The Alaska Earthquake 

March 27, 1964 

Regional Effects 

Surface Faults 

on Montague Island 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 543-G 
/ 

IRDDIIillliBD~I 3 1819 00086481 5 

THE ALASKA EARTHQUAKE, MARCH 27, 1964: 

REGIONAL EFFECTS 

Surface Faults 

On Montague Island 

Associated with the 

1964 Alaska Earthquake 

By GEORGE PLAFKER 

A description and tectonic analysis of ground 

breakage and surface warping along two 

reactivated reverse faults 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 543-G 

1\PR 1 3. iOSI 

m 14 ,~ss 

UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary 

GEOLOGICAL SURVEY 

William T. Pecora, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1967 

For sale by the Superintendent of Documents, U.S. Government Prmtmg Office 

Washmgton, D.C. 20402 
THE 

ALASKA EARTHQUAKE 

SERIES 

The U.S. Geological Survey is publishing the results of investigations of the Alaska earthquake of 

March 27, 1964, in a series of six professional papers. 

Professional Paper 543 describes the regional effects 

of the earthquake. Other professional papers describe 

the history of the field investigations and reconstruction effort; the effects of the earthquake on communities; the effects on the hydrologic regime; and the 

effects on transportation, communications, and 

utilities. 

Abstract ____________________ _ 

Introduction _________________ _ 

Regional tectonic setting ______ _ 

Geographic and geologic setting_ 

Description of the faults _______ _ 

Patton Bay fault ___________ _ 

Beach and sea cliff near Neck Point_ _________ _ 

From the sea cliff to Tortuous Creek _________ _ 

1. Map showing regional 

setting of Montague 

Island _______________ 

2. Map showing tectonic 

displacements on southwestern Montague Island _________________ 

3-5. Photographs: 

3. Patton Bay fault in 

sea cliff near Jeanie 

Point ____________ 

4. Patton Bay fault 

scarp crossing 

shore near Jeanie 

Point ___________ 

5. Shear zone along 

Patton Bay fault __ 

Page 

G1 

1 

2 

4 

6 

7 

7 

13 

Page 

G3 

5 

8 

9 

9 

CONTENTS 

Description of the faults-Con. Page 

Patton Bay fault-Con. 

Tortuous Creek to the valley 

of Patton River_ _____ _ G16 

Patton River valley segment _______________ _ 21 

Patton River valley to 

Purple Bluff _________ _ 22 

Submarine extension of Patton 

Bay fault ______________ _ 26 

ILLUSTRATIONS 

PLATES 

[Plates are In pocket] 

1. Geologic map of part of the Patton Bay fault. 

2. Geologic map of the Hanning Bay fault. 

FIGURES 

3-5. Photographs-Continued Page 

6. Sketch map of tectonic 

cracks near Patton Bay 

fault ________________ GlO 

7-13. Photographs: 

7. Tectonic crack in 

warped upthrown 

fault block _______ 11 

8. Crack along joints in 

a graywacke bed __ 12 

9. Crack in massive indurated sandstone._ 12 

10. Fissure in glacial deposits along trace 

of Patton Bay 

fault ____________ 13 

Description of the faults-Con. 

Hanning Bay fault _________ _ 

South of Fault Cove ______ _ 

At Fault Cove ___________ _ 

Fault Cove to Hanning Bay ________________ _ 

Horizontal displacements indidicated by geodetic meas- urements ________________ _ 

Summary and conclusions _____ _ 

References ___________________ _ 

7-13. Photographs-Continued 

11. Warped muskeg along trace of Patton Bay fault ____ 

12. Warped and fissured 

muskeg along tracf' 

of Patton Bay 

fault_ ___________ 

13. Tectonic fissures and 

landslides on ridge 

near Patton Bay 

fault_ _________ -

14-16. Aerial views: 

14. Landslides along 

Patton Bay fault 

trace __________ 

v 

Page 

G27 

27 

29 

35 

40 

41 

42 

Page 

G14 

15 

15 

17 
VI CONTENTS 

14-16. Aerial views-Continued Page 20-33. Photographs-Continued Page 20-33. Photographs-Continued Page 

15. Patton Bay fault 25. Air view of scarp at 33. Tectonic crack in 

trace showing off- south end of reef near HanseL ___________ 017 Hanning Bay ning Bay fault __ 034 

16. Large landslide fault_ _______ --- 027 34. Sketch map of tectonic 

scars near Nellie 26. Hanning Bay fault cracks near Hanning 

Martin River ___ 18 scarp in glacial Bay fault_ ___________ 35 

17. Sequential sketch of for- deposits ________ 28 35-39. Photographs: 

mation of landslides 27. Fissured and warp- 35. Air view of Hanalong the trace of a ed scarp along ning Bay fault reverse fault __________ 18 Hanning Bay north of Fault 

18. Photograph of sheared fault ___________ 28 Cove __________ 36 

rock along Patton Bay 28. Pre- and post- 36. Toppled trees along fault ________________ 19 earthquake ver- Hanning Bay 19. Photograph and sketch tical air views of fault __________ 37 of incised channel of Fault cove ______ 30 37. Ponded stream be- Nellie Martin River ___ 20 29. Air view of Han20-33. Photographs: ning Bay fault hind Hanning 

20. Tilted trees along scarp at Fault Bay fault scarp_ 38 

Patton Bay fault Cove __________ 31 38. Air view of Hantrace __________ 22 30. Hanning Bay fault ning Bay fault 

21. Air view of tectonic scarp at south southwest from 

fissures on ridge side of Fault the bay ________ 38 

summit ________ 23 Cove ________ - __ 32 39. Warped and fis22. Tectonic fissures on 31. Hanning Bay fault sured beach de- ridge summit ___ 23 scarp at north posits near north 23. Minor normal side of Fault Cove_ 33 end of Hanning faults with downhill side uplifted_ 24 32. Displaced storm Bay fault _______ 39 

24. Vertical air view beach along Han- 40. Diagram illustrating the 

of reactivated ning Bay fault horizontal displacefaults at Purple at north side of ments indicated by 

Bluff ___ - __ ----- 25 Fault Cove _____ 33 re-triangulation ______ 4 
THE ALASKA EARTHQUAKE, MARCH 27, 1964: REGIONAL EFFECTS 

SURFACE FAULTS ON MONTAGUE ISLAND ASSOCIATED WITH 

THE 1964 ALASKA EARTHQUAKE 

Two reverse faults on southwestern 

Montague Island in Prince William 

Sound were reactivated during the 

earthquake of March 27, 1964. New fault 

scarps, fissures, cracks, and flexures appeared in bedrock and unconsolidated 

surficial deposits along or near the fault 

traces. Average strike of the faults is 

between N. 37o E. and N. 47° E.; they 

dip northwest at angles ranging from 

50° to 85°. The dominant motion was 

dip slip ; the blocks northwest of the 

reactivated faults were relatively upthrown, and both blocks were upthrown 

relative to sea level. No other earthquake faults have been found on land. 

The Patton Bay fault on land is a 

complex system of en echelon strands 

marked by a series of spectacular landslides along the scarp and (or) by a 

zone of fissures and flexures on the upthrown block that locally is as much as 

3,000 feet wide. The fault can be traced 

on land for 22 miles, and it has been 

mapped on the sea floor to the southwest 

of Montague Island an additional 17 

miles. The maximum measured vertical 

component of slip is 20 to 23 feet and 

the maximum indicated dip slip is about 

The great earthquake of March 

27, 1964, in south-central Alaska 

was accompanied by regional tectonic warping that caused both extensive subsidence and uplift relative to sea level. During the months 

after the earthquake geologists 

made a concerted search for evidence of surface faulting. A U.S. 

Geological Survey field party 

headed by the writer found two 

By George Plafker 

ABSTRACT 

26 feet. A left-lateral strike-slip component of less than 2 feet occurs near 

the southern end of the fault on land 

where its strike changes from northeast 

to north. Indirect evidence from the 

seismic sea waves and aftershocks associated with the earthquake, and from 

the distribution of submarine scarps, 

suggests that the faulting on and near 

Montague Island occurred at the northeastern end of a reactivated submarine 

fault system that may extend discontinuously for more than 300 miles from 

Montague Island to the area offshore of 

the southeast coast of Kodiak Island. 

The Hanning Bay fault is a minor 

rupture only 4 miles long that is marked 

by an exceptionally well defined almost 

continuous scarp. The maximum measured vertical component of slip is 16Ya 

feet near the midpoint, and the indicated dip slip is about 20 feet. There 

is a maximum left-lateral strike-slip 

component of one-half foot near the 

southern end of the scarp. Warping and 

extension cracking occurred in bedrock 

near the midpoint on the upthrown 

block within about 1,000 feet of the 

fault scarp. 

