PRINCE WILLIAM SOUND EARTHQUAKE, MARCH 28, 1964
The Prince William Sound magnitude 8.4 earthquake at 03:36 UT on March 28, 1964, was one of the largest shocks ever recorded on the North American Continent. The quake was felt over 500,000 square miles. The epicenter was located at 61.1 degrees N, 147.7 degrees W in the wilderness at the head of Prince William Sound. The quake took 131 lives and caused $350-500 million in property damage. (One hundred twenty two of the deaths were attributed to the tsunami.)
The area of the damage zone (50,000 square miles) and the duration of the quake (3 to 4 minutes) were extraordinary. Certainly the quake would have claimed many more lives had the population not been sparse, the weather clement, and had the quake not occurred during the off-season for fishing and on the evening of a holiday when the schools were empty and most offices deserted.
The quake was accompanied by vertical displacement of earth over a 100,000 square mile region. The maximum uplift recorded was 33 feet (10 m) on land, and as much as 50 feet (15 m) on the sea floor. Subsidence exceeded 7 feet (2 m). The uplift destroyed or greatly impaired the usefulness of many harbors. The habitats of many animals, trees and other vegetation were destroyed or damaged by subsidence. Low-lying settlements and many miles of railroad and highway were dropped below the level of high tide so that they were periodically flooded and attacked by storm waves. Crustal deformation associated with this earthquake was the most extensive ever recorded and extended far beyond the epicentral area.
Faulting of bedrock at the earth's surface during the earthquake was found only in the area of maximum tectonic uplift on southwest Montague Island in Prince William Sound and on the sea floor southwest of Montague Island. No faulting at the surface was found in the zone between the areas that were tectonically uplifted and downdropped. Grabens (elongated down-dropped blocks between faults) formed in many places. The strong ground motion induced many snowslides, rockfalls, and subaerial and subaqueous landslides. Large subaerial slides in Anchorage and subaqueous slides at Valdez and Seward damaged streets, buildings, utilities, and shore side structures. Numerous slope and embankment failures harmed railways, highways, and particularly bridges.
Rock avalanches and snow avalanches, subsidence, and consolidation occurred; and cracks, fissures, and sand spouts developed in many places. Soil liquefaction played a major roll in the development of most landslides.
DAMAGE TO STRUCTURES, TRANSPORTATION, AND UTILITIES
Anchorage, Cordova, Homer, Kodiak, Seldovia, Seward, and Valdez were damaged severely by uplift or subsidence, shaking, landslides, tsunamis, and fires. In Anchorage damaging landslides occurred in Turnagain, Fourth Avenue, "L" Street, and Government Hill areas. Structural damage was largely the result of landslides. Seismic vibration caused severe structural damage in Anchorage, Valdez, and the large delta of the Copper River. Damage from seismic vibration was most common in buildings and structures constructed of heavy materials and tended to be most severe in tall buildings.
Notable among the partly or completely collapsed buildings in Anchorage were the Four Seasons apartment building, the Government Hill School, and the J.C. Penney building. However, many of the heavy structures in these areas sustained minimal seismic damage. Generally well-built wood-frame buildings of seismic resistant design sustained very little damage from vibration generated by the earthquake. Valdez was severely damaged by a large submarine landslide and the resulting waves that destroyed the waterfront facilities. The ground beneath the town was deformed damaging the foundations of structures. The town was moved to a new site at a cost of $37,500,000.
Damage to surface transportation facilities was extensive. Landslides, embankment failures, subsidence of ground, tsunami action, and soil movements that distorted or destroyed bridges were the main causes of damage. The Alaska Railroad lost its port facility at Whittier, its docks at Seward, and numerous bridges on the Kenai Peninsula. Reconstruction of the railroad facilities was completed in two and one half years at a cost of $22 million. Many highway bridges, especially on the Seward and Copper River highways, were damaged. Many port and harbor facilities, especially at Seward, Valdez, Kodiak, Whittier, Cordova, and Homer, were destroyed.
The major damage to utilities occurred in Anchorage where the earth slides set in motion by the earthquake caused extensive damage to all utility systems. Oil storage tanks at Valdez, Seward, and Whittier ruptured and burned.
The submarine landslides resulting from the earthquake created local sea waves or tsunamis, which, together with the major tsunami generated by the crustal deformation, smashed port and harbor facilities, disturbed and killed salmon fry, leveled forests, and caused the saltwater invasion of many coastal freshwater lakes. In addition to the local tsunamis the earthquake generated a major tsunami that was recorded throughout the Pacific Basin and lapped against Antarctica.
The major tsunami caused extensive damage outside Alaska in Port Alberni British Columbia and took 16 lives in Oregon and California. Of the one hundred twenty-two deaths resulting from the tsunamis, at least 71 deaths were blamed on the local slump-generated tsunamis in Alaska. The quake also generated seiches in rivers, harbors, channels, lakes, and swimming pools as distant as the United States Gulf Coast States. Total tsunami damage amounted to about $84 million in Alaska.