The Honomu,

-,' .. : '~.

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PB 293025

Hawaii, Earthquake

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REPORT DOCUMENTATION J1C-REPORT NO.

PAGE NSF/RA-770256 4. Title and Subtitle

Honomu, Hawaii, Earthquake, Report of Inspection 6.

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National Academy of Sciences Committee on Natural Disasters Washington, D.C.

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----------------------~-----_._---IS. Supplementary Notes

------------- -------- .-- _._._- . - -- ._------._-----------------16. Abstract (Limit: 200 words)

The April 1973 earthquake was the first one for which strong motion accelerograms were obtained in Hawaii. Ground motion in the volcanic ash turned out to be quite different from the ground motion of the lava rock. This was evident not only from the damage picture but also from the recorded aftershocks. Volcanic ash re­mained stable during this earthquake; it is not necessarily true that the volcanic ash would not liquefy during an earthquake of longer duration. Damage was not as great as found in other earthquakes of this magnitude (6.2). This can be attributed to several facts; the earthquake was very deep-seated (41 km); the duration of the strong motion was short (7 sec); and the island of Hawaii is sparsely populated (its total population is 70,000, of whom 30,000 live in Hilo). There are very few tall build­ings in Hi10; most are one- or two-story residential units. A significant portion of the damage was to public roads and bridges. Seismometric data and preliminary strong-motion instrumental results and aftershocks are presented. Soil mechanics and foundations, soil dynamic analyses, and earthquake damages are discussed.

17. Document Analysis a. Descriptors

Earthquakes Accelerometers

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Earthquake damage Honomu, Hawaii

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Volcanic ejecta Soil dynamics

Seismic arrays Soil mechanics

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2/\;='0"_ 3':SrE~f;S GROUP, INC. r,.,;) ,.\'::,:UT1\:: t'(l~JLEVARD

THE HONOMU, HAWAII, EARTHQUAKE

report of inspection

by

N. Norby Nielsen and Augustine S. Furumoto

University of Hawaii, Honolulu, Hawaii

Walter Lum

Walter Lum Associates, Inc., Honolulu, Hawaii

B. J. Morrill

Seismological Field Survey Earth Sciences Laboratory, NOAA

San Francisco, California

submitted to the

Committee on Natural Disasters

Commission on Sociotechnical Systems

~ATIONAL RESEARCH COUNCIL

National Academy of Sciences

Washington, D.C.

1977

NOTICE

The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the Councils of the National Academy of Sciences, the National Acad­emy of Engineering, and the Institute of Medicine. The members of the Committee responsible for the report were chosen for their special compe­tences and with regard for appropriate balance.

This report has been reviewed by a group other than the authors ac­cording to the procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine.

Financial support for publication of this report was provided by the National Science Foundation.

The National Research Council was established in 1916 by the National Acad­emy of Sciences to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and of advising the federal government. The Council operates in accordance with general poli­cies determined by the Academy by authority of its Congressional charter of 1863, which established the Academy as a private, non-profit, self­governing membership corporation. Administered jointly by the National Academy of Sciences, the National Academy of Engineering, and the Insti­tute of Medicine (all three of which operate under the charter of the National Academy of Sciences), the Council is their principal agency for the conduct of their services to the government, the public, and the sci­entific and engineering communities.

Copies of this report may be obtained from the office of the Committee on Natural Disasters, National Academy of Sciences, 2101 Constitution Avenue, Washington, D.C. 20418

Printed in the United States of America

ii

FOREWORD

The National Academy of Engineering formed the Committee on Natural

Disasters to foster study of the engineering aspects of disasters such as

earthquakes, floods, windstorms, and major fires. The objective of the

studies is to improve the level of protection against these hazards and

to stimulate the research needed to understand their nature.

This report is sponsored by the Committee's Panel on Earthquakes and

contains results of inspection and study of the Honomu, Hawaii, earthquake

of April 26, 1973.

Paul C. Jennings Chairman, Panel on Earthquakes

iii

COMMITTEE ON NATURAL DISASTERS

Chairman: Nathan M. Newmark Department of Civil Engineering University of Illinois (Urbana)

Members:

Jack E. Cermak Department of Civil Engineering Colorado State University

Alan G. Davenport The Faculty of Engineering Science The University of Western Ontario

Chairman, Panel on Earthquakes:

Paul C. Jennings Division of Engineering and

Applied Science California Institute of Technology

Ray W. Clough Department of Civil Engineering University of California (Berkeley)

George W. Housner Division of Civil Engineering

and Applied Mechanics California Institute of Technology

Chairman, Panel on Fire:

Howard W. Emmons Division of Engineering and

Applied Physics Harvard University

Chairman, Panel on Landslides:

Kenneth L. Lee School of Engineering & Applied Science University of California at Los Angeles

Chairman, Panel on Wind:

Richard D. Marshall Building Research Division National Bureau of Standards

Members, Panel on Wind:

Gary C. Hart School of Engineering & Applied

Science University of California at

Los Angeles

Kishor C. Mehta Department of Civil Engineering Texas Tech University

James T. P. Yao

Harold I. Laursen Department of Civil Engineering Oregon State University

Dale C. Perry Department of Civil Engineering Georgia Institute of Technology

School of Civil Engineering Purdue University

iv

Chairman, Panel on Wind Engineering Research:

Jack E. Cermak Department of Civil Engineering Colorado State University

Steering Group, Panel on Wind Engineering Research:

Alan G. Davenport Frank A. Gifford The Faculty of Engineering Science The University of Western Ontario

Atmospheric Turbulence & Diffusion Laboratory

National Oceanic & Atmospheric Administration

L. E. Robertson Skilling, Helle, Christiansen, Robertson

Liaison Member, Panel on Wind Engineering Research:

Michael P. Gaus Engineering Division National Science Foundation

Staff: Executive Secretary, Committee on Natural Disasters:

Nelson T. Grisamore Commission on Sociotechnical Systems National Academy of Sciences

Administrative Secretary, Committee on Natural Disasters:

Joan M. Sieber Commission on Sociotechnical Systems National Academy of Sciences

v

PREFACE

Shortly after it was learned that the April 26, 1973, earthquake on

the island of Hawaii had caused damage in the millions of dollars, the

National Research Council's Committee on Natural Disasters asked for an

investigation and report on damage caused by the earthquake. After a

preliminary inspection it became apparent that there were many interesting

aspects, such as the differences in response and damage depending on wheth­

er the soil was a soft volcanic ash or hard volcanic rock. To add needed

expertise, Messrs. Furumoto, Lum, and Morrill agreed to be a part of an

investigating and reporting team.

N. Norby Nielsen

vii

ACKNOWLEDGMENTS

R. B. Matthiesen and R. P. Maley of the Seismic Engineering Branch,

U. S. Geological Survey (SEB, USGS), gave much assistance in reviewing

the portion on strong motion data. V. Perez produced the spectra. D. W.

Peterson and several others at the Hawaii Volcano Observatory provided in­

formation on aftershocks and local seismicity. The assistance of property

owners on whose property our temporary stations were located is appreciated.

W. M. Adams of the University of Hawaii made timely installation of pre­

earthquake strong-motion instrumentation. The help of E. D. Sembera of

SEB while in the field is much appreciated. We are thankful for the co­

operation and help received from the Civil Defense offices in Honolulu and

Hilo. The Special Projects Party, USGS (K. W. King, Chief), of Las Vegas

provided analysis of the aftershock moniter records. The following members

of the Hawaii Volcano Observatory, USGS, provided data on preliminary mag­

nitudes: John D. Unger, Robert Y. Koyanagi, and A. T. Okamura. The Appen­

dix discussing the intensity distribution was prepared by Patricia Principal

and Karen Fujishima, both graduate assistants in Geology and Geophysics,

University of Hawaii. The draft report was typed by Mrs. Mary Kamiya, Cen­

ter for Engineering Research, College of Engineering, University of Hawaii.

viii

ABSTRACT

The island of Hawaii is the most seismically active of the Hawaiian

Islands. Since 1929 twelve earthquakes of magnitude 6 or larger have been

recorded. There are two volcanoes on the island that are still active.

However, for larger earthquakes there seems to be no connection with vol­

canic activity. At the time of the earthquake the Kilauea volcano was in

active eruption, but the epicenter was far removed from the volcano. The

earthquake occurred on a known fracture zone; the depth of focus was ap­

proximately 41 km; Hawaiian earthquakes usually occur at much shallower

depths. The magnitude of the earthquake was 6.2. The epicenter was

located at Honomu, which is 10 km north of Hilo and about 2 km inland.

About 2 months before the earthquake occurred two strong-motion ac­

celerographs and four seismoscopes were installed in the islands. One

of the strong motion accelerographs was installed at Kilauea on the island

of Hawaii; its distance from the epicenter was 50 km. Another accelero­

graph was installed in Honolulu, about 300 km from the epicenter. Both

instruments were triggered by the earthquake and the first strong-motion

accelerograms were obtained in Hawaii. The maximum acceleration at Kilauea

was 0.17 g and strong ground motion lasted about 7 seconds. The Honolulu

record showed a maximum acceleration of 0.03 g. Three days after the earth­

quake additional instrumentation was flown in from Las Vegas to permit mon­

itoring of aftershocks. The aftershock monitors recorded approximately 10

shocks of magnitudes between 2 and 3.

The Wailuku River, which runs into the ocean just north of downtown

Hilo, is the dividing line between the Mauna Kea and the Mauna Loa lava

flows. Mauna Kea is the older volcano and Mauna Loa is younger and still

active. At the last stages of volcanic activity of Mauna Kea, ash deposits

from the volcano covered the northeast portion of the island north of the

Wailuku River. The result is that soil conditions are quite different on

the two sides of the river. North of the river the ash cover is about 20

to 30 feet thick. The ground south of the river is lava rock. It was evi­

dent from the earthquake damage that behavior of the two soils was different;

damage seemed to be much heavier on the volcanic ash north of the river.

Aftershock equipment was installed on both sides of the river to explore the

differences in response. From the records it is very clear that the velocity

ix

response was much greater on the volcanic ash than it was on the lava rock.

For most frequencies the velocity response of the volcanic ash was five to

ten times as large as the response measured on the lava rock. There were

no signs of liquefaction, even though the volcanic ash tends to liquefy

under traffic of heavy construction equipment.

Damages were rather minor considering the 6.2 magnitude of the earth­

quake. This can be attributed to several facts: (a) the earthquake was

very deep-seated (41 km); (b) the duration of the strong motion was short

(7 sec); and (c) the island of Hawaii is sparsely populated (its total

population is 70,000, of whom 30,000 live in Hilo). There are very few

tall buildings in Hilo; most are one- or two-story residential units. The

total amount of damage has been estimated at $6,000,000. A significant

portion of this was damage to public roads and bridges. Numerous land and

rock slides occurred in the northeastern portion of the island. Most of

the damage to residential units occurred to buildings located on volcanic

ash deposits within about a 20-km radius of the epicenter.