INTRODUCTION 

reverse faults on southwestern 

Montague Island in Prince William Sound through combined air 

reconnaissance and studies of 

shoreline displacements. Although 

it is assumed that the fault displacements occurred during the 

main shock, or possibly during 

some of the subsequent large aftershocks, there were no eyewitnesses 

to fix the precise time of rupture. 

The reverse faults on Montague Island and their postulated submarine 

extensions lie within a tectonically important narrow zone of crustal attenuation and maximum uplift associated 

with the earthquake. However, there 

are no significant lithologic differences 

in the rock sequences across these faults 

to suggest that they form major tectonic boundaries. Their spatial distribution relative to the regional uplift 

associated with the earthquake, the 

earthquake focal region, and the epicenter of the main shock suggest that 

they are probably subsidiary features 

rather than the causative faults along 

which the earthquake originated. 

Approximately 70 percent of the new 

breakage along the Patton Bay and the 

Hanning Bay faults on Montague Island was along obvious preexisting 

active fault traces. The estimated ages 

of undisturbed trees on and near the 

fault trace indicate that no major disc 

placement had occurred on these faults 

for at least 150 to 300 years before the 

1964 earthquake. 

The faulting definitely occurred 

prior to March 31 ( 4 days after 

the earthquake), when a part of 

one scarp was photographed during a reconnaissance flight over the 

island. The faults could not be examined on the ground until 2 

months later, at the end of May. 

As far as could be determined, 

no movement occurred along any 

other surface faults on land durGl 
G2 

ing the earthquake. A diligent 

search was made for indications of 

rene>ved movement on known preexisting faults, particularly in the 

vicinity of the zero isobase between 

the major zones of regional tectonic uplift and subsidence, but 

no measurable surface faulting 

was found. There were no anomalous abrupt changes in amounts of 

uplift ,or subsidence along the coast 

or along level lines inland from 

the coast suggestive of displacement along concealed faults. All 

reported suspected surface faulting that was checked in the field 

turned out to be linear zones of 

landslides or surficial cracks in unconsolidated deposits. Although 

some of these lines of landsliding 

or cracking could possibly reflect 

fault movements at depth, no direct evidence for such movements 

is available. 

This report substantially enlarges upon preliminary summaries of the nature and tectonic significance of the surface faulting 

that were based on data acquired 

during the 1964 field season (Plafker, 1965; Plafker and Mayo, 

1965). It presents details of the 

varied and unusually well exposed surface manifestations of 

the faults on Montague Island 

which have an important bearing 

on tectonic analyses of the earthquake. The methods used in deALASKA EARTHQUAKE, MARCH 27, 1964 

termining the location, displacement, and surface dip of the faults 

are fully described because detailed descriptions of overthrusts 

involving predominantly reverse 

or thrust movements are scarce 

compared to the literature on 

strike-slip or normal faulting. 

Such data are of increasing practical importance to geologists and 

others who are concerned with 

identifying potentially active 

faults and evaluating the possible 

effects of renewed activity on engineering works. 

Previous descriptions of the surface manifestations of overthrust 

faults are limited to studies of the 

great earthquake of 1931 centered 

on Hawke Bay, New Zealand 

(Henderson, 1933), the 1945 Mika wa earthquake in southeastern 

Honshu, Japan (Tsuya, 1950), the 

1952 Kern County, Calif., earthquakes (Buwalda and St. Amand, 

1955), and the great 1957 GobiAltai earthquake in Mongolia 

(Florensov and Solonenko, 1963). 

With the possible exception of 

some Gobi-Altai faults, the relative displacements on the faults on 

Montague Island are considerably 

larger than any overthrusts pre viously described. They are also 

unique in that absolute, as well as 

relative, displacements could be 

determined across these faults at 

four points where they intersect 

the shoreline. 

I am grateful to colleagues in 

the U.S. Geological Survey for 

assistance in the field and for much 

stimulating and helpful discussion. Field mapping of the faults 

was carried out by a boat-based and 

helicopter-supported U.S. Geological Survey party from May 30 to 

June 3, 1964, and by a helicoptersupported party from July 31 to 

August 7, 1965. L. R. Mayo and 

J. B. Case assisted in the 1964 

fieldwork, and L. R. Mayo and 

M. G. Bonilla collected much of 

the data during the 1965 season. 

Additional critical observations on 

the northeastern segment of the 

Patton Bay fault were made by 

L. C. Cluff, of the firm WoodwardClyde-Sherard and Associates, 

who visited the area briefly during 

the summer of 1966. The faults 

and related features were mapped 

on postearthquake vertical and 

oblique aerial photographs taken 

by the U.S. Army at scales of 

1 : 15,000 and 1 : 20,000 and on vertical photographs taken by the 

U.S. Coast and Geodetic Survey at 

scales ranging from 1 : 4,000 to 

1 : 20,000. Preearthquake vertical 

photographic coverage available 

for the entire island at a 'scale of 

1 : 20,000 proved to be invaluable 

for determining the relationship 

of the fault movements to older 

geologic structures. 

REGIONAL TECTONIC SETTING 

The surface breaks on Montague Island lie within the focal region of the earthquake, as defined 

by aftershock distribution, and 

within a region of tectonic deformation associated with the earthquake (fig. 1). The regional deformation has been described briefly 

in preliminary reports (Grantz 

and others, 1964; Plafker and 

Mayo, 1965; Plafker, 1965). Only 

the broad aspects of the regional 

tectonic movements will be outlined here to provide a proper perspective for the tectonic significance of these surface faults. A 

detailed description and analysis of 

the overall tectonic displacements 

will be given in a separate chapter 

on regional earthquake effects in 

this series. 

Tectonic movements, both vertical and horizontal, occurred over 

an area of at least 70,000 square 

miles, and possibly more than 110,-

000 square miles, of south-central 

Alaska. The deformed region, 

which is more than 500 miles long 

and as much as 200 miles wide, is 

roughly parallel to the Gulf of 
156' 

62' 

60' 

58' 

56' 

0 50 100 

SURFACE FAULTS ON MONTAGUE ISLAND 

150 KILOMETERS 

Epicenter of main shock 

Dashed line is boundary of zone 

of major aftershocks (M:?:J..J,) 

• 

Epicenter of major aftershock 

(M26.0) 

G3 

142' 

EXPLANATION 

~~ "' GJ) 

Area of uplift or probable uplift 

Dashed where inferred 

Area of subsidence 

Axis of uplift 

Dashed where inferred 

Axis of subsidence 

Volcano * 

Outer edge of continental shelf 

(600 feet) 

!.-Setting of Montague Island with respect to regional tectonic deformation and seismicity that accompanied the March 27, 

1964, earthquake. 
G4 

Alaska coast from the Kodiak 

group of islands northeastward to 

Prince William Sound and thence 

eastward to about long 143° W. 

It consists of a major seaward zone 

of uplift bordered on the northwest and north by a major zone of 

subsidence. These two zones are 

separated by a line of zero landlevel change that trends northeastward to intersect the mainland between Seward and Prince William 

Sound. It then curves eastward 

through the western part of Prince 

William Sound to the vicinity of 

Valdez and crosses the Copper 

River valley about 50 miles above 

the mouth of the river. 

The zone of subsidence includes 

most of the Kodiak group of islands, Cook Inlet, the Kenai 

Mountains, and the Chugach 

Mountains. The axis of maximum 

subsidence within this zone trends 

roughly northeastward along the 

ALASKA EARTHQUAKE, MARCH 27, 1964 

crest of the Kodiak and Kenai 

Mountains and then bends eastward in >the Chugach Mountains. 

Maximum recorded downwarping 

is about 71;2 feet on the south coast 

of the Kenai Peninsula. 

In the northern part of the deformed area, uplift that averages 

about 6 feet occurred over a wide 

zone including most of the Prince 

William Sound region, the mainland east of the sound, and offshore islands as far southwest as 

Middleton Island at the edge of 

the Continental Shelf. Large-scale 

uplift of the Continental Shelf 

and slope southwest of Montague 

Island is inferred from the trend 

of isobase contours in the northeastern part of >the deformed zone 

and from the presence of a fringe 

of uplifted capes and points along 

the outer coast of the Kodiak Island area. The minimum extent of 

this inferred offshore zone of uplift is thought to be roughly outlined by the earthquake focal region, or belt of major a:£tershocks, 

shown in figure 1. 

Montague Island lies within the 

earthquake focal region along the 

axis of maximum tectonic uplift. 

Combined surface faulting andregional warping have elevated the 

southwestern end of the island 

relative to sea level by as much as 

38 feet (fig. 2). Southwest of 

Montague Island the sea bottom 

may have been uplifted more than 

50 feet where pre- and postearthquake bottom soundings show residual vertical displacements at 

least as large as those on the adj acent land. As discussed later (p. 

26), there is indirect evidence 

which suggests that the axis of 

maximum uplift and faulting may 

extend southwestward more than 

300 miles to the area off the southeast coast of Kodiak Island. 

