Wor&crJoaai AIA-H.M" 
Ground Deformation Associated with the 

1975 Magnitude-7.2 Earthquake and 

Resulting Changes in Activity of 

Kilauea Volcano, Hawaii

By PETER W. LIPMAN, JOHN P. LOCKWOOD, REGINALD T. OKAMURA, 

DONALD A. SWANSON, and KENNETH M. YAMASHITA

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1276

The 1975 earthquake, the largest on Hawaii Island 

in more than 100 years, was associated with major 

gravitational slumping of the seaward flank of 

Kilauea Volcano; maximum displacements were 

as much as 3.5 m vertically and 8 m horizontally

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1985
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Library of Congress Cataloging in Publication Data

Ground deformation associated with the 1975 magnitude-7.2 earthquake and resulting changes in activity of 

Kilauea Volcano, Hawaii.

(Geological Survey professional paper ; 1276)

iii, 45 p.

Bibliography: p. 44-45.

Supt. of Docs. No.: 119.16:1276

1. Earth movements Hawaii Kilauea Volcano. 2. Earthquakes Hawaii. 3, Kilauea Volcano (Hawaii) 

Eruption, 1975. I. Lipman, Peter W. II. Series. 

QE598.2.G76 1984 551.2'1'099691 84-600143

For sale by the Branch of Distribution

U.S. Geological Survey

604 South Pickett Street

Alexandria, VA 22304
CONTENTS

Page

Abstract ....................... ........ 1

Introduction ............................. 1

Acknowledgments .................. ........ 3

Relations between structural features and eruptive activity .... 3

The 1975 earthquake ................ ........ 4

Ground breakage ........................... 4

Faulting in the Hilina system ................. 4

Landslides and ground cracks ................. 6

Vertical displacements ........................ 7

Coastal measurements ..................... 8

Precise leveling ......................... 8

Page

Horizontal displacements ..................... 16

Summit deformation 1974-77 ................... 27

Discussion ............................. 34

Scale of movements ..................... 34

Gravitational slump hypothesis ............... 34

Relation between the earthquake and surface deformation. . 35

Effect on summit magma system .............. 41

Implications for the future .................. 41

References cited .......................... 44

ILLUSTRATIONS

FIGURE 1. Map of Kilauea and adjacent part of Mauna Loa ............................... ....... 2

2. Epicenters of the November 29, 1975, magnitude-7.2 earthquake ...................... ....... 5

3. Major zones of new ground breakage in the Hilina fault system ...................... ....... 6

4. Photographs of Hilina fault system ........................................ ....... 7

5. Ground cracking and landslides in Park ..................................... ....... 11

6. Road damage and en echelon cracks ....................................... ....... 12

7. Pre- and post-earthquake views of south coast ................................. ....... 14

8. Amount of subsidence at points along the coastline .............................. ....... 15

9. Vertical displacements on Kilauea Volcano ................................... ....... 16

10. Profiles of vertical displacement ......................................... ....... 20

11. Kilauea flank trilateration net........................................... ....... 21

12. Kilauea summit trilateration net ......................................... ....... 22

13. Preferred displacement solution for fall 1974 to spring 1976 trilateration .................. ....... 23

14. Displacement solution for deformation on southwest flank. .......................... ....... 25

15. Interpretation of displacements .......................................... ....... 26

16. East-west and north-south components of tilt .................................. ....... 28

17. Horizontal and vertical deformation of the summit area of Kilauea from 1974 to 1977 ................. 28

18. Contours of the ratio of horizontal to vertical displacement between 1974 and 1976 ................... 36

19. Oblique map of the south half of the island of Hawaii ............................ ....... 37

20. Diagrammatic cross section through the summit region and south flank of Kilauea ................... 39

21. Interpretation of relations between seismicity and deformation ........................ ....... 40

22. Changes in length of two Geodimeter lines ................................... ....... 42

in

GROUND DEFORMATION ASSOCIATED WITH THE 1975

MAGNITUDE-7.2 EARTHQUAKE AND RESULTING CHANGES IN

ACTIVITY OF KILAUEA VOLCANO 1975-1977, HAWAII

By PETER W. LIPMAN, JOHN P. LOCKWOOD, REGINALD T. OKAMURA, 

DONALD A. SWANSON, and KENNETH M. YAMASHITA

ABSTRACT

A magnitude-7.2 earthquake on November 29, 1975, the largest 

in Hawaii in over a century, was associated with large-scale deformation of the entire south flank of Kilauea Volcano. Surface ground 

breakage occurred along a 25-km-long sector of the Hilina fault system, with vertical displacements of as much as 1.5 m along individual 

preexisting fault scarps. Reoccupation of extensive horizontal and 

vertical geodetic networks on Kilauea demonstrated that the entire 

volcanic edifice and adjacent lower slopes of Mauna Loa were displaced downward and seaward. Maximum horizontal and vertical displacements, about 8 and 3.5 m respectively, occurred along the 

coastline south of Kilauea's summit area, about 30 km southwest of 

the earthquake hypocenter.

Large ratios of horizontal to vertical displacements, associated with 

the 1975 earthquake, strongly support a gravitational slump interpretation, both for the deformation associated with this earthquake and 

also for the long-term tectonic evolution of the south flank of Kilauea. 

In addition to the major displacements along the Hilina system of 

normal faults, more inland ground deformation appears to reflect secondary adjustments to displacements along the Hilina system and 

to changes in the Kilauea summit area and along the rift zones related 

to movement of magma. Analysis of the tsunami associated with the 

1975 earthquake indicates that a large part of the submarine south 

flank of Kilauea was uplifted by deformation at the toe of the slump 

terrain complementary to the subsidence on land. Focal-mechanism 

determinations for the earthquake and aftershocks indicate seaward 

displacements along gently dipping fault planes at depths of 6-10 km, 

near the base of the volcanic edifice where it is inferred to rest on 

old sea floor. Aftershocks were concentrated largely along the upper 

part of the south flank of Kilauea, between the rift zones and the 

Hilina fault system, indicating that faults of the Hilina system mark 

a major structural boundary on Kilauea, rather than just constituting 

surficial slump features.

These relations favor an interpretation of the 1975 earthquake as 

due primarily to gravitational slumping along faults of the Hilina system that penetrate most of the thickness of the south flank of Kilauea 

Volcano and that flatten at depths of 6-8 km to accommodate seaward 

displacements. The basic cause of slumping was accumulation of contractional strain throughout the 20th century along the upper part 

of the south flank, as a result of intrusion of magma as dikes along 

Kilauea's rift zones. In addition, inflation of Mauna Loa Volcano to 

the north, culminating in its July 1975 summit eruption, may have 

contributed to destabilizing Kilauea and triggering the earthquake.

Since the 1975 earthquake, deformation patterns on Kilauea Volcano have changed notably. Previously, rates of horizontal and vertical deformation at the summit were very high (several mm/day) in 

the 20th century, mainly reflecting inflation-deflation cycles related

to eruptive activity as magma accumulated in or was withdrawn from 

a 2-3 km deep magma reservoir centered near the summit. Since 

the earthquake, deformation patterns have been complex. The volcano has failed to maintain sustained inflation cycles similar to those 

of the recent past, and the dominant deformation pattern has been 

seaward displacement of the south flank, presumably reflecting ongoing adjustments to effects of the 1975 earthquake. In September 

1977, Kilauea erupted along its middle east rift zone after the longest 

period of inactivity in 10 years. No summit inflation preceded this 

eruption, which, nevertheless, may indicate the beginning of stabilization and return of the volcano to a more typical deformation pattern.

INTRODUCTION

At 0448 hours on the morning of November 29, 1975, 

a magnitude-7.2 earthquake the largest in more than 

100 years struck the island of Hawaii; the epicenter 

was located on the south flank of Kilauea Volcano (fig. 

1). The earthquake was preceded by numerous 

foreshocks, the largest of which was a magnitude-5.7 

jolt 70 minutes earlier. As summarized in a preliminary 

report (Tilling and others, 1976), the south flank of 

Kilauea Volcano moved downward and seaward, and 

ground breakage occurred along a 25-km-long zone, 

mainly along preexisting faults in the Hilina system. 

A tsunami, accompanying the earthquake, locally 

reached heights of 12-15 m above mean sea level. A 

brief small-volume volcanic eruption, presumably 

triggered by the earthquake and associated ground 

movements, occurred within Kilauea's summit caldera 

about 45 minutes later. The earthquake and tsunami 

together caused property damage estimated at about 

$4.1 million in the southeastern part of the island; the 

tsunami also caused two deaths. Thousands of aftershocks were recorded during the next year.

Here we report detailed studies of the ground deformation associated with the 1975 earthquake, made possible by the previously established geodetic network of 

extensive vertical and horizontal controls developed 

primarily for monitoring Kilauea Volcano. These
1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

155°00'

EXPLANATION

 APPROXIMATE BOUNDARY BETWEEN 

KILAUEA AND MAUNA LOA

FAULT Bar and ball on 

downthrown side

PIT CRATER 

CONE

155°30

19°00

FIGURE 1. Map of Kilauea and adjacent part of Mauna Loa, showing main structural features and locations of important 

faults, cones, and pit craters. Modified from Stearns and Macdonald (1946, pi. 1) and Swanson, Duffield. and Fiske 

(1976a, fig. 2); bathymetry from U.S. Naval Oceanographic Office (1973). Land contour interval, 75 m; bathymetric 

contour interval, 500 m. Limits of submarine slump terrane from Moore and Peck (1965) and U.S. Geological Survey 

marine seismic data (W. R. Normark and J. G. Moore, unpub. data, 1976).
RELATIONS BETWEEN STRUCTURAL FEATURES AND ERUPTIVE ACTIVITY

studies show that the entire subaerial part of Kilauea 

was deformed, with maximum downward and seaward 

displacements of about 3.5 and 8 m, respectively. The 

general form of the surface deformation was large-scale 

block slumping involving much of the southeast side of 

the island of Hawaii. The 1975 deformation was accommodated largely by movement along preexisting structures that show evidence of repeated seaward-directed 

block slumping in the past.

In addition, ground deformation studies of Kilauea's 

summit area have indicated a changed pattern of magmatic behavior for several years after the 1975 earthquake (Lipman and others, 1978). Before the earthquake, summit inflation-deflation cycles yielded radial 

patterns of tilt and horizontal displacement confocal 

with concentric patterns of vertical displacement. Since 

the earthquake, vertical changes have been sporadic 

and relatively subdued, which indicates that the summit region has ceased to undergo sustained inflation; 

however, horizontal displacements have continued in a 

uniform seaward direction, similar to the pattern developed in response to the earthquake. At the time of 

writing this report (fall 1979), it was unclear when the 

summit area would stabilize from the disruptive effects 

of the 1975 earthquake, but it has become clear that 

such earthquakes have after-effects lasting many years.

ACKNOWLEDGMENTS

Virtually the entire staff of the Hawaiian Volcano 

Observatory (HVO) of the U. S. Geological Survey assisted at various times in the extensive geodetic measurements on which this report is based. We thank 

them all, especially Maurice Sako and Jack Harris. Essential helicopter support was provided by the County 

of Hawaii and their able pilot, Kenneth Ellard. Many 

of the interpretations presented here evolved and were 

improved during discussions with our associates, including Lennart A. Anderson, Robert S. Crosson, 

Daniel Dzurisin, Gordon P. Eaton, Robert Y. 

Koyanagi, James G. Moore, and Robert I. Tilling.

RELATIONS BETWEEN STRUCTURAL 

FEATURES AND ERUPTIVE ACTIVITY

Interpretation of the geodetic changes associated 

with the 1975 earthquake must be made in the context 

of the major structural features and patterns of deformation and seismicity associated with volcanic activity 

on Kilauea. Much has been learned in recent years 

about these interactions by combined geologic, seismic, 

geodetic, and other geophysical studies at the Hawaiian 

Volcano Observatory.

The major eruption-related structures on Kilauea are

a collapse caldera in the summit area and the roughly 

opposed southwest and east rift zones (fig. 1). Between 

eruptions, magma has recently been generated in the 

mantle beneath Kilauea at a nearly steady rate of about 

0.1 km3/yr (Swanson, 1972). The magma gradually accumulates in a shallow reservoir 2-5 km below and 

slightly south of the summit caldera, causing uplift and 

inflation, as indicated by both seismic and deformation 

studies (Eaton, 1962: Fiske and Kinoshita, 1969). The 

rift zones are also typically uplifted between and during 

eruptive and intrusive events, commonly with the development of a keystone graben along the linear crest 

of the uplift (Macdonald and Eaton, 1964; Fiske and 

Koyanagi, 1968; Jackson and others, 1975).

Summit eruptions commonly are accompanied by little or no deflation over the magma reservoir, apparently as overflow of an essentially open magma column. 

During rift eruptions, in contrast, magma drainage 

from the summit reservoir causes measureable summit 

subsidence, at times more than a meter (Kinoshita and 

others, 1974; Jackson and others, 1975). The rift zones 

are interpreted as marking the loci of underlying 

magma conduits, in the shape of shallow blade-like 

dikes largely confined within the volcanic edifice and 

fed from the summit region (Fiske and Jackson, 1972). 

At the surface, each rift zone is marked by a broad 

topographic crest, along which are alined many open 

cracks, pit craters, and small cones and shields.

In addition to the rift zones, major structural divisions of Kilauea Volcano include the Koae fault sytem, 

the south flank, and the north flank. Eruptions seldom, 

if ever, occur within these areas. The Koae fault system (Duffield, 1975) is an east-northeast-trending zone 

of open cracks and dominantly north-facing normal 

faults that connect the east and southwest rift zones 

and mark the southern margin of summit-related subsidence structures. The south flank is the region south 

of the rift zones and the Koae fault system. It includes 

two distinctive subdivisions: (1) a northern part between the Koae and Hilina fault systems that consists 

of little-faulted lava flows dipping gently seaward, and 

(2) a southern part that is disrupted by the predominantly south-facing normal faults of the Hilina system. 

