A111D3 D731M1

NATL INST OF STANDARDS & TECH R.I.C.

A1 1103073141

/An Investigation of the Miyagi-ken-okl QC100 .U5? NO.592, 1980 C.I NBS-PUB-C 1£ a NBS SPECIAL PUBLICATION 592

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

An Investigation of the

Miyagi-ken-oki, Japan, Earthquake

of June 12, 1978
NATIONAL BUREAU OF STANDARDS

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aUTlOJVAL BUBBAl:

Or STANDARD?

_ LIBRARY APR 1 7 1981

An Investigation of the

Miyagi-ken-oki, Japan, Earthquake

of June 12, 1978

c

Issued under the auspices of the United States—Japan Program

in Natural Resources (UJNR) Panel on Wind and Seismic Effects

Bruce R. Ellingwood, Editor

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, DC 20234

Contributing authors:

A. Gerald Brady, U.S. Geological Survey, Menlo Park, CA

James D. Cooper, Federal Highway Administration, Washington, DC

Bruce R. Ellingwood, National Bureau of Standards, Washington, DC

Hugh H. Fowler, Federal Emergency Management Agency, Bethell, WA

Edwin L. Harp, U.S. Geological Survey, Menlo Park, CA

David K. Keefer, U.S. Geological Survey, Menlo Park, CA

Carl M. Wentworth, U.S. Geological Survey, Menlo Park, CA

Peter I. Yanev, URS/John A. Blume & Associates, San Francisco, CA

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity, Technology and Innovation

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued October 1980
Library of Congress Catalog Card Number: 80-6001 16

National Bureau of Standards Special Publication 592

Nat. Bur. Stand. (U.S.), Spec. Pub!. 592, 232 pages (Oct. 1980) CODEN: XNBSAV

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WASHINGTON: 1980

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FOREWORD

I am very pleased that a report on the investigation of the Miyagi-ken-oki , Japan

earthquake of June 12, 1978, has been prepared by U.S. engineers and scientists as an activity of the joint program of the UJNR Panel on Wind and Seismic Effects.

I hope this report will play an important role not only in improving understanding of the

Miyagi-ken-oki earthquake and other circumstances about earthquakes in Japan but also in

contributing to the earthquake research of your country.

Through the field survey conducted by U.S. members at the sites where damage occurred from

this earthquake, the importance of cooperating research activities in our panel was

reaffirmed.

Finally, I deeply respect the effort to compile the report and hope our relationship will

continue.

Yoshijiro Sakagami , Chairman (Japan)

UJNR Panel on Wind and Seismic Effects

Director General

Public Works Research Institute

Ministry of Construction

A part of the mission of the U.S. -Japan Panel on Wind and Seismic Effects of UJNR" is to carry out joint projects on the investigation of natural disasters. Immediately after the

Miyagi-ken-oki, Japan earthquake of June 12, 1978, a team of U.S. panel members and other

engineers and scientists was dispatched to Miyagi Prefecture. The investigation was coordinated by members of the Japan Panel on Wind and Seismic Effects.

This document is the result of the investigation by the U.S. team on the earthquake. It describes geologic features of the earthquake-stricken area, and damage to human-made

structures. It is hoped the information presented in this document will add to the knowledge of seismology and earthquake engineering.

The U.S. Panel expresses its sincere appreciation to the Japan Panel for their cooperation

in arranging the investigation and the fullest assistance given to the U.S. team. We look

forward to the continuation of these cooperative efforts.

Edward 0. Pfrang, Chairman (U.S.)

UJNR Panel on Wind and Seismic Effects

Center for Building Technology

National Bureau of Standards

U.S. -Japan Cooperative Program in Natural Resources

iii
ABSTRACT

On June 12, 1978, a destructive earthquake with Richter magnitude of 7.4 occurred off the

east coast of Miyagi Prefecture, Japan. Preliminary estimates by the National Land Agency

of Japan indicated that the earthquake caused an equivalent of $800 million in total

damage. There is a cooperative agreement between the governments of the United States and

Japan termed the U.S. -Japan Program in Natural Resources (UJNR) . Following the earthquake,

it was arranged through UJNR that teams of U.S. structural engineers and geologists would

visit Miyagi Prefecture and inspect the damage caused by the earthquake. This report

assembles the information and collective experiences of the investigation team so as to describe the earthquake and document its effects. Field investigations conducted by

geologists and structural engineers are described in detail and some of the implications

for seismic resistant design and construction of structures in the United States are also

discussed.