GEOGRAPHIC AND GEOLOGIC SETTING 

Montague Island is the most 

southerly of three long narrow islands that trend northeast across 

the south side of Prince William 

Sound (fig. 2). The island, which 

is 51 miles long by 4 to 12 miles 

wide, consists of a topographically 

rugged mountainous backbone 

ridge with average summit altitudes of 2,400 feet and a maximum 

altitude of 2,841 feet. A dense 

growth of timber and brush mantles much of the valley floors, 

raised beaches, and lower mountain slopes below an altitude of 

1,000 feet. Access through the 

vegetated areas is difficult, and is 

mainly along streams, beaches, 

and bear trails. Open areas of muskeg-a ma:t of sphagnum moss several feet thick-sedge, and opengrowth scrub occur wherever 

drainage is impeded by low and 

gently sloping topography or by 

impermeable soils. There are no 

permanent roads or inhabitants on 

the island although a few loggers 

and hunters usually live there 

intermittently during the summer 

months. No one was on Montague 

Island during the earthquake. 

The geology of Montague Island 

is known only in a general way 

from regional reconnaissance studies (Grant and Higgins, 1910; 

Moffitt, 1954; Case and others, 

1966; Plafker and MacNeil, 1966). 

The bedrock is part of the Orca 

Group, which consists of a thick 

sequence of well-indurated interbedded sandstone and siltstone, 

minor amounts of limestone as thin 

beds or lenses, and tabular to lenticular masses of basaltic lava. 

The Orca is at least in part of 

early Tertiary (probably middle 

to late Eocene) age. 

The rocks were complexly 

folded and faulted in early Tertiary time. They generally strike 

northeast parallel to the trend 

of the island, but there are numerous local deviations from this 

trend. Folds on the island are 

characteristically overt~rned towards the northwest with nearhorizontal axes; folds in most of 

the remainder of Prince William 

Sound are overturned mainly toward the southeast. Faults associated with the folding are 

mainly southeast-dipping overthrusts. Well-developed sets of 

steeply dipping conjugate shear 

joints trend at high angles to the 

strike o£ fold axes and faults in 
SURFACE FAULTS ON MONTAGUE ISLAND G5 

60"00' 

59"45' 

/ 

I 

I 

I 

I 

148"00' 

24MM 0 

30-42MM0 

24MM " 

.,., ....... 

/ 

oo' 

/ ....... --""3 

I 

Base from U.S. Geol. Survey. Blying Sound 

and Seward 1:250,000 quadrangles 1953 

' 

' 

' 

I 

0 10 MILES 

I 

I ' 

0 15 KILOMETERS 

L---~---~---_j 

10 

CO NTOUR INTERVAL 200 FEET 

DATUM IS MEAN SEA LEVEL 

A 40' 

30' 

20' 

10' 

0 

0 

14 7"30' 

,_ 

<( 

.,j "' 

Z::> 

-<( 

~lL 

<( 

I 

/ 

/-..:____ 

/ 

I 

/ 

I 

~XPLANATION 

__ u _______ _ 

Reverse fault 

/ Dashed where approximately located; dotted 

/ whe1·e irifer-red. U, upthrown side 

----10---

Isobase contour 

Showing amount of uplift, in feet. Dashed 

where approximate 

Sta'rA-63 

Relative horizontal displacement of 

triangulation station 

Arrow indicates direction; numeral is amount 

in feet (After Parkin, 1966) 

.16.58 .16.5 88 

16.58* 16.588• 

Vertical tectonic displacement, in feet, 

from measured difference between 

upper growth limit of preearthquake 

barnacles and sea level (B) or difference 

between the upper growth limits of preand postearthquake barnacles (B B). 

Asterisk indicates 1965 measurement; all 

others are 1964. Displacements within 

areas shown on plates are not included 

on the figure 

24MM 

Approximate vertical displacement, in 

feet, from difference between preearthquake and postearthquake water depths 

(After R. J. Malloy, oral commun., Apr. 

1966) 

-----300------

Submarine contour 

Showing depth, in feet 

,_ 

<( 

"'>- z-' 

o" f-<( 

>-"- A' 

-------- -----) 30' 

L__ 20· 

Postquake land surface~ <r: 140' 

10' 

__L_requake land surface ----- ------ --------- 0 

10 MILES 

0 10 15 KILOMETERS 

PROFILE OF LAND-LEVEL CHANGE ALONG LINE A-A' 

2.-Map and profile showing faults and horizontal and vertical tectonic displacements on southwestern Montague Isl•and. 
G6 

the southwestern part of the 

island. Surface faults associated 

with the 1964 earthquake parallel 

or cut obliquely across the strike 

of the older bedrock folds and 

faults at a small angle and are 

ALASKA EARTHQUAKE, MARCH 27, 1964 

clearly discordant with the dip of 

these structures. 

Unconsolidated Quaternary glacial till of variable thickness veneers bedrock on low-lying parts 

of the island, and thick deposits of 

coarse alluvium occur along the 

lower reaches of the larger streams. 

Talus, landslide deposits, and frost 

rubble commonly conceal bedrock 

on and at the base of the steeper 

slopes. 

DESCRIPTION OF THE FAULTS 

The locations of mapped fault 

traces on Montague Island and the 

distribution of vertical uplift relative to sea level are summarized in 

figure 2, and details of the features 

associated with the Patton Bay 

and Hanning Bay faults are shown 

on plates 1 and 2, respectively. The 

following general features are 

common to both the Patton Bay 

and Hanning Bay faults: (1) Both 

strike northeast almost parallel to 

the long axis of Montague Island; 

(2) both blocks are uplifted relative to sea level, with the northwest blocks upthrown relative to 

the southeast blocks; ( 3) the faults 

are northwest-dipping reverse 

faults; (4) both faults may have 

small components of left-lateral 

strike-slip displacement near their 

southern limits of exposure 

amounting to less than one tenth 

the dip-slip component; and (5) 

the new breakage occurred along 

or near the traces of preexisting 

faults which appear to have undergone earlier Holocene displacements. 

Measurement of the inclination 

of the fault plane and the dip-slip 

component of displacement is 

hampered by the general tendency 

(1) for the slip plane to be concealed by slumping or landsliding 

across the steep to overhanging 

fault scarps or (2) for bedrock 

displacements to be reflected at the 

surface by flexing and fissuring of 

overlying unconsolidated deposits 

and surface vegetation. Approximate surface dips could be determined from the inclination of 

sheared rock at several places 

along the fault scarps (pis. 1, 2) ; 

the dip of the Patton Bay fault is 

also visible in the sea cliff where 

the fault intersects the coast. 

Absolute, as well as relative, vertical displacements could be determined at shoreline intersections of 

the faults by measurement of 

shoreline changes relative to sea 

level. The isobase contours of figure 2 show the amount and direction of vertical displacement that 

accompanied the earthquake. Directions and relative amounts of 

change were determined at about 

75 localities on southwestern Montague Island from measurements 

of the displacement of the upper 

growth limit of sessile intertidal 

organisms along the seashore and 

from changes in the altitudes of 

storm beach berms. Measurements 

were made at 14 of these localities 

both in 1964 and 1965. Data-point 

locations and measured vertical 

displacements are shown in figure 

2 and on plates 1 and 2. 

The technique used for measuring vertical displacements from 

the height of the upper growth 

limit of barnacles above tidal 

planes has been outlined elsewhere 

(Plafker, 1965, p. 1675-1679) and, 

consequently, will not be elaborated upon here. Those measurements based on differences in preand postearthquake altitudes of 

the upper growth limits of barnacles are thought to be generally 

accurate to about 1 foot. Many of 

the 1964 measurements, however, 

are based only on the postearthquake altitude of these organisms 

above sea level; they contain inherent errors due to deviation of 

sea level from predicted heights 

and to variations in the growth 

limits of these organisms resulting 

from local factors of exposure, 

rock type, and water characteristics. The measurements made on 

the eastern side of the islands are 

estimated to be accurate to within 

1% feet in sheltered bays and to 

within 2% feet on segments of the 

coast exposed to heavy surf and 

swells along the ocean side. At two 

localities on sandy stretches of 

beach where barnacles were not 

present, the vertical movements 

were determined from differences 

in altitude of the pre- and postearthquake storm beach berms. 

The accuracy of these measurements is unknown, although they 

give results consistent with those 

obtained from barnacle-line measurements at nearby rocky shores. 

Submarine control for the isobase contours southwest of Montague Island is provided by comparisons of pre- and postearthquake 

bathymetric charts. Because of 

navigational and other technical 

problems in carrying out such surveys, the inferred submarine displacements could locally be in error 

by 10 feet or more. 
Measurements of vertical displacement away from the ~hore are 

based mainly on the heights of 

slope breaks in surficial deposits 

which may or may not accurately 

reflect the vertical displacement 

within the underlying bedrock. In 

those rare instances where the displacement is apparently Iocaiized 

along a scarp in bedrock, the scarp 

heigllt is taken as the net vert~cai 

displacement. Only the vertical 

component of surface displacement is shown on plates I and 2; 

dip-slip displacements may be as 

much as 25 percent greater, depending on the indicated dip of 

tlze fault at any given locality. 

