Alaska, in relation to fault line
Well-constructed light wood frame buildings
and the Prince William Sound area.
for the most part resisted the shock forces of the
earthquake that occurred in Alaska on Good Fri�
day of 1964. This was not generally true of other
types of construction. Because the majority ofthe
homes in the Anchorage area were of wood frame
construction, damages were usually superficial
except in those areas where severe earth subsid�
ence had occurred. There was some variation in
the performance of the houses, basedoften on ma�
terial choice, fastening methods, andconstruction
details. Because the primary purpose of the sur�
vey was the investigation of wood frame struc�
tures, the majority of the descriptions cover such
units. However, in the interest ofprovidinginfor�
mation for development of better constructionde�
tails for small buildings constructed of a combi�
nation of materials, illustrations and details of
many types of failures are included. WOOD STRUCTURE PERFORMANCE
IN AN EARTHQUAKE
1
IN ANCHORAGE, ALASKA-MARCH 27, 1964
by
L. O. ANDERSON, Engineer
and
J. A. LISKA, Chief,
Division of Wood Engineering Research
FOREST PRODUCTS LABORATORY,
2
FOREST SERVICE
U . S. DEPARTMENT OF AGRICULTURE
INTRODUCTION
On Friday, March 27, 1964, an earthquake of
intensity estimated at 8.6 on the RichterScale oc�
curred in the Prince William Sound area at 5:40
p.m. Anchorage time. It is stated that the epi�
center was located at approximately 148� longi�
tude and 61� latitude, which would put it some
80 miles southeast of Anchorage. The fault has
been described as a line from the epicenter to�
ward Kodiak Island (fig. 1). It is reported that
the land west of the fault sank from 1 to several
feet, while the land east of the fault was raised
in comparable amounts. The earthquake damage
was variable, from severe to minor in various
localities throughout the Prince William Sound
area.
Early reports and news photographs indicated
severe property damage. However, details of the
kind of structural failures and the types of build�
ings that suffered the greatest damage were gen�
erally lacking. Because of U.S. Forest Service
interest in the performance of wood structures,
the Division of Forest Products and Engineering
Research requested the Forest Products Labora�
tory to conduct a survey of the damaged area.
These are the observations made during that
survey.
Severe damage resulted from tsunami (seismic
sea wave) action to several Alaskancities, includ�
ing Seward, Kodiak, and Valdez. In these latter
areas, the wave action had carried many or most
of the damaged structures into the sea.
Observations to evaluate the effect of the earth�
quake on structureswere, therefore, confined pri�
marily to the Anchorage area. The shock in the
1The authors inspection was greatlyfacilitated bythe excellent assistance from the personnel of the Forest
Service Region 10 office, including W. H. Johnson, Regional Forester; Richard W. Wilke, Regional
Engineer; Cecil A. Stowell, Assistant Regional Engineer; and Malcolm Greany, Photographer; and by
J. F. Grant, Supervisor of the Chugach Forest, and John F. Mufich, Forest Engineer.
'Maintained at Madison, Wis., in cooperation with the University of Wisconsin. ZM 126411
Figure 2.--Anchorage.The large cross-hatched area
on the left is the Turnagain bluff housing area
where damage to houses was caused by major
earth slides.
Anchorage area was reportedly very severe over
the entire city and lasted a period of several min�
utes. Therefore, building damage in varying
amounts occurred throughout the city.
In general, it might be said that the major
buildings were damaged because of the acceler�
ation forces on the buildings and lack of frame
action; damage to the smaller buildings and houses
resulted primarily from foundation failures. It is
reported that Anchorage is deep in an earthquake
zone and that most of the city is built on a glacial
outwash of sand and gravel up to 50 feet thick,
which rests on 100-foot-thickbeds of saturated
Bootlegger Cove clay. When this soil was set
in motion by the quake, destructive slides oc�
curred that were responsible for severe damage
in many areas.
The concentrated earthquake damage in Anchor�
age was confined to three major areas (fig. 2).