Key Words: Bridges; buildings; dikes; earthquakes; foreign engineering; geology; highways;

housing; landslides; liquefaction; power plants; railroads; rockslides;

seismicity; structural engineering.

Lv
Table of Contents

Page

1. Introduction 1

1.1 General Situation 1 1.2 Acknowledgments 3

2. Social Effects and Government Response 4

2 . 1 Damage 4 2.2 Response 8 2.3 Reconstruction 10

2.4 Insurance 10 2.5 Conclusions 11

3. Tectonic and Geologic Setting 12

3.1 Introduction 12 3.2 Tectonic Setting 12 3.3 Seismic Gap and Precursors 19 3.4 Miyagi-ken-oki Earthquake of June 12

3.5 Location of Energy Source 25 3.6 Geology of the Damage Region 25 3.7 References 33

4. Strongmotion Records and Data 36

4.1 Introduction 36 4.2 The SMAC Accelerograph 36

4.3 Acceleration Records at Ground Level 37 4.4 Intensities 40

4.5 Records from Structures 43

4.6 A Comparison with Recorded Results of the San Fernando

Earthquake 1971 47

4.7 Tohoku University Engineering Building 48

4.8 Tracing of Records 48

4.9 References 48

5. Earthquake Performance of Buildings ^1

5.1 Introduction 61 5.2 Seismic Engineering and Construction Practice 61

5.3 Commercial and Retail Establishments

5.4 Schools 96

5.5 Residences H3

5.6 Summary

5.7 References H"7

120

6. Effects to Industrial Facilities and Lifelines

i in

6.1 Introduction

1 20 6.2 Fukushima Nuclear Power Plant Complex

6.3 New Sendai Power Plant, Tohoku Electric Power Company

6.4 Sendai Substation, Tohoku Electric Power Company 132

6.5 Haranomachi Plant of Sendai City Gas Bureau 137

6.6 Sendai Refinery, Tohoku Oil Co., Ltd 137

6.7 Concrete Batch Plant, Sendai 154

v
Page

7. Earthquake Performance of Transportation Lifelines . 158

7.1 Introduction 158

7.2 Bridge Design Criteria 158

7.3 Bridge Damage 159

7.4 Highway Damage 186

7.5 Railroad Damage 186

7.6 Tunnel Performance 190

7.7 Conclusion 190

7.8 References , 190

8. Liquefaction and Damage to Dikes 195

8.1 Introduction 195

8.2 Summary of Dike Damage 195

8.3 Geologic Setting 195

8 . 4 Field 0 bservations of Dike Damage 198

8.5 Liquefaction in the Port of Ishinomaki 206

8.6 Conclusion 206

8.7 References 206

9. Seismic-Induced Landslides 209

9.1 Introduction 209

9.2 Rock falls and Rock slides in Natural Slopes 209

9.3 Rock falls and Rock slides in Cut Slopes 213

9.4 Landslides in Artificial Fill 219

9.5 Summary of Findings 223

9.6 References 223

10. General Conclusions 224

vi
1. INTRODUCTION

1 . 1 GENERAL SITUATION

Sendai City, located in Miyagi Prefecture, Japan, is a modern industrial and commercial city

located some 350 km northeast of Tokyo (Figure 1.1). Miyagi Prefecture has a population of

about 1.9 million, of which approximately 600,000 reside in Sendai City. Another million

are found in the suburbs of Sendai or in nearby cities and villages. This section of Japan

is quite mountainous, and the population is restricted to coastal plains and mountain

valleys. The population density is much more concentrated than in the United States. For

instance, Sendai City occupies an area that is probably about one-third the size of Seattle,

Washington, which has a similar population. There are about 6,500 business /manufacturing

firms in Miyagi Prefecture and about 452,000 households (homes and apartments). Critical

facilities within the area of damage include police, fire, power plants (nuclear and fossil

fuel), oil and gas processing and storage, dams, hospitals, schools, and prefectural and

municipal buildings.