PATTON BAY FAULT 

After the earthquake, the Patton 

Bay fault was traceable by a succession of exceptionally interesting 

and complex features, such as 

fresh fault scarps, surface flexures, 

and gigantic landslides. From the 

pface where the fault strikes out 

to sea 11;2 miles west of Neck 

Point, the rupture extends 11 miles 

northeastward to the valley of the 

Patton River (pl. 1). Northeast 

of Patton River, displacement is 

distributed across a broad zone of 

subparallel fissures as much as half 

a mile wide that can be traced an 

additional 11 miles as far as Purple Bluff on the southeast coast 

of the island. 

In the following account, the 

fault on land is described from 

southwest to northeast. Places referred to, including the locations 

photographed and diagramed, are 

shown on the map of the surface 

ruptures (pl. 1). The northeastern 

segment of the fault is not shown 

on the detailed map, but is shown 

at a smaller scale in figure 2. Figure 2 also shows the measured and 

inferred vertical displacement-s 

relative to sea level at and near the 

two faults and along a section 

across them. 

SURFACE FAULTS ON MONTAGUE ISLAND 

BEACH AND SEA CLIFF NEAR 

NECK POINT 

The Patton Bay fault is best exposed at its southwestern end. at 

the beach and sea cliff 11;2 miles 

west of Neck Point. It is marked 

by a pronounced scarp 6 to 81/z feet 

high which trends north-south 

across the beach and the newly uplifted surf-cut platform seaward 

from the beach (figs. 3, 4, following pages). Beach gravel draped 

across the scarp conceals the 

actual fault plane everywhere except at the one small outcrop at 

the toe of the beach prism where a 

4-foot-wide zone of sheared siltstone dips westward at an angle 

that averages about 85° (fig. 5). 

The near-vertical fissure exposed 

in the sea cliff is along the most 

probable continuation.of the ~ault. 

Its steep dip, which IS consistent 

with the fault attitude indicated 

by the sheared siltstone along the 

scarp, may represent only a nearsurface steepening of the fault 

plane where it breaks to the surface along the most direct path. 

Previous movement could have occurred along the dipping faults 

exposed in the sea cliff ( fi~. 3), 

which are undoubtedly associated 

with this same line of faulting but 

which apparently were not reactivated during the earthquake. 

The position of the barnacle line 

along the shore in the vicinity of 

the fault provides an excellent 

means of determining the absolute 

vertical displacement of the blocks 

at and near the fault as well as the 

relative vertical displacement. The 

measurements indicate that both 

blocks are uplifted relative to s~a 

level and that the western block IS 

upthrown 20 to 23 feet in relat~on 

to the eastern (pl. 1~ sectiOn 

A-A'). Uplift of the western block 

decreases progressively from 35 to 

38 feet at a distance of 800 feet 

from the fault scarp to 21 to 231/z 

feet at the scarp; uplift of the 

G7 

eastern block is about 15 feet at 

the scarp. Only 6 to 8% feet of the 

displacement occurred along the 

fault scarp that cuts the beach 

gravel and the reef at the shore 

(fig. 3) ; the remainder of the offset takes the form of a pronounced 

downwarping of the upthrown 

block within 800 feet of the fault. 

Numerous surface cracks ~s 

much as 170 feet long formed m 

bedrock on the reef part of the upthrown block within 400 feet of the 

scarp. These newly opel}ed cracks 

can be readily differentiated from 

preearthquake cracks because they 

expose fresh surfaces that do not 

have a white coating of calcareous 

algae. Locations, orientations, and 

displacements of the largest and 

most conspicuous of these cracks, 

which \vere mapped by a pace-andcompass survey, are shown in figure 6. Three typical cracks are 

illustrated in figures 7-9; the 

photographs were taken at the 

locations indicated in figure 6. No 

newly opened cracks were found 

near the fault in the downthrown 

block; close to the fault, however, 

this block is largely covered by 

beach deposits. 

The cracks all dip steeply or are 

vertical, and they appe~r to occur 

exclusively along beddmg planes 

and preexisting joints .. Displ~cement in the overwhelmmg maJority of cracks is an extension 

perpendicular to the crack face 

ranging from less than 0.01 to 0.4 

foot. Locally, the cracks are substantially widened where loose 

narrow wedge-shaped. rock slivers 

as much as 1.4 feet wide have 

dropped down along them. Le-ftlateral displacements occurred 

along two of the cracks. One of 

the two trends northeast at an 

oblique angle to the fault scarp 

and was displaced 1.0 foot (fig. 9) · 

The other crack, which is almost 

parallel to the scarp, had 0.4 foot 

of lateral offset. 


GlO 

147"43'15" 

ALASKA EARTHQUAKE, MARCH 2 7, 1 9 6 4 

d ' 

CJ 

Jeanie Cove 

Postearthquake lower low 

0 100 

Geology and planimetry by M.G. Bonilla 

and George Plafker 8 / 4/65 

200 FEET 

0 

. o 0 0 

0 

0 

EXPLANATION 

D 

57°48' 15" 

--~ 0 \<> 0 

.-; \ " 

/' c_ \0 0 Preearthqueke 

~~ IQwf):r low w-•te r~\ 

·C \0 0 

~ "1--\ 0 

"---- !15 

o , o . . -;-_::, \0 . ) 

. ......__ \0 0 0 

~ I " '::> 

"' 0 

0 

0 

0 

0 

0 

0 

0 0 

0 

'0 

Beach gravel Talus Orca Group 

D 0 . 

Mud, sand, and gravel 

u ~0--

0 'o.1·-r 

0.2 

" 

0 b 

~ 

0 

~ 

0 

0 

1J 

<J 0 

Contact Crack, showing dip and horizontal 

separation, in feet 

Vertical crack, showing horizontal 

separation in feet 

U, upthrown side; D, downthrown side 

80 

-'-

Strike and dip of beds 

®. Ground photograph location and text figure 

number 

0 

G.-Sketch map of the ooarp and open cracks in the upthrown !}lock of the Patton Bay fault at the shore near Jeanie Point. 





G16 

the adjacent wooded area. A continuous sharp flexure about 60 feet 

wide in the muskeg is broken by 

a series of open fissures parallel 

to the trend of the fault that displace the muskeg-covered surface 

and underlying stream gravel (fig. 

12). Relative vertical displacement 

across the part of the flexure in 

the bog is roughly 16% feet. This 

estimate of the vertical movement 

is minimal, because it includes only 

part of the zone of surface warping associated with the fault. The 

total width of the zone, as indicated by the distribution of spruce 

trees which are tilted towards the 

downthrown block owing to warping of the surface, is roughly 125 

feet at this locality. 

From Strike Creek to Tortuous 

Creek the fault trends across heavily timbered terrain in which the 

trace is indicated by a vaguely defined discontinuous broad zone of 

tilted trees, ground fissures, and 

small landslides. These features 

were mapped from vertical and 

oblique photographs and from 

aerial observation. An outcrop 

consisting of highly sheared siltstone was observed in the bank of 

Slide Creek at about the point 

where the fault trace would cross 

the creek, but no indications of 

new surface displacement were 

found in the densely vegetated valley bottom. 

Immediately to the north of 

Tortuous Creek, displacement is 

indicated by a zone of fissuring 

about half a mile wide that lies 

between the 'southern and central 

segments of the fault (pl. 1; fig. 

13). The fissures range from a few 

hundred to more than 1,000 feet 

in length, and most have east-facing scarps. The more continuous 

of these fissures are clearly tectonic features inasmuch as they 

ignore topography and trend 

obliquely across mountain slopes 

and even over ridges as high as 

ALASKA EARTHQUAKE, MARCH 27, 1964 

1,800 feet. Ho·wever, apparent tectonic fissures that nearly parallel 

the contours of steep slopes are 

difficult to distinguish from scarps 

at the heads of incipient landslides. 

Scarps parallel to the slopes that 

show evidence of downhill movement of the downhill side are arbitrarily mapped as landslide 

scarps; undoubtedly some represent fissures along which sliding 

has subsequently developed. 

TORTUOUS CREEK TO THE 

VALLEY OF PATTON RIVER 

The 5%-mile-long segment of 

the Patton Bay fault bebveen Tortuous Creek and the valley of Patton River trends N. 35° E. and is 

the most continuous and impressive of all the segments. It lies at 

the base of a line of imposing ridge 

spurs whieh are part of the modified searp formed on the upthro"·n 

bloek of the Patton Bay fault. 

