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The
Great Alaska EarthquakeMarch 27, 1964,
George Pararas-Carayannis
(Excerpts
from studies undertaken under contract with the National Science
Foundation and the Office of Naval Research and from review of
the literature. Additional data obtained from the Historical
Catalogs of Tsunamis in Alaska. Most photographs were obtained
from archives of the International Tsunami Information Center).
Introduction
The second largest
earthquake of the 20th Century and the largest ever recorded
in the northern hemisphere,occurred in Alaska on March 27, 1964
(3/27/64 05:36:14.0 p.m., local time; 3/28/64 03:36:14.0 GMT).
The earthquake had a magnitude 9.2 (Moment Magnitude) and caused
extensive damage in Alaska. Local tsunami waves triggered by
this earthquake were extremely destructive in Prince William
Sound and other areas of Alaska. A Pacific-wide tsunami was generated
which was destructive in Western Canada, Oregon, California and
the Hawaiian islands. It was recorded by tide gages throughout
the Pacific. Even tide gauges in Cuba and Puerto Rico recorded
sea level oscillations from that event. A Tsunami Warning was
issued by the Tsunami Warning System in Honolulu for Hawaii and
the West coast of United States and Canada. Regional Tsunami
Warning Centers in Japan, Chile, the former Soviet Union and
elsewhere, issued warnings. Combined, the earthquake and tsunami
took 125 lives (tsunami 110, earthquake 15), and caused about
$311 million in property loss (in 1964 dollars).
Seismic Parameters
Origin Time: (3/27/64, 05:36:14.0 p.m., local
time)
Earthquake Magnitude: The Surface-wave magnitude
calculated in 1964, was 8.4 on the Richter scale. The Moment
Magnitude calculated later was 9.2, making this event the second
largest earthquake ever recorded in the world and the largest
for the Northern Hemisphere. (Moment Magnitude provides a better
measure of energy release for larger earthquakes; the May 22,
1960 earthquake in Chile had a Moment Magnitude of 9.5, the largest
earthquake ever recorded).
Epicenter: The epicenter was at 61.04 N.
- 147.73 W. (About 10 km east of the mouth of College Fiord,
approximately 90 km west of Valdez and 120 km east of Anchorage.)
Focal Depth: Approximately 25 km.
Duration of Rupture: Estimated at approximately 4 minutes (240
sec)
Aftershock Distribution
There were 52 larger
aftershocks which were heavily concentrated on the northeast
and the southwest of the uplifted region (USC&GS, 1964),
(which was also the tsunami generating region). The largest had
a magnitude of 6.7. The first 11 of these aftershocks, with magnitude
greater than 6.0 on the Richter scale, occurred in the first
day; in the next three weeks there were 9 more of similar magnitude.
Aftershocks continued for more than a year. Thousands of such
smaller aftershocks were recorded in the months following the
main earthquake.
The aftershock zone
of the Great Alaska Earthquake was about 250 km wide and extended
from about 15 km north of Valdez in Prince William Sound for
800 km to the SW end of Kodiak Island to about 55 km. south of
the Trinity Islands. The main shock and its aftershocks occurred
on a fault which marks part of the boundary between the Pacific
and North American tectonic plates.
Earthquake Energy: Earthquake Energy can be
calculated from empirical relationship of maximum earthquake
focal depth H (in km) and Richter earthquake magnitude M (Iida
1958) :
M- 6.42 + 0.01 H
where M is the Richter
magnitude given by log E(ergs) - 11.8 + 1.5 M . An estimatesof earthquake
energy of approximately 6x10 (raised to the 25 power) in ergs
given by the author elsewhere for this earthquake, represents
only a portion of the total earthquake energy of the Great Alaska
earthquake. Richter magnitude saturates and does not provide
a very accurate measure of total earthquake energy. Presently,
Moment Magnitude is used as it is a better measure of earthquake
energy release. Thus, the energy of the Great Alaska Earthquake
was much greater than what has been reported.
Tectonic Movements and
Earthquake Triggering Mechanism
 Plate
Tectonics: The
tectonic history of the region shows that the Pacific plate moves
in a northwestern direction at about 5 to 7 cm per year. This
Pacific tectonic plate movement causes the crust of southern
Alaska to be compressed and warped, with some areas along the
coast being depressed while other areas inland are being uplifted.
At time intervals ranging from tens to hundreds of years, this
compression is relieved by the sudden motions of large portions
of the coastal portion of Alaska moving back in a southeastern
direction over the subducting Pacific plate.
Area Affected by the
Earthquake: The
tectonic dislocations associated with the Alaska earthquake of
27 March 1964 ranged over a distance of 800 km, from the upper
portion of Prince William Sound to southwest of the Trinity Islands,
in the Gulf of Alaska. The dislocations follow a dipole pattern
of positive and negative displacements on either side of a zero-line
which, intersects the east coast of Kodiak Island and continues
northeast to the western side of Prince William Sound. There,
changing direction, it runs east along the upper part of the
Sound. This line roughly parallels the Aleutian Trench axis and
separates the Kodiak geosyncline from the shelf geanticline.