On Monday, June 12, 1978, at 1714 hours local time, a destructive earthquake with Richter magnitude of 7 . 4 occurred off the east coast of Miyagi Prefecture. The earthquake hypocenter

was located at 38° 9'N latitude, 142° 13'E longitude, at a depth of 30 km. This places the

epicenter at a point approximately 120 km ESE from Sendai City and 95 km SE of the fishing

town of Ishinomaki. The distance to the nearest instrumented recordings is about 70 km. Historically, this is a seismically active area; in fact, an earthquake of Richter magnitude

6.7 occurred as recently as February 20, 1978. Although the effects were felt as far away

as Tokyo, where a window fell from a new high-rise building, major damage was confined primarily to Miyagi Prefecture. The intensity of ground shaking was reported to be V on the

Japan Meterological Agency (JMA) scale in an area approximately 180 km by 60 km along the

coast which includes the cities of Ofunato, Ishinomaki, Shiogama, Sendai, and Fukushima. JMA

intensity V is approximately equivalent to a Modified Mercalli intensity in the range VIIVIII. It is partially described as "Very strong - cracks in walls, overturning of tombstones and stone lanterns; damage to masonry chimneys and mud-plastered warehouses." The

main earthquake was preceded by a smaller shock at 1703 hours; several aftershocks were felt

during the following 4 days.

As of July 1, 1978, 27 deaths had been attributed to the earthquake in Miyagi Prefecture, of

which 17 were caused by collapsing walls, nearly 1,600 people were injured. Electrical power

was lost in Sendai for approximately 6 hours, and was not completely restored for several

days. Damage to the natural gas distribution system upon which much of the city relies was

a significant problem, and some areas of Sendai were still without gas 2 weeks following

the earthquake. Other critical services were disrupted, but not to the extent that disaster

recovery operations could not begin immediately following the earthquake. Preliminary estimates by the National Land Agency indicate that the earthquake caused an equivalent of about

$800 million in total damage.

There exists, between the Governments of the United States and Japan, a cooperative agreement termed the U.S. -Japan Program in Natural Resources (UJNR) . The principals for the UNJR

Panel on Wind and Seismic Effects are the U.S. National Bureau of Standards (NBS) and the

Public Works Research Institute (PWRI) of the Japanese Ministry of Construction. Other Government agencies are also involved in the program, including the U.S. Geological Survey

and Federal Highway Administration on the U.S. panel and the Building Research Institute and

the National Research Center for Disaster Prevention on the Japanese panel. Following the

earthquake, it was arranged through UJNR that teams of U.S. structural engineers and geologists should visit Miyagi Prefecture and inspect the damage. Concurrently, the Federal Disaster Assistance Administration arranged for the visit of their representative through the

American Embassy in Tokyo.

Team members traveled as individuals or as groups as their interests and circumstances dictated. Mr. Brady arrived June 19th and spent 2 days in the Sendai area viewing general damage.

Messrs. Cooper, Ellingwood, and Yanev arrived on June 22nd and spent 5 days in Miyagi Prefecture inspecting damage to buildings, industrial facilities, and transportation structures.

Messrs. Harp, Keefer, and Wentworth arrived on June 23rd; their primary interests were in

geology, seismicity, liquefaction and dike damage, and landslides and rock falls. Mr. Fowler

arrived on June 24th to investigate the social effects of the earthquake and how the Japanese

authorities responded to the disaster.

1
Map of Japan showing locations of

Miyagi Prefecture, Sendai City and

epicenters of 1978 earthquakes.

2
The purpose of this report is to assemble the information and collective experiences of the

team members so as to describe the earthquake and document its effects. The field investigations conducted by geologists and structural engineers are described in detail, and some

of the implications for the seismic resistant design and construction of structures in the

United States are discussed.

1 .2 Acknowledgments

The investigation of the Off-Miyagi earthquake would not have been possible without the

assistance of numerous Japanese engineers, geologists, and Government officials who handled

logistics and provided U.S. team members with unpublished data. Thanks first of all are

due to Mr. Kazuto Nakazawa, former Director-General of the Public Works Research (PWKI) and

former Chairman of the Japan panel of UJNR, for enabling us to work with his staff at a very

busy and inopportune time for them. In particular, Dr. Tadayoshi Okubo, former Director of

the Planning and Research Administration Division within PWRI and now Assistant DirectorGeneral, who also served as secretary for the Japan Panel of UJNR, arranged itineraries,

made travel arrangements within Japan, arranged meetings with Japanese engineers and geologists, and facilitated entrance to sites of damage that otherwise would have been inaccessible. Mr. Toshio Iwasaki, Head of the Ground Vibration Division in PWRI, accompanied

Messrs. Cooper, Ellingwood and Yanev on their field investigation trip to Fukushima, Sendai

and Ishinomaki, while Dr. Masamitsu Ohashi, former Director of the Earthquake Disaster

Prevention Department of PWRI, accompanied Mr. Brady for 2 days. Mr. Toyokazu Shimizu of

the Tohoku Regional Construction Bureau spent 2 days escorting team members to sites of

damaged buildings in Sendai City while Mr. Kunimatsu Hoshihata of the same Bureau hosted the

visit to Ishinomaki. Representatives from the U.S. Geological Survey were hosted by Mr. Tadayuki Tazaki and were accompanied to Miyagi Prefecture by Mr. Eiichi Kuribayashi,

both of the Earthquake Engineering Division, PWRI.