In the Turnagain bluff area, the earth tended to
crack, slide, and fold over toward Cook Inlet
with resulting severe damage to 77 houses.
2 ZM 126 414
Figure 3.--Woodframe home in Turnagain bluff area.
Earth subsidence destroyed a portion of the base�
ment but caused little harm to house. Temporary
bracing has been placed under the left portion.
There were massive slides in this area, and at
the time of the inspection much of the remaining
bluff area was in hazardous condition.
Other major areas of damage occurred in the
central area of Anchorage, and resulted from a
major subsidence of the earth known as a graben.
In these areas, which varied from narrow cracks
to those 300 or 400 feet in width, the structural
damage was most often due to the slumpingof the
soil.
A similar type of failure occurred in the Govern�
ment Hill area where the earthhadsubsidedsome
15 to 20 feet and resulted in the collapse of the
Government Hill School and several houses in the
area (fig. 2). In this area,, however, very little
damage to structures was noted outside of the
major subsidence zone.
It was reported that 215 homes were destroyed
in the Anchorage area and 157 commercialbuild-
Figure 4.--Failureof a section of basement wall did
not harm this two-storywood frame house.
ZM 126 416
ZM 126 419
Figure 5.--Fissure in earth (center, foreground)
caused slight movement of floor slab and twisting
of garage door. This home is near the Turnagain
housing area where severe earth slides occurred.
ings were made unusable. The estimate of damage
was approximately $200 million. At the time the
examination was made, 1-1/2 weeks after the
quake, undamaged homes and businesses were
back in operation with gas, lights, and water
facilities.
In general, it might be said that structural fail�
ures resulted from inability of the structure to act
as a unit or because inadequate provisions were
made for resistance to lateral loads. Well-
constructed wood buildings usually came through
the earthquake with a minimum of damage. Many
steel and concrete buildings came through the
earthquake very well, but many were severely
damaged. Size and height of the building and the
severity and duration of the shocks may have been
important factors in the variation in damage to
the many structures.
Figure 6.--Inadequatefastening of wall to floor system
caused some floor damage. Little racking of the
house was apparent though one end had fallen into
an
earth fault.
ZM 126 421
3 4
ZM 126 422
Figure 7.--Althoughthe porch is somewhat awry, this
small wood frame house was rigid enough to span
the hole caused by earth subsidence.
SMALL
WOOD FRAME
BUILDINGS
The greater portion of the time spent on exam�
ination and analysis of earthquake damage was
concentrated on wood frame houses and apart�
ments. It was felt that inspection of both sound
and failed buildings would reveal factors relating
to good performance, and result in improved con�
struction details for wood structures.
Foundations
The majority of the wood frame houses in the
earth subsidence areas and in adjacent areas con�
tained basements, although both crawl space and
slab construction were noted in homes and in
Figure 8.--Earth collapse caused failure of the
concrete block foundation wall of this crawl space
house. A portion of the top course of the block is
still attached to the floor plate. The rigidity of the
wood-framed walls prevented deflection and
damage to the house proper.
ZM 126 424
ZM 126 425
Figure 9.--Thisone-story office building constructed
on a concrete slab was racked and badly damaged
in an earth subsidence area, primarily because of
slab failure. Wood roof decking and laminated
beams are practically undamaged.
medium-size apartments. A number of houses re�
mained in place, partially supported on relatively
solid ground, even though portions of the masonry
wall basement were destroyed when the earth
dropped from under the house (figs. 3 and 4).
However, the inherent rigidity of the exterior and
interior walls of the wood frame houses was
sufficient to prevent any significant deflection or
Figure 10.--Althoughthis wood house had been
exposed to earth slides as well as shocks from the
earthquake, only moderate damagetothe structural
frame was apparent.
ZM 126 427 ZM 126 428
Figure 11.--Althoughtipped and dropped many feet,
this wood frame 'house still retained its identity.
damage. Most of the buildings under these con�
ditions were to be moved to new locations.
Under conditions of earth subsidence, most con�
crete or masonry foundation walls or concrete
slabs w