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### Effects of the earthquake of March 27, 1964, at Seward, 
Alaska: Chapter E in The Alaska earthquake, March 27, 1964: effects on 
communities

#### Professional Paper 542-E

###### This report is Chapter E in The Alaska earthquake, March 27, 1964: 
effects on communities.  For more information, see: Professional Paper 542

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#### Abstract

Seward, in south-central Alaska, was one of the towns most devastated by the 
Alaska earthquake of March 27, 1964. The greater part of Seward is built on an 
alluvial fan-delta near the head of Resurrection Bay on the southeast coast of 
the Kenai Peninsula. It is one of the few ports in south-central Alaska that is 
ice free all year, and the town’s economy is almost entirely dependent upon its 
port facilities.

The Alaska earthquake of March 27, 1964, magnitude approximately 8.3–8.4, 
began at 6:36 p.m. Its epicenter was in the northern part of the Prince William 
Sound area; focal depth was 20–50 km.

Strong ground motion at Seward lasted 3–4 minutes. During the shaking, a 
strip of land 50–400 feet wide along the Seward waterfront, together with docks 
and other harbor facilities, slid into Resurrection Bay as a result of 
large-scale submarine landsliding. Fractures ruptured the ground for'severa1 
hundred feet back from the landslide scarps. Additional ground was fractured in 
the Forest Acres subdivision and on the alluvial floor of the Resurrection River 
valley; fountaining and sand boils accompanied the ground fracturing. 
Slide-generated wares, possibly seiche waves, and seismic sea waves crashed onto 
shore; ware runup was as much as 30 feet above mean lower low water and caused 
tremendous damage; fire from burning oil tanks added to the destruction. Damage 
from strong ground motion itself was comparatively minor. Tectonic subsidence of 
about 3.6 feet resulted in low areas being inundated at high tide.

Thirteen people were killed and five were injured as a result of the 
earthquake. Eighty-six houses were totally destroyed and 260 were heavily 
damaged. The harbor facilities were almost completely destroyed, and the entire 
economic base of the town was wiped out. The total cost to replace the destroyed 
public and private facilities was estimated at $22 million.

Seward lies on the axis of the Chugach Mountains geosyncline. The main 
structural trend in the mapped area, where the rocks consist almost entirely of 
graywacke and phyllite, is from near north to N. 20° E. Beds and cleavage of the 
rocks commonly dip 70° W. or NW. to near vertical. Locally, the rocks are 
complexly folded or contorted. So major faults were found in the mapped area, 
but small faults, shear zones, and joints are common.

Surficial deposits of the area hare been divided for mapping into the 
following units: drift deposits, alluvial fan deposits, valley alluvium, 
intertidal deposits, landslide deposits, and artificial fill. Most of these 
units intergrade and were deposited more or less contemporaneously.

The drift deposits consist chiefly of till that forms moraines along the 
lower flanks of the Resurrection River valley and up tributary valleys. The till 
is predominantly silt and sand and lesser amounts of clay-size particles, 
gravel, cobbles, and boulders. Glacial outwash and stratified ice-contact 
deposits constitute the remainder of the drift deposits.

Fans and fan-deltas have been deposited at the valley mouths of tributary 
streams. Some, including the one upon which Seward built, project into 
Resurrection Bay, and deltaic-type deposits form their distal edges. The larger 
fans—composed chiefly of loosely compacted and poorly sorted silt, sand, and 
gravel—form broad aprons having low gradients. The fan deposits range in 
thickness from about 100 feet to possibly several hundred feet and, at least in 
some places, lie on a platform of compact drift. Smaller fans at the mouths of 
several canyons have steep gradients and considerable local relief.

Valley alluvium, deposited chiefly by the Resurrection River, consists mostly 
of coarse sand and fine to medium gravel. In the axial part of the valley it is 
probably more than 100 feet thick. Near the head of Resurrection Bay, the 
alluvium is underlain by at least 75 feet of marine deltaic sediments, which are 
in turn underlain by 600 or more feet of drift in the deepest part of the 
bedrock valley.

Beach, deltaic, and estuarine sediments, deposited on intertidal flats at the 
head of the bay and along far1 margins that extend into the bay, arc mapped as 
intertidal deposits. They consist mostly of silt, sand, and fine gravel, and 
lesser amounts of clay-size particles.

The earthquake reactivated old slides and trigged new ones in the mountains. 
Rock and snow avalanches, debris flows, and creep of talus deposits 
characterized slide activity on the steeper slops. The Seward waterfront had 
been extended before the earthquake by adding artificial fill consisting of 
loose sand and gravel; part of the lagoon area had been filled with refuse. 
After the earth- quake, fill, consisting of silt and sand dredged from the head 
of the bay, was pumped onto part of the lagoon area and also on land at the 
northwest corner of the bay.

