The 1964 Alaska earthquake, also known as the Great Alaska earthquake and Good Friday earthquake, occurred at 5:36 PM AKST on Good Friday, March 27, 1964. Across south-central Alaska, ground fissures, collapsing structures, and tsunamis resulting from the earthquake caused about 139 deaths.
Lasting four minutes and thirty-eight seconds, the magnitude 9.2–9.3 megathrust earthquake remains the most powerful earthquake ever recorded in North America and the second most powerful earthquake ever recorded in the world since modern seismography began in 1900. Six hundred miles (970 km) of fault ruptured at once and moved up to 60 ft (18 m), releasing about 500 years of stress buildup. Soil liquefaction, fissures, landslides, and other ground failures caused major structural damage in several communities and much damage to property. Anchorage sustained great destruction or damage to many inadequately earthquake-engineered houses, buildings, and infrastructure (paved streets, sidewalks, water and sewer mains, electrical systems, and other man-made equipment), particularly in the several landslide zones along Knik Arm. Two hundred miles (320 km) southwest, some areas near Kodiak were permanently raised by 30 feet (9 m). Southeast of Anchorage, areas around the head of Turnagain Arm near Girdwood and Portage dropped as much as 8 feet (2.4 m), requiring reconstruction and fill to raise the Seward Highway above the new high tide mark.
In Prince William Sound, Port Valdez suffered a massive underwater landslide, resulting in the deaths of 32 people between the collapse of the Valdez city harbor and docks and inside the ship that was docked there at the time. Nearby, a 27-foot (8.2 m) tsunami destroyed the village of Chenega, killing 23 of the 68 people who lived there. The survivors outran the wave, climbing to high ground. Post-quake tsunamis severely affected Whittier, Seward, Kodiak, and other Alaskan communities, as well as people and property in British Columbia, Washington, Oregon, and California. Tsunamis also caused damage in Hawaii and Japan. Evidence of motion directly related to the earthquake was also reported from Florida and Texas.
On March 27, 1964, at 5:36 p.m. AKST (March 28, at 3:36 a.m. UTC), a fault between the Pacific and North American plates ruptured near College Fjord in Prince William Sound. The epicenter of the earthquake was 12.4 mi (20.0 km) north of Prince William Sound, 78 miles (126 km) east of Anchorage and 40 miles (64 km) west of Valdez. The focus occurred at a depth of approximately 15.5 mi (24.9 km). Ocean floor shifts created large tsunamis (up to 220 feet (67 m) in height), which resulted in many of the deaths and much of the property damage. The earthquake also caused large rockslides, resulting in great property damage. Vertical displacement of up to 38 feet (12 m) occurred, affecting an area of 100,000 square miles (260,000 km2) within Alaska.
Studies of ground motion have led to a peak ground acceleration estimate of 0.14–0.18 g. The earthquake was assigned a maximum Modified Mercalli intensity of X (Extreme). Shaking was felt across much of Alaska and parts of western Yukon and British Columbia in Canada.
The Alaska earthquake was a subduction zone (megathrust) earthquake, caused by an oceanic plate sinking under a continental plate. The fault responsible was the Aleutian Megathrust, a reverse fault caused by a compressional force. This caused much of the uneven ground, the result of shifting to the opposite elevation. Uplift occurred across 520,000 km2 (200,000 sq mi) from southern Kodiak to Prince William Sound and further east of the sound. The maximum uplift was in Montague Island, where the ground was raised 13–15 m (43–49 ft) relative to sea level. The uplift also affected Kodiak, Sitkalidak, and Sitkinak islands. Subsidence was observed for 285,000 km2 (110,000 sq mi) from north and west of the sound, in Chugach Mountains, most of Kenai Peninsula, and almost all the Kodiak Island group.
