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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 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. This set of slides shows geologic changes, damage
to structures, transportation systems, and utilities and tsunami damage. It features
the effects of four major landslides in Anchorage during the 1964 event. 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.Geologic
Changes - 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 Coper 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.Tsunamis - 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.
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