Along the ridge spurs the fault is 

marked by a spectaeular series of 

gigantic landslides with headvmll 

searps as high as 300 feet, soil 

flows, and surface cracks associated with incipient slides on the 

slopes (figs. 14~16). The line of 

landslides along these spurs is 

broken only at the valleys of 

deeply incised streams that dissect 

the upthrown block intersecting 

the fault approximately at right 

angles. In some of these incisedstream valleys the actual fault 

trace could be seen, but in the interfluves the trace was coneealed by 

the ehaotic mass of crushed and 

pulverized landslide debris and a 

virtually impenetrable tangle of 

fallen brush and timber. The 

process by which landslide debris 

tends to bury the fault trace where 

it follmvs along the base of a 

prominent scarp is illustrated diagrammatically in figure 17. This 

process of automatic self-concealment undoubtedly occurs on most 

active overthrust faults and is 

probably one of the major reasons 

why faults of this type are commonly difficult to recognize and 

map by surfaee geologic methods. 

These ridge spurs were especially susceptible to mass gravitational movements through a combination of ( 1) steep slopes 

composed in part of unstable 

debris resulting from prior faulting; (2) bedding dips that tend to 

parallel the slopes; and ( 3) local 

zones of sheared and shattered 

bedrock along the fault plane and 

near it within the upthrown block. 

In view of this inherent instability, 

it is not surprising that oversteepening resulting from renewed 

14.~Looking southwest along the Patton Bay fau,lt in the vicinity of Jeanie 

Creek. Fault trace (dashed) is marked 

by the line of landslides at the base of 

the prominent scarp that is formed on the relatively uptiuown block. ~ 

uplift along a steep or overhanging fault scarp at the base of the 

slopes, coupled with transient accelerations due to the elastic 

ground vibrations and tectonic displacements during the earthquake, 

should have caused the massive 

slope failures. The transient movements alone seem to have been sufficient to trigger landslides under 

comparable circumstances elsewhere in the area, such as along 

upper Slide Creek, even where 

renewed faulting did not oecur. 

From Tortuous Creek to Jeanie 

Creek the fault trace is marked by 

a line of landslides at the base of 

an imposing eastward-facing slope 

that rises 1,500 feet at an average 

15.-Patton Bay fault (dashed) looking northeast toward Jeanie Creek. The 

segment of the fault north of Jeanie 

Creek is offset about 0.4 mile to the east 

relative to the segment south of the 

creek. ~ 




SURFACE FAULTS ON MONTAGUE ISLAND 

'attou Bay fault scarp. The rejuvenated riYer has eroded about-± feet of boulder , 1005. Photograph by L. R. J'lfayo. 

G21 

As shown in the profile, the indicated maximum vertical displacement at this locality is abourt 20 

feet. 

To the north, the fault trace is 

again concealed by landslides for a 

distance of almost 1% miles until it 

reappears as a zone of fissures and 

tilted trees in the alluvial fan deposits of Braided Creek and the 

nearby streams. Individual fissures 

have as much as 4 feet of vertical 

displacement, the northwest sides 

invariably upthrown. At one point 

along this trace, the fault zone is 

defined by a 40- to 60-foot-wide 

swath of trees tilted at a uniform 

angle of about 70°, resulting from 

a southeastward surface tilt of 20°. 

Approximate vertical displacement across the zone, as calculated 

from its width and surface slope 

is 14% to 22 feet. 

North of Braided Creek the 

fault follows the contact between 

predominantly massive greenstone 

tuff along the base of the mountain 

front on the upthrown block and 

the alluvial flats on the downthrown side. At the most northerly 

point on this segment, where it 

strikes into the alluvial valley of 

Patton River, the fault is exposed 

in a dry creek bed as a 3-foot-wide 

zone of sheared, crumpled, and 

scricitized siltstone that strikes N. 

10°E. and dips 67° nortlnYest. On 

the flood plain immediately north 

of this outcrop, a vertical displacement of roughly 21 feet is indicated by an average 12° downslope 

tilt of the surface over a zone 

about 100 feet "·ide (determined 

from the tilting of trees). 

PATTON RIVER VALLEY 

SEGMENT 

The Patton River Valley segment of the Patton Bay fault is 

unique in that it is entirely in an 

area of low relief underlain by 

thick deposits of unconsolidated 
G22 

alluvium. A climax forest of Sitka 

spruce composed of imposing trees 

as much as 4 feet in base diameter 

and 140 feet in height occupies the 

entire valley floor except for the 

poorly drained swampy areas or 

activo stream channels. Within 

this forest, the fault trace is defined by a remarkably persistent 

line of discontinuous. surface 

cracks and associated tilted trees 

that can be traced to the northern 

margin of the valley, a distance 

of nearly a mile. 

Tho cracks, which occur in peat 

moss and soil, are subparallel and 

trend N. 10° to 30° E. They are 

open 1 to 4 inches at the surface 

and show a few clown-to-the southeast dip-slip displacements of 2 to 

3 inches and no measurable strikeslip components. A minor set of 

cracks with a general N. 55° E. 

orientation \ras observed near the 

north end of the segment. All the 

cracks occurred in a \Yell-defined 

zone lL few hundred feet wide; no 

other newly opened cracks "·ere 

found outside this zone in the same 

general area of the valley floor. 

Tilted trees arc associated with 

the line of cracks, particularly 

south of Patton River (fig. 20), 

where anwagc tree heights of more 

than 125 feet make tilts of as little 

as 5° from the vertical readily 

apparent. 

PATTON RIVER VALLEY TO 

PURPLE BLUFF 

The character of the surface displacements along the Patton Bay 

fault zone changes markedly to the 

north of Patton RiYer ntlley. In 

this 11-mile-long segment (pl. 1; 

figs. 21, 22), tectonic movements 

are strongly suggested by numerous peculiar subparallel northeast-trencling fissures consisting 

of open cracks or normal faults 

1rith small Yertical clisp 1 acements 

that, for the most part, are uninALASKA EARTHQUAKE, MARCH 27, 1964 

20.- Looking soutlnnst along the Patton Bay fault in the alluviated valley of 

Pn:tton Ri\·er. The fault trace is indicated l.Jy the tilted giant Sitka spru~ trees 

and 1>.1· ground fissurf's that roughly parallel tilE' zone of tilted trees. 

fluenced by the topography. The 

southeastern margin of this zone 

of fissures is a conspicuous lineament, trending N. 30° E., similar 

to much of the Patton Bay fault 

to the south in that it forms a 

boundary between an imposing 

rugged ridge on the north west and 

terrain of l01rer relief on the southeast, but different in not having a 

single continuous scarp or " ·ellILj 

defined narrmr zone of displacement. The character of the fissures 

in this segment suggests the possibility that the displacement here 

is taken up mainly by a broad anticlinal flexure of the upthrown 

block and that the longitudinal 

zone of extension cracks and minor 

normal faults results from local 

t·ensile stress along the crest of the 

flexure. 
21.-Part of the zone of tectonic fissures at 3,000 feet altitude on the ridge summit north of Patton Rh·er. The fissures, some 

of which are indicated by arrows, could be traced almost continuously to the northeast through the peak (center of photograph) and the notch on the skyline to the left of the peale 0 Q 111_ 

22.-Subparallel minor normal faults within the area shown in figure 21. Note that some of these fissures coincide with preexisting linear scarps. 
G24 

The fissures were studied in detail only at one locality on the 

ridge immediately north of the 

Patton RiYer valley (pl. 1, profile 

0-0'). Here the fissures occur over 

a zone about 1,500 feet wide and 

are generally subparallel. Their 

average strike is N. 20° E. parallel 

to the ridge crest, although some 

individual fissures and segments of 

nonlinear fissures trend at an 

oblique angle to the zone- between 

N. 80° W. and N. 70° E. Some of 

the fissures arc several hundred 

feet long and as much as 17 inches 

wide. Most are nearly vertical with 

dip-slip displacement of as much 

as 21 inches (figs. 21, 22; })I. 1, 

profile 0-0'). The overall width 

of this zone of fissures is difficult 

to determine because cracks on the 

steep southeast-facing ridge slope 

cannot be readily differentiated 

from incipient landslides. The 

zone shom1 on plate 1, which is 

3,000 feet wide, includes the entire 

area in " ·hich surface cracks of 

possible tectonic origin have been 

observed. 

That the fissures on the ridge 

are tectonic features is indicated 

by ( 1) the linearity and lateral 

continuity of the zone; (2) the 

fact that most of the fissures displace bedrock ; ( 3) the occurrence 

of some fissures in which uplift on 

the downhill side, in relation to the 

uphill, precludes the possibility 

of landslide origin (fig. 23) ; and 

( 4) coincidence of many of the 

fissures with preexisting linear 

scarps in rock along which previous movements may have occurred. 

The fissure zone could be readily 

followed northward from the area 

shmn1 on profile 0-0' of plate 1 

across the highest peak on the 

ridge at an altitude of 2,200 feet. 