Off-rift seismicity is concentrated largely in the northern part of the south flank, which appears to represent 

a structurally rigid region capable of accumulating 

stress. In contrast, seismic activity is more diffuse and 

lower in intensity along the southern part (Koyanagi 

and others, 1972). The submarine south flank of Kilauea 

consists mainly of a block-faulted terrane, similar to the 

adjacent subaerial part, as indicated by bathymetric 

data (Moore and Peck, 1964) and by U.S. Geological 

Survey marine seismic profiles (W. R. Normark and 

J. G. Moore, unpub. data, 1976). The north flank of 

Kilauea, bounded by the summit area and the east rift
1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

zone, is relatively stable and low in seismicity; it is 

characterized by northeasterly dipping lava flows that 

abut and interfinger with flows from Mauna Loa.

Geodetic evidence presented by Swanson, Duffield, 

and Fiske (1976a) suggests that forceful injection of 

magma along Kilauea's rift zones has uplifted the south 

flank and displaced it several meters seaward during 

the 20th century. In contrast, the north flank has remained relatively stable, presumably because of buttressing effects of the neighboring volcanic edifices, 

principally Mauna Loa (Fiske and Jackson, 1972). By 

these interpretations, the Hilina fault system is considered to be a gravity-controlled zone of block slumping, 

not directly related to the rift zones. Strain that has 

accumulated from uplift and seaward displacement of 

the south flank is intermittently relieved by normal 

faulting along the Hilina system and related submarine 

faults along the south flank of Kilauea. Swanson, Duffield, and Fiske (1976a) documented a buildup of strain 

within the Hilina system throughout the 20th century, 

and anticipated "a subsidence event in the not too distant future." While their report was in press, the 

November 1975 earthquake and associated ground deformation confirmed their anticipation.

THE 1975 EARTHQUAKE

Data from HVO seismometers placed the magnitude7.2 earthquake of November 29, 1975, about 6 km westsouthwest of Kalapana on Hawaii's southeastern coast 

(lat 19°20.1' N., long 155°01.4' W.), at a depth of about 

5-6 km (fig. 2). The earthquake was felt on the island 

of Oahu, more than 400 km from the epicenter. Damage 

estimates and an isoseismal earthquake intensity map 

for the island of Hawaii (Tilling and others, 1976, fig. 

4) clearly show that the maximum intensity of the 

earthquake did not coincide with its epicenter, but lay 

further to the east, close to the zone of maximum 

ground deformation documented in this report.

Thousands of aftershocks, which continued in diminishing numbers for several years after the 1975 

earthquake, were distributed over a broad zone mainly 

west of the epicentral region (fig. 2). The main concentration of aftershocks was beneath the unfaulted northern part of the south flank of Kilauea the region between the two rift zones and the Hilina fault system 

(fig. 2). Most of these earthquakes occurred at depths 

of 5-7 km (Ando, 1979, fig. 1; Crosson and Endo, 1981, 

fig. 8). Many aftershocks also took place beneath the 

southwest rift zone, but few were recorded along the 

east rift zone. The virtual lack of aftershocks within 

the faulted part of the south flank south of Hilina Pali 

is striking; seismicity was also limited in this part of 

Kilauea prior to the earthquake (Tilling and others, 

1976, p. 9).

GROUND BREAKAGE

Extensive ground rupture in the summit and south 

flank areas of Kilauea, along with easily recognized subsidence along the south coast, gave the first indications 

that substantial deformation accompanied the earthquake.

FAULTING IN THE HILINA SYSTEM

Ground breakage was nearly continuous along the 

Hilina fault system (fig. 3). The Hilina system is characterized by south-facing normal fault scarps as high 

as 500 m (fig. 4). The new breakage consists of a series 

of steep normal faults, mostly along preexisting fault 

traces, with displacements systematically down to the 

south. In places, the new fault displacements are 

obscured by extensive slumps and landslides that occurred during the earthquake along all of the steep 

scarps; in many other places, the amount of new offset 

is difficult to distinguish from older displacements along 

the same fault scarp.

The new faulting extends about 25 km along the 

trend of the Hilina fault system, and individual faults 

have vertical displacements of as much as 1.5 m. In 

detail, the new faults are discontinuous and are en 

echelon in pattern; individual breaks extend a few tens 

to several hundreds of meters. Overall, they define a 

nearly continuous zone of normal faulting bounding 

more coherent structural blocks; elsewhere on Kilauea, 

the most conspicuous ground breakage involves widespread chaotic landsliding and slumping of relatively incoherent material from steep slopes.

In the past, lava flows have cascaded over most of 

the "palis" (Hawaiian for cliffs or scarps) of the Hilina 

fault system (fig. 4A), gradually building them southward toward the sea. The new ground rupture commonly took place near the top of the palis, presumably 

along the buried faults that originally created the cliffs. 

Some palis, such as the seaward flank of Puu Kaone 

(fig. 45), have not been built seaward by draping of 

younger flows, but rather they have retreated northward through erosion; hence, ground rupture took place 

near the base of these scarps (fig. 4C).

Much of the new faulting was along the northern part 

of the Hilina system; several old faults near the coast 

showed no new ruptures. The most continuous zone of 

breakage and the largest vertical offsets are along the 

northeast edge of the system, where vertical displacements were 0.5-1.5 m for a distance of more than 15 

km. South and southwest of this zone of maximum 

faulting, vertical displacements of as much as 0.5-1.0 

m are common along other faults. Accordingly, the 

cumulative observed fault displacement is at least as 

much as 2.5 m and accounts for about two-thirds of 

the maximum measured coastal subsidence along 

Kilauea's south coast.
GROUND BREAKAGE
19°30'

1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

155°00'

19°00'

SYSTEM Kamoamoa

FIGURE 3. Major zones of new ground breakage in the Hilina fault 

system, related to the 1975 earthquake, and amounts of associated subsidence along the south coastline. Measured offsets 

along the Hilina fault system are amounts of new displacement 

along large preexisting fault scarps, in places draped by prehistoric Kilauea lava flows. Most coastal measurements were made 

directly from postsubsidence sea level to points of previously

known elevation, including bench marks, triangulation stations, 

topographic control points, and tide gages. All measurements 

were adjusted to mean sea level, using tide tables to determine 

the absolute subsidence. Estimated uncertainties in the amounts 

of subsidence are based on the method of determination and the 

quality of the observation. (Modified from Tilling and others, 

1976, fig. 16.)

Along the southwestern part of the Hilina fault system, new ground breakage is evident along several 

northeast-trending zones over an extent of at least 5 

km (fig. 3), with vertical displacements locally as much 

as 1 m. Much of the ground movement in this area, 

however, seems to have resulted in only slight readjustment along preexisting fractures. Ground breakage was minimal along the eastern part of the Hilina 

system and was notably lacking near the epicenter or 

along buried fault scarps inland from there.

In addition to the main faults, widening of many 

cracks within the Hilina system indicated significant 

horizontal extension (fig. 4D). Most cracks are old, but 

freshly broken rocks and torn vegetation are evidence 

of renewed movement during the 1975 events. Small 

new cracks in alluvium, with openings of as much as 

a few centimeters, were common near the larger bedrock cracks.

LANDSLIDES AND GROUND CRACKS

Shaking during the main earthquake caused numerous rockslides and ground cracks, especially on steep 

slopes such as fault scarps, crater walls, and road cuts. 

Some of this relatively superficial ground breakage is 

difficult to distinguish from deeper fault-controlled 

structures. Rockfalls and landslides along every major 

cliff in the Hilina fault system and soil cracks within 

50-100 m of the edges of cliffs, suggest local lurching 

of the ground toward cliff faces during the shaking.

Some of the largest ground cracks and rockslides 

were along the rims of Kilauea Caldera and the pit craters of the upper east rift zone. These dislocations 

caused more than $675,000 damage to roads, trails, and 

viewing overlooks in Hawaii Volcanoes National Park. 

Visitor overlooks slumped downward and outward, 

parts of them crashing into the craters; and gaping
VERTICAL DISPLACEMENTS

A. Post-earthquake aerial view of Kilauea's south flank, looking northeastward along lava-drapped Holei Pali (cliff) of the Hilina fault 

system. Foreground shows the coast at Keauhou Landing (note palm trees in the water and the dark swath indicating the 

area washed by the tsunami).

FIGURE 4. HILINA FAULT SYSTEM

cracks as wide as 25 cm rendered the parts still left 

too unstable for continued use by park visitors (figs. 

5A, B). Unstable roadcuts collapsed, locally blocking 

roads in the national park (fig. 5C).

Cracks as wide as 1 m on the northeast side of 

Kilauea Caldera destroyed a 1-km segment of the Crater Rim Road (fig. 6A). Most of the ground breakage 

was extensional, producing new cracks or widening old 

ones, but local compressional features formed where 

slices of ground swayed between bounding open fractures and ended on one side or the other. A 5-cm partial closing of one crack in this manner produced a 

striking chevron fold across a road on the north side 

of Kilauea caldera (fig. 65). In a few places movement 

along cracks produced lateral components of offset of 

as much as 10 cm (fig. 6C).

Cracking was also conspicuous along the Koae fault 

system south of Kilauea Caldera. This area is characterized by numerous open fissures (Duffield, 1975); 

some old cracks opened, others closed, and small new

cracks formed in many sand-covered areas (fig. QD). 

Vertical offsets were not conspicuous, but suitable visible reference points are typically lacking. Geodimeter 

and leveling data indicate horizontal extensions of as 

much as 2 m and northward tilting of as much as 0.1 

m/km across the Koae fault system.

VERTICAL DISPLACEMENTS

Major subsidence was evident along the south coast 

of Kilauea immediately after the earthquake. At the 

Halape campground, a grove of coconut palms was 

partly submerged, with an average water depth of 1.2 

m and with the new shoreline extending 100-150 m 

landward of the presubsidence shoreline (fig. 7). A shallow lagoon now covers 2.2 hectares of what formerly 

was a sand-covered flat above a low sea cliff at Kaaha, 

4.5 km west of Halape. At Keauhou Landing, 2.3 km 

east of Halape, a brackish Hawaiian well was submerged and the narrow beach was destroyed. Near
1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

B. Pre-earthquake aerial view of part of the Hilina fault sytem, looking northeast along Puu Kaone (top of cliff at left center) 

and Puu Kapukapu (top of cliff at upper right). Arrow points to location of figure 4C.

FIGURE 4. HILINA FAULT SYSTEM Continued

Kalapana, segments of the main highway became subject to regular flooding, and an area that was previously only muddy or even dry during low tides is now 

continually occupied by a broad shallow lagoon. At the 

renowned Kaimu black-sand beach, 1 km northeast of 

Kalapana, waves now enter the fringing coconut grove, 

and the beach has been extensively eroded.

COASTAL MEASUREMENTS

Amounts of subsidence could be measured directly 

at several localities along the coastline from Honuapo 

to Kaimu (fig. 3). The maximum measured subsidence, 

about 3.5 m, was in the Halape-Keauhou Landing area, 

about 25 km west of the epicenter of the main earthquake. Kalue, 3 km west of Halape, may have subsided 

as much or even more than the measured subsidence, 

as suggested by visual estimates near a previously established tidal reference point that could not be found 

after the earthquake. This reference point is thought 

to have dropped below the post-earthquake shoreline.

Subsidence decreases in both directions from this 

central area. Toward the southwest, measurements indicate definite subsidence at Na Puu o Na Elemakule 

and Kuee but not farther southwest (fig. 3). Continuously recorded water-level data for a well at Punaluu 

indicated about 0.1 m uplift of land the only detected 

uplift anywhere in the region, but the Honuapo area 

showed no detectable change within limits of the measurements.

Subsidence decreases eastward from Keauhou Landing to Kaena Point, then remains at about 1 m to 

Kupapau. Subsidence was about 75 cm at the Kupapau 

tide gage. The Kaimu area sank a maximum of about 

85 cm; releveling suggests that about 64 cm of this 

amount resulted from regional subsidence and that 

about 21 cm from differential dropping or abrupt northward or eastward tilting of the previously known 

Kalapana graben (fig. 8). As seen in figure 8, the zone 

of coastal subsidence is asymmetric, terminating more 

abruptly on the west side than on the east side.

PRECISE LEVELING

Every major precise leveling line previously established on Kilauea was reoccupied early in 1976; in all
VERTICAL DISPLACEMENTS

C. Vertical offset of about 1.5 m along reactivated fault on south face of Puu Kaone (see fig. 4B). The amount of new 

displacement is indicated by distance between hands and feet of the standing figure.

FIGURE 4. HILINA FAULT SYSTEM Continued

about 250 km of line were releveled. The methodology 

and precision of leveling by the Hawaiian Volcano Observatory have been discussed by Okamura and Swanson (1975); some compromises in quality are made to 

increase speed of coverage because of the instability 

of the volcano, but the quality is typically good second 

order. Results of the releveling are summarized in figure 9; the complete data are on file at HVO. The Hilo 

tide gage was taken as a zero datum for interpreting 

elevation changes. Absolute changes of elevation were 

probably small in the Hilo area, as indicated by the 

limited relative changes observed within 10 km of Hilo 

(less than 1 cm), but short-term absolute changes of 

less than about 5 cm would not be observable directly 

from the tide-gage data (Moore, 1971, fig. 3).

