughly 200,000 km² of fault surface — an enormous zone by any measure.

The Earthquake: Four Minutes That Changed Everything

Ground Shaking and Duration

The earthquake began with a sudden jolt followed by violent rolling and shaking that lasted approximately four to five minutes in the epicentral region. Witnesses in Anchorage, 120 km northwest of the epicenter, described waves rolling through the ground like ocean swells, with the shaking so severe that standing was impossible.

In Anchorage, the state's largest city with a 1964 population of approximately 82,000, the effects were catastrophic despite the city being some distance from the epicenter. The Turnagain Heights neighborhood experienced a massive translational landslide, with an area roughly 2.6 km long and 300 meters wide sliding toward the sea. Seventy-five homes were destroyed. Fourth Avenue in downtown Anchorage dropped as much as 3.3 meters when an entire block subsided into a graben created by lateral spreading.

The Government Hill Elementary School was split in two by a landslide — had the earthquake struck during school hours rather than on a holiday evening, the death toll could have been vastly higher.

Magnitude and Energy Release

The earthquake was originally assigned a Richter magnitude of 8.4–8.6 by early measurements. As the moment magnitude scale (Mw) was developed and applied retroactively, the event was upgraded to Mw 9.2, reflecting its true energy release. The earthquake released seismic energy equivalent to approximately 1.8 × 10¹⁸ joules — roughly 10 million times the energy of the atomic bomb dropped on Hiroshima.

Only the 1960 Valdivia earthquake in Chile (Mw 9.5) has exceeded it in the instrumental record. To understand what these magnitude numbers mean in practice: the jump from M9.0 to M9.2 represents approximately 2.8 times more energy released.

Ground Deformation: Reshaping a Coastline

The most geologically remarkable aspect of the 1964 earthquake was the sheer scale of permanent ground deformation. An area of approximately 250,000 km² — larger than the United Kingdom — was measurably uplifted or subsided.

Uplift

The zone of maximum uplift ran along the seaward side of the rupture, from Montague Island through the Kenai Peninsula coast and out toward Kodiak Island. Montague Island experienced the most extreme uplift: up to 11.5 meters on its southeastern coast, as measured by displaced intertidal organisms. Middleton Island was raised approximately 3.3 meters. Entire sections of seafloor were thrust above sea level, creating new land. Reefs and marine terraces that had been submerged were suddenly exposed.

At the port of Cordova, uplift of approximately 1.8 meters left the harbor too shallow for fishing boats to use, devastating the local economy.

Subsidence

Inland and northwest of the uplift zone, a broad area subsided by up to 2.3 meters. Portage, a small community at the head of Turnagain Arm south of Anchorage, sank below high-tide level and was permanently flooded — its ruins are still visible at low tide. Parts of Kodiak Island also subsided, flooding coastal infrastructure.

The pattern of seaward uplift paired with landward subsidence is now recognized as the classic signature of megathrust earthquake deformation, where the overriding plate snaps upward as it releases centuries of accumulated strain against the subducting slab.

Table 1: Ground Deformation and Damage by Location

The Tsunamis: Waves of Destruction

The 1964 earthquake generated two distinct types of tsunamis, and the distinction proved critical for understanding the disaster's death toll.

Tectonic Tsunami

The massive seafloor uplift generated a basin-wide tectonic tsunami that radiated across the Pacific Ocean. This wave traveled at speeds of approximately 700 km/h in the open ocean, reaching Hawaii in about five hours and the U.S. West Coast in roughly four to five hours.

The tectonic tsunami struck Kodiak Island with waves up to 9 meters, destroying the downtown waterfront. It reached Crescent City, California — over 2,500 km from the epicenter — where a series of waves arrived beginning around 11:52 PM local time. The third and largest wave, approximately 6.3 meters above mean lower low water, surged through the downtown district. Eleven people died in Crescent City, most of them residents and business owners who had returned to the waterfront after the first two smaller waves, not realizing larger waves were still coming.

Local Tsunamis from Submarine Landslides

The most lethal waves were generated not by tectonic displacement but by submarine landslides triggered by the shaking. At Valdez, a massive section of the waterfront — roughly 600 meters of shoreline — slid into the bay as the unstable glacial sediments beneath the port liquefied. The resulting local wave reached 52 meters in the narrow confines of the fjord. Thirty-two people on the dock, including children watching the unloading of the freighter SS Chena, were killed instantly.

At Chenega, a Chugach Alaska Native village on Evans Island in Prince William Sound, a wave estimated at 21 meters swept through the community. Twenty-three of the village's 76 residents were killed — nearly one-third of the population. The village was never rebuilt at its original site.