Dr. Hiroshi Tanaka of Tokyo Electric Power Company conducted the tour of the Fukushima power

plant and later was available for discussions in Tokyo. Dr. Shinsuke Nakata of the Structural Engineering Division, Building Research Institute, was available for discussion on damage to building structures following our return to Tokyo. Mr. Hajime Tsuchida of the

Port and Harbour Research Institute made some of the strong motion records available to the team and provided information on damage in the port of Ishinomaki.

In addition to those already mentioned, acknowledgments are due Mr. Keiichi Ohtani of the

National Research Center for Disaster Prevention, Science, and Technology Agency; Mssrs.

Haruo Yoshikoshi and Yasou Watanabe of the Sendai Construction Office, Ministry of Construction; Mr. Shigeyoshi Shima, Tohoku Regional Construction Bureau, Ministry of Construction,

Messrs. Kunimatsu Hoshihata, Chutaro Chiba and Tsuyoshi Soto of the Kitakami-Karyu Construction Office, Ministry of Construction; Mr. Kazuhiko Kawashima of PWRI, Messrs. Nagahisa

Ikuta, Masaki Takahashi and Osamu Yotsuyanagi of the National Land Agency, Messrs. Hidenao

Miyamoto and Toshio Shono of Tohoku Petroleum Co., Ltd., Mr. Chunchiro Kiowa of the City of Sendai, Messrs. Masashige Sasaki, Tokashi Shibuya, Yokio Matsuzaki and Akira Tokano of

Miyagi Prefecture; and Professors Akio Takagi, Ishii, Hisao Nakagawa, Akenori Shibata and

Toshio Shiga of Tohoku University, Messrs. Takashi Hirai, Yoichi Fujii, and Noboru Inouchi of

the Geographical Survey Institute in Tokyo.

On the U.S. side, Drs. Edward 0. Pfrang and H. S. Lew of NBS , chairman and secretary,

respectively, of the U.S. Panel of UJNR, made the initial arrangements which were necessary

to facilitate the visit of the U.S. structural engineers to Miyagi Prefecture. Mr. Yanev's

visit was supported, in part, by the Earthquake Engineering Research Institute. Mr. Louis

Cattaneo of the National Bureau of Standards assisted in assembling the material for this

report. Mr. Justin L. Bloom, Counselor for Scientific and Technological Affairs of the U.S. Embassy and his assistant, Mr. Bruce Carter assisted Mr. Fowler in his visit.

3
2. SOCIAL EFFECTS AND GOVERNMENT RESPONSE*

2.1 DAMAGE

There are about 6,500 business and manufacturing firms and about 452,000 households (homes

and apartments) in Miyagi Prefecture. In Miyagi Prefecture, 803 dwellings were destroyed

(309 in Sendai). Major causes of the destruction were landslides, inadequate foundations,

and inadequate lateral bracing. A number of 2- to 4-story apartment buildings were rendered

uninhabitable when their first-floors, housing shops or parking space, collapsed.

According to data compiled by the National Land Agency, the earthquake caused damage amounting to 166 billion yen ($830 million). A detailed outline of the various types of damage

and the economic loss that resulted is presented at the end of this chapter. In some cases

the amounts listed represent the cost of replacing a building or facility with a modern

structure even though the damage caused by the earthquake could be repaired at a lower cost. Almost half of the total damage estimate represents the cost of repairing or replacing factories, stores, and other business establishments as shown in Table 2.1.

Most buildings in Japan have tile roofs. Literally thousands were damaged, this was the

most apparent type of damage in the area. (Tile falling from roofs caused a number of

injuries.) Item 9 of the damage indicates that 20,634 structures were flooded. Sendai City

and Miyagi Prefecture officials reported that four homes were flooded as a direct result of

the earthquake. Because of the extensive roof damage, and because the area received heavy

rains after June 12, it may be that secondary water damage is reflected in the table.