There was a good deal of "nonstructural" damage. Many students in

school buildings were injured from falling light fixtures and false ceil­

ings. Many residential units were shifted on their foundations; it was

evident that an earthquake of longer duration would have caused consider­

ably more damage. One IS-story shear wall building about 18 km from the

epicenter h~d cracks in the shear walls at the first story level. It also

suffered a good deal of flnonstructural" damage; in addition, its eleva­

tors jumped their tracks. The 8-story Mauna Kea Beach Hotel, about 7S km

from the epicenter, suffered "nonstructural" damage; the damages were

from minor design details. Footbridges connect the various wings of the

hotel; the bridge seats were designed for sliding but apparently dowels

were installed in the field, resulting in a good deal of spalling. Where

additions were made to an elevator tower cracks showed up in the joints.

Damage to power lines, water supply, and telephone lines was severe.

The northeastern portion was in a state of emergency for several days.

In Honolulu, about 300 km from the epicenter, damage was very minor;

some pendulum clocks stopped and there were minor plaster cracks. Appar­

ently, the long period waves' arriving coincided rather closely with the

x

natural periods of some of the tall (20 to 3D-story) buildings, resulting

in sways of relatively large displacements. Near panic broke out in sev­

eral buildings.

The earthquake was the first one for which strong motion accelerograms

were obtained in Hawaii. Ground motion in the volcanic ash turned out to

be quite different from the ground motion of the lava rock. This was evi­

dent not only from the damage picture but also from the recorded after­

shocks. Volcanic ash remained stable during this earthquake; it is not

necessarily true that the volcanic ash would not liquefy during an earth­

quake of longer duration. Damage was not as great as found in other earth­

quakes of this magnitude. Most of the lessons to be learned from a structural

engineer's point of view are similar to those that already should have been

learned from other earthquakes.

xi

· . xu

CONTENTS

Page SEISMOMETRIC DATA .................................................... 1

Introduction .....................•...•................••.•...•.. 1

General Parameters of the Earthquake ......•••••.......•••....... 1

Consideration of Past Large Earthquakes •.....•.................. 2

Source Mechanism and Related Tectonics •..•..•................... 2

Strain Seismograms.............................................. 4

Calculation of Source Parameters ..................•............. 4

Absence of Field Data ...•.....•...........•........•...••....... 6

Summary and Discussion ........................................ " 7

PRELIMINARY STRONG-MOTION INSTRUMENTAL RESULTS AND AFTERSHOCKS ....... 8

SOIL MECHANICS AND FOUNDATIONS ...................•................... 13

Observations and Comments .....•................................. 16

SOIL DYNAMIC ANALYSES ................................................ 17

EARTHQUAKE DAMAGES ................................................... 19

General .........................•........••.•.•.........•.•.•.•. 19

Roads and Bridges ..................•......•.......•............. 20

Buildings ..............•........................................ 20

Some Anomalies ..•...•..••.....•.•..........••.•.•...•..••...•... 22

BIBLIOGRAPHY .....................................•....•..•........... 25

TABLES ..............................•................................ 28

FIGURES ........... , ........ " ....................•..•.......... " .... 36

APPENDIX Seismic Intensity Distribution ...................... , ...... 75

xiii

Table 1

Table 2

Table 3

Table 4

Table 5

Table 6

Table 7

LIST OF TABLES

Major Earthquakes in Hawaii

Some Aftershocks of the Honomu Earthquake of April 26, 1973

Site Characteristics of Temporary Stations

Accelerograph Results and Site Characteristics for Honomu Earthquake of April 26, 1973

Seismoscope Results, Honomu Earthquake of April 26, 1973

Estimated Shear Modulus, Shear Wave Velocity, and Natural Period of the Soil Deposit

Soil Dynamic Studies

xiv

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

LIST OF FIGURES

Occurrences of Earthquakes with Magnitudes Larger than or Equal to 6 since 1929 in Hawaii

Epicenter of Large Earthquakes (M~6) in Hawaii since 1929

Source Mechanism of the April 26, 1973, Earthquake and the Location of Rift Zones

Strain Seismogram of the Earthquake from Station Kipapa (KIP) on Oahu

Locations of Strong-Motion and Aftershocks Monitoring Equipment Installed in Hawaii Before and After the Earth­quake of April 26, 1973

Reproduction of Accelerograms Recorded During the April 26, 1973, Earthquake

Type of Strong-Motion Acce1erograph Installed in Hawaii

Seismoscope Installed in Hawaii

Seismoscope Damping Curve

Seismoscope Records from Honomu Earthquake of April 26, 1973

Velocity Response Spectra for Earthquake of April 26, 1973, at Kilauea, Hawaii

Attenuation of Maximum Recorded Acceleration Showing the New Hawaii Data

Relative Response on Volcanic Ash and Lava Flow at Hila, Hawaii; Aftershock Recorded on April 30, 1973

Road Damage and Areas with Volcanic Ash

Volcanic Ash, Typical Test Data

Soil Moduli and Damping Factors for Dynamic Response Analyses (Seed and Idriss, 1970)

Ranges of Maximum Acceleration in Rock

Predominant Periods for Maximum Accelerations in Rock

Ground Surface Motion

Upward Deflection of Ground Surface Due to Static Point Load at Depth

xv

Figure 21

Figure 22

Figure 23

Figure 24

Figure 25

Figure 26

Figure 27

Figure 28

Figure 29

Figure 30

Figure 31

Figure 32

Figure 33

Figure 34

Figure 35

Figure 36

Figure 37

Figure 38

Figure 39

Figure 40

Figure 41

Figure 42

Figure 43

Figure 44

Figure 45

Recorded Earthquakes of 1963 and Faults

Typical Landslide

Heavy Cane Truck; Road on Volcanic Ash

Typical Road Damage, Northeastern Portion of the Island

Tension Cracks, Volcanic Ash

Kaiwilahilahi Bridge, 15 km from Epicenter

Kaiwilahilahi Bridge, 15 km from Epicenter

Typical Failure of Rock Wall, North Hilo

Typical Failure of Rock Wall, North Hilo

Residence, North Hilo

House Shifted on Foundation, North Hilo

House Shifted on Foundation, North Hilo

Carport Collapse, North Hilo

Concrete Block Building, North Hilo

Cesspool Failure, Volcanic Ash

Soil Fall, Volcanic Ash, 3 km North of Hilo

Business District, Downtown Hilo

Typewriter Center, Downtown Hilo

Val-Hala Apartment Building, 18 km South of Epicenter

Val-Hala Apartment Building, 18 krn South of Epicenter

Bayshore Tower, 18 km South of Epicenter

Bayshore Tower, Canopy Beams Attached to Shear Walls

Bayshore Tower, Concrete Spalling

Settlement, Front of Bayshore Tower

Wall at Parking Lot, Bayshore Tower

xvi

Figure 46

Figure 47

Figure 48

Figure 49

Figure 50

Figure Sl

Figure 52

Figure 53

Figure 54

Figure A.l

Figure A.2

Mauna Kea Beach Hotel, 75 km from Epicenter

Bridge Seat Detail, Mauna Kea Beach Hotel

Hilo Harbor, Pier 1

Concrete Curb, Hilo Harbor, Pier 1

Hilo Harbor, Pier 1

Hilo Harbor, Pier 1

Tombstone, Toppled Over

Tombstone, Rotated

Tombstone, Rotated

Seismic Intensities, Hawaiian Archipelago

Seismic Intensities, Island of Hawaii

xvii

xviii

SEISMOMETRIC DATA

Introduction

On the morning of April 26, 1973, at 10:27, Hawaiian Standard Time,

residents throughout the Hawaiian Islands were disturbed by an earthquake.

Damage amounting to 6 million dollars occurred on the island of Hawaii;

people rushed out of buildings in Honolulu, 300 km from the epicenter; and

tremors were felt on the island of Kauai, the farthest inhabited island

from the epicenter.

This report will deal with data obtained from recordings on seismo­

graphs in Hawaii and in other parts of the world. Although the analysis

and interpretations are only partially completed, a preliminary report is

hereby made.

General Parameters of the Earthquake

The general parameters of the earthquake as published in the Prelimi­

nary Determination of Epicenters by the National Earthquake Information

Center, National Oceanic and Atmospheric Administration, are:

Origin Time CUT)

Epicenter

Depth of focus

Magnitude

1973 April 26

Lat 19.933°N;

SO km

MB 6.0, MS 6.1

ML 6.2 (HVO)

ML 6.3 (PAS)

ML 6.1 (BRK)

20h 26m 2S.0 sec

Long lSS.lOoW

CERL)

The U.S. Geological Survey has provided the following parameters, based

on calculations using known local crustal structure and travel time (HVO,

1973):

Origin Time 20h 26m 40.6 sec

Epicenter Lat 19°5l'N ±l.S'

Long lSSoOS'W ±l.S'

Depth of focus 41 km ±4.S km

The difference in distance between the two epicentral determinations

is 9.5 km. In seismometric discussions, usually such a difference is not

1

too relevant, but in this case the difference is significant. The PDE

data put the epicenter at sea, whereas the Geological Survey epicenter

is on land. In our discussion we shall choose the Geological Survey de­

termination as the epicenter, as the calculations were based on local

crustal structure and travel times.

Consideration of Past Large Earthquakes

Since 1929, when magnitudes of Hawaiian earthquakes began to be tab­

ulated instrumentally, there have been 12 earthquakes with magnitudes equal

to or larger than 6. The list of earthquakes with location of epicenters

is given in Table 1.

An examination of the occurrence shows that large earthquakes have oc­

curred in clusters at intervals of 11 years. Figure 1 shows the occurrence

of the ~~rthquakes with respect to time. Except for the two earthquakes in

1954, the earthquakes cluster around the years 1929, 1940, 1951, 1962, and

1973.

A map showing epicenters and volcanoes is given in Figure 2. An im­

mediate conclusion is that epicenters are not obviously associated with

centers of volcanism. Furthermore, a comparison with times of eruptive

activity since 1929 shows that most of these large earthquakes did not oc­

cur at times of volcanic activity. Neither do large earthquakes occur

preceding significant eruptions. The May 3D, 1950, earthquake occurred

just before a Mauna Loa eruption, but its epicenter was far removed from

the Mauna Loa central vent or rift zone. Earthquakes associated with vol­

canic activity have been of smaller magnitude, being at most 4 or 5. The

mechanism of large earthquakes seems to be quite independent of volcanic

activity.

The April 26, 1973, earthquake was no exception to the rule. The epi­

center was far removed from Kilauea Volcano, although Kilauea was then in

active eruption.

Source Mechanism and Related Tectonics

Fault plane solution by first arrivals indicates strike-slip motion

with alternate possibilities of (1) left lateral motion along a nodal plane

2

striking N700W and (2) a right lateral motion along a nodal plane striking

N300E (Koyanagi, Endo, and Ward, 1976). The fault plane solution of strike-,

slip motion agrees with strong-motion accelerograph data obtained at Nama­

kani Paio, 50 km from the epicenter (Figure 6). There the maximum horizontal

motion was 0.17 g while the maximum vertical motion was 0.07 g.

