Fourth Avenue in Anchorage, Alaska,
looking east from near Barrow Street. The southern edge of one of
several landslides in Anchorage, this one covered an area of over a
dozen blocks, including 5 blocks along the north side of Fourth Avenue.
Most of the area was razed and made an urban renewal district
The
1964 Alaskan earthquake, also known as the
Great Alaskan Earthquake, the
Portage Earthquake and the
Good Friday Earthquake, was a
megathrust earthquake that began at 5:36 P.M. AST on
Good Friday, March 27, 1964. Across south-central Alaska, ground fissures, collapsing structures, and
tsunamis resulting from the earthquake caused about 143 deaths.
The powerful earthquake produced
earthquake liquefaction
in the region. Ground fissures and failures caused major structural
damage in several communities, much damage to property and several
landslides.
Anchorage sustained great destruction or damage to many
inadequately 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 southwest, some areas near Kodiak were
permanently raised by 30 feet (9.1 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 30 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; survivors out-ran 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, Oregon, and California.
Tsunamis also caused damage in Hawaii and Japan. Evidence of motion
directly related to the earthquake was reported from all over the earth.
Geology
The Alaska Earthquake was a
subduction zone earthquake (
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 which is the result of ground shifted to the
opposite elevation.
Calculated travel time map for the tectonic tsunami produced by the 1964 Prince William Sound earthquake in Alaska
Various sources indicate that about 131 people died as a result of the
earthquake: nine as a result of earthquake itself, 106 from subsequent
tsunamis in Alaska and 16 from tsunamis in
Oregon and
California. Property damage was estimated at over $310 million ($2.25 billion in current U.S. dollars).
Anchorage area
Most damage occurred in Anchorage, 75 mi (120 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 60-foot concrete
control tower at
Anchorage International Airport was not engineered to withstand earthquake activity and collapsed, killing one employee.
The house at 918 W. 10th Avenue suffered damage peripherally, but one
block away the recently completed and still unoccupied Four Seasons
Building on Ninth Avenue collapsed completely with one whole wing
sticking up out of the rubble like a seesaw.
The hamlets of
Girdwood and
Portage, located 30 and 40 mi (60 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.
A winter scene of a "Ghost forest"
that was killed and preserved by salt water along with ruined
buildings at the site of the former town of Portage, 2011
Elsewhere in Alaska
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 was not totally destroyed, but after three years, the town
relocated to higher ground 7 km (4 mi) west of its original site. Some
Alaska native villages, including
Chenega and
Afognak, were destroyed or damaged. The earthquake caused the Cold-War era 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 collapsed. The community of Girdwood
was also confined to the southern side of the Seward Highway when water
rushed into Turnagain Arm arm and flooded or destroyed any buildings
left standing to the north of the highway. Interestingly, 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, now covered by countless thousands of
years of sediment and glacial deposits.
Canada
A 4.5 ft (1.4 m) wave reached
Prince Rupert, British Columbia, just south of the
Alaska Panhandle, about three hours after the quake. 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 $10
million Canadian ($65 million in 2006 Canadian dollars, or $56 million
in 2006 U.S. dollars).
Elsewhere
Twelve people were killed by the tsunami in or near
Crescent City, California, while four children were killed on the Oregon coast at
Beverly Beach State Park. Other towns along the U.S.
Pacific Northwest and
Hawaii were damaged. Minor damage to boats reached as far south as
Los Angeles.
As the entire planet vibrated as a result of the quake, minor effects were felt worldwide. Several fishing boats were sunk in
Louisiana, and water sloshed in wells in
Africa.
Aftershocks
There were thousands of aftershocks for three weeks, following the main
shock. In the first day alone, eleven major aftershocks were recorded
with a magnitude greater than 6.2. Nine more occurred over the next
three weeks. It was not until more than a year later that the
aftershocks were no longer noticed.
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