In considering the damage, one must understand the topography and construction siting areas

in and near Sendai. Sendai has three distinct areas: the old (original) city, which is

centrally situated on solid level ground, a new section on the eastern side, toward the

coast, much of which is constructed on soft, flat ground (some of which includes fill

areas), and an area of hills to the north and west, where people have constructed homes and

buildings on terraces. Damage and losses were much greater in the soft and hill areas than

in the old section.

In the hill areas, unstable fill surfaces in combination with saturated soil caused many

landslides. Cracks, mostly associated with the landslides, formed in the terraced ground

where houses and apartment buildings were built. According to officials, a total of 337

landslides occurred throughout the prefacture.

Liquefaction in conjunction with inadequate foundations contributed to heavy damage in the

flat (soft) area. Reports of dike and levee subsidence were verified in many areas along

streams. At Nokahura, which is near Sendai, a dike that was originally 7 to 8 m high

settled 1.5 m because of liquefaction.

Reinforced concrete buildings, bridge piers, and bridge abutments settled and sustained

damage in many areas due to liquefaction and inadequate footings. Soft soil layers under

reinforced concrete structures contributed to much of the damage. It is interesting to note that damage to buildings from north-south shaking motion was often noticeably more severe and extensive than damage from east-west movement. Steel-frame buildings by and

large survived the earthquake better than reinforced concrete structures. Some lost facades

and windows, and only one collapsed. Older buildings constructed of wood frames were damaged because of inadequate lateral bracing.

A major oil refinery in the port area of Sendai, containing 98 storage tanks of varying

sizes, suffered damage when three large tanks containing fuel oil sprang leaks. Several

million gallons of oil flooded the refinery area, and some reached the waterway serving

the port.

The major cause of deaths and injuries from the earthquake was collapsing or falling walls

made of stone or cinderblock. These structures serve as fences, privacy walls, and noise

barriers. There is a National Code that requires that walls of this kind that are over

Prepared by Hugh H. Fowler, Emergency Management Agency, Bothell, Washington.

4
Table 2.1 Outline of Preliminary Damage from June 12, 1978, Miyagi-ken-oki Earthquake

1. Dead

2. Missing

3. Injured

4. Households suffering damage

5. Individuals suffering damage

6. Buildings wholly destroyed or burned or washed away

7. Partially destroyed buildings

8. Partially damaged buildings

9. Flooded building

Subtotal

10. Hospitals

11. Clinics

12. Medical equipment

13. Water Works

14. Sanitation facilities

15. Other sanitation facilities

Subtotal

16. Factories and stores

17. Other business establishments

Subtotal

18. Paddy fields (ha)

19. Fields or farms (ha)

20. Agricultural facilities

Subtotal

21. Farm produce (ha)

22. Joint-use facilities

Subtotal

23. Livestock

24. Livestock facilities

25. Livestock products

Subtotal

26. Sericultural (silkworm) facilities

27. Fishing boats

28. Fishing port facilities

29. Fishery and aquaculture facilities

30. Fishery products

31. Fishing equipment

Subtotal

32. Forest land, roads

33. Forestry facilities

34. Forestry products

Subtotal

35. Primary schools

36. Middle schools

37. High schools

38. Other schools

39. Cultural assets

Subtotal

40. Roads (sites of damage)

41. Bridges

42. Rivers (sites of damage)

43. Shores

44. Erosion control facilities

45. Ports and harbors

Subtotal

46. Railways

47. Electrical facilities

48. Communications facilities (sites of damage)

Quantity

27

0

1 ,052

3,477

13,768

803

5,227

58,927

20,634

119

194

735

29

33

55,078

5.5

535

541 .1 424

2,100

35

3

12

17 109

341

64

5638

b

367

170

102

323

22

720

65

115

5 1285

Value

(million $)

108.7

31.0

139.0

1.7

0.2

1.0

4.8

5.3

7.4

20. 4 455.0

455.0

0.3

24.1

24.5

1 .

1

5.8

6.9

0.6

O.b

13.5

5.0

0.2

la.

9

1.6

0.9

0.1

2.D

7.0

2.1

7.0

14.7

1.2

2

8

16

1

76

2,660

33

1632

6

1

17 66.0

34.8

13.7

2.3

5
Quantity

Value

(million $)

49. Social welfare facilities 166 3.0

50. Urban facilities 76 4.1 51. Gas facilities 53 2.0

52. Other facilities 231 3.1

Subtotal 62.8

Total loss 830.0

Number of people evacuated by order or recommendation 26,017

Number of communities where headquarters

for disaster countermeasures were set up 56

6
1-1/2 m high must be reinforced in both directions with steel bars. (The bars must be at least 9 mm in diameter and must consist of an 80 cm grid across and down the wall.) Some of

the walls that fell contained inadequate reinforcing and were more of a danger than

those with none: those with no reinforcement tended to crumble, while those with inadequate reinforcing toppled on people who were nearby or who held onto them for stability as the earthquake occurred.