Interpretation of the leveling data is complicated 

somewhat by the disparate times at which various lines 

were previously occupied the time intervals before 

the 1976 releveling varied from 3 months to 18 years 

(fig. 9A) and also is complicated by the high rates of

deformation in the Kilauea summit area. All the summit 

and upper rift lines had been releveled and tied to the 

tide gage at Hilo within a few months prior to the 1975 

earthquake (fig. 9A). Data from the less recently occupied lines, especially those on the eastern side of 

Kilauea last previously leveled in 1958 or 1964, have 

been adjusted to more recent data. For example, the 

1958-76 changes between Keaau and Pahoa were recomputed, using the 1975 elevation at Keaau, the 1973 

elevation at Pahoa, and apportioning the necessary internal adjustment linearly with distance. The resulting 

net changes (fig. 9B) are thought to convey a generally 

valid portrayal of the vertical displacements on Kilauea 

associated with the 1975 earthquake, especially because 

these displacements are very large and commonly different in pattern or sense from those observed previously, which were mainly associated with magmatic behavior. For example, the Pahoa-Kaimu line, which 

documented continued uplift of the east rift zone at 

rates of 1-5 cm/year between 1958 and 1973 (Swanson 

and others, 1976a, fig. 13A), showed subsidence of 92
10 1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

D. Stretched goat-control fence, indicating horizontal extension across Kukalauula Pali, 3 km northwest of Naliikakani Point. Right

margin of photograph shows approximate unstretched geometry of fence. 

FIGURE 4. HILINA FAULT SYSTEM Continued

cm between 1973 and 1976, a change likely related almost entirely to the 1975 earthquake.

An interpretative contour map, based on the adjusted leveling data (fig. 96) supplemented by coastal 

sea-level measurements (fig. 3), shows a coherent pattern of subsidence over the entire edifice of Kilauea 

Volcano (fig. 9C). The maximum subsidence of about 

3.5 m is along the coast due south of the summit area, 

and areas of subsidence exceeding 1 m are confined to 

the region seaward of Hilina Pali and to the summit 

caldera. The area of summit subsidence extends outward as a well-defined trough along both rift zones. 

Along the lower east rift zone the trough is asymmetric 

and displaced to the south of the topographic crest of 

the rift zone (fig. 9C), as is uplift related to intrusive 

and eruptive activity in this sector of the rift zone 

(Swanson and others, 1976a, fig. 13A).

The amount of subsidence along the south flank of 

Kilauea decreases relatively abruptly to the west of 

Halape and more gradually to the east. Adjacent relatively positive and negative areas in the KalapanaKaimu area, superimposed on the general subsidence, 

correlate closely with preexisting horsts and grabens. 

Ground breakage or other marked effects of faulting 

were not recognized, however, in the epicentral area 

of the earthquake, about 6 km southwest of Kalapana.

Between the coastal region of maximum downdropping and the area of secondary subsidence at the summit of Kilauea is an area where subsidence was as little 

as 0.7 m (fig. 10). This relatively positive area coincides 

closely with the structurally unfaulted part of the south 

flank, which had been subjected to significant uplift in 

the decade prior to the earthquake (Swanson and 

others, 1976a, p. 19-20), and with the main loci of aftershock activity (fig. 2). The maximum gradient of increasing subsidence is located along the south margin 

of this block, where ground breakage involving individual offsets of as much as 1.5 m occurred widely along 

preexisting faults of the Hilina system.

The leveling data locally demonstrate northward tilting of fault blocks in some areas south of the zone of 

surface ground breakage along the Hilina fault system
VERTICAL DISPLACEMENTS 11

FIGURE 5. Ground cracking and landslides in Hawaii Volcanoes National Park. A, Back part of viewing 

overlook area at Puhimau Crater slumped completely into the crater, leaving guardrail projecting 

into space. B, Aerial view of large cracks in viewing overlook area of Pauahi Crater (photograph 

by Hugh Clark, Honolulu Advertiser). C, Small landslide from spatter and cinder cone partially 

blocking Chain of Craters Road (photograph by Boone Morrison).
12 1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII
VERTICAL DISPLACEMENTS 13

FIGURE 6 (above and facing page). Road damage and en echelon 

cracks in Hawaii Volcanoes National Park. A, Large crack in 

Crater Rim Road resulted from slumping toward the caldera 

rim, the edge of which is a few meters to left of view. B, Small 

compressional chevron fold across road on southeast side of 

Kilauea Military camp along north side of the caldera. C, Collapse offsetting center line of Chain of Craters Road, just south 

of Pauahi Crater. D, En echelon cracks in weakly consolidated 

volcanic ash along the Koae fault zone. Compass is alined with 

the main trend of Koae faults (N. 75° E.; Duffield, 1975), and 

the en echelon pattern indicates a left-lateral component of 

offset.
14 1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

FIGURE 7 (above and facing page). Pre- and post-earthquake views of south coast, illustrating subsidence near Halape. 

A, Pre-earthquake view of Halape area from Puu Kapukapu (photograph by Don Reeser, National Park Service). 

B, Post-earthquake view of Halape from Puu Kapukapu, showing the palm grove standing in the sea and an offshore 

island nearly submerged as a result of 3.5 m of subsidence. During the earthquake, campers were swept by the 

tsunami into the crack (arrows) behind the palm grove, and two persons died. C, After subsidence, surf surges through 

the palm grove at Halape (photograph by Boone Morrison).
VERTICAL DISPLACEMENTS 15

W

^o

UJ Z

i E < Q.

co +1 l

DC

UJ t 0 

UJ 2

z -1-

UJ

z -2-

Ul 

Q

co 3 -

00

o

w_4 J

^<^c3 < ^o <<\ ^z,^ z li; 0- trf

| 2|l B S g2 < ^i

1~ M "f"T 1}

-. Ul <- z ^i

< °

I X

<

^

s ? , ' ^

- +1 

- 0

- -1

- -2

- -3

- -4

FIGURE 8. Amount of subsidence at points along the coastline from 

Honuapo to Kaimu. Bars indicate estimated measurement uncertainties (from fig. 3); dashed horizontal line, zero change. Note disruption of profile along west edge of Kalapana graben, indicating 

dropping or abrupt tilting along graben fault.

and within the general area of maximum subsidence. 

Surveys near Kaena Point and Kaimu (fig. 9) indicate 

landward rotational tilting of about 1 cm/100 m and 1.5 

mm/100 m, respectively. A similar prehistoric pattern 

of back rotation is also indicated by anomalously flat 

and locally north-sloping topography at the bases of 

several other major faults of the Hilina system. (See 

Makaopuki Crater IVz topographic quadrangle; also 

Swanson and others, 1976a, fig. 22.)

Subsidence greater than 5 cm occurred north and 

west of Kilauea's rift zones and extends at least 10 km 

up the southeast slope of Mauna Loa adjacent to the 

summit region of Kilauea. Gradients of subsidence contours north and northwest of the summit region of 

Kilauea are approximately on trend with those across 

the unfaulted block south of the summit area (fig. 10), 

which indicates that subaerial Kilauea and adjacent portions of Mauna Loa were subjected to a relatively unified pattern of subsidence, although Mauna Loa was
16 1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

affected less than Kilauea as distance from the epicenter increased. Clearly, the deformation pattern was 

dominated by Kilauea's mobile subsiding seaward 

block, but the regional scale of the deformation 

suggests that other factors influenced the deformation 

patterns as well. In addition to detachment of the south 

flank of Kilauea along the Hilina fault system, the rift 

zones clearly opened, and much of the adjacent southeast side of Hawaii Island appears to have subsided 

sympathetically.

HORIZONTAL DISPLACEMENTS

The magnitude of horizontal displacements during 

the 1975 earthquake was not fully evident from the visible structures. Many cracks in the summit area and 

along the Hilina fault system opened, but others closed 

(fig. 6B). Only as the large Kilauea flank trilateration 

net (fig. 11) was reoccupied did it become apparent that 

the horizontal movements were generally greater than 

the more obvious vertical movements. Individual lines 

lengthened as much as a meter per kilometer, and the 

cumulative effect was displacement of the coastal areas 

as much as 8 m seaward.

The Kilauea trilateration network can be conveniently considered in two parts: (1) a summit net of 59 

lines (fig. 12) that can be reoccupied in about 3 days 

by a crew of 5 and has accordingly been measured several times each year on the basis of fluctuations in behavior of the volcano, and (2) the flank net of about 

150 lines (fig. 11) that takes 4 weeks or more to reoccupy and requires helicopter support for access to remote stations. The flank net was established in essentially its present configuration in 1970 and has been 

reoccupied twice in the fall of 1974 and, after the 

earthquake, in the spring of 1976. The horizontal distance measurements on Kilauea are routinely made 

with an AGA Model 8 Geodimeter1 , an electronic laserbeam instrument with a precision as used at HVO of 

about 2-3 parts per million, or 2-3 mm/km of line 

length. Methods of operation and data reduction are 

summarized by Kinoshita, Swanson, and Jackson (1974) 

and Swanson and Okamura (1975). Changes in line 

length for the periods bracketing the 1975 earthquake 

are summarized in figures 11 and 12; complete data for 

the trilateration measurements are on file at HVO.

Horizontal displacements were determined for the 

1974-76 interval, using graphic methods (Kinoshita and 

others, 1974) that were especially useful in evaluating

"Use of trade names in this report is for descriptive purposes only and does not constitute 

endorsement by the U.S. Geological Survey.

some special problems. One major difficulty was that 

a key trilateration station, Puu Koae (figs. 11, 12), was 

destroyed by slumping during the earthquake. An attempt was made to determine the position of this bench 

mark with respect to surviving reference marks, but 

all displacement solutions are nevertheless somewhat 

anomalous. Accordingly, Puu Koae was bypassed as 

completely as possible in the overall solution for the 

flank net, even though this unavoidably reduced the 

precision of solutions for adjacent stations.

Another problem concerned the stability of the "base 

stations" (Swanson and others, 1976a, p. 36-37). One 

standard base station for the summit net (Keakapulu; 

fig. 11) had been displaced during an intrusive event 

along the southwest rift zone in 1974, as discussed later 

(p. 24). Additionally, Mauna Loa Volcano, on whose 

southeast flank all but one of these base stations are 

located, was inflating during 1974-76 (Lockwood and 

others, 1976), so that geodetic changes of uncertain 

magnitude related to Mauna Loa are superimposed on 

the Kilauea "baseline" measurements. Given these factors and the scale of deformation associated with the 

1975 earthquake, including a measured contraction of 

12 cm along the 9 km line between two other primary 

base stations (Kulani and Strip, fig. 11) we tried to 

make the displacement solution as independent as possible of assumptions concerning base-line stability. Trial 

solutions using alternative assumptions indicated only 

small effects for the large indicated displacements on 

the south flank of Kilauea, although the much smaller 

interpreted movements of the stations on Mauna Loa 

could vary significantly. Accordingly, only the marginal 

stations of the flank net (Kaiwiki New and Kaaha 2,

FIGURE 9 (following 3 pages). Vertical displacements on Kilauea 

Volcano. Dashed lines separate major volcanic edifices; contour interval, 500 feet.

A, Major level lines on Kilauea occupied in 1976, showing times 

of last previous leveling and adjustment assumptions. Contour interval, 500 feet.

B, Locations of benchmarks along level lines and selected vertical 

changes between 1976 and last previous occupation, adjusted as indicated in figure 9A. Changes in elevation are 

relative to the Hilo tide gage; zeros have been deleted before the decimal point to save space. Quoted zero ("0") is 

arbitrary zero point. Contour interval, 500 feet. 

C, Interpreted contours of elevation changes associated with the 

1975 earthquake, based on data summarized in figures 3 

and 9B. Rift zones indicated by shaded pattern; locations 

of profiles shown in figure 10 are also plotted. Contour interval 0.1 m; supplemental 0.01 amd 0.05 m contours; alternate contours omitted for values larger than -1.0 m. 

Hachures show direction of relative movement.
HORIZONTAL DISPLACEMENTS 17
18 1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII
HORIZONTAL DISPLACEMENTS 19
3 o

H

s

I&

%»e. ^ aIT-

'S 5

B» 3

ELEVATION, IN METERS

§ 01 8

KILAUEA CALDERA

HILINA FAULT SYSTEM

ELEVATION, IN METERS

§ 01 8 __i_____i_____

KILAUEA CALDERA

HILINA FAULT SYSTEM

<| VERTICAL DISPLACEMENT, RELATIVE TO HILO TIDE GAGE, IN METERS

§

3d 

o

H 

-lj 

toH

HWEd

o 

> 2 

o

VERTICAL DISPLACEMENT, RELATIVE TO HILO TIDE GAGE, IN METERS
HORIZONTAL DISPLACEMENTS 21

1 tf I *

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bo

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1

1. § t-H to JS

'-H <D O

- C
22 1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

0 2 5 KILOMETERS

0123 MILES 

CONTOUR INTERVAL 500 FEET 

DATUM IS MEAN SEA LEVEL

FIGURE 12. Kilauea summit trilateration net, showing changes (in meters) in line lengths, September 1975 to January 1976. (Contour

interval 500 feet; hachures indicate craters.)

fig. 11) were assumed fixed; changes in line length between these and the nearest adjacent stations were 

only slightly greater than measurement uncertainties, 

which indicates relative stability in comparison with the 

large changes in other parts of the trilateration net on 

Kilauea. One other assumption was necessary. The 18- 

cm contraction between Kulani and Keaau was arbitrarily evenly divided between these two stations; then the 

remainder of the net could be solved including several 

other standard base stations (Strip, Keakapulu), without using the suspect values for Puu Koae.

The resulting preferred solution for 1974-76 horizontal deformation (fig. 13) yields a geologically coherent 

pattern of displacements that generally increase seaward and converge slightly toward the area of 

maximum subsidence on the south coast of Kilauea (fig.