In Figure 3 are shown the faults that are known and the rift zones

that radiate outward from volcanic centers. Geophysical data in recent

years from geothermal exploration over the east rift of Kilauea Volcano

support the theory that the rift zones are shallow structures and are sur­

face expressions of subterranean conduits through which magma from the magma

chamber under the central volcanic vent moves laterally to erupt along the

flanks of the volcano. These conduits are thought to be lodged within the

crust and not to extend to mantle depths. In Figure 3 it is shown that the

earthquake occurred beneath the east rift of Mauna Kea, with one nodal plane

deviating 25° from the trend of the rift zone. In spite of the geographical

coincidence, we do not think that there is a tectonic relationship between

the earthquake and the rift zone because the earthquake occurred at 41 km

depth, whereas the rift zone may extend to a depth of only about 8 km.

The predominantly strike-slip motion of the Honomu earthquake favors

the interpretation that the earthquake is of tectonic type, associated with

a fault at depth. The N700W nodal plane agrees with the general trend of

the island chain, as the major islands from Maui to Kauai are aligned in the

direction of N65°W. The volcanic centers on these islands also line up in

that general direction. Although there is no known surface expression of a

fault trending in that direction, it is very possible that a fault in that

direction could have been buried by lava flows. On the other hand, the

N300E nodal plane, if extended southward, parallels the Honaupo-Kaoiki fault,

which seems to separate Kilauea from Mauna Loa (Figure 3). In 1962, a shal­

low earthquake of 5 km depth and magnitude 6.1 occurred along that fault

(Koyanagi, Krivoy, and Okamura, 1966). Fault plane solution of the 1962

Kaoiki earthquake agreed to within several degrees with the mechanism of the

Honomu earthquake.

From the observation that earthquakes with magnitudes greater than 6

tended to occur at distances of tens of kilometers away from volcanic

3

centers (Figure 2) and from the consideration that the focal mechanisms of

the 1962 and 1972 earthquakes were predominantly strike-slip motions, the

conclusion is drawn that there is an active tectonic process in Hawaii quite

distinct from volcanic activity. Recent theories attribute Hawaiian volca­

nism to a hot spot (e.g., Dalrymple, Silver, and Jackson, 1973) beneath the

lithosphere. Other types of tectonic theory have not been proposed. Al­

though a major part of Hawaiian seismic data can be explained in terms of

subterranean magmatic activity, nevertheless, there exists a hard core set

of seismic data, especially data on large earthquakes, that cannot be ac­

counted for by magma movements or by variants of the hot spot theory. At

the present time, we can only say that midplate tectonics and seismicity

of the Pacific are not clearly understood and that further study is war­

ranted.

Strain Seismograms

A strain seismograph at Kipapa (KIP) on Oahu, installed by California

Institute of Technology but operated by NOAA, recorded the earthquake as

shown in Figure 4. The strain seismograph was oriented in the direction

N6loW and is practically in line with the direction to the 'epicenter.

The recording shows a rarefaction just preceding the earthquake.

Strain variations from meteorological origin are about that size and there­

fore we hesitate to attribute the rarefaction to stress buildup prior to the

earthquake.

The earthquake itself turned out to be a large compression strain. This

agrees with the source mechanism solutions.

A permanent strain of the order of 10-9 with a negative polarity was

registered after the earthquake. The order of magnitude of strain agrees

with the calculations by Press (1965), after fault length and source mecha­

nism orientation have been considered.

Calculation of Source Parameters

Several long-period vertical component seismograms from World Wide Seis­

mic Stations (WWSS) were obtained through the National Oceanic and Atmospheric

4

Administration. To obtain source parameters, analyses of these seismograms

were attempted. The results presented here are preliminary, as parameters

were sought to obtain their order of magnitude. A careful study using more

seismograms is being planned.

Using the P-Wave and S-Wave recordings of BKS (Berkeley, California),

GSC (Goldstone, California), PAS (Pasadena, California) and BAG (Baguio,

California), the following parameters were obtained.

Average Seismic Moment, Mo' 0.37xl026

dyne-cm

Corner Frequency for P-wave, f , 0.11 hertz o

The corner frequency was obtained by analyzing the record from GSC,

which contained a good portion of high-frequency components. At the time

of this report, short-period records from Hawaii were not available, as all

seismographs, even those in Honolulu, were off the record. The P-wave part

of the strong motion accelerograph at Namakani was not digitizable. In our

further study, it is hoped that records from a hydrophone situated north of

the island of Oahu will be made available.

If the Brune's method (1970, corrected version 1971) for determining

source dimension by corner frequency is used,

where

reP) = 2.34a 27ff

o

reP): radius of a circular source area,

a: P-wave velocity, 8.2 km/sec, and

f: corner frequency of P-wave spectrum, o

we obtain reP) = 28 km and 2 2 A = 7fr = 2460 km .

Stress drop was calculated by following the discussion of Hanks and

Wyss (1972) and Wyss and Hanks (1972)

where 60 is the stress drop. This gave 60~0.7 bar.

From the strain data at Kipapa of 10-9 , the dislocation at the source

parallel to the N700W striking fault was calculated, using the equations

5

provided by Press (1965). The dislocation was 2 cm. Then we applied Aki's

(1966) formula,

where p: shear modulus,

M = pAu o

A: area of fault surface, and -u: average displacement across the fault surface.

Here, the velocity of the S-wave is 4.73 kill/sec, density p=3.3g/cm3

, and

p=pS2=7.4xIOll dyne/cm2. The result of M =0.36xl026 is consistent with o

M from the spectral level data given above. o

If we use Knopoff's (1958) formula,

1 U max ~a = - h ~ 2

where h = 24, 3/4 U max = u, we obtain 0.2 bar. This is several factors

smaller than the previous calculation.

It is proper to emphasize at this time that the foregoing calculations

were based on available seismograms (October 1973) and that the ~im was to

obtain preliminary, order-of-magnitude estimates of source parameters. Even

the meager results threw considerable light on regional tectonics. The

stress drop of the earthquake was very low, a fraction of a bar, while the 2 fault area was rather large, about 2500 km .

Absence of Field Data

One of the frustrating factors in investigating this particular earth­

quake was the absence of geological field data on ground movements, because

of the depth of focus. No surface trace of fault movement, whether horizon­

tal or vertical, was found. Elevation changes were not measured by precise

surveying techniques as this was not felt necessary. A careful gravity sur­

vey was suggested but the available pre-earthquake data (Kinoshita, 1965)

were not usable as tidal variations that may amount to 1 milligal were not

taken out. The actual field notes of the gravity survey are being sought.

6

Summary and Discussion

The Honomu Earthquake of April 26, 1973, followed general patterns of

large earthquakes, magnitude? 6, in Hawaii. These earthquakes seem to come

in clusters chronologically at II-year intervals.

The earthquake was not associated with any center of volcanism, although

Kilauea volcano, which is about 50 km from the epicenter, was in active erup­

tion at that time. This dissociation is consistent with all other recorded

large earthquakes, which were never near centers of volcanism. Although the

epicenter coincided with the east rift zone of Mauna Kea, an inactive volca­

no, it is doubtful that there is any causal relationship with the rift zone,

since rift zones do not extend downward to mantle depths and the earthquake

was located at a depth of 41 km.

The fault plane solution was predominantly strike-slip motion, and its

nodal planes agreed with those of the Kaoiki fault earthquake of 1962. At

present only these two fault plane solutions for Hawaiian earthquakes have

been published. Although it may seem unwise to jump to conclusion from only

two fault plane solutions, nevertheless, the fact that strike-slip motions

have been observed twice is significant. Combined with other observations

that large earthquakes in the past occurred away from volcanic centers, the

conclusion is drawn that a tectonic process quite apart from volcanism is

in operation in the Hawaiian area. The examination of midplate tectonics and

seismicity around Hawaii is a topic that warrants further support.

Calculations of source parameters indicated a low-stress earthquake.

The low stress may be interpreted in terms of a regional thermal anomaly at

depth, for which the volcanoes are surface expressions. Superimposed on this

thermal anomaly are regional stresses, which can cause strike-slip earth­

quakes at depths of 40 km as well as at shallow places.

From the point of view of regional geology this earthquake contributes

significantly to the understanding of tectonic processes around Hawaii. It

provided another bit of evidence that a hot spot or spots beneath the litho­

sphere do not constitute adequate explanations for some of the observed geo­

physical phenomena. In addition to thermal processes at depth, whether they

are hot spots or other anomalies, there is another mechanism at work causing

strike-slip earthquakes in the magnitude 6 range.

7

/

PRELIMINARY STRONG-MOTION INSTRUMENTAL RESULTS AND AFTERSHOCKS

Early in 1973, the Seismological Field Survey, NOAA, shipped two

strong-motion accelerographs and four seismoscopes to the University of

Hawaii for installation in a Hawaiian Strong-Motion Network as proposed by

Furumoto, et al. (1972). Fortunately, the University of Hawaii personnel

were able to install all but one of the instruments prior to the April earth­

quake. The April 26 earthquake provided the first strong-motion recordings

from the Hawaiian Islands. During the 40-year history of the operation of

the Strong-Motion Network in California many records of ground motion have

become available to engineers but as pointed out by Furumoto and Nielsen

(1972) the characteristics of the strong ground motion could be different

for the various islands as compared to typical records obtained in

California.

Immediately following the April 26 earthquake Morrill was dispatched

to the Islands to recover records, install instruments, and assist the Uni­

versity of Hawaii in the investigation of the effects of the earthquake.

Within 24 hours following the earthquake, the earthquake investigation team

met with U.S. Geological Survey personnel at the Hawaii Volcano Observatory

at Kilauea, Hawaii, to determine the most efficient use of the personnel and

materials available to the team and to determine whether additional tempo­

rary instrumentation would be of use. The following approach was adopted:

1. Morrill would immediately recover the strong-motion records and in­

stall the two additional accelographs at Hilo and Honomu (10 miles

north of Hilo in the epicentral area).

2. Additional seismograph systems and technical assistance from the

Special Projects Party, NOAA, would be requested. The developed

area of Hilo is located on essentially two types of foundation ma­

terials, namely, volcanic flow in the south and east portions and

volcanic ash in the north portion. With the opportunity at hand to

record aftershocks it was apparent to all that siting of calibrated

instruments capable of recording the small and medium sized after­

shocks on these site materials could be of extreme importance to

the engineers.

3. The remainder of the team would make a survey of damage and earth­

quake effects throughout the area.

8

4. The Geological Survey personnel would assist the team by provid­

ing aftershock and other data in the course of the investigation.

The following is a list of all equipment installed after the main

shock:

Site No.

