INTRODUCTION
The Alaskan earthquake occurred on Good Friday, March
27, 1964, at 5:36 PM local time. It was the largest earthquake ever recorded
in North America.
Duration estimates range from 3 to 5 minutes.
Sources vary as to the magnitude of this earthquake,
in part because a variety of scales are used to measure earthquakes. Bruce
Bolt lists it as 8.6 Ms, where Ms is the surface-wave magnitude. The USGS
gives it a 9.2 Mw, where Mw is the moment magnitude.
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EPICENTER
The epicenter was located between Valdez and
Anchorage, near Prince William Sound.
The earthquake occurred on a thrust fault. This fault
was a subduction zone, where the Pacific plate plunges underneath the North
American plate.
The first slip occurred at a depth of 25 km (16
miles), which is a shallow depth.
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TSUNAMI
The sudden uplift of the Alaskan seafloor caused a
tsunami, which was responsible for 122 of the 131 deaths.
The tsunami propagated at speeds over 400 miles per
hour.
The tsunami reached the Hawaiian Islands.
The tsunami also struck Crescent City, California,
killing ten people. Giant redwood logs from a nearby sawmill were thrust
into the city streets.
A total of 16 people died in Oregon and California.
Seiches occurred in rivers, lakes, bayous, and
protected harbors and waterways along the Gulf Coast of Louisiana and Texas,
causing minor damage. Note that a seiche is a sloshing of water back and
forth.
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HARBOR WAVES
As landslides cascaded into the sea, they generated
gigantic harbor waves that smashed upward against the shore, in some places
as high as 100 feet above normal tide levels, per Reference 3.
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ANCHORAGE
The earthquake also caused ground liquefaction,
whereby the soil and sand temporarily turned from a solid to a liquid state.
Rockslides and avalanches occurred as a result of the
liquefaction. Some of the landslides occurred in Anchorage, particularly at
Turnagain Heights. Soft clay bluffs at this location collapsed during the
strong ground motion. About 75 homes were thus destroyed.
The property damage cost was about $311 million. Much
of the property damage occurred in Anchorage. For example, the J.C. Penney
Company building and the Four Seasons apartment building were damaged beyond
repair.
The Penney's building facade consisted of massive
concrete panels, which were five inches thick. The panels broke off from the
building and fell into the street. A woman driving by was struck and killed
in her car. A young man crouching on the street was also killed.
Several schools in Anchorage were also destroyed,
including the Government Hill elementary school. Fortunately, the schools
were closed due to the Good Friday holiday.
The 68 foot tall concrete control tower at Anchorage
International Airport toppled over, killing the air traffic controller.
In addition, water, sewer, and gas lines ruptured. Telephone and electrical
service was also disrupted.
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VALDEZ
The port of Valdez is 120 miles east of Anchorage.
The S.S. Chena freighter was unloading supplies at
the town dock when the earthquake began. A giant harbor wave lifted the S.S
Chena thirty feet. The wave killed 28 people who were at the dock. The S.S.
Chena was able to break free and move safely into the bay.
The Valdez waterfront and many homes and commerical
buildings were destroyed.
The ground in Valdez had rolling undulations, with an
amplitude of three feet from crest to trough.
Later in the evening at 10:30 pm, continuing waves
combing with a rising tide flooded broad sections of Valdez. The waves
occurred at 30 minute intervals, until 2 am.
The residents fled to the hills, where they spent the
night in subfreezing cold.
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SEWARD
Seward is an oil port and railroad terminus, located
80 miles south of Anchorage.
The events at Seward were similar to those at Valdez,
except that the Seward suffered an additional catastrophe of fire. Oil pipes
ruptured. Entire tanks at the Standard Oil storage facility exploded.
Burning petroleum spewed out in a sheet of fire across the harbor.
Twelve people at Seward died.
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KODIAK ISLAND
The initial ground shocks did little damage to
Kodiak. Fisherman nearby in St. Paul harbor noticed a long, gentle swell
followed by a sudden ebb. The water receded until the remaining depth was
only two feet. The 160 boat fishing fleet sat on the bottom of the harbor in
mud. A series of giant wave stuck the harbor, beginning at 6:20 pm. The
waves picked up boats and waterfront buildings, propelling them three blocks
into town. Two crab and salmon canneries were obliterated.
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CONCLUSION
The 1964 Alaskan earthquake was the largest
earthquake ever recorded in North America in terms of magnitude.
The 1906 San Francisco earthquake was the worst U.S. earthquake in terms of
death toll, however, resulting in at least 700 deaths.
The largest earthquake ever recorded was a 9.5 Mw earthquake in Chile in
1960.
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