13). All the inland stations not fixed (Keakapulu, Strip, 

Kulani, Keaau, fig. 11) show small but significant displacements (10-35 cm), also in a generally seaward direction. These stations may have moved either during 

the earthquake, during the inflation and the July 1975 

summit eruption of Mauna Loa, or at both times. Solutions for the stations on Mauna Loa, involving alternative assumptions, yield geologically less reasonable displacements. For example, if Keakapulu is held fixed 

along with Kaaha 2 (fig. 13), then displacements on the 

lower southwest side of Kilauea are rotated implausibly 

into northeasterly directions. Similarly, if Kulani is 

fixed along with Kaiwiki New, the displacements on 

the northeast side of Kilauea are rotated into more 

westerly directions than those shown in figure 13. None 

of these alternatives significantly modifies the coastal
155°30'

HORIZONTAL DISPLACEMENTS

155°15'

23

-2.0-,

EXPLANATION

FAULT 0.5-1.5m OF 1975 OFFSET Bar 

and ball on downthrown side

OTHER MAJOR FAULTS Bar and ball 

on downthrown side

SUBSIDENCE CONTOURS IN METERS 1974-1976 

Hachures show direction of increasing subsidence

VECTOR SCALE

i i i

012345 METERS

FIGURE 13. Preferred displacement solution for fall 1974 to spring 1976 trilateration of Kilauea flank network. See text for a discussion 

of assumptions. Arrow tails are at geodetic stations shown in figure 11; lengths of arrows indicate amounts of displacement. The 

summit caldera area and rift zones are patterned.
24 1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

pattern of large seaward displacements with southeasterly azimuths.

The cumulative displacements across Kilauea for the 

interval 1974-76 show a generally simple pattern of 

southeasterly movements increasing seaward, but the 

details of this pattern are complicated in the summit 

area and along the upper southwest rift zone of Kilauea 

where magmatic events took place between the two 

surveys. Just as with the leveling data, we have attempted to separate effects of these events from those 

of the earthquake-related deformation.

The eruption-related summit deformation of Kilauea 

between the fall 1974 survey and the November 1975 

earthquake can be considered in two phases: the December 1974 eruption, and subsequent re-inflation in 

1975. The summit area deflated and contracted during 

the upper southwest rift eruption on December 31, 1974 

(Lockwood and others, 1978), and a pattern of horizontal ground displacement away from the middle southwest rift zone developed adjacent to an area marked 

by a major earthquake swarm, presumably caused by 

intrusion of magma (fig. 14). Displacements along the 

middle southwest rift zone, as much as 1.3 m, were 

among the largest ever previously observed for a single 

event on Kilauea. Another notable feature of this event 

was that several stations on Mauna Loa showed displacements away from the area of intrusion, including 

the Keakapulu "base station." Following this magmatic 

event, Kilauea resumed a typical pattern of steady 

summit inflation that continued through 1975 until terminated by the November earthquake and associated 

deformation.

An interpretive displacement map, showing the horizontal displacements interpreted to be due mainly to 

effects of the November 1975 earthquake, was constructed by determining displacements for three subareas in different time frames (fig. 15).

For roughly the eastern half of the Kilauea flank net, 

the displacements are for fall 1974-spring 1976, the 

same as in figure 13, because no significant eruption-related deformation has been documented in this area for 

the interval prior to the earthquake. Changes were also 

small in this area for the period 1970-74. For Kilauea's 

southwest rift zone, displacements are for the interval 

spring 1975-spring 1976 for all stations for which data 

are available, so to avoid interfering effects of the eruption-intrusion event of Dec. 31, 1974. For the Kilauea 

summit area, the solutions are for the shortest possible 

interval, September 1975-January 1976, to minimize 

the effects of the December 1974 eruption and the summit inflation during most of 1975.

The resultant interpretation for the 1975 earthquake 

(fig. 15) differs from the geometrically more rigorous 

1974-76 solution (fig. 13) in several significant respects. 

In the Kilauea summit area, the amount of seaward 

displacement is reduced slightly and azimuths of the 

displacement vectors are more nearly parallel for the 

limited time interval related most directly to the earthquake. Seaward displacements on the southwest side 

of Kilauea are somewhat smaller, because of elimination 

of the December 1974 effects. The seaward displacement of the south flank decreases west of the HalapePuu Kapukapu area, just where effects of the 1974 

event begin to be significant. A possible implication is 

that some regional stress had been relieved during the 

1974 deformation along the southwest rift zone, so that 

strains in this area resulting from the 1975 earthquake 

were smaller than they otherwise would have been. In 

addition, the accumulation of contractional strain 

around margins of the 1974 intrusion area may have 

been significant in localizing the area of maximum horizontal displacement and the westerly increase in deformation from the epicentral area of the 1975 earthquake. 

The steep gradient of the coastal subsidence in the 

same area (fig. 9) may reflect a similar response to a 

preexisting strain pattern.

Another effect related to the 1974 events along the 

southwest rift zone may be the small but systematic 

deviation of the 1975 displacement vectors within the 

central region of maximum deformation, about S. 60°- 

65° E. (fig. 15), from the direction of dilation along the 

east rift zone and the Koae fault system about S. 75° 

E. (Duffield, 1975; Swanson and others, 1976a). Movement of the south flank is largely normal to trends of 

the dilation of the Koae system and the east rift zone, 

but the effect of opening along the southwest rift zone, 

because of its divergent trend, would be to introduce 

an oblique easterly component to south flank displacements. Such an effect is especially evident near margins 

of the region deformed during the December 1974 intrusion: small easterly displacements, nearly parallel to 

the trend of the east rift zone and the Koae system 

occurred on the upper south flank (figs. 14, 17A), requiring a component of left-lateral motion on these 

dominantly dilatant structures. Such strike-slip displacements are also shown by cracks that formed in 

alluvium and along paved roads during the 1975 deformation (fig. 6).

In a pattern consistent with the leveling data, terrain 

inland of Kilaeua's summit area and rift zones moved 

southeastward, the displacements increasing seaward. 

The maximum horizontal displacements are in the same
HORIZONTAL DISPLACEMENTS 25

155°3D' 155°15'

T

5 MILES

FIGURE 14. Displacement solution for deformation on southwest flank of Kilauea Volcano, associated with eruption and intrusion events 

on December 31, 1974. Location of seismic swarm is from Koyanagi, Stevenson, Endo, and Okamura (1978, figs. 7-8). Arrow 

tails are at geodetic stations shown in figure 11; lengths of arrows indicate amounts of displacement. The summit caldera area 

and rift zones are patterned. Hachures indicate craters. (Contour interval, 500 feet.)
26

155°30'

1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

155°15' 155°00'

-2.0i

EXPLANATION

FAULT 0.5-1.5m OF 1975 OFFSET Bar 

and ball on downthrown side

OTHER MAJOR FAULTS Bar and ball 

on downthrown side

SUBSIDENCE CONTOURS IN METERS 1974-1976 

Hachures show direction of increasing subsidence

VECTOR SCALE

i i i i i

012345 METERS

STATIONS

A FALL 1975 SPRING 1976 

o SPRING 1975 SPRING 1976 

 FALL 1974 SPRING 1976

FIGURE 15. Interpretation of displacements associated with November 1975 Kilauea earthquake. See text for discussion of assumptions 

involved. Arrow tails are at geodetic stations shown in figure 11; lengths of arrows indicate amounts of displacement. The summit 

caldera area and rift zones are patterned.
SUMMIT DEFORMATION 1974-77 27

area of the south flank as the maximum subsidence, 

far west of the earthquake epicentral area. Vectors at 

both margins of the region of maximum ground deformation tend to converge toward the central area, more 

notably on the southwest side, where the gradient in 

subsidence is also steep. Unlike the leveling data (fig. 

9C), however, the pattern of horizontal deformation is 

not conspicuously influenced by the rift zones, the caldera, or the unfaulted upper northern part of the south 

flank. Amounts of displacement increase seaward relatively uniformly across every sector of Kilauea, without 

obvious discontinuities across any of these structural 

zones.

SUMMIT DEFORMATION 1974-77

The summit deformation of Kilauea, which has been 

determined by trilateration and releveling several 

times a year before and after the earthquake, is of interest for several reasons. First, the style of deformation related to the earthquake may have been influenced by previous deformation, such as that associated 

with the December 1974 eruption. Also, to the extent 

that the 1975 earthquake is related to stressing of the 

south flank of the volcano by inflation of the summit 

area and dike injection along the rift zones (Swanson 

and others, 1976a), antecedent deformation of the summit area may offer some premonitory clues. Finally, 

the post-earthquake deformation of the summit area is 

significantly different from any previously observed 

pattern on Kilauea, and it offers insight into the manner in which the volcano has responded to disruptive 

effects of the earthquake. Accordingly, we briefly review the record of summit deformation from late 1974 

through September 1977, the time of the first postearthquake eruptive activity on Kilauea.

Interpretation of many geodetic measurements at 

Kilauea, including both leveling and trilateration, is 

complicated by the relative infrequency of reoccupation 

and by high rates of episodic deformation. Accordingly, 

continuously recorded deformation data are especially 

valuable. At present, the only such data are from 

tiltmeters; these tilt measurements, supplemented by 

seismic observations, are utilized both to monitor shortterm fluctuations in behavior of the volcano and to 

select times for reoccupation of the more extensive 

geodetic networks.

Tilt data from the Uwekahuna station, on the northwest side of the summit caldera (fig. 12), have proved 

especially informative and illustrate the general behavior of the volcano in the 1974-77 period (fig. 16). 

After a major deflation associated with the December

1974 eruption and intrusive event along the southwest 

rift zone, the summit area entered a period of steady 

inflation through much of 1975 that was terminated by 

the November 29 earthquake and associated major deflation. This deflation "bottomed out" early in 1976, but 

throughout 1976 and 1977 the volcano failed to maintain 

any sustained summit inflation. Periods of slow inflation 

during this interval were interrupted by significant 

summit deflations in June 1976, July 1976, August-September 1976, and February 1977. Each of these events, 

except the prolonged August-September deflation, was 

accompanied by earthquake swarms along the east rift 

zone, and each has been interpreted as marking intrusive activity along the east rift zone (Dzurisin and 

others, 1980). Similar rift intrusions have also occurred 

repeatedly in the past (Duffield and others, 1976; Swanson and others, 1976a, table 1). Finally, in September 

1977, a major east rift eruption the first eruption 

since the 1975 earthquake was accompanied by a similar but larger summit deflation.

The summit deformation of Kilauea can be 

documented in more detail by combining information 

from leveling and trilateration measurements with the 

tilt data for key periods. Figure 17 shows horizontal 

displacement vectors determined by graphical solution 

of the Kilauea summit trilateration net and contours 

of equal vertical displacements interpreted from releveling in the summit area (fig. 9A) and partly constrained by tilt vectors.

The period of September 1974 to January 1975 (fig. 

17A) is dominated by effects of the December 31, 1974 

eruption along the southwest rift zone and associated 

intrusive events. Summit deflation of more than 0.6 m 

occurred during and immediately after the eruption, 

amounting to a total of about 120 microradians of eastwest tilt as recorded on the Uwekahuna tiltmeter2 (fig. 

16). Subsidence occurred at peak rates of more than 

10 microradians/hour on December 31, and continued 

at decreasing rates until January 5. This eruption was 

also accompanied by significant horizontal changes. 

Convergence of horizontal vectors toward the deflation 

center defined by the contours of vertical change (fig. 

17A) is a typical pattern for summit deflation events 

associated with Kilauea rift eruptions, as has been 

documented repeatedly for eruptions in the late 1960's 

(Fiske and Kinoshita, 1969; Jackson and others, 1975). 

The inflation-deflation is typically eccentric to Kilauea's 

summit area, centered along or just outside the southeast topographic margin of the caldera. In addition to

20ne microradian represents a tilt of 1 mm in 1 km.
28 1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

i li i lull i In li i li i h i li i In li i h i h i In h ih i 111111111 In 111111111111111 In 11 ih i In 111111 In 111111 In In 111 In In 1700 

1600 

1500 

1400 

CO

< 1300 

Q

<

cc 

o

O 1200

1100 

1000 

900 

800 

I-DEC. 31, 1974 

ERUPTION

 NOV. 29, 1975 

EARTHQUAKE

JUNE-AUG. 1976 i- FEB. 1977 

INTRUSIONS INTRUSION

r SEPT. 1977 

ERUPTION

700 i 111 111111 111111 11 M 11 111111111 11111

a

1974

1 I 1 1 I 1 1 I 1 1 I 1 1 I 1 1 I 1 1 r TITTTr| I I 1 1 I 1 1 I 1 1 I 1 1 I |TI 1 1 I 1 1 I 1 1 I 1 1 I 1 1 I 1 1 1 1 1 I 1 I 1 1 I 1 1 1 |TT | I I 1 1 I | I I |l I |ll II | I I

-> ~> < to O 

1975 1976 1977 1978

FIGURE 16. East-west and north-south components of tilt, water-tube tiltmeter at the Uwekahuna vault on west rim of Kilauea caldera.

summit deformation, an intrusive event along the middle southwest rift zone was indicated by seismicity and 

by large horizontal ground movements, as already discussed (fig. 13). The easterly displacements near Mauna 

Ulu and the upper east rift zone (fig. 11 A) are thought 

to reflect dilation of the southwest rift zone in a more 

easterly direction than that of the dominant southward 

opening along the east rift zone. This difference in displacement probably introduces a small component of 

left-lateral displacement along the Koae fault system 

and between the south flank and the more stable area 

north of the east rift zone.