TA-l TA-2

HO-l HO-2 HO-3 HO-4

Equipment

Accelerographs l

SMA-I, SIN 853 SMA-I, SIN 852

Aftershock monitors 2

L-7-B, SIN 110 L - 7 - B , SIN 114 L-7-B, SIN 109 L-7-B, SIN 131

1 See Halverson (1971). 2See Navarro and Wuollet (1972).

Location

St. Joseph, Hilo Honomu

Univ. Hawaii, Hilo Honomu Lyman residence, Hilo Bayshore Apt., Hilo

Aftershocks Date recorded

4~28-73 0 4-29-73 0

4-29-73 4-29-73 4-30-73 4-30-73

7 2 ? 4

Table 2 lists aftershocks of magnitude 2 or greater which occurred in

the area prior to removal of the aftershock monitoring equipment. The data

in Table 2 are preliminary and subject to later correction by the Hawaii

Volcano Observatory. Due to the low magnitude of the aftershocks none were

recorded by the relatively insensitive accelerographs. Monitoring sites

at which the aftershocks were recorded are given in the table. The after­

shock monitors recorded approximately 10 shocks of magnitude 2 or greater.

The monitors were removed to the mainland on May 4, 1973, for another pro­

ject.

Table 3 provides site data on the equipment installed after the April

26 earthquake. With consideration of the limited amount and type of equip­

ment available, the siting of the equipment was directed towards obtaining

(1) relative response data on the various surficial geology representative

of the building sites in Hilo, and (2) response of a multistory reinforced

concrete building and the relation of such response to the free-field re­

sponse of its foundation geOlogy. In addition, backup instrumentation was

9

installed in Hilo and the epicentral area to record any larger aftershocks

that might overload the more sensitive aftershock monitoring equipment be­

ing operated by SEB and by the Hawaii Volcano Observatory, USGS. This in­

strumentation plan was agreed upon by the engineers and seismologists on

the scene.

Figure 5 shows the locations of the strong-motion instruments and the

aftershock monitoring equipment with respect to the epicenter of the April

26 earthquake. Each of the selected aftershock monitoring sites was instru­

mented with a three-component (orthogonally oriented) seismic system. The

system has a flat velocity response from 0.1 Hz to 34 Hz and a velocity re­

cording range from 10-4 cm/sec to 100 cm/sec. The high-frequency limit is

imposed by the recording rate of 3/16 in/sec on magnetic tape.

As noted before and in Figure 5, two accelerographs and four seismo­

scopes were installed in Hawaii prior to the April 26 earthquake. Figure

6 shows reproductions of the two accelerograph records. The Honolulu in­

strument failed to record the longitudinal trace. Table 4 provides station

and instrumental information along with maximum acceleration and distance

information for the Honolulu and Kilauea accelerograph stations.

The type of strong-motion accelerograph installed in Hawaii, pictured

in Figure 7, is the Kinemetrics Model SMA-I. It is described by Halverson

(1971). Figure 8 shows the seismoscope described by Cloud and Hudson (1967).

Essentially the seismoscope record represents the motion of a building whose

natural period is 0.75 sec and whose damping is 10% if critical. Hence seismo­

scopes are normally installed in "free-field." Seismoscope data can be very

useful when the instrument is used in conjunction with accelerographs, the

seismoscope record providing a point on the response spectra.

The three seismoscopes installed in Hawaii are Wilmot-type; hence their

sensitivities are about 5.5 cm/rad. For each record maximum displacement on

the plate is measured from the initial zero point. From the sensitivity of

the seismoscope in cm/rad, the maximum angular motion of the pendulum ¢ max 1S determined. The maximum relative displacement response spectrum value Sd

is then calculated from

_ gT ¢ n 2~ Sd - --2- max 10 4~

(Hudson and Cloud, 1967)

lQ

where T: period (sec),

n: damping (percent critical), and

~max: trace amplitude/sensitivity.

In addition to the seismoscope magnetic damping, dry friction between

the stylus and the glass record plate introduces some amplitude-dependent

damping. The Sd values are thus corrected by the In/lO term, where the per­

cent critical damping, n, is taken corresponding to the maximum trace ampli­

tude from the damping curve of Figure 9. This damping curve is an average

curve obtained from some 450 observations on 12 glass record plates. It was

shown from experience with a large number of records from the San Fernando

earthquake (Morrill, 1971) that the use of the average damping curve intro­

duces only negligible errors in the final corrected Sd values.

Table 5 gives the maximum relative displacement response spectrum value

Sd for the seismoscopes installed on the Island of Hawaii along with epicen­

tral distances. Values corresponding to the three or four largest peaks are

given for each of the three major records.' Vectors representing these Sd

values are plotted on the map in Figure 5. Figure 10 shows the three seis­

moscope records.

The accelerograph record obtained at Kilauea was digitized and Figure 11

shows a plot of the resulting velocity response spectra. At Kilauea a seis­

moscope was located alongside the accelerograph and its Sd value is repre­

sented by the black dot near the 10% damping curve. Due to its low amplitude

the Honolulu accelerograph record was not digitized. Figure 12 compares the

maximum recorded acceleration from this earthquake to those obtained in past

earthquakes (Cloud and Perez, 1971).

The seismic data from a selected aftershock, which was approximately

50 km from two of the aftershock monitoring stations, was analyzed by de­

riving a pseudo velocity response (PSRV) spectrum from the data. One sta­

tion was located in Hilo near the University of Hawaii campus on a deep,

weathered lava flow; the comparison station was located in the northern

part of Hilo on a relatively extensive volcanic ash bed. The PSRV spectrum

is derived from the seismic trace by digitally filtering the data and cal­

culating the peak response of a series of single-degree-of-freedom systems

to the ground motion. The systems were arbitrarily damped at 5%. Figure 13

11

shows the PSRV spectrum derived from the horizontal data. The spectrum for

the lava station indicates a simple response peak in the period range of 0.3

to 0.1 sec, with attenuation (or reduced response) at the shorter and longer

periods. The spectrum for the ash station is markedly different from that

found on the lava. The response is complex with at least three bands of per­

iods with high response. These bands are found in the 0.07-0.09, 0.3-0.5,

and 3.3-5.0 sec ranges. The motion on the ash was at a higher amplitude than

that on the lava.

It should be pointed out that the data on strong ground motion in Hawaii

are meager. Hopefully, additional accelerographs can be provided in the near

future for completion of the minimum array recommended by Furumoto et al.

(1972). Furthermore, owners or builders of major structures in the more

seismic zones of the Hawaiian Islands should be encouraged to provide in­

struments for their structures.

12

SOIL MECHANICS AND FOUNDATIONS

Hawaii, the largest and the youngest of the Hawaiian Islands, was formed

by five volcanoes: Mauna Kea, Mauna Loa, Hualalai, Kilauea, and Kohala.

Mauna Loa and Kilauea are still active. The bedrock under Hilo was formed

by the lava flows from Mauna Kea and Mauna Loa. Mauna Kea is the older

volcano and Mauna Loa is younger and still active. The Wailuku River, im­

mediately north of downtown Hilo, is the dividing line between the Mauna

Kea and Mauna Loa flows. Areas of volcanic ash deposits are shown in Figure

14.

Building foundations in downtown Hilo are mostly on lava rock and clink­

er from the flow lavas of Mauna Loa volcano. Except for Pier 1, where the

20-ft alluvial fill behind the retaining structure at the end of the pier

settled several inches, the structural damages in downtown Hilo were minor,

consisting mostly of broken glass windows, dishes, and jammed doors.

Most of the earthquake damage seemed to be concentrated around the low­

er slopes of the Mauna Kea lava flows just north of downtown Hilo and extended

as far as Ookala, within a radius of 12 miles of the epicenter. Minor dam­

age reports came from as far as Waimea and Puako near the Mauna Kea Beach

Hotel about 33 and 47 miles, respectively, from the epicenter.

The Mauna Kea lavas are much older than the Mauna Loa lavas. This can

easily be noted by the stream patterns on maps of the islands. Where lava

flows are young, streams are unable to develop definite water courses be­

cause the lava is very porous. For example, there are very few channels in

the Mauna Loa lavas which form the foundations for downtown Hilo. On the

other hand, high rainfall (over 200 inches per year) and runoff have cut

many "V"-shaped gulches into the ash and weathered rock slopes of the older

Mauna Kea lava flows. The toe of the slope of the Mauna Kea flow has been

cut away by waves to form the steep sea cliffs of the Hamakua Coast. The

height of the cliffs varies from about 30 ft near Hilo to more than 100 ft

toward the northwest near Laupahoehoe.

At the last stages of the volcanic activity of Mauna Kea, ash deposits

from the volcano covered the northwest coastline (Hamakua) of the island.

The ash cover over the sea cliff is about 20 to 30 ft thick near Hilo and

thins out to about 6 ft or less toward the northwest. Some of the ash from

Mauna Kea has blown over onto the Mauna Loa flow over parts of Hilo. The

13

ash is relatively thin, probably less than 10 ft, above Hilo in the Kaumana

area above (Mauka) downtown Hilo. Structural damage to residential founda­

tions seemed to be greatest in the 25-ft thick ash deposits in the Pueo res­

idential area which is immediately north of downtown Hilo and north of

Wailuku River.

Even though the earthquake damage to structures was minor, the perfor­

mance of the volcanic ash over the lava bedrock was unique. The natural

water content of the material is about 200% except for surface layers which

may be less than 100% in localized areas. The annual rainfall causes the

liquid limit to approximate the natural water content of the soil. The de­

gree of saturation is about 95 to 100%. The material plots below the "A"

line on the Casagrande plasticity chart. On air drying, the liquid limit

and plasticity index usually decrease and the material behaves much like a

slightly cemented silt. Typical test data on the volcanic ash are shown in

Figure 15.

Several failures of performance of foundations in the ash deposits will

be described:

Sea Cliffs -- The toe of the slope along the Hamakua sea cliffs are con­

stantly being eroded by wave action .. The slopes are nearly vertical to about

1/4 to 1 slope, from 40 to over 100 ft high. The ash cover above the rock

is actively falling back to about a 1/2 to 1 slope.

There may have been many soilfalls along the sea cliffs during the

quake. Only two were noted because they involved structures.

The backyard of the Bayshore Tower in the Pueo area just north of Hilo

fell and reduced a portion of the rear property about 5 ft. The height of

the cliff is about 35 to 40 ft.

Another soilfall was reported from the Alae residential area which is

about 2 miles north of Hilo. The soilfall extended halfway under the rear

lanai slab of the Windham residence. The height of the sea cliff is about

70 ft.

Roadway Cuts -- Roadway cut slopes along the Hamakua Coast approximate

the slopes of the sea cliffs. Cuts of 90 feet or more were made in the

weathered lava at 1/4 to 1 and 1/2 to 1 slopes.

14

Twenty-foot high cuts have been made in ash deposits at 1/2 to 1 or

steeper slopes.

Rock and soilfalls were greatest at Maulua Gulch Road on the state

highway system and at Laupahoehoe Point Road and Kalopa Sand Gulch Road

on the County road system. The rockfalls covered the roads and made them

impassable. At these locations, the roads were notched into the sidewalls

of gulches or seacliffs. The original cut slopes were almost vertical.

The rockfalls tended to flatten the slopes to 1/4 to 1.

Most of the soilfalls along the highway cuts were minor and involved

small quantities of debris. The soilfalls in ash slopes tended to flatten

the slopes to 1/2 to 1.