According to field measurements conducted by the U.S. Geological
Survey, the earthquake was accompanied by vertical displacements
over an area of about 520,00 square kilometers. These estimates
are considerably greater than those reported earlier in the literature
and reflect revisions due to subsequent, more complete surveys
of land displacements from that earthquake in Alaska. (See parenthetical notes below
regarding earthquake area and energy that contributed to the
generation of the open sea tsunami)
Area Over Which the
Great Alaska Earthquake Was Felt: The earthquake was the strongest ever felt in
North America. The area over which it was felt encompassed approximately
1,300,000 km2 (all of Alaska,parts of western Yukon Territory
and British Columbia, Canada and the State of Washington).
Horizontal Displacements: As a result of the 1964 earthquake
quake, the net horizontal movement of the Pacific plate under
the North American plate was about 9 meters on the average in
a southeast direction, although some sections apparently moved
considerably more. For example, Latouche Island area moved about
18 meters to the southeast.
Uplift and Subsidence: The earthquake caused vertical displacements
which ranged from about 15 meters of uplift to 2.3 meters of
subsidence relative to sea level. Patterns of uplift and subsidence
which had been slowly developing prior to the earthquake were
suddenly reversed. For example, average uplift at Montague Island
was 4-9 meters while off the southwest end of the island, there
was vertical displacement ranging around 13 - 15 meters. Uplift
also occurred along the extreme southeast coast of Kodiak Island
while at Women's Bay, on the same island, subsidence of 1.7 meters
was measured from tide gauges datum. Sitkalidak Island, and over
part or all of Sitkinak experience uplift while areas around
Portage subsided by as much as 3 meters. Other areas had no change.
The zero line (line of no vertical change separating the uplift
and subsidence zones) extended from near the epicenter in Prince
William Sound to the SE coast of Kodiak Island.
The zone of subsidence
covered about approximately 285,000 square kilometers. It included
the the west part of the Chugach Mountains, the north and west
parts of Prince William Sound, most of Kenai Peninsula, and almost
all the Kodiak Island group, all the way to Trinity islands.
AUTHOR'S NOTE: Although the dimensions of the
affected area were somewhat understated by the author in a previous
publication as land surveys were still pending (see Source Mechanism Study of the
Great Alaska Earthquake and Tsunami of 1964), in calculating the tsunami energy, the tsunami
generating area was correctly estimated to encompass approximately
140,000 km2 (sq. Km) as shown in the adjacent map. This is the
area of displacements under water as determined independently
from tsunami wave refraction. Similarly reasonable is the estimate
of total crustal volume of displacement of the ocean floor being
120 km3 (cubic km)(for tsunami energy calculations) in the tsunami-generating
area in the Gulf of Alaska. The area of Prince William Sound
was excluded. The estimates were arrived at from measurements
of subsidence and uplift at Kodiak, Sitkalidak, Sitkinak and
Portage and at Montague Island. Although these displacement measurements
were few and sporadic, using these values and dimensions established
indirectly by tsunami wave refraction results, a three-dimensional
isopach of changes was obtained through mathematical integration
to calculate the total volume of displacements in the ocean only.
These estimates were then used to calculate the total earthquake
energy that contributed to the generation of the open sea tsunami
in the Gulf of Alaska, and not for the tsunami waves generated
in the Prince William Sound.
Seismic Waves: In addition to damage in the
epicentral region immediately following the quake, long period
seismic waves traveled around the earth for several weeks. States
as far away as Texas and Florida were affected with vertical
motions of up to 5 to 10 cm. (adapted from D. Christensen, UAF).
In fact, these seismic surface oscillations contributed to the
generation of Seiches, as described below, in enclosed bodies
of water, at great distances away from the affected region in
Alaska
Seiches: The surface seismic waves traveling
around the earth caused numerous Seiches in small enclosed bodies
of water, such as boat harbors. In fact, seiche action in rivers,
lakes, bayous, and protected harbors and waterways along the
Gulf Coast of Louisiana and Texas caused minor damage. In Louisiana,
several fishing boats sunk. Oscillations in the level of water
in wells were reported from as far away as South Africa.
Earthquake Damage
The area where there
was significant damage covered about 130,000 km2. Major structural
damage occurred in many of the cities in Alaska, but primarily
in Anchorage. Most of the structural damage of other coastal
towns was primarily caused by the resulting tsunami waves. Also,
the nearly four minute duration of earthquake shaking triggered
many subaerial and underwater landslides, avalanches and caused
ground liquefaction. Earthquake damage from the earthquake was
heavy in many other towns, besides Anchorage. Towns such as Chitina,
Glennallen, Homer, Hope, Kasilof, Kenai, Kodiak, Moose Pass,
Portage, Seldovia, Seward, Sterling, Valdez, Wasilla, and Whittier
sustained considerable earthquake damage.