2.1.1 Public Facilities, Services, and Lifelines

Effects of the earthquake on so-called critical facilities, on public services, and on other

vital activities were varied. In some cases, functioning was interrupted only temporarily,

in other cases, the impact on segments of the population lasted for several weeks.

2.1.2 Law Enforcement and Emergency Services

Only slight damage was sustained by police facilities. The police communication system

played a vital role in maintaining order and dispersing factual information immediately

after the earthquake. Fire service facilities, also, received little damage, and units had no difficulty coping with the few (10) fires that started.

Of the 41 hospitals in the Prefecture (27 in Sendai), several sustained varying amounts of

damage. The natural gas and electricity outage interfered with medical services. However,

there were no reported problems with overloading because of the influx of injured to the

city for treatment.

2.1.3 Transportation

The National Railway stopped all train service in the area immediately after the earthquake

to insure against accidents and to assess damage to the system. Service was restored quite

soon after repairs were made, and the safety of the line and its control systems was ascertained. Public bus service in Sendai was hampered in the hours immediately following

the earthquake because of traffic light failure. Air service between Sendai and other

points was quickly restored after airport officials assessed damage and found that safe

service could commence.

2.1.4 Utilities

Damage to the natural gas distribution system in Miyagi Prefecture was a major recovery

problem. Gas distribution systems in six cities were severely affected. About 60% of

the 200,000 households in Sendai are dependent on gas for heating and cooking. As of

June 28, 1978, 22,000 of those households as well as 10,419 households in other cities of

the prefecture were still without gas.

Electrical service to 419,100 homes in the prefecture was interrupted. For the most part,

service was restored within a day or two. Few distribution line poles were toppled. Two

electrical generating plants serving Sendai were out of operation. One of those plants,

located near the oil refinery at the port, depended upon fuel from the one refinery that was rendered inoperative. The other, located in north Sendai, was rendered inoperative

when the city's storage plant for low-pressure gas caught fire and service had to be terminated. Electrical power from other areas and facilities was diverted and at the time of the

reconnaissance was meeting the needs of Sendai, although several factories in the prefecture

were still without power.

Within the prefecture, there are about 50 separate water and sewage conveyance systems,

most of which are publicly owned. Prefecture officials estimated the damage to these systems, all of which had been restored by June 25, 1978, at about $30,000,000. Several lift

station pumps had to be replaced. Damage to sewer lines in Sendai was minimal, however,

until electricity had been restored, the system was partially inoperative. Several nuclear

electrical generating plants are located near Miyagi Prefecture. It is interesting to note

that none experienced any significant earthquake-related problems or damage.

7
2.1.5 Communications

All telephone service in Sendai and in the surrounding areas was interrupted from 5:14 p.m. until 8:00 p.m. on June 12, 1978. By 8:00 p.m., 50% of the service in the Sendai area

and 75% of the service in areas north of Tokyo had been restored. The disruption extended

as far south as Tokyo.

With the loss of electricity, all television and radio stations were unable to broadcast.

Several came back on the air soon afterwards by using emergency generators and performed

an important service by broadcasting factual information provided by the police and local

government officials. However, because most of the population was without electrical service, only those people with battery-operated transistor radios could receive emergency

information. (No formal emergency broadcast system exists in Japan.

)

2 . 2 RESPONSE

Immediately after the earthquake, government officials in Tokyo (national), in Sendai

(prefecture and city), and in other communities met to take emergency-response action and

to plan recovery measures. Sendai established a Disaster Countermeasures Headquarters

headed by the mayor. Included in this group were representatives of the National Railway,

water, gas, and electric utilities; the police and fire departments, the Red Cross, and

others. This headquarters remained operational for 24 hours a day immediately after the

earthquake. It was still in operation of June 27, 1978. Actual response activities are the

City of Sendai's responsibility. If an emergency is beyond the means of their resources, City officials may request additional services or financial help from the prefecture or national government.