Tension Cracks -- Sugar plantation camp roads were usually constructed

by cutting into the sidewalls of the natural gulches along the tops of

slopes. The road beds are usually placed in cut sections of the ash

deposit.

During construction, the ash tends to liquefy after several passes of

heavy equipment. Excavated materials are usually too wet for constructing

embankments. They are usually wasted by casting over the side slopes of

the gulches. The ash road bed is then usually covered with 24 inches of

"aa" clinker and the pavement is capable of carrying heavy plantation truck

traffic.

Following the earthquake, tension cracks and slumps of several inches

were noted in the shoulders of the roadways, particularly in the northeast­

ern part of the island. The toes of slopes in the above cases were usually

being eroded by stream flows at the bottoms of the gulches.

Retaining Walls -- Retaining walls in ash may be better described as

rock facings over cut slopes. The usual practice is to cut ash banks at

1/4 to 1 slopes and face them with either loose or mortared rock.

Many loose rock walls fell. The rock facings were between 10 to 15 ft

in height. The natural slopes behind the rock facings that fell seem to

stand up very well or approach a 1/2 to 1 slope.

Building Foundations on Ash Building foundations for concrete block

bearing wall apartment buildings up to 3 stories in height have been con­

structed on ash with spread footing foundations. No bearing failures were

reported or noted. 15

Observations and Comments

The performance of the volcanic ash deposit is of great interest and

appears unique.

Even though the material has a high natural moisture content, over

200% (approximately equal to the liquid limit), and liquefies under the

working of construction equipment, it did not liquefy under the shaking

of the earthquake; strong shaking lasted less than 7 to 10 seconds. Steep

road cuts (at 1/4 to 1 slopes) fell in localized areas and flattened to

about 1/2 to 1 in localized areas. The volcanic ash behaved essentially

as a slightly cemented granular material.

The relatively good performance of the ash may be partially explained:

it probably is a wind or rain deposited material over very porous lava bed­

rock. The depth of the ash is relatively shallow, mostly less than 25 ft

and the heights of cuts in ash were mostly less than 15 ft. The water ta­

ble is tens of feet below the ash bed. Sufficient vertical drainage seems

to prevail. The overall physical properties of the ash seem to improve to­

ward a more siltlike material with air drying. Heavy rainfall, 200 inches

per year, keeps the soil moist and sufficiently cohesive to maintain the

steep roadside cuts at a 1/2 to 1 slope.

Whether or not the ash will perform as well under heavier shaking of

longer duration is an open question.

16

SOIL DYNAMIC ANALYSES

Most of the reported damage centered within a l2-mile radius of Honomu,

the epicenter. From a review of a soil map of the island (Figure 14), it

appeared that most of the damages, particularly to residential structures,

occurred in the ash deposits along the northeast coastline. The volcanic

ash deposit is quite unique. It is light, 60 to 80 lb/ft3 , with a high

water content over 200% that is close to the liquid limit. Typical soil

test data are shown in Figure 15.

Construction equipment working directly on the ash tends to bog down

after a few passes because the volcanic ash tends to liquefy under traffic.

Road pavements over the ash are generally 24 to 30 inches thick and seem to

carry heavy plantation truck traffic well. Soil dynamic analyses were made

using standard formulas and charts available by Housner, S~ed and others

(Figures 16 through 22 and Tables 6 and 7) to estimate the natural periods

and accelerations that may have contributed to the damages noted to struc­

tures constructed on ash.

Most formulas and design charts are based on the distance from the caus­

ative fault. On Hawaii, most of the faults have been covered by many thinly­

bedded fairly recent lava flows. The faults are not visible at the surface.

Furumoto, et al. (1972) have prepared a map (Figure 21) showing fault traces

that cross the Hawaiian Islands. One of these traces just about crosses un­

der Honomu, the epicenter.

Estimated values for natural periods and accelerations are given in

Table 7. From the tabulations, it appears that the accelerations of 0.23 g

may have acted on the structures near Hilo, 11 miles from the epicenter and

0.07 g at the Mauna Kea Hotel, 47 miles from the epicenter. Recalculating

estimated values for natural periods and accelerations using distances from

focus rather than from the causative fault, accelerations of 0.13 g were

noted for areas around downtown Hilo and 0.07 g around Mauna Kea. These

values seem to be more in line with the intensities of the damages noted in

the field.

First impressions from visual field observations and a review of soil

maps seemed to indicate that the damages were confined to structures built

on the ash deposits. A closer check in the field showed that the largest

land or rock slides occurred at Maulua Bay and Laupahoehoe Point, some 10 to·

17

12 miles north of the epicenter where the ash is very thin and the foundation

soil is mostly lava rock. The most serious damage to structural elements

probably occurred at Papaaloa, 10 miles from the epicenter. The concrete

rocker bearings cracked on the state's (Kaiwilahilahi) bridge.

Damages to structures of the same or larger degree as that found in

structures on ash were noted as far away as Waimea and Mauna Kea Beach Ho­

tel, 30 and 47 miles, respectively, northwesterly from the epicenter. The

soils at Mauna Kea are mostly weathered lava with very little ash. The area

is dry, with rainfall less than 20 inches per year.

From soil dynamic analyses for this earthquake, it appears that because

of the thinness of the ash deposit, the influence of the ash on multistory

buildings may not have been as much as one would suspect from casual obser­

vations. It appears that unreinforced masonry rock walls and small resi­

dential structures on volcanic ash soils suffered the greatest damage within

about an 11- or l2-mile radius of the epicenter. From analyses and field

checks, it appears that the 5- to 8-story shear wall buildings approached

resonant frequencies with the ground motions and were most susceptible to

damage from this quake.

How the ash would perform under a more intense earthquake of longer

duration is a question that needs to be resolved to assist the foundation

design engineer.

18

EARTHQUAKE DAMAGES

General

There were no fatalities and only 15 persons were injured in the earth­

quake. Damages were rather minor considering that the earthquake was of

magnitude 6.2. There are several reasons for this. (1) The earthquake was

very deep seated, 41 km. Usually earthquakes in Hawaii occur at much shal­

lower depths. (2) The duration of the strong motion was very short, about

7 sec. (3) The island of Hawaii is sparsely populated--the total population

of the island is 70,000; of this total 30,000 live in Hilo. There are very

few tall buildings in Hilo, most are one- or two-story buildings. The dam­

age to power lines, water supply systems, and telephone lines was severe.

The northeastern portion of the island was in a state of emergency for sev­

eral days. In most cases all lifelines were repaired within two days. The

earthquake did not trigger a tsunami. This was rather fortunate since, due

to a lack of funds, a system which gives immediate appraisal of a tsunami

via tide gauges connected to radio-telemetry facilities, was not operation­

al. If a tidal wave had been generated it would have reached densely popu­

lated Honolulu in 35 minutes.

In Honolulu, about 300 km from the epicenter, the damage was very mi­

nor; some pendulum clocks stopped and' there were minor cracks in plaster.

Apparently, the long period waves arriving coincided rather closely with

the natural periods of some of the tall (20- to 30-story) buildings result­

ing in sways of relatively large displacements. Near panic broke out in

several buildings.

Damage estimates as reported to the Civil Defense were:

Residences (738 reporting) $2,000,000

Businesses (180 reporting) 1,500,000

Roads and Bridges 1,350,000

Schools 500,000

Pier 1 350,000

Water Works 300,000

19

Roads and Bridges

State and County roads were heavily damaged by numerous land and rock

slides. Figure 14 shows the location of the damaged roads. Damage occurred

along the coast highway from Hilo to the northeastern portion of the island.

The heaviest damage occurred along the Laupahoehoe Gulch areas where the

highway was closed at three points on the day of the 26th, and limited to

one-way traffic on the 27th. Laupahoehoe is about 20 km north of the epi­

center; the ash is very thin and the foundation soil is mostly lava rock.

The heaviest damages occurred in the ash deposits from Hilo to Ookala. Typ­

ical pictures showing road damage, rock and soil slides are shown in Figures

22 through 26.

Several bridges suffered minor damages such as broken pipe railings and

minor cracks in concrete columns. The most heavily damaged bridge was the

Kaiwilahilahi Bridge, situated about 15 km from the epicenter. The concrete

rockers and the bearing ends of the bridge beams were heavily damaged (Fig­

ures 26 and 27).

Buildings

By far the most severe damage to residences occurred in the northern

portion of Hilo, north of the Wailuku River in the volcanic ash deposits.

There were numerous failures of rock walls (Figures 28 and 29). There were

many cases where "mixed" construction of rock walls and wood framing led to

damage (Figure 30). In many cases houses were shifted on their foundations

(Figures 31 and 32); carports fell down (Figure 33); concrete block build­

ings saw typical damage (Figure 34); cesspools in volcanic ash failed (Fig­

ure 35). A soil fall caused the collapse of the lanai (porch) of a house

located about 3 km north of Hilo on a sea cliff with a height of 25 m (Fig­

ure 36).

There were minor structural damages in downtown Hilo. In the business

district there was considerable damage to plate glass windows (Figure 37).

One building, the typewriter center, collapsed. One of the parapets of the

fire walls between the buildings apparently fell on the wood trusses of the

typewriter center and collapsed the roof. One man trapped in the building

20

was later freed with minor injuries. The building was old and termite­

ridden (Figure 38). There was a good deal of damage to school buildings;

the damage was in most cases nonstructural. Typically, false ceiling

panels and lighting fixtures fell. Several school children were injured.

The Val-Hala Apartment Building is located about 18 km south of the

epicenter. The building is a 5-story edifice constructed over 6 to 8 m

of volcanic ash. The building is supported on piles, the site being on a

gradual slope. The ground floor is a semibasement structure with filIon

one side and open on the other. There was considerable damage to one of

the end shear walls. Steps and the second-floor level serve as a bridge

to the parking lot which is on fill. Differential motions between the

building and the parking lot caused failure of the columns supporting the

steps (Figures 39 and 40).

The Bayshore Tower is 18 km south of the epicenter. It is a IS-story

building on 8 m of volcanic ash (Figure 41). The building is supported on

pile foundations that extend through the ash. The earthquake resistant

structural system consists of two heavy coupled shear walls running in both

principal directions. Two canopy beams at the front of the building are

rigidly attached to the shear walls (Figure 42). At the level where the

beams were attached to the shear walls there were cracks in the shear walls.

It is a possibility that the motions of the canopy beams during the earth­

quake could have thrown additional forces into the shear walls causing the

cracks. There were many cases of concrete spalling (Figure 43). There

was a good deal of nonstructural damage, especially in the upper stories.

Typical damages were found where walls tied in to staircases and elevator

shafts. The nonstructural damage was estimated to be approximately $10,000.

Hairline cracks were noted at the top floor in the tie beams that coupled

the shear walls together. The rear of the lot was reduced about 2 m by

soil falls into the sea. A swimming pool in the rear of the lot showed no

noticeable cracks. The parking lot in front of the building settled (Fig­

ure 44). The concrete block wall by the parking wall failed (Figure 45).