Earthquake Damage
at Anchorage
 Although almost 120 kilometers away from the
earthquake's epicenter, Anchorage sustained severe damage. Earthquake
shock waves lasting approximately 3 minutes caused extensive
damage or total destruction to buildings and houses over a large
area of approximately 30 city blocks, mostly in the downtown
area. All utilities were disrupted throughout the city and the
suburbs.
Enormous landslides
contributed to heavy damage in the downtown business section.
Among the many building that were destroyed or damaged beyond
repair in the downtown area, were the J.C. Penney Building and
the Four Seasons apartment building, the latter a newly erected
six-story structure which collapsed totally. Many other substantial,
multistory buildings were damaged severely beyond repair.
Another huge landslide,
the largest, at Turnagain Heights devastated about 130 acres
of residential property destroying about 75 houses. Another large
landslide at Government Hill caused severe destruction . All
schools in Anchorage were nearly demolished. The huge landslide
resulted in the severe damage to the Government Hill Grade School.
Also, Anchorage High School and Denali Grade School were damaged
severely. (photo of 4th Street in Anchorage after the earthquake;
ITIC archives)
Losses and Death Toll
from the Earthquake
The death toll was
extremely small for a quake of this size. This was primarily
due to the low population density of Alaska in 1964, the time
of day (A holiday - Good Friday) and the type of material used
to construct many buildings in Alaska(wood).
Deaths: 115 in Alaska, 16 in Oregon
and California
Monetary losses: Estimated losses were in the
$300-400 million dollars range(1964 dollars)
REFERENCES
COX, D.C. and Pararas-Carayannis,
George. A Catalog
of Tsunamis in Alaska.
World Data Center A- Tsunami Report, No. 2, 1969.
GRANTZ, A.G., G. Plafker,
and R. Kachadoorlan, 1964.
Alaska's Good Friday
Earthquake, March 27, 1964: A Preliminary Geologic Evaluation, U.S. Geol. Survey Circ. 491,
35 pp.
KACHADOORIAN, R.,
1965.
Effects of the Earthquake
of March 27, 1964 at Whittler, Alaska, U.S. Geol Survey Prof. Paper 542-B, 21 pp.
KACHADOORIAN, R. and
G. Plafker, 1966.
Effects of the Earthquake
of March 27, 1964 at Kodiak and Other Communities on the Kodiak
Islands, U.S. Geol.
Survey Prof. Paper 542-F, 41 pp.
LEMKE, R.W., 1966.
Effects of the Earthquake
of March 27, 1964 at Seward, Alaska, U.S. Geol. Survey Prof. Paper 542-E, 43 pp.
PARARAS-CARAYANNIS,
G., 1965.
Source Mechanism Study
of the Alaska Earthquake and Tsunami of 27 March 1964: Part I.
Water Waves, Univ.
of Hawaii, Hawaii Inst. Geophys. Tech. Rpt., HIG 65-17, pp. 1-28
PARARAS-CARAYANNIS,
G., 1967.
Source Mechanism Study
of the Alaska Earthquake and Tsunami of 27 March 1964, The Water
Waves. Pacific Science.
Vol. XXI, No. 3, July 1967.
PARARAS-CARAYANNIS,
G.1972.
"A Study of the
Source Mechanism of the Alaska Earthquake and Tsunami of March
27, 1964." Volume
on Seismology and Geodesy on the Great Alaska Earthquake of 1964,
National Academy of Sciences, Washington D.C., pp 249- 258, 1972.
PLAEKER, G. and R.
Kachadoorian, 1966.
Geologic Effects of
the March 1964 Earthquake and Associated Seismic Sea Wave on
Kodiak and Nearby Islands, Alaska, U.S. Geol. Survey Prof. Paper 543-D, 46 pp.
PLAFKER, G. and L.R.
Mayo, 1965.
Tectonic Deformation,
Subaqueous Slides and Destructive Waves Associated with Alaskan
March 27, 1964 Earthquake: An Interim Geologic Evaluation, U.S. Geol. Survey, Menlo Park,
Calif., 21 pp
SEISMOL. DIVISION,
USC & GS, 1964.
Preliminary Report:
Prince William Sound, Alaskan Earthquake, March-April 1964, U.S. Coast and Geod. Survey,
83 pp.
WOOD, F., ed., 1966.
The Prince William
Sound, Alaska, Earthquake of 1964 and Aftershocks, v. 1, Operational Phases, U.S.
Coast and Geodetic Survey, No. 10-3, 263 pp.
Source
Mechanism of the Great Alaska Earthquake and Tsunami of 27 March
1964
The
March 27, 1964 Tsunami in the Gulf of Alaska
The
March 27, 1964 Tsunami Waves in Prince William Sound, Alaska (under construction)
The
Effects of the March 27, 1964 Alaska Tsunami in Canada
The
Effects of the March 27, 1964 Alaska Tsunami In Californiaunder construction
The
Effects of the March 27, 1964 Alaska Tsunami in the Hawaiian
Islands
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