At Seward, the waterfront slid into Resurrection Bay, generating a local wave that ruptured fuel storage tanks. Burning fuel spread across the water, creating a wave of fire. Thirteen people died.

Table 2: Tsunami Impacts by Location

Deaths and Damage

Casualties

The earthquake killed 131 people — a remarkably low number given the earthquake's magnitude, attributable largely to Alaska's sparse population in 1964 (approximately 250,000 statewide) and the fact that the earthquake struck on a holiday evening when schools and many businesses were closed.

Of the 131 deaths, 119 (approximately 91%) were caused by tsunamis. Only 9 deaths were attributed directly to the earthquake shaking — from building collapses and landslides. The remaining deaths occurred from other causes including drowning and fires triggered by the event.

Outside Alaska, 16 people died: 11 in Crescent City, California; 4 in Oregon (Depoe Bay and nearby coastal communities); and 1 in Long Beach, California (a child swept off a beach by a surge).

Economic Damage

Property damage was estimated at $311 million in 1964 dollars — equivalent to roughly $2.8 billion in 2024 dollars. The damage included near-total destruction of several coastal towns, severe damage to Anchorage's infrastructure, destruction of port facilities, rail lines, highways, and bridges, and widespread disruption to Alaska's fishing industry.

Five communities — Valdez, Chenega, Afognak, Old Harbor (partially), and the Turnagain Heights neighborhood of Anchorage — were either relocated entirely or abandoned.

Scientific Legacy: Proving Plate Tectonics

Confirming Subduction

The 1964 earthquake occurred at a critical juncture in earth science. The theory of plate tectonics was emerging but far from universally accepted. Continental drift had been proposed by Alfred Wegener in 1912 but lacked a convincing mechanism. Seafloor spreading had been described by Harry Hess in 1962. But the concept of subduction — where one plate dives beneath another — was still largely theoretical.

The 1964 earthquake provided dramatic, measurable evidence. George Plafker, a USGS geologist who spent years mapping the deformation, demonstrated that the observed pattern of coastal uplift seaward and subsidence landward was exactly what would be predicted by thrust faulting on a shallow-dipping megathrust. His 1965 paper "Tectonic Deformation Associated with the 1964 Alaska Earthquake" became one of the foundational documents in plate tectonic theory.

Plafker showed that the fault responsible was not a vertical strike-slip fault, as some had initially proposed, but a gently dipping thrust fault — the interface between the Pacific and North American plates. This was among the first clear demonstrations that subduction zone megathrust faults could produce the world's largest earthquakes.

Seismic Gap Theory

The 1964 rupture zone filled a recognized gap in the pattern of large earthquakes along the Alaska-Aleutian arc. Combined with the 1957 Andreanof Islands earthquake and the 1965 Rat Islands earthquake (M8.7), the concept of "seismic gaps" — segments of plate boundaries that are overdue for large earthquakes based on the time since their last rupture — gained significant empirical support. This theory would become a major tool in seismic hazard assessment worldwide.

Policy Legacy: Building a Tsunami Warning System

Before 1964

When the earthquake struck, the United States had only one tsunami warning center: the Pacific Tsunami Warning Center in Honolulu, Hawaii, established in 1949 after a deadly 1946 tsunami (also generated by an Alaska earthquake). The system was designed primarily to protect Hawaii and had limited capability to warn Alaska's own coastlines.

There was no mechanism for rapid warning to communities in the earthquake's near field. Valdez, Chenega, and Seward had no warning whatsoever — their local tsunamis arrived within minutes, too fast for any system to help.

After 1964

The disaster catalyzed major improvements in tsunami preparedness:

National Tsunami Warning Center: Established in 1967 in Palmer, Alaska (originally called the West Coast and Alaska Tsunami Warning Center), this facility was specifically created to provide rapid warnings to Alaska and the U.S. West Coast. It remains operational today as the National Tsunami Warning Center (NTWC), serving the continental U.S., Alaska, and Canada.

Seismic monitoring expansion: The Worldwide Standardized Seismograph Network was expanded, and real-time seismic data transmission was improved, enabling faster magnitude estimates and tsunami assessments.

Tide gauge network: Additional coastal sea-level monitoring stations were deployed throughout Alaska and the Pacific, improving the ability to confirm tsunami generation and track wave propagation.

Community preparedness: Coastal communities in Alaska and the Pacific Northwest began developing tsunami evacuation maps and procedures, a practice that has since become standard in tsunami-prone areas. The importance of understanding the earthquake-tsunami connection for public safety became a central lesson.

Reconstruction and Recovery

Alaska's recovery from the 1964 earthquake was shaped by both federal assistance and the necessity of rebuilding in a seismically active environment.