The Mauna Kea Beach Hotel is located 75 km from the epicenter. The

hotel is an 8-story structure with foot bridges connecting the various wings

(Figure 46). The hotel is well designed for earthquakes, with separate

21

rectangular units. The bridge seats were designed for sliding, but did not

slide, apparently because dowels were installed connecting the bridge decks

to the seats. Spalling of concrete occurred (Figure 47). Minor cracks were

noted at handrail connections. Cracks were noted where plaster walls and

ceilings frame into the structural frame.

At Hilo Harbor, Pier 1, a 370 m-long concrete pier, was split from

end to end by a 1 to 3 cm crack (Figure 48). At the end of the pier the con­

crete curb was broken (Figure 49). The damage for necessary repairs was es­

timated at $350,000. The dock at Pier 1 is constructed on pile foundations.

The shed along the dock is partly on piles and partly on fill. A crack

runs longitudinally along the floor of the building and the joint between

the pile and fill supported floor. The crack was probably widened by the

earthquake (Figure 50). The center row of columns in the shed is supported

on piles. The floor probably settled before the quake below the concrete

guards at the base of the column. The earthquake probably caused additional

settlements (Figure 51).

Some Anomalies

As usually happens, tombstones toppled over in the earthquake (Fig­

ure 52). In quite a number of cases the tombstones did not topple over but

were rotated. Curiously enough, in almost all cases, the tombstones were

rotated in a counterclockwise direction (Figures 53 and 54).

An hour before the earthquake the Hawaiian station of the Navy's

worldwide, long-range, very low frequency omega navigation system was not

able to receive signals from the other stations in the network. At the

same time a research team from the University of Hawaii which was bouncing

waves off the ionosphere, transmitting from Kauai and receiving on Oahu,

found a "hole" in the ionosphere. What apparently happened was that the

ionosphere moved down to a level with higher absorption. It should be

pointed out that a solar flare was sighted at the same time but it was only

of a magnitude of 1+. In the past, interference with the transmission has

only occurred for solar flares of magnitude 3+ or more. It is highly like­

ly that these effects have nothing whatsoever to do with this earthquake.

22

However, since they happened such a short time before the earthquake, we

have felt that they should be reported.

Interestingly enough, the same research team found that the Tokachi­

Oki earthquake of May 1968 could be detected from their records. The long

period Rayleigh waves were affecting the ionosphere and this showed up as

Doppler effects in the data (Yuen, et al., 1969).

23

BIBLIOGRAPHY

Aki, K. (1966), "Generation and Propagation of G-Waves from the Niigata

Earthquake of June 16, 1964," Part 2: Estimation of Earthquake Mo­

ment, Released Energy and Stress-Strain Drop from the G-Wave Spec­

trum, Bulletin of the Earthquake Research Institute 3 Vol. 44, pp.

73-88, Tokyo University.

Brune, J. (1970), "Tectonic Stress and the Spectra of Seismic Shear Waves

from Earthquakes," Journal of Geophysical Research3 Vol. 75, No. 26,

pp. 4997-5009.

Brune, J. (1971), Correction. Journal of Geophysical Research3 Vol. 76,

No. 20, p. 5002.

Cloud, W.K. and V. Perez (1971), "Unusual Accelerograms Recorded at Lima,

Peru," BuUetin of Seismological Society of America3 Vol. 61, pp.

633-640.

Dalrymple, G.B., E.A. Silver, and E.D. Jackson (1973), "Origin of the Ha­

waiian Islands," American Scientist3 Vol. 61, pp. 294-308.

Furumoto, A.S., N.N. Nielsen, and W.R. Phillips (1972), "A Study of Past

Earthquakes, Isoseismic Zones of Intensity and Recommended Zones for

Structural Design for Hawaii," Engineering BuUetin3 University of

Hawaii, 53 pp.

Halverson, H. T. (1971), "Modern Trends in Strong-Movement (Strong-Motion)

Instrumentation, II Proc. Conf. Dynamic Waves in Civil Engineering3

Swansea, Wales.

Hanks, T.C. and M. Wyss (1972), "The Use of Body~Wave Spectra in the Deter­

minations of Seismic-Source Parameters,1l BuUetin of Seismological

Society of America~ Vol. 62, No.2, pp. 561-589.

Housner, G.W. (1965) "Intensity of Earthquake Ground Shaking Near the Caus­

ative Fault," Proc. 3rd World Conf. on Earthquake Engineering3 Vol. 1,

New Zealand.

Preceding page blank 25

Hudson, D.E. and W.K. Cloud (1967), "An Analysis of Seismoscope Data from

the Parkfield Earthquake of June 27, 1966," Bulletin of Seismological

Society of America~ Vol. 57, pp. 1143-1159.

Kinoshita, W.T. (1965), "A Gravity Survey of the Island of Hawaii," Pacific

Science~ Vol. 19, pp. 339-340.

Knopoff, L. (1958), "Energy Release in Earthquakes," Geophysical Journal~

Vol. 1, pp. 44-52.

Koyanagi, R. Y " H. 1. Kri voy, and A. T. Okamura (1966), "The 1962 Kaoiki,

Hawaii, Earthquake and its Aftershocks," Bulletin of Seismological

Society of America~ Vol. 56, No.6, pp. 1317-1335.

Lee, K.L. (1973) Private Communication.

Koyanagi, R.Y., E.T. Endo, and P.L. Ward (1976), "Seismic Activity on the

Island of Hawaii, 1970 to 1973." The Geophysics of the Pacific Ocean

Basin and its Margin~ American Geophysical Union, Geophysical Mono­

graph 19.

Morrill, B.J. (1971), Strong-Motion Instrumental Data on the San Fernando

Earthquake of Feb. 8~ 1971~ Earthquake Engineering Research Laboratory,

California Institute of Technology and Seismological Field Survey, Na­

tional Oceanic and Atmospheric Administration, U.S. Department of Com­

merce, D.E. Hudson, Editor, 72-124.

Navarro, R. and G.M. Wuollet (1972), "The L-7 Velocity Seismograph Shaking

Table Results," NVOO~ AEC-746-2.

Press, F. (1965), "Displacement Strains and Tilts at Teleseismic Distances,"

Journal of Geophysical Research~ Vol. 70, No. 10, pp. 2395-2412.

Schnabel, P.B. and H.B. Seed (1972), "Acceleration in Rock for Earthquakes

in the Western United States," Report No. EERC72-2, University of

California, Berkeley.

Seed, H. B. and I.M. Idriss (1969), "Characteristics of Rock Motions During

Earthquakes," Journal of Soi l Mechanics and Foundation Division~ ASCE~

Vol. 95, No. Sm5, Proc. Paper 6783, Sept. 1969, pp. 1199-1218.

26

Seed, H.B. and I.M. Idriss (1970), "Soil Moduli and Damping Factors for

Dynamic Response Analyses," Report No. EERC 70-10, University of

California, Berkeley.

U.S. Department of Agriculture (1955), "Soil Survey - Territory of Hawaii,"

Series 1939, No. 25.

Wyss, M. and T.C. Hanks (1972), "The Source Parameters of the San Fernando

Earthquake Inferred from Teleseismic Body Waves," Bulletin of Seismo­

logical Society of America, Vol. 62, No.2, pp. 591-602.

Yuen, P.C., P.F. Weaver, R.K. Suzuki and A.S. Furumoto (1969), "Continuous,

Travelling Coupling Between Seismic Waves and the Ionosphere Evident

in May 1968, Japan Earthquake Data," Journal of Geophysical Research,

Vol. 74, pp. 2256-2264.

HVO (1973) Private communication from staff at Hawaii Volcano Observatory,

April 27, 1973.

27

TABLE 1

Major Earthquakes in Hawaii

Date Location Lat. Long. Magnitude

1929 Oct. 5 7-51-99 19 3/4°N 156W 6 1/2

1938 Jan. 23 08-32-08 21. 2°N 156.1W 6 3/4

1940 June 17 10-26-47 20 1/2 155 1/4 6

1941 Sept. 25 17-48-37 19 155 6

1950 May 30 01-16-16 19.5 156 6 1/4

1951 Apr. 23 00-52-21 19 155 1/2 6.5

1951 Aug. 21 10-56-57.5 19.4 156 6.75-7

1952 May 23 22-12-26 20 156 6

1954 Mar. 30 16-40-03 19.5 155.1 6

1954 Mar. 30 18-41-54 19.5 155.1 6

1962 June 28 4-27-14.3 19°24' 155°25' 6.1

1973 Apr. 26 20-26-40.6 19°51' 155°08' 6.2

28

TABLE 2

Some Aftershocks of the Honomu Earthquake of April 26, 1973

Date Time (HST) Magnitude Recorded at Site No.

April 26 1053 3.8

1138 4.0

1221 3.5

1356 3.0

1558 3.6

1632 2.8

1726 3.4

2333 4.0

April 27 1034 3.0

1048 2.8

1415 2.5

1427 2.6

April 28 1208 3.5

1314 3.3

1444 2.4

2102 2.1

2252 3.0

April 29 0400 2.2 (Kilauea)

0917 2.0 (Kilauea)

1549 2.0 (Kilauea)

1656 2.2

April 30 0636 2.7 (Kilauea)

1927 3.1 HO-1, HO-2, HO-4

May 1 0058 2.1

0138 2.3 (Kilauea)

1614 3.1 HO-1, HO-2, HO-4

2352 2.9

May 2 0027 1.6

0415 1.8

29

TABLE 2 (continued)

Some Aftershocks of the Honomu Earthquake of April 26, 1973

May 2 (continued) 0716 2.2

1607 2.0

1641 1.8

2201 2.0

May 3 0212 2.0

0315 1.8 HO-1, HO-4

0444 2.0 (?) HO-1, HO-3

0519 2.0

1330 2.7 HO-1, HO-4

1514 2.5 (Kilauea) HO-1

1629 (?) HO-1

2140 1.5 HO-1

May 4 0913 HO-1

1039 HO-1

30

TABL

E 3

Sit

e C

hara

cte

rist

ics

of

Tem

pora

ry S

tati

on

s

Sit

e N

o.

Lo

cati

on

C

oo

rdin

ates

In

stru

men

t H

ousi

ng

Geo

logy

I S

t.

Jose

ph

1

9°4

3.I

'N

Acc

eler

og

rap

h

3x3m

Met

al

Lav

a fl

ow

Hig

h S

choo

l IS

SoO

S.2

'W

SMA

-I,

SIN

8S

3 co

ncr

ete

Hil

o,

Haw

aii

slab

2 H

onom

u,

Haw

aii

19

°52

.4'N

A

ccel

ero

gra

ph

R

esid

ence

V

olc

anic

ash

IS

So

07

.I'W

SM

A-I

, SI

N

852

con

cret

e sl

ab

3 C

loud

Ph

ysi

cs

Lab

. 1

9°4

2.3

'N

3-c

om

po

nen

t,

Fre

e-f

ield

L

ava

flow

U

niv

. o

f H

awai

i IS

So

04

.9'N

I

Hz

seis

mo

met

ers

Hil

o,

Haw

aii

L-7

-B

~

......