With regard to food and supplies and distribution of emergency rations, the Governor of the

Prefecture activated a Headquarters for Self-Suf f iciency for the purpose of monitoring food

supplies and prices as well as to insure the availability of other items necessary for the

populace to survive and recover. Among the tasks the Headquarters performed were:

° Checking on regional and central wholesale markets

° Checking on bread and dairy products

° Checking department and food stores

° Arranging for additional propane bottles and burners

° Monitoring the supply of electric cells (batteries) for flashlights

° Requesting cooperation from the sales industry to maintain stable prices (prices

of some critical items actually were lowered during the emergency period)

° Receiving and considering consumer complaints

° Providing propane burners and fuel to handicapped centers

° Providing coordination with producers and suppliers of lumber, glass s concrete, and

other building supplies to insure that adequate stocks were available where needed

Coordinating with National Government officials in Tokyo when necessary.

The headquarters used the media to the fullest extent possible to broadcast factual information concerning supplies and prices. Close daily contact was maintained with 30 designated stores in the area to monitor events.

The police force played a key role in maintaining order and providing information to the

populace. Because the lack of electric power limited the effectiveness of the mass media,

police used loudspeakers on vehicles. By 8:30 p.m. on June 12, more than 7,000 people had

gathered at the Sendai train station (all trains had stopped after the earthquake). The

police moved in portable generators, set up lights, and used loudspeakers to provide infor-
mation. By keeping them informed about the likelihood of tsunami or another earthquake and

about the damage situation, authorities were able to calm the public and avert panic. By

9:30 p.m., all but 600 of the crowd had dispersed.

A traffic control center was set up immediately after the earthquake to handle the severe traffic problem. Crowds of people and vehicles had gathered at crossings. To deal with

this the following measures were taken:

° All available police were ordered to duty

° The traffic control center monitored critical areas and dispatched police to handle

problems

° Loudspeakers were used effectively to inform the public.

The damage caused by the earthquake had been judged not great enough for the Prime Minister

to issue a National State of Emergency declaration for the Miyagi Prefecture. Article 105

of the Disaster Countermeasures Basic Law provides the basis for issuance of such a declaration. Officials of the Ministry of Construction have visited Miyagi Prefecture to assess

the damage caused by the earthquake. On the basis of their assessment, the National Government will determine the amount of national funds to be provided (usually two-thirds of the

cost, with the remaining third to be borne by the prefecture).

Japan has a Disaster Relief Act, which is administered by the Ministry of Health and Welfare. Under this authority, which does not require a declaration by the Prime Minister of a National State of Emergency in order to act, relief was approved for two cities and four

towns. Each municipality (or prefecture) submits a request, accompanied by data, photographs, and loss statistics to the National Government. Included as benefits under the Act

are low interest loans (5.05%) to replace buildings of wood construction. The period of

repayment can be extended to 25 years. Homeowners with existing loans on their property are

not eligible for much assistance under the Disaster Relief Act other than a low-interest

loan. This means that they would need to carry two loan payments, City of Sendai and Miyagi

Prefecture officials are trying to get National funding to cover the initial load balance.

The prefecture disaster plan provides that local government heads can request military support and assistance (from the Self-Defense Force). Between June 12 and June 19, such help

was requested by the provided to six cities and seven towns. A total of 2,117 military personnel were involved in supplying water to people in areas where normal systems were not operative. They were also instrumental in saving three lives.

Two factors influenced the need for evacuation: the danger of a Tsunami and the unsafe con- ditions caused by the earthquake damage.

A Tsunami warning was issued at 5:21 p.m. on June 12. The actual order to evacuate must be given by a Mayor or head of government. The Sendai Mayor did not order an evacuation but

did issue a warning. Local officials in other coastal communities did issue evacuation

orders, and more than 20,000 people moved inland. The "all clear" was received at 8:15

p.m., and those who had left their homes were permitted to return.

Evacuation was necessary to protect people whose homes had been destroyed or judged unsafe

for habitation. Approximately 70 families were ordered from their homes in the hill areas

of Sendai because of continuing danger of landslides.

Most displaced, evacuated individuals and families stayed with relatives and friends. riow- ever, the city and prefecture response plans provide for the use of schools, hospitals, and

other public buildings as shelters. Under extreme conditions, the National Defense Force

can provide tents or other types of shelter for transient population.

Little search-and-rescue activity was associated with the earthquake. Life-saving measures

were performed as necessary by fire and police forces working in the Fire Defense Headquarters, established in affected municipalities immediately after the quake. Two apartment

buildings were involved when their first floors collapsed, and evacuation of the occupants

of other floors required the assistance of fire departments. The National Self-Defense

9
Force assisted in locating the body of a missing person. Two other bodies were recovered by

neighborhood groups.