Town Relocations

Valdez was rebuilt at a new site approximately 6.5 km from the original townsite, on more geologically stable ground. The original waterfront, built on unstable glacial outwash, was recognized as fundamentally unsafe. The new site, chosen after geological evaluation, was located on bedrock.

Chenega was eventually rebuilt as Chenega Bay on a different island (Evans Island) in the 1980s, after survivors had dispersed to other communities for nearly two decades. The relocation of these communities was among the first examples of managed retreat from natural hazard zones in the United States.

Building Codes

The earthquake prompted revisions to seismic building codes nationwide. The performance of engineered structures during the earthquake — including the near-complete failure of several reinforced concrete buildings — led to updated requirements for ductile reinforcement and improved foundation design in seismic zones. Alaska adopted some of the most stringent seismic building codes in the United States.

Could It Happen Again?

The Alaska-Aleutian subduction zone remains fully capable of producing M9+ earthquakes. The plate boundary continues to accumulate strain at 55–65 mm per year, and no amount of smaller earthquakes can fully relieve that strain.

Alaska's seismic hazard extends across the entire southern coast of the state. USGS hazard models identify the Shumagin Gap (west of Kodiak Island) and the Yakataga Gap (east of Prince William Sound) as segments that have not ruptured in a major earthquake for over a century and may be accumulating significant strain.

A repeat of the 1964 earthquake today would be far more destructive in economic terms. Anchorage's population has grown from 82,000 to over 290,000. Kenai Peninsula communities, Valdez (now the terminus of the Trans-Alaska Pipeline), and Kodiak have all grown significantly. The pipeline infrastructure alone represents a critical vulnerability that did not exist in 1964.

However, warning systems have improved enormously. The NTWC can issue tsunami warnings within minutes. Alaska's coastal communities have evacuation plans. Seismic building codes are far more advanced. The question is not whether another great earthquake will strike Alaska — it will — but whether the lessons of 1964 will prove sufficient when it does.

Map Specification

Title: 1964 Great Alaska Earthquake — Epicenter, Deformation Zones, and Tsunami Path

Map Coverage: Southern Alaska from Anchorage to Kodiak, with inset showing transpacific tsunami travel to U.S. West Coast

Key Features to Display:

• Epicenter: 61.04°N, 147.73°W (northern Prince William Sound)
• Approximate rupture zone: ~800 km from Prince William Sound SW to Kodiak Island
• Uplift zone (seaward): shaded area along coast, label maximum +11.5 m at Montague Island
• Subsidence zone (landward): shaded area inland, label maximum -2.3 m near Portage
• Key damaged locations: Anchorage, Valdez, Seward, Whittier, Cordova, Chenega, Kodiak
• Tsunami propagation arrows: to Crescent City (CA), Hawaii
• Inset: Pacific Ocean with tsunami travel time contours (4 hr, 5 hr, 8 hr)

Chart Specification

Chart 1: Deaths by Cause — 1964 Alaska Earthquake

• Type: Horizontal bar chart or pie chart
• Data:
  • Tsunami (local submarine landslide waves): 81 deaths
  • Tsunami (tectonic/distant): 29 deaths
  • Earthquake shaking (building collapse, landslides): 9 deaths
  • Other (drowning, fire, related causes): 12 deaths
  • Total: 131
• Note: Approximately 91% of all deaths were tsunami-related

Chart 2: Vertical Ground Deformation at Key Locations

• Type: Bar chart (positive = uplift, negative = subsidence)
• Data:
  • Montague Island: +11.5 m
  • Middleton Island: +3.3 m
  • Cordova: +1.8 m
  • Girdwood: -1.5 m
  • Kodiak: -1.8 m
  • Portage: -2.3 m

Sources

1. Plafker, G. (1965). "Tectonic Deformation Associated with the 1964 Alaska Earthquake." Science, 148(3678), 1675–1687.
2. U.S. Geological Survey. "M9.2 — 1964 Great Alaska Earthquake." USGS Event Page
3. National Research Council (1970). The Great Alaska Earthquake of 1964. National Academy of Sciences, Washington, D.C.
4. Lander, J.F. (1996). Tsunamis Affecting Alaska: 1737–1996. NOAA National Geophysical Data Center.
5. NOAA National Tsunami Warning Center. "History of the Tsunami Warning Centers." NOAA Tsunami Warning
6. Brocher, T.M., et al. (2014). "The 1964 Great Alaska Earthquake and tsunamis — A modern perspective and enduring legacies." USGS Fact Sheet 2014-3018. USGS Fact Sheet 2014-3018
7. Christensen, D.H., and Beck, S.L. (1994). "The rupture process and tectonic implications of the Great 1964 Prince William Sound Earthquake." Pure and Applied Geophysics, 142(1), 29–53.