4 O

. H

. Ly

man

R

es.

19

°44

.I'N

3

-co

mp

on

ent,

F

ree-f

ield

V

olc

anic

ash

H

ilo

, H

awai

i IS

SoO

S.7

'W

I H

z se

ism

om

eter

s L

-7-B

S B

aysh

ore

Tow

er

19

°44

.I'N

6

-co

mp

on

ent,

IS

-sto

ry,

Vo

lcan

ic

ash

H

ilo

, H

awai

i IS

SoO

S.S

'W

I H

z se

ism

om

eter

s re

info

rcec

l L

-7-B

co

ncr

ete

6 C

. T

anim

oto

Res

. 1

9°5

2.4

'N

3-co

mpo

nent

, R

esid

ence

V

olc

anic

as

h

Hon

omu,

H

awai

i IS

So

07

.I'W

I

Hz

seis

mo

met

ers

Fre

e-f

ield

L

-7-B

tM

N

TABL

E 4

Acc

eler

og

rap

h R

esu

lts

and

Sit

e C

hara

cte

rist

ics

for

Hon

omu

Ear

thq

uak

e o

f A

pri

l 2

6,

1973

Lo

cati

on

T

ype

and

Com

pone

nt

Max

imum

an

d S

eri

al

and

Per

iod

S

en

siti

vit

y A

ccel

erat

ion

Per

iod

C

oo

rdin

ates

N

umbe

r D

irec

tio

n

(sec

) D

ampi

ng

(cm

/g)

Nam

akan

i P

aio

SM

A-l

L

0.0

38

0

.59

1

.82

K

ilau

ea,

Haw

aii

320

S300

W

19

°25

.8'N

V

0

.03

8

0.5

9

1.8

6

15

5°1

7.9

'W

Dow

n T

0

.03

8

0.5

7

1. 7

0 S6

00E

L

oca

tio

n

from

ep

icen

ter:

D

irecti

on

= 2

40

°;

dis

tan

ce

50

.3 k

m.

Ala

Wai

G

olf

SM

A-l

L

0.0

39

0

.59

1

.80

C

ours

e 31

8 S

ou

th

Ho

no

lulu

, O

ahu

V

0.0

39

0

.57

1

. 86

2lo

l6.8

'N

Dow

n l5

7°4

9.3

'W

T

0.0

40

0

.59

1

. 84

Eas

t L

oca

tio

n

from

ep

icen

ter:

D

irecti

on

= 3

00

°;

dis

tan

ce =

325

km

.

Hou

sing

and

Geo

logy

:

Kil

auea

-W

ood

fram

e;

one

sto

ry;

5 x

7 m

on

-gra

de

con

cret

e sl

ab

. S

hal

low

all

uv

ium

, m

ost

ly v

olc

anic

as

h o

ver

lav

a f

low

s.

Les

s th

an 3

.2 k

m

to

rim

of

acti

ve v

olc

ano

. E

lev

atio

n 1

.23

km

.

Ho

no

lulu

-

Woo

d fr

ame;

on

e st

ory

; 2

.5

x 2

.5 m

on

-gra

de

con

cret

e sl

ab

. 20

0 m

eter

s o

f se

dim

ent

rest

ing

on

basa

lt.

Ele

vat

ion

sea

lev

el.

(g)

(sec

)

0.1

7

0.1

5

0.0

7

0.1

0

0.1

1

0.1

6

Inst

rum

ent

fail

ure

0.0

1

0.2

0.0

3

0.1

5

TABL

E 5

Sei

smo

sco

pe

Resu

lts,

H

onom

u E

arth

qu

ake

of

Ap

ril

26

, 19

73

Lo

cati

on

L

oca

tio

n

from

Ep

icen

ter

Max

imum

R

ela

tiv

e

Dis

pla

cem

ent

and

Seri

al

Dir

ecti

on

D

ista

nce

<j>

max

Dam

ping

D

irecti

on

Sd

* C

oo

rdin

ates

N

umbe

r (d

eg)

(km

) (c

m)

(%)

(deg

) (c

m)

Uni

v.

of

Haw

aii

682

160

17

.0

2.2

0

8.2

05

9 1

. 99

Hil

o,

Haw

aii

(743

5)

1.4

5

9.3

23

0 1

.40

1

9°4

2.3

'N

1.1

5

9.7

14

5 1

.13

l5

5°0

4.9

'W

Nam

akan

i P

aio

69

7 20

4 5

0.3

1

.10

9

.8

193

1.0

9

Kil

auea

, H

awai

i (7

436)

0

.84

1

0.3

03

6 0

.85

1

9°2

5.8

'N

0.7

0

10

.6

346

0.7

2

l55

°l7

.9'W

0

.50

1

1.0

10

4 0

.52

tJ

.l tJ

.l K

ailu

a P

ark

68

9 25

6 9

3.0

0

.20

1

5.0

18

0 0

.25

K

ailu

a,

Haw

aii

(744

5)

0.1

5

17

.0

360

0.2

0

19

°38

.4'N

0

.09

2

0.0

09

0 0

.13

l5

5°5

9.7

5'W

Ala

Wai

G

olf

70

3 30

0 3

25

.0

Neg

lig

ible

Am

pli

tud

e C

ou

rse

(743

1)

Ho

no

lulu

, O

ahu

2lo

l6.8

'N

l57

°49

.3'W

*Bas

ed o

n st

and

ard

co

nst

an

ts:

Per

iod

=

0.7

5

sec;

sen

sit

ivit

y =

5

.45

cm

/rad

and

sta

nd

ard

dam

ping

cu

rve.

VI

.j:>.

TABL

E 6

Est

imat

ed S

hea

r M

odul

us,

Sh

ear

Wav

e V

elo

cit

y,

and

Nat

ura

l P

erio

d o

f th

e S

oil

D

epo

sit

G C

lb/f

t2)

G

Str

ain

D

ampi

ng

@ S

u =

: @

S

-S

u 30

0 Ib

/ft2

600

19

/ft2

(%)

(%)

10

-3

3 18

00

5.4

x

10 5

10

.8 x

10

10

-2 5

1000

3

.0 x

10

5 6

.0 x

10

10

-1 10

40

0 1

. 2 x

10

5 2

.4 x

10

-------

--

~

---------

*V

=:/f

S - P

whe

re V

: sh

ear

wav

e v

elo

cit

y

s G:

shear

mod

ulus

o

f th

e so

il

p:

mas

s d

en

sity

of

the so

il

5 5 5

=

1.

p g

*Vs

(ft/

sec)

**T

s (s

ec)

@ S

u =

: @

S

=:

H

@Su

=:

3 30

0 lb

/ft2

600

1~/ft2

(ft)

30

0 lb

/ft2

Slu

gs/

ft

2.4

85

46

7 66

0 20

0

.17

2.4

85

34

7 49

0 20

0

.23

2.4

85

21

9 31

0 20

0

.37

~

""-------~---

**F

or t

he

case

of

a si

ng

le so

il

lay

er

ov

er

bed

rock

:

T s

4H

V s

whe

re

T:

peri

od

of

the

inco

min

g w

ave

H:

V

: s

lay

er

thic

kn

ess

velo

cit

y o

f p

rop

agat

ion

o

f th

e

shear

wav

e in

th

e so

il

@S

=

600

Yb

/ft2

0.1

2

0.1

6

0.2

6

I

TABLE 7

Soil Dynamic Studies

Tabulation of Estimated Periods and Maximum Accelerations of Rock and Volcanic Ash

Building Description

Distance from Epicenter (miles)

Ash Thickness over Bedrock (ft)

Natural Period of Building (Tb) (sec)

Tb ::: N/lO == N/20

Natural Period of Ash Deposit (sec)

T 4H :::

V s s

Predominant Period of Rock Motion (T ) p (sec)

Maximum Rock Acceleration (g)

Maximum Ground Acceleration (g)

Damage

*Computation based **Computation based

on on

3-Story Crescent (Hilo)

12

20±

0.3 0.15

0.2-0.3±

0.27±

0.26* 0.13**

0.23* 0.13**

5' Retain-

5-Story Val-Hala

(Pueo)

11

20-25±

0.5 0.25

0.2-0.3±

0.27±

0.26* 0.13**

0.23* 0.13**

Stairway

8-Story Moanalua

Shores (So. Hilo)

11

0

0.8 0.4

0.27±

0.26* 0.13**

0.23* 0.13**

Walkway

8-Story IS-Story Mauna Kea Bayshore

(Puako) (Pueo)

47 11

0 25±

0.8 1.5 0.4 0.75

0.2-0.3±

0.33± 0.27±

0.07* 0.26* 0.13**

0.07* 0.23* 0.13**

Foot Hairline ing Wall Bridge Bet. Bldgs, Bridge Cracks, Collapsed Concrete Spalls @ Concrete Ground

Spalls Bearings Spalls @ Floor Bearing Shear Wall

distance from epicenter. distance from focus.

35

CJ-l

0\

V')

U

J ~ « ~ c I t­ o:

: « UJ

I 1

92

0

1930

19

40

1950

19

60

1970

19

80

TIM

E

(YE

AR

S)

FIG

URE

1

OCCU

RREN

CES

OF

EART

HQUA

KES

WIT

H M

AGNI

TUDE

S LA

RGER

THA

N OR

EQ

UAL

TO

6 SI

NCE

19

29

IN

HAW

AII

tI-l

'-

l

1-0

1220

KA

UA

I

MO

LOK

AI

~HU

Hono

lulu

•

~

lAN

AIc

;) ~AUI

1210

I cl~

• E

arth

qu

ake

Ep

icen

ter

~~:;-

Vol

cano

1590

1580

KA

HO

OLA

WE

fJ . ( r<:

HA

WA

II . I

157

0 15

60

FIGU

RE

2 EP

ICEN

TER

OF L

ARGE

EA

RTHQ

UAKE

S (M

~6)

IN

HAW

AI I

SIN

CE

1929

• ~

120

0

~

Hilo

• ~1

-. ~ /'

.---J

190

• I

155

0

20-N

I " I .,.1

HUALALAI'

. , .......

KOHALA ......

...... -..

, , ,

\ \ •

o I o

155-

10 20 miles I I ii'

10 20 30 km

~ I ~ " I ",~' KAPOHO

Kealakek a."" A .. MP.UNA LOA ~ '" PUNA • - u "V ". .';'

Kaholo I ~"KILAUEA ........... ,. ....

156-

\ \ . ~,"""- ......,. \ Fault I ~.;) /v-, .". 'System' . ~ • ...... ste m I .' .~ /. ~~ fau" Sy -c---K-AlAPANA

I 0 I ~ 's~\ ~~ ,. / '(' ~--....-

• I ., •

I i/">;/ , • (;) I /

~I • ~ I _. -Principal Rift Zone

HONUAPO - -Sobordinate Rift Zone

y- Known Fault System (arrow indicates downthrown side'

- - - Suspected Fault System

FIGURE 3 SOURCE MECHANISM OF THE APRIL 26,1973, EARTHQUAKE AND THE LOCATION OF RIFT ZONES

38

<.N

\0

1.14

X 1

0-9

Stra

in f

or 1

hr P

erio

d W

ove

1830

19

00

1930

2

00

0

20

30

21

00

2130

TIM

E (

U.T

.)