Beyond this point it is discontinuously evident from subparallel 

cracks and landslide scarps on the 

steep mountain slopes that were 

ALASKA EARTHQUAKE, MARCH 27, 1964 

23.-:.\Iinor normal faults along a preexisting linear groove on a steep ridge slope. 

The downhill side is uplifted 16 inches. Patton Ri\·er valley visible in the 

background. 

tracerl to Purple Bluff by aerial 

recon na 1ssance. 

Two loca 1 it ies in this zone of fissures that "·ere examined on the 

ground lJy L. C. Cluff of \Voodmtrd-Clyde-Sherard and Associates in .July 1D6G are "·orthy of 

specia ]mention. One is at the slope 

lJreak near the lJase of the ridge 

2 miles north of the Patton River 

,·alley, "·here a southeast-facing 

scarp about. half a mile long and 

-! feet high displaces Yegetation 

and soil. The length of !his scarp 

and evidence of surface displace117 

ment suggest that it may be a 

fault. The second locality is at the 

northern end of the zone, where 

renewed nrtical sm·face displacement of no more than a few inches 

occurred along several preexisting 

lineaments that extend inland 

from Pmple Bluff for a distance 

of alJout 1,600 feet (figs. 2, 24). 

Some of these fissures near the 

upper edge of the bluff may be 

along the heads of gigantic landslide lJlocks, but most of them, including many with relatively 

uplifted do,vnhill sides, seem to be 
SURFACE FAULTS ON MONTAGUE ISLAND G25 

24.-Vertical aeri,al photograph in the vicinity of Purple Bluff showing conspicuous lineaments (arrows) along the inferred 

northeastward extension of the Patton Bay fault. Renewed displacement occurred on some of these lineaments after the 1964 

earthquake. A large earthquake-induced landslide may be seen at the base of the high bluff at bottom center. Photograph by 

U.S. Coast and Geodetic Survey, August 25, 1964. r 
G26 

of tectonic or1gm. The fissures 

strike about N. i30° E. and intersect 

the coast at an acute angle immediately north of Purple Bluff. No 

detailed studies of shoreline displacement were made across the 

zone of fissures at the coast; the 

available measurements of shoreline changes (fig. 2) suggest that 

the displacement here is no more 

than a few feet or that there may 

be no displacement at all. 

An alternative possibility is that 

the fault may once again be offset 

en echelon to the southeast and 

that it continues northeastward as 

a submarine feature. Although 

there is no direct evidence for such 

an offset, the precipitous linear 

coast of Montague Island northeast of Purple Bluff, a concentration there of aftershock activity, 

and the occurrence of abrupt submarine scarps in the vicinity of 

Hinchinbrook Island (Van Huene 

and others, 1966) are suggestive 

of possible active faulting in this 

area. 

SUBMARINE EXT'ENSION 

OF PATTON BAY FAULT 

Subsequent to the discovery of 

the faults on Montague Island, the 

U.S. Coast and Geodetic Survey 

made hydrographic and seismic 

surveys of the ocean floor southwest of the island. These surveys 

have revealed a prominent southeast-facing bedrock scarp 40 to 90 

feet high that is in line with, and 

inferred to be a continuation of, 

the Patton Bay fault (fig. 2). 

Comparison of detailed bottom 

soundings taken in 1927 with 

others taken after the earthquake 

in 1964 indicates that the vertical 

uplift of the bottom on either side 

of this scarp is in the same sense 

as, and is comparable in amount to, 

that recorded on land for a distance of at least 17 miles southwest 

of the point where the fault strikes 

out to sea near Neck Point (MalALASKA EARTHQUAKE, MARCH 27, 1964 

loy, 1965a, p. 1048-1049; 1965b, 

p. 22-26). The hydrographic surveys do not come closer than 61;2 

nautical miles to the fault trace on 

land, so it is not known whether 

the onshore and offshore segments 

of the fault scarp are a continuous 

strand or perhaps are offset en 

echelon. 

Malloy (1965b, figs. 6, 7) believes that a sharp 18-foot-high 

break in slope on the continuous 

sounding and seismic profiles 

closest to shore may represent the 

1964 movement; an underwater 

photograph of what appears to be 

fresh breakage of the sea floor at 

this locality tends to support this 

interpretation. It is also significant 

that the vertical displacement 

across the submarine scarp indicated by the bathymetric surveys 

is compatible with the displacement of 20 to 2:3 feet measured 

across the scarp and warped upper 

plate along the nearby shore at the 

southern end of the fault. 

The fault probably continues 

farther southwestward, although 

the 1964 reconnaissance surveys 

did not track it as a continuous 

scarp beyond the limits of the pre1964 hydrographic survey, which 

was confined mainly to shoal 

waters. The lines of evidence discussed below suggest that the Patton Bay fault may be but the 

northern end of a fault, or of a 

system of discontinuous faults, 

that extends southwestward an additional 300 miles to the area offshore from Sitkalidak Island m 

the Kodiak Island group. 

1. That this postulated line of 

faulting is along a narrow 

zone of probable maximum 

submarine uplift is inferred 

from the spatial distribution 

and run up heights of the seismic sea waves associated with 

the earthquake (Van Dorn, 

1964, fig. 6; Plafker and 

Mayo, 1965, p. 11; Plafker 

and Kachadoorian, 1966, p. 

38-39). The waves clearly 

were generated on the Continental Shelf within the zone 

of regional uplift by vertical 

displacements of the sea 

floor. The direction of travel 

and reported arrival times of 

the initial wave crest-the 

crest that struck the shores of 

the Kenai Peninsula nearest 

to Montague Island within 19 

minutes and the southeast 

coast of Kodiak Island within 38 minutes after start of 

the earthquake-indicate that 

the wave crest was generated 

within the regional zone of 

uplift along one or more line 

sources in a narrow elongate 

belt that extends southwestward from Montague Island 

approximately along the axis 

of maximum uplift shown in 

figure 1. Furthern1ore, the 

similarities in maximum 

wave runup heights along 

physiographically comparable segments of coast, both on 

the Kenai Peninsula opposite 

Montague Island and on Kodiak Island, suggest that the 

vertical sea-floor displacements which generated the 

waves in these two areas may 

be of the same order of magnitude. 

2. The inferred zone of :fault displacement also has an especially large concentration of 

features that seem to be aresult of recent subbottom tectonic movements (D. F. 

Barnes, unpub. data, 1966; 

Von H uene and others, 1966) . 

These features include sharply defined submarine fault 

scarps similar to those near 

Montague Island, subbottom 

discontinuities that displace 

possible Holocene deposits, 

and small folds in the Holocene deposits. 


scarp in surficial deposits, tilted or 

toppled trees, and gaping extension cracks. The scarp is clearly 

visible along the extreme southern part of the fault where it 

crosses open ground along a slight 

preexisting break in slope. The 

fault trace is marked by a scarp 

as much as 511z feet high; the surficial muskeg layer and underlying glacial till on the northwest 

block has ridden up and over the 

southeastern block to form a prominent pressure ridge (fig. 25). 

'Where visible beneath the surface 

vegetation, the overhanging scarp 

in till dips about 80° NW. At its 

southern end the scarp becomes 

progressively lower and finally 

disappears. No indication of fault 

displacement was found anywhere 

along the north shore of MacLeod 

Harbor---an area which -was examined in some detail. 

The displacement is entirely 

dip-slip except for about 4 inches 

of le-fit-lateral strike-slip displacement near the south end of the 

fault. The lateral component of 

movement is indicated by rootlets 

that trend obliquely across the 

scarp (fig. 26), by the rake of striations in the fault plane, and by the 

regular right-handed en echelon 

arrangement of gaping fissures 

that follow the general course of 

the flexure but intersect it at an 

angle of about lf) 0 (fig. 27). The 

absence of lateral displacements 

elsewhere along the fault, or of 

systema6cally offset drainage 

across the fault trace, demonstrates that the strike-slip component of displacement during this 

earthquake and during earlier 

movements was relatively minor. 

27 (left).-Segment of Banning Bay 

fault trace looking northeast showing 

Rurface flexture 3 to 5 feet high broken 

by gaping sub-parallel right-handed en 

echelon cracks, 3 to 6 feet apart. Gullies that intersect the scarp at right 

angles show no evidence of lateral offset that would suggest strike-slip displacement. Arrow indicates location of 

figure 25. 

SURFACE FAULTS ON MONTAGUE ISLAND 

North of the locality shown in 

figure 27, the fault trace trends in 

a N. 35° E. direction along the 

heavily timbered channel of a 

small stream, which drains into 

the beach-barred lake at the shore. 