During the first 9 months of 1975, both the 

Uwekahuna tiltmeter (fig. 16) and the leveling and 

trilateration data (fig. 11 B) show a typical pattern of

FIGURE 17 (following 4 pages). Horizontal and vertical deformation 

of the summit area of Kilauea from 1974 to 1977, as interpreted 

from leveling, tilt, and trilateration measurements for successive 

time intervals. Note the variable contour intervals for vertical displacements; also the change in scale for horizontal displacement 

vectors in diagram encompassing period of the 1975 earthquake 

(17C). Vertical displacement contours are relative to assumed stable benchmark in town of Volcano; therefore, the zero contour has 

quotation marks. Horizontal displacement vectors are relative to 

standard "base stations" (Keakapulu, Strip, and Kulani, see fig. 

11), which are assumed to be stable except for period encompassing 

the earthquake (17C). Solutions for this period are based on control 

from the Kilauea flank trilateration net (fig. 11). Hachures indicate 

craters and faults.
SUMMIT DEFORMATION 1974-77 29

EXPLANATION

HORIZONTAL DISPLACEMENT VECTORS

0 500 mm

 -100 

VERTICAL DISPLACEMENTS Contour 

Interval 100mm

MAUNA 

ULU

A. September 1974 to January 1975. Includes December 31, 1974, eruption and intrusion along the southwest rift zone.

EXPLANATION

HORIZONTAL DISPLACEMENT VECTORS

0 500 mm 

 400 

VERTICAL DISPLACEMENTS Contour 

interval 50mm

B

MAUNA 

ULU

B. January to September 1975. A period of sustained summit inflation.

FIGURE 17. HORIZONTAL AND VERTICAL DEFORMATION OF THE SUMMIT AREA OF KILAUEA
30 1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

EXPLANATION

HORIZONTAL DISPLACEMENT VECTORS

VERTICAL DISPLACEMENTS Contour

C. September 1975 to January 1976. Includes November 29, 1975, magnitude-7.2 earthquake.

EXPLANATION

HORIZONTAL DISPLACEMENT VECTORS

0 500 mm

 150 V O] 

VERTICAL DISPLACEMENTS Contour 

interval 50mm

D

MAUNA 

ULU

D. January to September-October 1976. Includes several intrusive events along the east rift zone.

FIGURE 17. HORIZONTAL AND VERTICAL DEFORMATION OF THE SUMMIT AREA OF

KILAUEA Continued
SUMMIT DEFORMATION 1974-77 31

EXPLANATION

HORIZONTAL DISPLACEMENT VECTORS

0 500 mm 

 100 v <3 

VERTICAL DISPLACEMENTS Contour 

interval 20mm

MAUNA 

ULU

E. September-October 1976 to March 1977. Includes one intrusive event along the east rift zone.

EXPLANATION

HORIZONTAL DISPLACEMENT VECTORS

0 500 mm

 -50 /o:

VERTICAL DISPLACEMENTS Contour 

interval 10mm

MAUNA 

ULU

F. March to August 1977. A period of general structural and seismic quiescence.

FIGURE 17. HORIZONTAL AND VERTICAL DEFORMATION OF THE SUMMIT AREA OF

KILAUEA Continued
32 1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

EXPLANATION

HORIZONTAL DISPLACEMENT VECTORS

I 

500 mm

-1 00

VERTICAL DISPLACEMENTS Contour 

interval 50mm

G. August 25 to September 23, 1977. Includes early phase of eruption along the middle east rift zone.

FIGURE 17. HORIZONTAL AND VERTICAL DEFORMATION OF THE SUMMIT AREA OF

KILAUEA Continued

sustained summit inflation. The inflation contours determined by leveling and tilt measurements focus near 

the south margin of the caldera, and the horizontal displacement vectors radiate outward from a nearly confocal center. Nothing seems anomalous about this deformation pattern, in comparison with other well 

studied recent periods of inflation between eruptive 

events at Kilauea (Kinoshita and others, 1969; Swanson 

and others, 1976b, figs. 4, 5), and in the fall of 1975, 

HVO scientists anticipated renewed eruptive activity 

at Kilauea in the near future.

Instead, the magnitude-7.2 earthquake struck on 

November 29, 1975, triggering the largest overall 

ground deformation thus far recorded at Kilauea Volcano. The summit area subsided more than 1.2 m (fig. 

17C), as also indicated by the approximately 145 microradians of eastward tilt at Uwekahuna (fig. 16). Unlike 

the confocal deformation patterns of previous inflationdeflation cycles, the horizontal and vertical components 

of movement were spectacularly decoupled in the summit region, with horizontal displacements trending uniformly south-southeasterly toward the coastline and increasing in amount seaward, independently of patterns 

of subsidence in the summit region and upper rift 

zones. This pattern of summit deformation thus provides a more detailed documentation for the similar 

geometry of deformation already described for the entire subaerial edifice of Kilauea. (Compare fig. 9C and 

fig. 15.)

Post-earthquake deformation patterns for the Kilauea 

summit area during three successive time intervals of 

6-9 months each (figs. 17D-F) are relatively similar. 

All show a component of continued seaward horizontal 

displacement, independent of vertical changes, that 

contrasts notably with the inflation-deflation sequences 

(figs. 17A, 5), normal for Kilauea prior to the 1975 

earthquake.

The period January 1976 to September-October 1976 

(fig. 17Z>) includes two small inferred intrusive events 

along the east rift zone, as indicated by seismic swarms 

associated with abrupt deflation at the summit in June 

and July (fig. 16). A more prolonged episode of aseismic 

deflation also occurred between mid-August and midSeptember; no locus of accumulation has been identified 

for the magma that drained from the summit region 

during this episode. This general time interval is characterized by deformation patterns roughly similar to 

those associated with the 1975 earthquake (fig. 17C), 

but at greatly reduced magnitudes. Horizontal displacement vectors show a coherent pattern of continued seaward movement in a south-southeasterly direction, independent of continued deflation centered along the 

south margin of the summit caldera. A significant 

change, however, is the uplift along the Koae fault sys-
SUMMIT DEFORMATION 1974-77 33

tern and the unfaulted upper part of the south flank. 

Uplift of this general area was a significant feature of 

the regional deformation of Kilauea prior to the 1975 

earthquake (Swanson and others, 1976a, p. 17-23), and 

the uplift along the Koae fault system early in 1976 

may have indicated the beginning of renewed stabilization of the south flank (fig. 17Z>). The absence of continued uplift centered in this area for later post-earthquake time intervals (figs. 17E-F) suggests, however, 

that the episode of uplift alternatively may have reflected some more ephemeral post-earthquake isostatic 

readjustment.

The period of September-October 1976 to March 1977 

shows a more complex pattern of relatively small-scale 

deformation. This period includes another intrusive 

event along the east rift zone, in February, as indicated 

by a concentrated seismic swarm accompanying abrupt 

summit deflation (fig. 16). Loci of such seismic swarms 

commonly have coincided with areas of intrusion and 

uplift along Kilauea rift zones (Duffield and others, 

1976), but, in this case,the location of the seismic 

swarm coincided with an area of net subsidence just 

uprift of Maunu Ulu (fig. HE}. Horizontal extensions 

of as much as 25 cm in individual Geodimeter lines 

across the area of the seismic swarm provide additional 

evidence of an intrusive event; some of the subsidence 

may be due to formation of an apical graben over the 

intrusion, analogous to the troughs of subsidence along 

both of Kilauea's rift zones (fig. 9C). However, lack 

of local uplift adjacent to the area of February 1977 

subsidence, as well as detailed analysis of continuously 

recorded tilt data, suggest that magma migrated downrift from this area during later stages of the intrusion 

event (Dzurisin and others, 1980). Some magma probably accumulated 15-20 km farther east along the rift 

zone, in an area where steaming cracks had developed, 

where tilt measurements indicated sizeable inflation 

early in 1977, and where the September 1977 eruption 

subsequently broke out. In contrast to the subsidence 

along the upper east rift zone, the overall change in 

the summit area from September 1976 to March 1977 

was weak inflation centered near the south margin of 

the caldera. The pattern of horizontal displacements 

was still dominated by seaward motion increasing to 

the southeast, but deviations from this pattern occurred locally near the deflation locus along the upper 

east rift zone and in the north part of the caldera. Thus, 

on its northern flank the weak inflation at the main 

deformation center appears to have reduced and partially reversed the still prevalent regional pattern of 

seaward displacement. Elsewhere, this regional pattern 

continued to dominate the orientation of horizontal 

movements, although at reduced rates.

From March 1977 until August 1977 just before the 

September eruption, the same general style of deformation prevailed, but the changes were smaller and slower 

than previously. This 6-month period was geodetically

one of the most stable periods thus far observed at 

Kilauea's summit. Virtually no net tilt occurred at 

Uwekahuna (fig. 16), and there was essentially no net 

change of elevation on the caldera floor (fig. HF). Modest deflation was centered along the south side of the 

caldera, which cancelled out much of the weak inflation 

of the previous observation period (fig. HE). A weak 

pattern of seaward displacement still characterized the 

horizontal deformation, but the changes were so small 

that the vector solutions are uncertain for many stations.

The general pattern of summit deformation for nearly 

2 years after the November 1975 earthquake can thus 

be characterized by two significant features: a lack of 

sustained inflation and the seaward displacement of the 

south side of Kilauea at gradually decreasing rates. 

This pattern appears to have represented continued deformation like that triggered by the earthquake, gradually evolving into greater structural stability. At no 

time did the loci of horizontal and vertical deformation 

share a common focus, as had been characteristic prior 

to the earthquake (fig. 17J5). If magma is generated 

and accumulates at a steady rate of about 0.1 km3/yr 

beneath Kilauea, as inferred by Swanson (1972), all of 

it could not have been stored in the summit reservior 

after the 1975 earthquake. Some magma may have 

filled voids generated by the earthquake in the summit 

region, but calculations based on microgravity measurements (Jachens and Eaton, 1980; Dzurisin and others, 

1980) suggest that any such voids would have been 

largely filled within 6-8 months after the earthquake. 

Subsequently, most of the newly generated magma appears to have moved into the east rift zone, instead 

of accumulating at a summit magma reservoir. Attempts to evaluate volumetric relations between rift expansion and rates of magma supply at Kilauea are not 

very satisfactory, because of limited geodetic information along the heavily forested east rift zone, but on 

the basis of seemingly plausible assumptions, the 

magma supply of Kilauea for about 1 year may have 

emptied into voids opened along the east rift zone by 

the 1975 earthquake. This rift zone was the site of repeated intrusive events, and magma accumulated along 

the middle part of the rift zone, where sizeable inflation 

was documented by tilt and Geodimeter measurements 

in the spring and summer of 1977.

A major eruption broke out along the middle east 

rift zone of Kilauea on September 12, 1977 (Moore and 

others, 1980), after a several-week period of gradually 

increasing seismicity. A lack of any premonitory summit inflation makes this eruption different from any 

other Kilauea eruption since detailed ground-deformation studies began. Major subsidence in the summit region (fig. 17G) associated with this eruption was rather 

similar to subsidence associated with earlier Kilauea 

rift eruptions such as in December 1974. (Compare fig. 

17A with fig. 17G.) However, detailed examination of
34 1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

the horizontal deformation patterns for this period, August to October 1977, suggests that a component of seaward horizontal displacement was still present but 

largely obscured by the contraction accompanying subsidence. In particular, the southeasterly displacements 

on the north and west sides of the caldera were larger 

than complementary inward displacements on the south 

and east sides (fig. 17G), which suggests that some of 

the movement on the south and east sides was counterbalanced by opposing seaward movement.

The summit area of Kilauea began to reinflate by 

mid-October 1977, a pattern that continued until 

November 1979, when a brief east-rift eruption occurred. Trilateration measurements of the summit net 

indicate continued seaward mobility of the south flank 

as recently as fall 1980, largely independent of the vertical changes, in a pattern similar to that documented 

above for the entire period between the 1975 earthquake and the 1977 eruption. Clearly, the period of 

post-earthquake stabilization has been prolonged.

DISCUSSION

Analysis of ground deformation data related to the 

1975 earthquake has yielded several significant results: 

(1) the large size of ground movements, (2) supporting 

documentation for a gravitational slump or glide 

hypothesis for the main structural features of Kilauea's 

south flank, (3) insights into the cause of the earthquake and associated surface deformation, (4) evidence 

of the profound effect of the earthquake on the nature 

of subsequent deformation in the Kilauea summit area, 

and (5) implications for future seismic and volcanic hazards on the Island of Hawaii.

SCALE OF MOVEMENTS

The scale of the extensional ground deformation related to the 1975 earthquake and associated normal 

faults was as much as 3.5 m vertically and 8 m horizontally on land, with a strong probability that even larger 

downdip displacements occurred below sea level. These 

are among the largest movements recorded in the 

United States that can be related to a single seismic 

event. By way of comparison with other major North 

American earthquakes, the 1906 San Francisco earthquake of magnitude 8.3 was associated with lateral 

movement of as much as 6.5 m along the San Andreas 

fault (Richter, 1958, p. 476-486). As much as 4.5 m 

of dominantly vertical movement occurred during the 

7.1-magnitude Hebgen Lake earthquake in Montana in 

1959 (Myers and Hamilton, 1964). Among 20th century 

American earthquakes, only the 1964 Alaska earthquake of magnitude-8.4+ caused greater earth movements than those observed in Hawaii in 1975, as much

as 14 m vertically and 19.5 m horizontally (Plafker, 

1969).

An important aspect of the deformation pattern related to the 1975 Kilauea earthquake is the distinct spatial separation between the epicenter, which marks initiation of the earthquake, and the region of maximum 

ground deformation, centered nearly 30 km farther 

west along the south coast. Strong-motion seismograms 

of the earthquake document at least 5 maxima of energy release over an interval of 65 seconds (Rojahn and 

Morrill, 1977, fig. 3A), and together with asymmetry 

of the deformation maxima, strongly indicate that the 

initial earthquake triggered a sequence of dislocations 

that migrated westward along the Hilina fault system.