Response to the disaster was immediate and decisive. City, State, and Federal 
agencies, as well as other organizations and individuals, gave unstintingly of 
their time and facilities. Within a few days, there was temporary restoration of 
water, sewerage, and electrical facilities.

The U.S. Army Corps of Engineers was authorized to select sites and construct 
a new dock for the Alaska Railroad, a new small-boat basin, and related 
facilities. The firm of Shannon and Wilson, Inc., under contract to the Corps of 
Engineers, investigated subsurface soils extensively to determine the factors 
responsible for the sliding along the Seward waterfront and to assist in site 
selection for reconstruction of the destroyed harbor facilities. Borings also 
made along the Seward waterfront and at the head of the bay, and laboratory 
tests were conducted on pertinent samples. These studies were augmented by 
geophysical studies both on land and in the bay. In addition, the Corps of 
Engineers made shallow borings on the intertidal flats at the head of the bay 
and performed pile-driving and load tests. Borings also were drilled and test 
pits were dug in the subdivision of Forest Acres.

Sliding along the Seward waterfront markedly deepened the water along the 
former shoreline. Post-earthquake slopes of the bay floor immediately offshore 
also are steeper in places than before the earthquake. The strong ground motion 
of the earthquake triggered the landsliding, but several factors may have 
contributed to the magnitude and characteristics of the slides. These factors 
are: (1) the long duration of strong ground motion, (2) the grain size and 
texture of the material involved in the sliding, (3) the probability that the 
finer grained materials liquefied and flowed seaward, and (4) the added load of 
manmade facilities built on the edge of the shore, Secondary effects of the 
slides themselves—sudden drawdown of water, followed by the weight of returning 
waves—also may have contributed to the destruction.

Submarine sliding at the northwest corner of the bay occurred in fine-grained 
deltaic deposits whose frontal slopes probably were in metastable equilibrium 
under static conditions. Uplift pressures from aquifers under hydrostatic head, 
combined with the probable liquefaction characteristics of the sediments when 
vibrated by strong ground motion, probably caused the material to slide and flow 
seaward as a heavy slurry.

Under static conditions, no major shoreline or submarine landsliding is 
expected in the Seward area; in the event of another severe earthquake, however, 
additional sliding is likely along the Seward waterfront and also in the deltaic 
deposits at the northwest corner of the bay. Fractured ground in back of the 
present shoreline along the Seward waterfront is an area of incipient landslides 
that would be unstable under strong shaking. For this reason the Scientific and 
Engineering Task Force placed the area in a high-risk classification and 
recommended no repair, rehabilitation, or new construction in this area 
involving use of Federal funds; it was further recommended that the area should 
be reserved for park or other uses that do not involve large congregations of 
people. The deltaic deposits at the head of the bay probably also would be 
susceptible to sliding during another large earthquake. This sliding would 
result in further landward retreat of the present shoreline toward the new 
railroad dock. Specifications for the new dock, whose seaward end is now 
approximately 1,100 feet from the back scarp of the subaqueous landslide, 
require design pro- visions to withstand seismic shock up to certain 
limits.

Earthquake-induced fracturing of the ground in the subdivision of Forest 
Acres was confined to the lower part of a broad alluvial fan. There, sewer and 
water lines were ruptured and the foundations of some homes were heavily 
damaged. Landsliding, such as occurred along the shoreline of the bay, was not a 
contributing cause of the fracturing. Two hypotheses are offered to explain the 
fracturing:

1. Seismic energy was transformed into visible surface waves of such 
amplitude that the strength of surface layer was exceeded and rupturing 
occurred; tensional and compressional stresses alternately opened and closed the 
fractures and forced out water and mud.

2. Compaction by vibration of the fine-grained deposits of the fan caused 
ground settlement and fracturing; ground water under temporary hydrostatic head 
was forced to the surface as fountains and carried the finer material with 
it.

Water waves that crashed onto shore, while shaking was still continuing, were 
generated chiefly by onshore and offshore landsliding. Waves that overran the 
shores about 25 minutes after shaking stopped and that continued to arrive for 
the next several hours are believed to be seismic sea waves (tsunamis) that 
originated in an uplifted area in the Gulf of Alaska. During the time of seismic 
sea-wave activity and perhaps preceding it, seiche wares also may have been 
generated within Resurrection Bay and complicated the wave effects along the 
shoreline.

#### Study Area



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