For most of this distance the fault 

parallels the northwest edge of the 

stream channel except at one point 

where it cuts across a meander and 

through a small bedrock hill on the 

opposite side of the creek. The 

trace is clearly marked by a break 

in slope with associated ground 

cracks and a swath of tilted and 

downed trees ,-.,hose crowns all 

point toward the relatively downthrown block. In one locality the 

slope break is 811z feet high and 24 

feet wide; right-handed en echelon 

tension cracks trending N. 15° E. 

at the top of the slope are as much 

as 1 foot 'vide and 611z feet deep. 

At the north end of this segment, the fault scarp forms the 

linear southwest shore of the 

beach-barred lake. An overhanging scarp that dips 80° northwest 

displaces glacially derived pebblecobble gravel in a blue-gray siltyclay matrix. Striations in the soft 

clay are in the direction of dip. 

AT FAULT COVE 

By far the most spectacular segment of the Hanning Bay fault is 

the part shown in figure 28 (next 

page}. It crosses a former inconspicuous embayment in the coastline, which has been transformed 

by vertical displacement during 

the earthquake into a shallow cove 

(christened Fault Cove). The 

movement produced tc single continuous scarp 1.4 miles long that 

displaces bedrock and sediments 

of the former sea floor and beach 

deposits along the shore. The fault 

trace curves gradually from 

N. 35° E. toN. 45° E. as it crosses 

the cove. At extreme low tide it 

is exposed at the surface almost 

continuously except for the perG29 

manently submerged part at the 

cove entrance which, however, is 

readily visible from the air (fig. 

29). 

The existence of a preearthquake 

submarine scarp in bedrock at this 

locality is clearly indicated by the 

fact that unconsolidated deposits 

were ponded on the shoreward side 

of the scarp, whereas bare rock is 

exposed almost everywhere else on 

the upthrown block. 

Along the south shore of Fault 

Cove, the scarp is a prominent 

southeast-facing break in slope 

about 81f2 feet high; marine sand 

and pebble-cobble-boulder gravel 

that constitute the beach prism 

have slumped across the scarp and 

thereby concealed the actual fault 

surface (fig. 30) . Linear strand 

lines on the uplifted beach, and 

bands of marine sand and gravel 

on the former submarine part of 

the beach that cross the fault at 

an oblique angle, show no evidence 

of lateral offset. 

The part of the fault trace along 

the north shore of Fault Cove in 

the area sea ward from the former 

beach prism is marked by an 

abrupt scarp in bedrock or in bedrock mantled with a thin veneer of 

unconsolidated marine deposits. 

The scarp trends either parallel to 

the strike of bedding planes in the 

bedrock or intersects them at an 

acute angle of less than 10°. It 

varies in height from 121j2 to 131/z 

feet, and along most of its length 

it consists of slumped bedrock and 

the overlying unconsolidated deposits (fig. 31). Segments of the 

scarp that originally were vertical 

or overhanging have subsequently 

slumped back to the steep angle of 

repose shown in figure 31. In part, 

the slumping was accelerated by 

undercutting of the scarp toe and 

by removal of slump debris both 

by stream runoff diverted along 

the uphill-facing scarp and by current scouring. A shallow pond oc-
G30 ALASKA EARTHQUAKE, MARCH 27, 1964 

28.-Pre- and postearthquake high-tide shorelines at Fault Cove. The cove was formed by relative uplift of the to·rmer sea 

floor northwest of the fault scarp. The white color on· the elevated bedrock surface· northwest of the fault results from dessication of oalcareous algae and other calcareous marine organisms. Upper photograph by U.S. Forest Service, June 8, 1959; 

lower photograph by U.S. Coast and Geodetic Survey, April17, 1964. 

I I .J 




SURFACE FAULTS ON MONTAGUE ISLAND G35 

34.-Sketch map Qf the larger tectonic cracks in the upthTown lblock of the Hanning Bay faurt at Fault Cove. I\'"umerous 

smaller crackSI in the same general area are not plotted. Location of photograph is shown on plate 2. Geology by M. G. Bonilla 

and George Plafker August 1, 1965. Base photograph by U.S. Coast and Geodetic Survey, July 28, 1964. 

sion cracks to the Hanning Bay 

fault is uncertain. One possibility 

is that the cracks result from local 

tensional stresses due to surface 

flexing at the culmination of a 

distinot anticlinal warp that parallels the fault trace within the upthrown block in this area (fig. 2, 

profile A-A') . 

FAULT COVE TO HANNING BAY 

North of Fault Cove the apparent strike of the Hanning Bay 

fault swings to N. 50° E. as it 

crosses the 850-foot-high drainage 

divide between Faul<t Cove and 

Hanning Bay (fig. 35, next page). 

South of the divide, the fault 

trace follows along the nort]nyest 

side of alined incised linear stream 

valleys that undoubtedly are controlled by a preexisting fault. The 

fault trace in this heavily timbered and topographically rugged 

segment is marked by a swath of 

fallen trees and brush, intermingled with debris from soil slips 

and small landslides (fig. 36). 

Ponds have formed where two 

small streams flow across the uphill-facing scarp (fig. 37). Soundings made near the scarp at the 

downstream end of these ponds, 

indicate a minimum vertical fault 

displacement of 10 feet. 

North of the ponds, the fault 

scarp follows a peculiar course 

that is northwest of, and parallel 

to, the incised linear stream valley 

{ :3 ) 
G36 ALASKA EARTHQUAKE, MARCH 2 7, 196#4 

35.-EIanning Bay fault north of Fault Core The average 65"-NW. (left) dip of this segment of the fault causes the trace 

(dashed) to be deflected uphill (right) as it crosses the 850-foot-high ridge between Fault Cove and Hanniizg Bay. The pond, 

at the intersection of the fault scarp and the fonner beach ridge, occupies a closed twtonic depression in the do~vnthromll 

block. 
left to right.


G40 

block along the northeastern margin of this flexure, and the drainage is diverted along the base of 

the scarp, which faces upslope. Net 

vertical displacement across the 

fault zone is uncertain because 

many boulders have slumped along 

the scarp and the top and bottom 

ALASKA EARTHQUAKE, MARCEr 27, 196.4 

of the flexure are not clearly defined. Measurements of the height 

of the barnacle line on either side 

of the zone indica>te that the northwest block is upthrown about 7 feet 

in relation to the southeast block 

(pl. 2). 

The fault apparently dies out 

somewhere beneath Hanning Bay. 

A detailed examination of the 

northeast shore along its projected 

strike did not reveal any of the 

features characteristics of the fault 

trace on land or any anomalous 

vertical displacements o:f the 

shoreline. 

HORIZONTAL DISPLACEMENTS INDICATED BY GEOHETIC 

MEASUREMENTS 

A re-triangulation, by the U.S. 

Coast and Geodetic Survey, of 

part o:f the network of primary 

horizontal control stations in the 

vicinity of Montague Island suggests that both the horizontal 

shortening and left-lateral component o:f displacement in this area 

may be substantially greater than 

is indicated by the surface ruptures (Parkin, 1966, fig. 4). 

Differences in displacement o:f 

two stations in the triangulation 

net-Stair (610) and Cape Cleare 

(553)-which straddle the Patton 

Bay fault as shown in figure 2, 

provide a geodetic check on the 

indicated :fault movement obtained 

:from field geologic studies. Station 

Cape Cleare is on the down thrown 

block 1 mile east of the fault trace; 

Station Stair is on the upthrown 

block 7 miles ·west o:f Station Cape 

Cleare and about 6 miles from the 

:fault. Consequently, the indicated 

relative displacement between the 

two stations results :from both 

movement on the fault and deformation of the crust between each 

o:f the stations and the fault. 

Unfortunately, the stations are 

not tied together directly across 

Montague Island, but rather are 

connected through a third -order 

triangulation net (containing a 

number of geometrically weak 

figures) , which extends around the 

Stair 

Cape Cleare 

0 5 MILES 

0 5 Kl LOM ETERS 

40.-0rientation of horizontal displacement vectors (solid arrows) at triangulation stations Stair and Cape Cleare relative to the average strike of the 

Patton Bay fault. Dashed arrows are the indicated components of horizontal 

displacement perpendicular to, and parallel to, the fault. Numerals are horizontal 

displacement in feet relative to station Fishhook ( 40 miles northeast of Anchorage), which was held fixed in the adjustment. Triangulation data from 

Parkin (1900, table 1). 

northeast end of the island. As a 

consequence, the original position 

of Station Cape Cleare relative to 

the remainder of the net is especially uncertain. Added to this uncertainty is the :fact that during 

the earthquake all stations in this 

area experienced large differential 

vertical movements with resultant 

shifts in horizontal positions of 

the stations at high altitudes. 

Nevertheless, the general similarity in orientation of the two 

vectors and their striking difference in magnitude are suggestive 

of substantial relati>v.e movements 

between them. 

As shown in figure 40, the prin-
cipal vector of horizontal movement derived from the geodetic 

data is between N. 10° W. and N. 