Two types of tsunami were produced by this subduction zone earthquake. There was a tectonic tsunami produced in addition to about 20 smaller and local tsunamis. These smaller tsunamis were produced by submarine and subaerial landslides and were responsible for the majority of the tsunami damage. Tsunami waves were noted in over 20 countries, including Peru, New Zealand, Papua New Guinea, Japan, Mexico, and in the continent of Antarctica. The largest tsunami wave was recorded in Shoup Bay, near Valdez, Alaska, with a height of about 220 ft (67 m).
Death toll, damage, and casualties
As a result of the earthquake, 139 people are believed to have died: Fifteen died as a result of the earthquake itself and another 124 died from the subsequent tsunamis in Alaska, Oregon, and California. Five died from the tsunami in Oregon, and 13 died from the tsunami in California, mostly in or near Crescent City. Property damage was estimated at $116 million ($894 million in 2024 dollars).
Most damage occurred in Anchorage, 75 mi (121 km) northwest of the epicenter. Anchorage was not hit by tsunamis, but downtown Anchorage was heavily damaged, and parts of the city built on sandy bluffs overlying "Bootlegger Cove clay" near Cook Inlet, most notably the Turnagain neighborhood, suffered landslide damage. The neighborhood lost 75 houses in the landslide, and the destroyed area has since been turned into Earthquake Park. The Government Hill school suffered from the Government Hill landslide, leaving it in two jagged, broken pieces. Land overlooking the Ship Creek valley near the Alaska Railroad yards also slid, destroying many acres of buildings and city blocks in downtown Anchorage. Most other areas of the city were only moderately damaged. The concrete control tower at Anchorage International Airport collapsed, killing the controller on the top floor, as well as trapping two cooks on the first floor, who were later rescued.
One house on W. 10th Avenue suffered peripheral damage, but only one block away the recently completed (and still unoccupied) Four Seasons Building on Ninth Avenue collapsed completely, with the concrete elevator shafts sticking up out of the rubble like a seesaw.
The hamlets of Girdwood and Portage, located 30 and 40 mi (48 and 64 km) southeast of central Anchorage on the Turnagain Arm, were destroyed by subsidence and subsequent tidal action. Girdwood was relocated inland and Portage was abandoned. About 20 miles (32 km) of the Seward Highway sank below the high-water mark of Turnagain Arm; the highway and its bridges were raised and rebuilt in 1964–66.
Most coastal towns in the Prince William Sound, Kenai Peninsula, and Kodiak Island areas, especially the major ports of Seward, Whittier and Kodiak were heavily damaged by a combination of seismic activity, subsidence, post-quake tsunamis and/or earthquake-caused fires. Valdez with 32 dead was not totally destroyed, but after three years, the town relocated to higher ground four miles (6.4 km) west of its original site. Some Alaska Native villages, including Chenega and Afognak, were destroyed or damaged. The earthquake caused the ballistic missile detection radar of Clear Air Force Station to go offline for six minutes, the only unscheduled interruption in its operational history. Near Cordova, the Million Dollar Bridge crossing the Copper River also suffered damage, with Span #4 slipping off its pylon and collapsing. The community of Girdwood was also confined to the southern side of the Seward Highway when water rushed into Turnagain Arm and flooded or destroyed any buildings left standing to the north of the highway. Only the ground immediately along the highway and that on the north side of the road dropped, prompting geologists to speculate that Girdwood may rest upon an ancient cliff face covered by thousands of years of sediment and glacial deposits.
A 4.5 ft (1.4 m) wave reached Prince Rupert, British Columbia, just south of the Alaska Panhandle, about three hours after the earthquake. The tsunami then reached Tofino, on the exposed west coast of Vancouver Island, and traveled up a fjord to hit Port Alberni twice, washing away 55 homes and damaging 375 others. The towns of Hot Springs Cove, Zeballos, and Amai also saw damage. The damage in British Columbia was estimated at CA$10 million ($100 million in 2025 Canadian dollars or $96 million in 2025 US dollars).