GRAVITATIONAL SLUMP HYPOTHESIS

The generally large ratios of horizontal to vertical 

displacement associated with the 1975 Kilauea earthquake strongly support a gravitational slump or blockglide interpretation, both for the deformation associated with this earthquake and also for the long-term 

tectonic evolution of the south flank of Kilauea. The 

hypothesis that the block-faulted terrain on the south 

flank may be due to "landsliding on a huge scale" goes 

back many years (Stearns and Macdonald, 1946, p. 130) 

and has more recently been argued persuasively (Moore 

and Krivoy, 1964; Fiske and Jackson, 1972). A recent 

comprehensive model for structural evolution of the 

south flank (Swanson and others, 1976a), based on 20th 

century seismic and ground-deformation studies, relates seaward displacement of the unbuttressed south 

flank of Kilauea to the result of forceful injection of 

magma into the rift zones. By this interpretation, 

gravitational instability of the south flank, which results from uplift and seaward displacement along the 

rift zones, is expected to be relieved intermittently by 

normal faulting and slumping along the Hilina fault system. Contractional strains were shown to have been 

accumulating within the south flank during the 20th 

century, destabilizing the Hilina fault system, and a 

possible subsidence event was anticipated "in the not 

too distant future" by Swanson, Duffield, and Fiske 

(1976a, p. 35). The 1975 earthquake occurred while 

their report was in press.

The patterns of ground breakage along the central 

Hilina fault system (fig. 3) and the leveling contours, 

showing maximum gradients of subsidence in the same 

area (figs. 9C, 15), offer convincing evidence that much 

of the earthquake-related deformation involved seaward gravitational slumping or block gliding. In detail, 

however, the geometry of displacement is more complex. The entire subaerial surface of Kilauea moved 

seaward, and the patterns of vertical deformation (fig.
DISCUSSION 35

9C) were significantly different from those of the horizontal deformation (fig. 15).

While the horizontal displacements show a relatively 

uniform seaward increase, with little or no reflection 

of the summit caldera, inflation center, or rift zones, 

the patterns of vertical movements reflect these 

primarily volcanic structures and apparently were 

much more influenced by movement of magma. The 

subsidence at the summit and along both rift zones is 

most readily accounted for by movement of magma into 

voids that opened during the earthquake. The volume 

of summit deflation, computed from the leveling data, 

was at least 68xl06 m3 , about 270 times the volume 

of the lava erupted during the brief earthquake-induced 

caldera-floor eruption on November 29, 1975 (estimated 

at about 25xl04 m3 ; Tilling and others, 1976, p. 26).

The contrast in behavior between horizontal and vertical components of the deformation is well illustrated 

by contours of the ratios of horizontal to vertical components (fig. 18). Because the seaward increase in horizontal displacement is quite uniform, the contours of 

the ratios largely mimic the changes in vertical displacement (fig. 9C). Clearly evident are effects related 

to the summit subsidence, the axial troughs along both 

rift zones, and the positive upper part of the south 

flank. The ratio of horizontal to vertical changes is 

greatest at inland parts of the deformed area, where 

deformation was relatively slight, and the ratio generally decreases as the intensity of deformation increases.

Both the dominance of the horizontal component of 

movement over the vertical component, and the semiindependent behavior of the two components, suggest 

that the earthquake-induced deformation is related 

primarily to seaward movement along gently dipping 

master slip structures, with the vertical changes on 

land at least reflecting magmatic movements and 

jostling of the horizontally displaced mass along 

preexisting steeply dipping faults. If the primarily 

magma-related subsidences at the summit and along 

the rift zones are disregarded, three-dimensional displacement vectors, determined by combining the horizontal and vertical data, plunge gradually more steeply 

seaward, from horizontal on Mauna Loa to approximately 30° at the coastline. This pattern differs from 

simple models of block slumps, in which vectors would 

be steepest near the breakaway zone and would decrease gradually downslope to the toe of the slump. 

If, however, the main detachment zone for the 1975 

deformation was along the Hilina fault system, as 

suggested by the areas of observed ground breakage, 

most of the primary slump structures may be underwater, with major deformation perhaps extending all the 

way to the base of the volcanic edifice at water depths 

of about 5000 m (fig. 1). The bulk of the subaerial deformation would, accordingly, reflect adjustments upslope 

of the primary slump feature. The large area affected 

and the relatively smooth gradients of horizontal deformation (and also vertical changes, if features related 

to movement of magma are neglected: see fig. 10) are 

a qualitative measure of the lack of rigidity and delicate 

balance of most of the volcanic edifice.

Both the main 1975 earthquake and most aftershocks 

were at depths of 5-10 km beneath the south flank, 

close to the basal contact of the volcano on the Pacific 

sea floor. This geometry suggests that the block slumping involved nearly the entire thickness of the volcanic 

edifice, with much of the lateral movement possibly accommodated within originally poorly consolidated submarine rubble, formed low on Kilauea's south flank during early stages of its growth. Fragmental submarine 

volcanic deposits have been interpreted as significant 

to the structural evolution of Hawaiian volcanoes by 

Moore and Fiske (1969), Swanson, Duffield, and Fiske 

(1976a), and Nakamura (1980).

Step topography, similar in geometry to the Hilina 

fault system, is present on submarine slopes of the 

south flank (fig. 1), and a prominent bulge low on the 

submarine slope may be a reflection of the toe of the 

slump structure (fig. 19). The sparcity of post-earthquake seismicity on lower parts of Kilauea's south flank 

(fig. 2) suggests that this area especially the submarine flank is structurally incompetent, and that 

major stress accumulations occur mainly close to the 

rift zones.

RELATION BETWEEN THE EARTHQUAKE AND 

SURFACE DEFORMATION

An incompletely resolved problem is the relation between the cause of the earthquake and the deformation 

patterns observed at the surface. Was the earthquake 

a direct reflection of catastrophic failure along the 

Hilina system, along which large displacements are observed, or is the deformation observed at the surface 

a relatively superficial second-order reflection of gravitational slumping, fundamentally different from deformation processes associated with the observed seismicity deeper within the volcano?

Teleseismic focal-mechanism studies and analysis of 

other seismic parameters indicate that initial failure 

during the 1975 earthquake occurred along a fault plane 

striking approximately N. 70° E. and dipping gently. 

Solutions for dip angle, vary from about 20° southeast 

(Ando, 1979), to 4° northwest (Furumoto and Kovach, 

1979), but regardless of the exact dip, motion of the 

upper block is seaward (to the southeast). Determinations of focal mechanisms from the detailed local seismic 

network on the Island of Hawaii also favor a low-angle
19°45' 155°30' 155° 15' 155°00'

19°30' - I 10 15 KitfiMEWS

' '- " .'.I

a '«"

CONT OUft tNTE RVAl 500 FEET

FIGURE 18. Contours of the ratio of horizontal to vertical displacement between 1974 and 1976. Data from interpretative maps of figures 9C and 13. The 

summit caldera area and rift zones are patterned. Gaps in contours are areas for which displacement data are lacking, mainly because of heavy 

vegetation. Hachured contours indicate direction of decrease in ratios of displacement data.

£

H

Or1 

o

1
DISCUSSION 37

C . '" ' '' &%'. f&^ffi

FIGURE 19. Oblique map of the south half of the island of Hawaii, as viewed from the east, showing marine topography. 

Physiographic drawing by Tau Rho Alpha (1977). Heavy solid lines define new faulting related to the 1975 earthquake, dashed line indicates possible boundary of the submarine slump terrane, and numbers along coastline give 

amount of measured subsidence on transects marked by dotted lines.
38 1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

normal fault solution, dipping gently seaward (Crosson 

and Endo, 1981; Wyss and others, 1981), although the 

interpretation is strongly model dependent.

These relations have led to a deformation model, accepted with only minor variations in all these seismic 

studies, in which the major dislocation is along a gently 

dipping master fault at a depth of 8-10 km, near the 

base of Kilauea Volcano, that permits the south flank 

to move seaward and release compressional strain 

acummulated during injection of dikes along the rift 

zones. Deformation along the Hilina system is 

interpreted as secondary gravitational slump features, 

bottoming at 2-3 km depth and triggered by movements along the deeper low-angle fault (Ando, 1979; 

Wyss and others, 1981), or disregarded entirely 

(Furumoto and Kovach, 1979).

Various structural, geodetic, and seismic features 

suggest to us, however, that the Hilina fault system 

and its associated gravitational slump structures penetrate a large part, perhaps the entire thickness, of the 

south flank of Kilauea Volcano and flatten at a depth 

of 6-8 km to accommodate seaward displacement of the 

lower south flank (fig. 20). The best evidence that 

faults of the Hilina system penetrate deeply comes from 

the concentration of earthquakes along the upper part 

of the south flank (fig. 2; also Koyanagi and others, 

1972; Wyss and others, 1981, fig. 10). Earthquakes as 

deep as 7-8 km are strikingly concentrated in a 10-kmdeep volume bounded by the rift zones and the Hilina 

system; this pattern has been quite consistent since a 

seismic net sufficiently detailed for accurate epicentral 

locations was established in the middle 1960's. The region seaward of the bounding Hilina faults has been 

characterized by much lower levels of seismic activity, 

probably reflecting lower strengths of rocks within the 

block-faulted area. Even after the 1975 earthquake, aftershocks were sparse in the region seaward of the 

main Hilina faults where the ground deformation was 

most intense. Whatever the cause for the contrast in 

seismicity across the Hilina fault system, these structures seemingly constitute a major structural control 

on seismicity, extending through much of the edifice 

of Kilauea volcano.

The Hilina system and the area to the south clearly 

accomodated major deformation in 1975, as indicated 

by the horizontal and vertical displacements documented in this report (figs. 9, 13) and by the geometry 

of the associated tsunami, which required uplift of a 

large portion of the submarine south flank of Kilauea 

(Hatori, 1976). The location and area interpreted by 

Hatori (1976, fig. 2) for the source of the tsunami coincide closely with the submarine slump terrain on the 

south flank of Kilauea (figs. 1, 19), and his estimate 

of the required deformation (1 m of uplift for an area

of 2,200 km2 of sea floor) is approximated by the 

subaerial volume changes on Kilauea. We estimate 

these changes as an average of 1 m of subsidence over 

an area of about 1,000 km2 (figs. 9C, 19) IxlO9 m3, 

plus an average of 3 m seaward displacement along 40 

km of coastline (fig. 13) to a depth of 8 km (the base 

of the volcano) 0.96 xlO9 m3, or a total of about 2xl09 

m3.

A relatively deep sole to the gravitational slump 

blocks of the Hilina system is also indicated by the listric geometry of the faults, which are wedge-shaped 

and curved in plan view but all dip steeply (70°-90°) 

at the surface. Large displacements along curved normal faults of listric geometry tend to preserve a relation in which bedding remains approximately perpendicular to the fault plane (Anderson, 1971; Proffett, 

1977). Relatively old basalt flows of the Kahuku Volcanics (>20,000 years before present: Kelley and others, 

1979), which normally dip 3°-5° away from the summit 

of Kilauea (Stearns and Macdonald, 1946, pi. 1), mostly 

dip subhorizontally to a few degrees seaward where exposed in scarps of Hilina faults, which indicates only 

limited back rotation. Ponding of lava flows and closed 

depressions near bases of some fault scarps indicate 

local back tilting (Swanson and others, 1976a, fig. 22), 

but the generally limited tilting requires that any curvature present along Hilina faults must penetrate 

deeply. The limited tilting along the Hilina fault blocks 

also demonstrate a style of deformation somewhat 

transitional between block slumping (rotation significant) and block gliding (rotation limited or absent).

The main fault along the lava-draped Hilina Pali has 

a displacement of at least 500 m, the height of the present topographic scarp; this amount of offset along a 

curved fault plane flattening at depth of only 3 km, 

as assumed by Wyss, Klein, and Johnston (1981), would 

produce 9.5° rotation of bedding. These considerations 

strongly suggest that upper parts of Hilina faults have 

steep average dips, probably in the range of 60°-80°, 

similar to many measurements on actual fault surfaces 

and open cracks along the Hilina system (Easton, 1978); 

dips as low as 35° on some small Hilina faults and 

cracks are adjacent to steep scarps and are likely related to surficial sliding. The broadly arcuate planimetric traces of the individual fault scarps, extending as 

much as 20 km along strike and with radii of curvature 

of 10-15 km, also qualitatively suggest relatively deep 

penetration to a master sole fault.

In light of these considerations, the initial rupture 

of the 1975 earthquake could have occurred along a 

fault of the Hilina system that flattened from near vertical at the surface to about 20° at a depth of about 

6±1 km, the depth and dip indicated by focalmechanism determinations. The hypocenter is about 2
DISCUSSION 39

- 5

--10

- -15

FIGURE 20. Diagrammatic cross section, with no vertical exaggeration, through the summit region and south flank of Kilauea. Location of section 

shown in figure 1. Thickness and dip of pre-Mauna Loa oceanic crust are from Hill (1969) and Zucca and Hill (1979).

km south of the main Hilina fault along this sector of 

the south flank and would lie along the downward projection of this fault if the average dip is about 70°. If 

the epicentral depth is correct, the main shock may 

have occurred deep within the edifice of Kilauea Volcano, rather than along its basal contact with old sea 

floor, at a depth of approximately 9 ± 1 km at this site 

as indicated by seismic refraction data (Hill, 1969; 

Zucca and Hill, 1979).

Whether the initial rupture of the 1975 earthquake 

occurred along some such gently dipping deep part of 

a Hilina fault, or within the margin of the adjacent 

more structurally coherent upper part of the south 

flank, the rupture clearly propagated rapidly westward, causing major failure along the Hilina system. 