5° E. at an oblique angle to the 

fault system, whereas the direction 

indicated by the predominantly 

dip-slip displacements across the 

scarps is actually about N. 53° W., 

or approximately normal to the 

average strike of the faults. The 

re-triangulation data further indiSURFACE FAULTS ON MONTAGUE ISLAND 

cate that the two stations moved 

34 feet relatively toward one another in the direction of fault dip 

and that they were relatively displaced 21 feet in a left-lateral 

sense (fig. 40). The dip-slip shortening could have been taken up by 

bending of the upthrown block in 

addition to the fault displacement. 

The strike-slip displacement, on 

the other hand, should have been 

G41 

readily observable had it occurred 

along the fault. Absence of a large 

lateral-slip component on the fault 

suggests that either the displacement was taken up mostly by 

warping between the fault and the 

stations or, more probably, that an 

error has been introduced into this 

part of the triangulation adjustment through a slight clockwise 

rotation of displacement vectors. 

SUMMARY AND CONCLUSIONS 

The Patton Bay fault on land is 

represented by a complex system 

of right-handed en echelon reverse 

faults and associated flexures that 

has an average N. 37° E. strike. 

The fault at the surface dips about 

85° NW. near its southern end and 

50° to 75° elsewhere along the 

scarp. Displacement on the fault is 

almost entirely dip slip, the northwest side upthrown relative to the 

southeast side. The maximum 

measured vertical component of 

slip is 20 to 23 feet and maximum 

indicated dip slip is about 26 feet. 

A left-lateral displacement component of less than 2 feet near the 

southern end of the fault is probably a local phenomenon related 

to a change in strike of the fault 

that causes it to trend at a small 

oblique angle to the principal horizontal stress direction. 

The fault system oan be traced 

on land for 22 miles from shore to 

shore and is known to continue 

seaw~trd to the southwest for at 

least 17 miles. Indirect evidence 

suggests that the fault system may 

extend southwestward on the sea 

floor more than 300 miles. The 

fault apparently dies out on its 

north western end but it could be 

offset en echelon in a right-handed 

sense and continue northeastward 

offshore from Montague Island at 

least as far as Hinchinbrook Island. 

The Hanning Bay fault is a virtually continuous reverse fault 

with an average strike of N. 47° 

E., a total length of about 4 miles, 

and surface dips of 52° to 75° 

NW. Displacement is almost entirely dip slip except for a leftlateral strike-slip component of 

about a third of a foot near the 

southern limit of exposure. The 

maximum measured vertical component of slip is 16113 feet, and the 

maximum indicated dip slip is 

about 20 feet. 

The reverse faults on Montague 

Island and the postulated submarine extension of the Patton Bay 

Fault lie within a tectonically important zone of crustal shortening 

and maximum known uplift associated with the earthquake. The 

principal horizontal stress direction is oriented roughly normal to 

the average strike of the faults in 

a general N. 53° W. to S. 53° E. 

direction. 

The displacements that occurred 

along these two faults during the 

earthquake are large, but there are 

four convincing indications that 

the faults are not the primary features along which the earthquake 

occurred: ( 1) The lithology of the 

rock sequences is not significantly 

different on the two sides of the 

faults, as it commonly is along 

faults that form major tectonic 

boundaries. (2) Displacement 

along these known and postulated 

faults is insufficient to explain the 

areal extent of regional upliftparticularly the uplift seaward 

from the known and inferred 

trace. (3) Not enough movement 

occurred on these faults to account 

for the size and spatial distribution of the earthquake focal region, as defined by the aftershocks; this region extends in all 

directions far beyond the maximum concehnable limits of the 

known and postulated surface 

faults. ( 4) The epicenter of the 

main shock is roughly 90 miles 

away from the fault traces and in 

a position where it is not likely to 

lie on the down-dip projeetion of 

the fault planes. 

Both the Patton Bay and the 

Hanning Bay faults on Montague 

Island are along prominent linear 

breaks in slope or linear stream 

valleys that, for the most part, 

were clearly visible on aerial 

photographs taken before the 

earthquake (Condon and Cass, 

1958). Only the southern segment 

of the Patton Bay fault, for a dis-
G42 

tance of 3.3 miles, does not follow 

a well-established prior fault trace 

but instead breaks away from a 

pronounced scarp along which 

much of the previous movements 

undoubtedly occurred. Net Quaternary vertical displacement on and 

near the Patton Bay fault, as indiBuwalda, J. P., and St. Amand, Pierre, 

1955, Geological effects of the 

Arvin-Tehachapi earthquake: California Div. Mines Bull. 171, pt. 1, 

Geology, p. 41-56. 

Case, J. E., Barnes, D. F., Plafker, 

George, and Robbins, S. L., 1966, 

Gravity survey and regLonal geology of the Prince William Sound 

epicentral region, Alaska: U.S. 

Geol. Survey Prof. Paper 543-C, 

p. Cl-C12. 

Condon, "\V. H., and Cass, J. T., 1958, 

Map of a part of the Prince William 

Sound area, Alaska, showing linear 

geologic features as shown on 

aerial photographs: U.S. Geol. Survey Misc. Geol. Inv. Map I-273, 

scale 1 :125,000. 

Florensov, N. A., and Solonenko, V. P., 

eds., 1963, Gobi-Altayskoye zemletryasyeniye: Akad. Nauk SSSR, 

391 p. Also, 1965, The Gobi-Altai 

earthquake: U.S. Dept. Commerce, 

424 p. [English translation.] 

Grant, U. S., and Higgins, D. F., 1910, 

Reconnaissance of the geology and 

mineral resources of Prince William Sound, Alaska: U.S. Geol. Survey Bull. 443, 89 p. 

Grantz, Arthur, Plafker, George, and 

ALASKA EARTHQUAKE, MARCH 27, 1964 

cated by maximum topographic 

relief across it, could be 1,500 feet; 

it is probably no more than 100 feet 

on the Hanning Bay fault. 

Many of the preearthquake 

scarps along these faults are sharp 

postglacial topographic features. 

The straight spruce trees along the 

REFERENCES 

Kachadoorian, Reuben, 1964, Alaska's Good Friday earthquake, 

March 27, 1964: U.S. Geol. Survey 

Circ. 491, 35 p. 

Henderson, J., 1933, The geological 

aspects of the Hawke's Bay earthquakes: New Zealand Jour. Sci., v. 

15, no. 1, p. 38-75. 

Malloy, R. J., 1965a, Crustal uplift 

southwest of Montague Island, 

Alaska: Science, v. 146, no. 3647, p. 

1048-1049. 

---1965b, Seafloor upheaval: GeoMarine Technology, v. 1, p. 22-26. 

Moffitt, F. H., 1954, Geology of the 

Prince ·william Sound region, 

Alaska: U.S. Geol. Survey Bull. 

989-E, p. 225-310. 

Parkin, E. J., 1966, Horizontal displacements, pt. 2 of Alaskan surveys t•o 

determine crustal movement: U.S. 

Coast and Geodetic Survey, 11 p. 

Plafker, George, 1965, Tectonic deformation associated with the 1964 

Alaska earthquake: Science, v. 148, 

no. 3678, p. 1675-1687. 

Plafker, George, and Kachadoorian, 

Reuben, 1966, Geologic effects of the 

March 27, 1964, earthquake and associated seismic sea waves on 

Kodiak and nearby islands, Alaska : 

0 

faults, including many giants as 

much as 4 feet in base diameter that 

are probably 150 to 300 years old 

( J. Standerwick, U.S. Forest Service, oral commun., Oct. 4, 1966), 

indicate that no major displacement has occurred for at least that 

length of time. 

U.S. GeoL Survey Prof. Paper 543-

D, p. D1-D46. 

Plafker, George, and MacNeil, F. S., 

1966, Stratigraphic significance of 

Tertiary fossils from the Orca 

Group in the Prince William Sound 

region, Alaska: U.S. Geol. Survey 

Prof. Paper 550-B, p. B62-B68. 

Plafker, George, and Mayo, L. R., 1965, 

Tectonic deformation, subaqueous 

slides, and destructive waves associated with the Alaskan March 27, 

1964, earthquake-an interim geologic evaluation: U.S. Geol. Survey 

open-file report, 21 p. 

Tsuya, Hiromichi, ed., 1950, The Fukui 

earthquake of June 28, 1948: Tokyo, 

Report of the special committee for 

the study of the Fukui earthquake, 

197 p, 

Van Dorn, W. G., 1964, Source mechanism of the tsunami of March 28, 

1964, in Alaska: Coastal Eng. Conf., 

9th, Lisbon 1964, Proc., p. 166-190. 

Von Huene, Roland, Shor, G. R., Jr., and 

St. Amand, Pierre, 1966, Active 

faults and structure of the continental margin in the 1964 Alaskan 

aftershock area [abs.] : Am. Geophys. Union, 47th Ann. Mtg., April 

19-22, 1966, p. 176.