FIG

URE

4

STRA

IN

SEIS

MOG

RAM

OF

THE

EA

RTHQ

UAKE

FR

OM

STA

TIO

N

KIP

APA

(K

IP)

ON

OAHU

22

00

LKAILUA r (S)

FIGURE 5

HILO, HAWAII o ,5 I ~ KILOMETER

SCALE

.HONOMU f-\ (A M)

EPICENTER \.!J '

HA W A

KILAUEA ~ (S,A) I ~

ISLAND OF HAWAII o 25 I I ! I I

KILOMETERS

S= Seismoscope A= Accelerogroph M= Aftershock Monitor

.~ Selsmoscope

Sd vectors o ""M

b LI_..l...---l1 V

LOCATIONS OF STRONG-MOTION AND AFTERSHOCKS MONITORING EQUIPMENT INSTALLED IN HAWAI I BEFORE AND AFTER THE EARTHQUAKE OF APR I L 26, 1973

40

"'Tl

~ C ;AJ rn

'" ;AJ rn "'0 ;AJ a o c n -l

a z a "'Tl

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r

N

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rn » ;AJ -l :J: P c » 7' rn

TV

SEISMIC ENGINEERING BRANCH, USGS

NAMAKANI PAlO CAMPGROUND SMA-I SIN 320 KILAUEA (ISLAr:W OF HAWAII), HAWAII

EARTHQUAKE OF 26 APRIL 1973, 1026 HST

0 m . ~ 0 0 m

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~ -il:_ v, '1J-

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SEISMIC ENGINEERING BRANCH, USGS

ALA WAI GOLF COURSE SMA-I SIN 318 HONOLULU (iSLAND OF OAHU), HAWAII

EARTYQUAKE OF 26 APRI L 1973,10.26 HST

o~m

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UNIVERSITY OF HAWAII

HILO,HAWAII SERIAL 682

KA I LUA PARK KAILUA, HAWAII

SERIAL 689

NAMAKANI PAlO KILAUEA, HAWAII

SERIAL 697

FIGURE 10 SEISMOSCOPE RECORDS FROM HONOMU EARTHQUAKE OF APRIL 26, 1973 (Dashed arrow points to epicenter)

45

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RE

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TION

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UR

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RIL

30

,19

73

)

10

10

0

N

MAUNA KEA

o

MAUNA LOA

o

o

• County road system damaged by earthquake

~ Volcanic ash

10 20 30 miles

FIGURE 14 ROAD DAMAGE AND AREAS WITH VOLCANIC ASH

49

x Q) -0 C

.......

VOLCANIC ASH ALONG HAMAKUA COAST

Annual Rainfall

Typical Soil Test Data

Wet Dens ity .

Water Content

Dry Dens i ty .

Degree of Saturation

Unconfined Compression

Vane Shear

% Passing #200

120

About 200 inches

60 to 80 Ib/ft3

± 200%

25 to 30 Ib/ft3

± 95 to 100%

700 to 1200 Ib/ft2

300 to 600 Ib/ft2

Over 90%

• , " . ," ~ , ,

I ' . ~" Pueo Area*

~ 80 • • • Sample from

5 ft depth ...... u ......

+.> III ~ r-0...

• • •

40 .... -~Pueo Area* , ., {! .. _, Surface Sample

(Air Dried?)

O~--~~~~--~--~---L---L--~--~--~ __ ~ __ ~~ o 40 80 120 160 200 240

Liquid Limit

PLASTICITY CHART

*Pueo Area, residential area immediately north of downtown Hilo, site of l5-story Bayshore and 5-story Val-Hala buildings.

FIGURE 15 VOLCANIC ASH, TYPICAL TEST DATA

50

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FIG

UR

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scen

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M = 5

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n Fe

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FIGURE 22 TYPICAL LANDSLIDE

FIGURE 23 HEAVY CANE TRUCK; ROAD ON VOLCANIC ASH

57

FIGURE 24 TYPICAL ROAD DAMAGE, NORTHEASTERN PORTION OF THE ISLAND

58

FIGURE 25 TENSION CRACKS, VOLCANIC ASH

FIGURE 26 KAIWILAHILAHI BRIDGE, 15 km FROM EPICENTER

FIGURE 27 KA1W1LAHILAHI BRIDGE, 15 km FROM EPICENTER

59

FIGURE 28 TYPICAL FAILURE OF ROCK WALL, NORTH HILa

FIGURE 29 TYPICAL FAILURE OF ROCK WALL, NORTH HILO

60

FIGURE 30 RESIDENCE, NORTH HILO

FIGURE 31 HOUSE SHIFTED ON FOUNDATION, NORTH HILO

61

FIGURE 32 HOUSE SHIFTED ON FOUNDATION, NORTH HILO

FIGURE 33 CARPORT COLLAPSE, NORTH HILO

62

FIGURE 34 CONCRETE BLOCK BUILDING, NORTH HILO

FIGURE 35 CESSPOOL FAILURE, VOLCANIC ASH

63

FIGURE 36 SOIL FALL, VOLCANIC ASH, 3 km NORTH OF HILO

FIGURE 37 BUSINESS DISTRICT, DOWNTOWN HILO

64

FIGURE 38 TYPEWRITER CENTER, DOWNTOWN HILO

FIGURE 39 VAL-HALA APARTMENT BUILDING, 18 km SOUTH OF EPICENTER

65

FIGURE 40 VAL-HALA APARTMENT BUILDING, 18 km SOUTH OF EPICENTER

FIGURE 41

66

BAYSHORE TOWER, 18 km SOUTH OF EPICENTER

FIGURE 42 BAYSHORE TOWER, CANOPY BEAMS ATTACHED TO SHEAR WALLS

FIGURE 43 BAYSHORE TOWER, CONCRETE SPALLING

67

FIGURE 44 SETTLEMENT, FRONT OF BAYSHORE TOWER

68

FIGURE 45 WALL AT PARKING LOT, BAYSHORE TOWER

FIGURE 46 MAUNA KEA BEACH HOTEL, 75 km FROM EPICENTER

FIGURE 47 BRIDGE SEAT DETAIL, MAUNA KEA BEACH HOTEL

69

FIGURE 48 HILO HARBOR, PIER 1

FIGURE 49 CONCRETE CURB, HILO HARBOR, PIER 1

70

FIGURE 50 HILO HARBOR, PIER 1

FIGURE 51 HILO HARBOR, PIER

71

FIGURE 52 TOMBSTONE, TOPPLED OVER

FIGURE 53 TOMBSTONE, ROTATED

72

FIGURE 54 TOMBSTONE, ROTATED

73

-11-

Introduction

APPENDIX

Seismic Intensity Distribution

by

Patricia Principal* and Karen Fujishima*

The island of Hawaii contains roughly 80,000 inhabitants. Although

most of the population is concentrated in urban centers such as Hilo and

Kailua-Kona, there are a number of villages and hamlets scattered through­

out the island. The earthquake occurred in the midst of a well-populated

rural area.

Almost immediately after the earthquake, the State of Hawaii set up a

temporary civil defense headquarters in Hilo. As the number of injured

people was very small and no one was really left homeless, the major task

of the headquarters evolved into processing damage reports and claims. In

about a week, damage claims amounted to four million dollars.

Data for Intensity Determination

The major source of data for determining the seismic intensity distri­

bution was the 500 damage reports submitted to the State Civil Defense by

the inhabitants of the island of Hawaii. The President of the United States

had declared the island a disaster area, and since the island then qualified

for Federal assistance, damage claims and reports were numerous. The State

Civil Defense staff summarized these claims, divided them into business

claims and private claims, and arranged them in alphabetical order of claim­

ant's names. These summarized and classified reports were made available

to the authors. The authors wish to thank the late Honorable John A. Burns,

Governor of Hawaii, Robert E. Schank, and John Butchart of the State Civil

Defense for providing these reports.

The second source of information was the standard U.S. Coast and Geo­

detic Survey questionnaires, which were sent to all the postmasters of the

post office located in the state of Hawaii. The response was over 90%. The

islands covered by the questionnaires were: Hawaii, Maui, Molokai, Lanai,

*Graduate assistants in Geology and Geophysics, University of Hawaii

75

Oahu and Kauai.

The third source of information was newspaper reports.

The fourth source of information was actual field observation by the

investigating team. The field survey made obvious the difference in damage

on the opposite side of the Wailuku River, which runs through Hilo. The

north side had sufficient damage to warrant an intensity VIII on the Modi­

fied Mercalli Scale, while on the south side of the river, the intensity

was on the low side of VII.

Determining Seismic Intensity

The information from damage claims submitted to the Civil Defense Head­

quarters was very detailed and therefore most useful. The intensities for

the island of Hawaii were evaluated from them, supplemented by information

from questionnaires answered by the postmasters. For the other islands, the

questionnaires were the sole source of data.

Each individual damage report and each questionnaire were evaluated and

assigned an intensity based on the Modified Mercalli Scale. It must be re­

membered that this is an observed intensity, not an instrumental measure­

ment of parameters of motion. The number assigned to each report is derived

from observed effects on people, ground and structures. Admittedly, there

is a large amount of subjectivism.

Intensities were then collated according to city, village, or hamlet

and mode intensity was determined for each particular area. It was hoped

that this would average out subjectivism. Consideration was given to special

circumstances and obviously divergent reports. "Special circumstances" con­

stituted mainly overt overreaction by persons, peculiar structural weakness

of buildings and scarcity of data in certain areas.

Intensities were plotted on a map of the Hawaiian Archipelago as far

as Oahu. Isoseismals were then drawn as boundaries between regions of suc­

cessive intensities, as opposed to connecting points of equal intensity.

The isoseismal contours are for actual observed intensity with no correc­

tion for inferred local ground irregularities.

Figure A.I shows the resulting distribution of seismic intensities

for the Hawaiian Archipelago. The island of Hawaii experienced intensities

76

ranging from VIII to V. The contour bounding intensity V has been omitted

for lack of data. Intensity IV includes Lanai and all but the northeastern

part of Maui. Within intensity III are Molokai and most of Oahu, the re­

mainder ranging from II to I. Again the contour separating I and II is

omitted for lack of data.

For the island of Hawaii the greatest intensity extending over the

north section of Hilo is situated just south of the epicenter at Honomu.

Structural damage as observed warrants a maximum intensity of VIII. The

contours in general follow closely the major structural trends of the is­

land. The southern boundary of VIII is along the Wailuku River which ap­

proximately delineates the structural border between Mauna Kea and Mauna

Loa volcanoes. The VIr isoseismal includes the major portion of the Mauna

Kea and Mauna Loa shields, falling off to the north at Kohala and Hualalai

volcanoes (Figure A.2). Isoseismal VI falls off to the south where there

are the most recent Mauna Loa flows.

77

z-

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FIGURE A.2 SEISMIC INTENSITIES, ISLAND OF HAWAI I

79