This failure and the associated subsidence occurred 

largely within a minute or so of the beginning of the 

earthquake, as indicated by observations of initially 

slowly rising water by beach campers, prior to arrival 

of the first tsunami wave (Tilling and others, 1976, p. 

2). The coastal subsidence could not have been primarily a secondary adjustment over a period of weeks following the earthquake, as suggested by Furumoto and 

Kovach (1979, p. 207). The horizontal and vertical displacements, increasing seaward, define a coherent pattern that clearly continued below sea level, with the 

sense of vertical displacement reversing, as indicated 

by analysis of the tsunami (Hatori, 1976).

By our interpretation (fig. 21), the seaward and 

downward movements of the adjacent parts of Kilauea, 

inland of the Hilina fault system, reflect adjustment to 

decreased support from the seaward flank, plus 

magma-related movements in the summit region and 

along the rift zones. The displacement of the lower 

south flank was sufficiently large to stabilize this part 

of the Kilauea edifice. From late 1975 to 1977, the 

upper south flank, now less supported from the south, 

continued to deform slowly seaward in a pattern much

like that during the earthquake, as indicated by displacements within the summit trilateration net (figs. 

17C-F) and by continued seismicity on the upper south 

flank at rates higher than typical for Hawaiian aftershock sequences (Tilling and others, 1976, fig. 5). In 

contrast to relations at many major earthquakes, aftershocks of the 1975 event thus do not define the fault 

plane responsible for the associated ground deformation, which is at a maximum seaward of the bounding 

faults of the Hilina system.

We are uncertain what features account for the contrasting structural behavior of the relatively immobile 

but seismically active upper part of the south flank versus the mobile but seismically inactive lower part. 

Large-scale gravitational slump structures occur widely 

on Hawaiian volcanoes, largely on the submarine slopes 

(Moore, 1964; Normark and others, 1979). Could the 

boundary between gravitationally stable and unstable 

regions on these volcanoes be related to thermal gradients away from the summit areas and rift zones, 

which results in contrasts between a thermally dehydrated central region and flanking areas of cooler lavas 

that have reduced frictional coefficients because of saturation by seawater? Whatever the fundamental cause, 

the boundary between the upper and lower parts of 

the south flank is a major structural feature of Kilauea 

Volcano.

An equally speculative question involves the possible 

role of Mauna Loa in destabilizing Kilauea and triggering the 1975 earthquake. The earthquake occurred essentially concurrently with the first significant seismic 

and volcanic activity on Mauna Loa in 25 years, culminating in the July 1975 summit eruption (Lockwood 

and others, 1976), and magma-related deformation of 

a large region of Mauna Loa was seemingly indicated 

by the instability of the baseline stations for the 

Kilauea summit trilateration net during 1974-76. Could 

inflation of Mauna Loa have exerted a destabilizing in-
40

SUMMIT AREA

1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII 

SOUTH FLANK OCEAN FLOOR

Upper part Lower part

Intrusion

along

rift zones

1868-1975

Old ocean floor

November 29, 

1975

fi

Seaward displacement uplift of the submarine flank, and extension 

 _ Tsunami

After shocks \ 

* \

-T*

Old ocean floor

Renewed 

intrusion

along

rift zones

1975-?

Continued seaward displacement

Old ocean floor

FIGURE 21. Interpretation of relations between seismicity and deformation within the south flank of Kilauea, associated with the 1975 

earthquake. Dashed lines are former positions of moved blocks. No scale. 

A. Twentieth-century intrusion in the summit region and emplacement of dikes along the rift zones wedge the upper part of

the south flank seaward and upward. Contractional strain accumulates within this block, and seismicity is concentrated at

depths of 5-10 km within its lower parts.

B. In November 1975, accumulated strain within the upper part of the south flank causes failure and seaward displacement along 

its southern margin, perhaps along the gently dipping lower part of a Hilina fault that marks the boundary between upper 

and lower parts of the south flank. Displacements increase seaward, and the maximum displacements occur along faults 

of the Hilina system, which extend through the south flank of Kilauea to merge with the zone of adjustment at the base 

of the volcano. Uplift of the submarine flank along the toes of the Hilina faults causes a major tsunami. The smaller displacements in upper parts of the south flank and farther landward on Kilauea largely represent second-order adjustments to 

failure along the Hilina system.

C. Since 1975, regeneration of magmatic pressures in the summit area continues to displace the upper part of the south flank, 

which is less buttressed on its seaward side as a result of the earthquake-related movements. As a result, the upper south 

flank continues to deform in a seaward direction at gradually diminishing rates for several years after the 1975 earthquake, 

accompanied by high levels of aftershock activity.

fluence on an already delicately balanced Kilauea 

edifice? The plausibility of this possibility is enhanced 

by comparisons with events in 1868, the time of the 

last similarly large historic earthquake on the Island 

of Hawaii. The 1868 earthquake, of magnitude about 

7.5-8.0, occurred one week after a Mauna Loa summit 

eruption and during a time of marked change in eruptive behavior of this volcano (Lipman, 1980). The earthquake was associated with major deformation on the 

south side of Mauna Loa (Wood, 1914, p. 196-199), including several meters of offset along the Waiohinu 

fault, near the south coast. It also caused as much as 

2.1 m of subsidence and a devastating tsunami along 

the south flank of Kilauea.

In addition to recording the response of an oceanic 

basaltic volcano to stressing of its flanks by dike intru-
DISCUSSION 41

sion and loading of its slopes by lava accumulation, the 

deformation associated with the 1975 Kilauea earthquake has significance for other tectonic environments. 

The geometry of the deformed south flank of Kilauea 

(fig. 20) is strikingly similiar to that currently inferred 

for large-scale thrust and fold belts on the cratonic 

sides of Cordilleran tectonic regimes. For example, just 

as on the south flank of Kilauea, the Cordilleran foreland in the southern Canadian Rocky Mountains has 

been interpreted as an allochthonous wedge that has 

been thrust up along gently dipping regional basal detachment faults, as a consequence of lateral gravitational spreading under its own weight down a regional 

surface slope with more than 20 km of structural relief 

(Price and Montjoy, 1970; Price, 1981). Although gravitational spreading in the Canadian Rockies is thought 

to have been caused by buoyant upwelling of a hot 

metamorphic core and associated magmatic rocks, in 

contrast to the stressing of the Kilauea rift zones by 

dike intrusion, geometric relations are similar in the 

two regions. Thus, active deformation of the Kilauea 

south flank may provide an intermediate-scale model 

for interpretation of large thrust faults in Cordilleran 

tectonic belts.

EFFECT ON THE SUMMIT 

MAGMA SYSTEM

The summit deformation pattern at Kilauea subsequent to the earthquake (figs. 17D-G) clearly demonstrates that the 1975 earthquake and associated ground 

displacements caused long-term disruptions in the magmatic conduit system of the volcano. Prior to 1975, 

summit ground deformation was dominated by inflation-deflation events related to a magma reservoir centered near the south margin of the caldera. Inflation 

was reflected by uplift and a pattern of outward-radiating vectors of horizontal displacement; whereas, deflation and subsidence were associated with a pattern of 

inward-converging vectors, all confocal at nearly the 

same center. Since 1975, one major effect has been a 

decoupling of horizontal and vertical components of displacement. Vertical changes have continued to reflect 

magmatic movements in the summit region, and they 

show relatively small changes, both positive and negative, in a pattern generally confocal with pre-earthquake changes. In contrast, horizontal displacements 

have documented continued southward displacement of 

the summit area, with amounts of displacement increasing seaward. This pattern essentially represents a continuation, at a reduced rate, of the same style of deformation as occurred during the earthquake period. The 

net effect appears to have been to keep the upper east 

rift zone open for intrusion of magma and, simultaneously, to have impeded magmatic inflation of the summit area.

IMPLICATIONS FOR THE FUTURE

The 1975 earthquake and accompanying activity represent the latest events in a recurring pattern of behavior for Kilauea. A large earthquake of about the 

same magnitude, with associated coastal subsidence, 

tsunami, and eruption, occurred at Mauna Loa and 

Kilauea in 1868, and a less powerful earthquake and 

similar related events are believed to have occurred in 

1823. The deformation associated with the 1975 earthquake had a geometry appropriate for formation of the 

large scarps and palis of the Hilina fault system, and 

this event is almost certainly the latest in a series of 

many similar episodes that have formed the present 

palis. The subaerial Hilina system has about a kilometer of structural relief, which suggests that approximately 1000 events of the magnitude of the 1975 earthquake may have occurred, perhaps at a tempo 

suggested by the earthquakes and associated subsidence events of 1823(?), 1868, and 1975. As long as 

Kilauea remains active, gravitational and magmainduced stresses will inexorably accumulate, and the 

mobile south flank will shift seaward and downward 

episodically and abruptly, providing stress relief. Then 

the cycle will begin anew.

How may we tell when to anticipate another such 

event? One approach would be to search for seismic 

precursors, as has been attemped by Johnston (1978) 

in connection with the 1975 earthquake. Johnston recognized compressional-velocity decreases at the nearest 

seismometer station to the epicentral area, beginning 

about 3.5 years prior to the earthquake. In addition, 

much information may come from ground-deformation 

studies. The 1975 events were preceded by accumulation of contractional strain on Kilauea's south flank 

throughout the 20th century (Swanson and others, 

1976a, fig. 5), and many years of such strain accumulation is probably a necessary prerequisite for a major 

subsidence event. Advance warning of a subsidence 

event may be, accordingly, decipherable from changes 

in strain rates. For example, Swanson, Duffield, and 

Fiske (1976a, p. 16) noted that strain along a frequently 

measured 5.4-km-long line normal to the south flank 

of Kilauea, which consistently contracted during the 

late 1960's, experienced alternate periods of extension 

and contraction in the early 1970's related to east rift 

magmatism and to nearby earthquakes (fig. 22A; Swanson and others, 1976a, p. 16). Unfortunately, the bench 

mark at one end of this line was covered by new lava 

flows early in 1971, ending the measurements.

Another line to the south coast, although occupied 

relatively infrequently, showed contraction until about 

a year before the 1975 earthquake (fig. 22B). Extension 

during this last period may have been signaling that 

the south flank was strained to a point that further 

contraction was not possible and a subsidence event
42 1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

5404.18 -

HVO 60 

Geodimeter line

HVO 78

5404.00 -

5403.98

.90 -

.88 -

.86 -

.84

5403.82 1966 1967 1968 1969 1970

A. Contraction of 5.4-km-long Geodimeter line (upper right inset) on south flank of Kilauea between August 1965 

and early December 1970. Major magmatic and structural events are (1) December 1965 eruption and ground 

cracking, (2) November 1967-July 1968 summit eruption, (3) August 1968 eruption, (4) October 1968 eruption, 

(5) February 1969 eruption, (6) beginning of May 1969-October 1971 Mauna Ulu eruption, (7) new fissure 

north of Alae Crater, December 1969, (8) new fissure and cracks in and west of Aloi Crater, April 1970, 

(9) intrusion and cracking in southern part of Kilauea Caldera, May 1970, (10) new fissure east of Mauna 

Ulu, July 1970 (from Swanson and others, 1976a, fig. 10).

FIGURE 22. CHANGES IN LENGTH OF TWO GEODIMETER LINES ACROSS THE SOUTH FLANK OF

KILAUEA, 1970-77
DISCUSSION 43

+0.90

+0.80 -

+0.70 -

CO DC

LLJ

I- +0.60 -

+0.50 -

2 +0.40 -

+0.30 -

+0.20 -

+ 0.10 -

1970 1971 1972 1973 1974 1975 1976 

TIME

1977 1978 1979 1980

B. Changes in length of line between Apua Point and Goat or Goat 2 stations. Observations until 1974 are to Goat station; subsequent

measurements are to Goat 2.

FIGURE 22. CHANGES IN LENGTH OF TWO GEODIMETER LINES ACROSS THE SOUTH FLANK OF KILAUEA,

1970-77 Continued

was imminent. Since the 1975 earthquake, this line has 

shown steady contraction, interupted only by the 

period encompassing the September 1977 eruption, 

which indicates that strain is again accumulating along 

the south flank.

A similar change in strain pattern is indicated by 

fragmentary data for the upper south flank. A 5.1-kmlong Geodimeter line between Puu Huluhulu and Goat 

2 (fig. 11), first established in 1974, has shown extension for every subsequent occupation, including the preearthquake interval October 1974 to January 1975, indicating continued seaward movement of Goat 2 relative 

to Puu Huluhulu. In contrast, displacement solutions 

of the Kilauea flank net suggest that this line contracted about 25 cm between October 1970 and October 

1974. Thus, this area, like the two Geodimeter lines 

shown in figure 20, also changed from a contractional

to extensional strain regime prior to the 1975 earthquake.

Much might be learned about the stability of the 

south flank by establishing a chain of short frequently 

measured lines or triangles normal to the south coast, 

which would permit locating and monitoring the boundary between domains of extensional and contractional 

strain. Since the earthquake, this boundary appears to 

be relatively low on the south flank, as indicated in 

the summit area by the increasing size of displacements 

toward the coastline (figs. Y1D-E). In the future this 

boundary can be expected to migrate northward, as the 

south flank and southern part of the summit area stabilize further, and as a typical pre-1975 pattern of confocal horizontal and vertical deformation becomes reestablished in the summit area. When the accumulated 

compressive strain on the south flank exceeds some
44 1975 MAGNITUDE-7.2 EARTHQUAKE, KILAUEA VOLCANO, HAWAII

presently unknown level, however, destablization similar to that during 1970-75 (fig. 225) should be reflected 

by a reversal in strain pattern and seaward migration 

of the compensation boundary. A major gravitational 

slump event could then be expected in the near future.

A concluding caution, however: only a small portion 

of the diverse eruptive behavior of Kilauea Volcano indicated by the geologic record has actually been observed during the relatively short period of recorded 

history, beginning only with observations by the missionaries in the early 19th century. Unknown to us are 

the premonitory patterns of magmatic behavior with 

associated ground deformation and seismicicity leading up to such major events as (1) caldera collapse, 

which appears to have occurred at Kilauea several 

times in the past thousand years or so (Holcomb, 1979), 

(2) large-scale phreatomagmatic activity, such as apparently occurred in 1790 (Christiansen, 1979) and at least 

twice more in the preceding 2,000 years (Kelley and 

others, 1979, p. 318-319), or (3) the long-continued 

summit overflow and rift eruptions of tube-fed 

pahoehoe that appear to have covered nearly the entire 

surface of Kilauea in late prehistoric time, probably 

largely in the 17th and 18th centuries (Holcomb, 1979). 

Future studies may be expected to document patterns 

of ground deformation and other geophysical changes 

at Kilauea related to events such as these, that we can 

only dimly anticipate from present experience.

REFERENCES CITED

Anderson, R. E., 1971, Thin skin distension in Tertiary rocks of 

southeastern Nevada: Geological Society of America Bulletin, v. 

82, p. 43-58.

Ando, Masataka, 1979, The Hawaii earthquake of November 29, 1975: 

low dip angle faulting due to forceful injection of magma: Journal 

of Geophysical Research, v. 84, p. 7616-7626.

Apha, Tau Rho, 1977, Physiography of the Island of Hawaii and its 

submarine slopes: U.S. Geological Survey Open-File Report No. 

77-814, 1 map.

Christiansen, R. L., 1979, Explosive eruption of Kilauea Volcano in 

1790 [abs.]: Abstract volume, Hawaii Symposium on Intraplate 

Volcanism and Submarine Volcanism, Hilo, Hawaii, p. 158.

Crosson, R. S., and Endo, E. T., 1981, Focal mechanisms of earthquakes of earthquakes related to the November 29, 1975, 

Kalapana earthquake: the effect of structure models: Bulletin of 

the Seismological Society of America, v. 71, p. 713-729.

Duffield, W. A., 1975, Structure and origin of the Koae fault system, 

Kilauea Volcano, Hawaii: U.S. Geological Survey Professional 

Paper 856, 12 p.

Duffield, W. A., Jackson, D. B., and Swanson, D. A., 1976, Shallow, 

forceful intrusion of magma and related ground deformation at 

Kilauea Volcano, May 15-16, 1970: Proceedings of Symposium 

of Andean and Antarctic Volcanology Problems, International 

Association of Volcanology and Chemistry at the Earth's Interior, p. 577-597.

Dzurisin, D., Anderson, L. A., Eaton, G. P., Koyanagi, R. Y., Lipman, P. W., Lockwood, J. P., Okamura, R. T., Puniwai, G. S., 

Sako, M. K., and Yamashita, K. M., 1980, Geophysical observations of Kilauea Volcano, Hawaii: 2. Constraints on the magma 

supply during November 1975-September 1977: Journal of Volcanology and Geothermal Research, v. 7, p. 241-269.

Easton, R. M., 1978, The stratigraphy and petrology of the Hilina 

Formation: the oldest exposed lavas of Kilauea Volcano, Hawaii: 

unpublished M.S. thesis, University of Hawaii, Manoa, 263 p.

Eaton, J. P., 1962, Crustal structures and volcanism in Hawaii, in 

G. A. Macdonald, and Hisashi Kuno, eds., Crust of the Pacific 

Basin: American Geophysical Union Monograph 6, p. 13-29.

Fiske, R. S., and Jackson, E. D., 1972, Orientation and growth of 

Hawaiian volcanic rifts: the effect of regional structure and gravitational stresses: Royal Society [London] Proceedings, v. 329, 

p. 299-326.

Fiske, R. S., and Kinoshita, W. T., 1969, Inflation of Kilauea Volcano 

prior to its 1967-1968 eruption: Science, v. 165, p. 341-349.

Fiske, R. S., and Koyanagi, R. Y., 1968, The December 1965 eruption of Kilauea Volcano, Hawaii: U.S. Geological Survey Professional Paper 607, 21 p.

Furumoto, A. S., and Kovach, R. L., 1979, The Kalapana earthquake 

of November 29, 1975: an intra-plate earthquake and its relation 

to geothermal processes: Physics of the Earth and Planetary Interiors, v. 18, p. 197-208.

Hatori, T., 1976, Wave source of the Hawaii tsunami in 1975 and 

the tsunami behavior in Japan: Journal of the Seismological Society of Japan, v. 29, p. 355-364.

Hill, D. P., 1969, Crustal structure of the Island of Hawaii from 

seismic-refraction measurements: Seismological Society of 

America Bulletin, v. 59, p. 110-130.

Holcomb, R. T., 1979, Century-scale changes in eruptive behavior 

of Hawaiian volcanoes [abs.]: Abstract volume, Hawaiian Symposium on Intraplate Volcanism and Submarine Volcanism, Hilo, 

Hawaii, p. 164.

Jachens, R. C., and Eaton, G. P, 1980, Geophysical observations of 

Kilauea Volcano, Hawaii, 1. Temporal gravity variations related 

to the 29 November, 1975, M=7.2 earthquake and associated 

summit collapse: Journal of Volcanology and Geothermal Research, v. 7, p. 225-240.

Jackson, D. B., Swanson, D. A., Koyanagi, R. Y., and Wright, T. 

L., 1975, The August and October 1968 east rift eruptions of 

Kilauea Volcano, Hawaii: U.S. Geological Survey Professional 

Paper 890, 33 p.

Johnston, A. C., 1978, Localized compression velocity decrease percursory to the Kalapana, Hawaii, earthquake: Science, v. 199, 

p. 882-885.

Kelley, M. L., Spiker, E. C., Lipman, P. W., Lockwood, J. P., Holcomb, R. T., and Rubin, M., 1979, US Geological Survey, Reston, Virginia radiocarbon dates XV: Mauna Loa and Kilauea Volcanoes, Hawaii: Radiocarbon, v. 21, p. 306-320.
REFERENCES CITED 45

Kinoshita, W. T., Koyanagi, R. Y., Wright, T. L., and Fiske, R. 

S., 1%9, Kilauea Volcano The l%7-68 summit eruption: Science, v. 166, no. 3904, p. 459-468.

Kinoshita, W. T., Swanson, D. A., and Jackson, D. B., 1974, The 

measurement of crustal deformation related to volcanic activity 

at Kilauea Volcano, Hawaii, in L. Civetta, P. Gasparini, G. 

Luongo, and A. Rapolla, eds., Physical volcanology: Elsevier, 

Amsterdam, p. 87-115.

Koyanagi, R. Y., Stevenson, P., Endo, E. T., and Okamura, A. T., 

1978, Hawaiian Volcano Observatory Summary 74: January to 

December 1974: U.S. Geological Survey, 164 p.

Koyanagi, R. Y., Swanson, D. A., and Endo, E. T., 1972, Distribution of earthquakes related to mobility of the south flank of 

Kilauea volcano, Hawaii, in Geological Survey Research 1972: 

U.S. Geological Survey Professional Paper 800-D, p. D89-D97.

Lipman, P. W., 1980, Rates of volcanic activity along the southwest 

rift zone of Mauna Loa Volcano, Hawaii: Bulletin Volcanologique, 

v. 43, p. 705-725.

Lipman, P. W., Okamura, R. T., and Yamashita, K. M., 1978, 

Changed deformation mode of Kilauea volcano since the 1975 

M=7.2 earthquake [abs.]: Geological Society of America, 

Abstracts with Programs, v. 10, p. 113.

Lockwood, J. P., Koyanagi, R. Y., Tilling, R. L, Holcomb, R. T., 

and Peterson, D. W., 1976, Mauna Loa threatening: Geotimes, 

v. 21, p. 12-15.

Lockwood, J. P., Peterson, D. W., and Tilling, R. L, 1978, 

Chronological summary: Hawaiian Volcano Observatory Summary 74, U.S. Geological Survey, p. 2-6.

MacDonald, G. A., and Eaton, J. P., 1964, Hawaiian volcanos during 

1955: U.S. Geological Survey Bulletin 1171, 170 p.

Moore, J. G., 1964, Giant submarine landslides on the Hawaiian 

Ridge: U.S. Geological Survey Professional Paper 501-D, p. 

D95-D98.

 1971, Relationship between subsidence and volcanic load, 

Hawaii: Bulletin Volcanologique, v. 34, p. 562-576.

Moore, J. G., and Fisk, R. S., 1969, Volcanic substructure inferred 

from dredge samples and ocean-bottom photographs, Hawaii: 

Bulletin Geological Society of America, v. 80, p. 1191-1202.

Moore, J. G., and Krivoy, H. L., 1964, The 1962 flank eruption of 

Kilauea Volcano and structure of the east rift zone: Journal of 

Geophysical Research, v. 69, p. 2033-2045.

Moore, J. G., and Peck, D. L., 1965, Bathymetric, topographic, and 

structural map of the south-central flank of Kilauea Volcano, 

Hawaii: U.S. Geological Survey Miscellaneous Geologic Investigations Map 1-456.

Moore, R. B., Helz, R. T., Dzurisin, D., Eaton, G. P., Koyanagi, 

R. Y., Lipman, P. W., Lockwood, J. P., and Puniwai, G. S., 

1980, The September 1977 eruption of Kilauea volcano, Hawaii: 

Journal of Volcanology and Geothermal Research, v. 7, p 189- 

210.

Myers, W. B., and Hamilton, W., 1964, Deformation accompanying 

the Hebgen Lake earthquake of August 17, 1959 in The Hebgen 

Lake, Montana, earthquake of August 17, 1959: U.S. Geological 

Survey Professional Paper 435, p. 55-98.

Nakamura, Kazu, 1980, Why do long rift zones develop in Hawaiian 

volcanoes A possible role of thick oceanic sediments: Bulletin 

Volcanological Society of Japan, v. 25, p. 255-269.

Normark, W. R., Lipman, P. W., and Moore, J. G., 1979, Regional 

slump structures on the west flank of Mauna Loa Volcano, 

Hawaii [abs.]: Abstract volume, Hawaii symposium on intraplate 

volcanism and submarine volcanism, Hilo, Hawaii, p. 172. 

Okamura, R. T., and Swanson, D. A., 1975, January-March 1971 

leveling at Kilauea and tabulated comparisons with previous 

data: Hawaiian Volcano Observatory Summary 61, p. 7-42. 

Plafker, George, 1969, Tectonics of the March 27, 1964, Alaska 

earthquake: U.S. Geological Survey Professional Paper 543-1, 

74 p.

Price, R. A., 1981, The Cordilleran foreland thrust and fold belt in 

the southern Canadian Rocky Mountains, in Thrust and Nappe 

Tectonics: The Geological Society of London, p. 427-448. 

Price, R. A., and Montjoy, E. W., 1970, Geologic structure of the 

Canadian Rocky Mountains between Bow and Athabasca rivers a progress report, in J. 0. Wheeler, ed., Structure of the 

southern Canadian Cordillera: Geological Association of Canada 

Special Paper 6, p. 7-25.

Proffet, J. M., Jr., 1977, Cenozoic geology of the Yerington district,

Nevada, and implications for the nature and origin of Basin and

Range faulting: Geological Society of America Bulletin, v. 88,

p. 247-266.

Richter, C. F., 1958, Elementary seismology: San Francisco, Calif.,

W. H. Freeman and Co., 768 p.

Rojahn, Christopher, and Morrill, B. J., 1977, The island of Hawaii 

earthquakes of November 29, 1975 strong-motion data and 

damage reconnaissance report: Seismological Society of America 

Bulletin, v. 67, p. 493-515.

Stearns, H. T., and Macdonald, G. A., 1946, Geology and groundwater resources of the Island of Hawaii: Hawaii Division of Hydrography Bulletin 9, 363 p. 

Swanson, D. A., 1972, Magma supply rate at Kilauea Volcano, 1952-

1971: Science, v. 175, p. 169-170.

Swanson, D. A., Duffield, W. A., and Fiske, R. S., 1976a, Displacement of the south flank of Kilauea volcano: the result of forceful 

intrusion of magma into the rift zones: U.S. Geological Survey 

Professional Paper 963, 39 p.

Swanson, D. A., Jackson, D. B., Koyanagi, R. Y., and Wright, T. 

L., 1976b, The February 1969 east rift eruption of Kilauea Volcano, Hawaii: U.S. Geological Survey Professional Paper 891, 

30 p.

Swanson, D. A., and Okamura, R. T., 1975, Trilateration network 

on Kilauea, Fall 1970: Hawaiian Volcano Observatory; Summary 

60, p. 3-12.

Tilling, R. L, Koyanagi, R. Y., Lipman, P. W., Lockwood, J. P., 

Moore, J. G., and Swanson, D. A., 1976, Earthquake and related catastrophic events, island of Hawaii, November 29, 1975: 

a preliminary report: U.S. Geological Survey Circular 740, 33 

PUnited States Navel Oceanographic Office, 1973, Bathymetric atlas

of the North Pacific Ocean, Map Sheet 1064N. 

Wood, H. 0., 1914, On the earthquakes of 1868 in Hawaii: Bulletin

of the Seismological Society of America, v. 4, p. 169-203. 

Wyss, M., Klein, F. W., and Johnston, A. C., 1981, Precursors to 

the Kalapana M=7.2 earthquake: Journal of Geophysical Research, v. 86, p. 3881-3900.

Zucca, J. J., and Hill, D. P., 1979, Velocity structure of the south 

flank of Kilauea from a profile of marine shots [abs.]: Abstract 

volume, Hawaii symposium on intraplate volcanism and marine 

volcanism, Hilo, Hawaii, p. 178.