The City of Sendai has five rescue teams on alert at all times. When the earthquake occurred and electrical power was lost, the traffic signal system (there are more than 40U signals

in the city) became inoperative. Major traffic congestion developed at most intersections,

and ambulances were able to respond to only 2 4 of the more than 200 calls for aid. A central

emergency facility, where people could obtain medical treatment, was quickly established in

Sendai. Hospitals activated an emergency medical information center, which consisted of

computerized data on doctors, hospital bed space, ambulances, etc.

On June 25, only 705 people (in three cities and nine towns) remained in shelters. Sites

used for shelters included school gymnasiums, citizens halls, and other public facilities.

Emergency rations were distributed by volunteer agencies. The Japanese Red Cross was not asked to participate in the emergency-response or recovery phases of this disaster.

Because both gas and electricity were lacking in many homes, people bought food that did

not require cooking. Stores received additional quantities of precooked foods from areas

not affected by the earthquake. Fortunately, most grocery stores and markets in the area

remained intact, and there was ready access for shopping. Food prices remained stable

despite the heavy demand for particular types of food. Because most homes depend upon gas

for cooking and heating, the Sendai Gas Company (public) distributed portable gas heaters

for purchase at less than cost.

More than 300 homes in Sendai were destroyed. Under certain conditions, the local and prefectural governments may construct prefabricated dwellings for those who lose their homes.

Approximately 70 such dwellings were under construction in Sendai to provide shelter to those who did not have other means.

Neither the City of Sendai nor Miyagi Prefecture attempted to establish or maintain a locater service for missing persons. As soon as the radio and television stations resumed service, selected stations set aside an hour each day to broadcast names and messages. The

telephone company also liberalized its use of phones to assist victims.

2.3 RECONSTRUCTION

New construction in Japan must conform with the Architectural Law, which contains special

requirements to mitigate earthquake damage and is administered by the Ministry of Construction. Builders must submit plans to prefectural or larger municipal governments for review

and approval before starting construction. With very few exceptions, buildings destroyed

or seriously damaged had been constructed before the law was in effect.

The Sendai City and Miyagi Prefecture government formed a Reconstruction Planning Committee

to ensure that building replacement and repair will contribute toward safety. The committee

includes representatives of higher education institutions, commercial and business concerns,

industry, and the architectural profession. The Sendai Construction Bureau will insure that new construction in the city meets the requirements of the National Building Code.

2 . 4 INSURANCE

2.4.1 Unemployment Insurance

Although manufacturing firms and business were hard hit by the earthquake, a large majority

of those whose jobs were affected were back at work soon after the earthquake. Some manufacturers who were operating on a marginal basis had not reopened at the time of the reconnaissance; the workers affected were drawing unemployment insurance.

2.4.2 Earthquake Insurance

There are at least two types of earthquake insurance available in Japan. Both are expensive .

10
One type of protection, available to a farmers association, covers 100% of the damage up to

a maximum of 25,000,000 yen. Lesser amounts of coverage can be obtained.

The other (major) type of earthquake insurance, is a plan that is endorsed and guaranteed by

the government. This program was initiated five years ago but has not met with general

acceptance. What appear to be major limitations are its high cost and the limitations on coverage. The maximum coverage for goods is 1.5 million yen ($7,500), the maximum coverage

for homes is 2.4 million yen ($12,000). (The average home in Japan cost 15 to 20 million

yen.) Both city and prefecture officials in Sendai stated they felt that there is a need

to equalize the program. It was their consensus that the insurance program will become popular if coverage can be increased and rates adjusted. This type of insurance is required of

those who request and receive low-interest disaster-relief loans.

2.5 CONCLUSIONS

The 1977 Disaster Countermeasures Act of Japan, administered by the National Land Agency,

requires that each level of government have a plan and a competent organization for dealing

with disasters. The rapid and effective response by all levels of government (national,

prefectural, and municipal) towards alleviating the affects of the earthquake was the result

of a unified, integrated program of disaster preparedness and response.

The amount of recovery work accomplished or under way within two weeks after the earthquake

occurred was impressive. The speed and efficiency with which a vast amount of work had

been performed was most admirable. Officials responsible for directing operations and

others working to accomplish the monumental task of recovery exhibited unusual industry and

knowledge about the problems they faced and how to solve them. All, without exception,

devoted their efforts exclusively to serving the needs of the people and communities that were adversely affected.

11
3. TECTONIC AND GEOLOGIC SETTING

3.1 INTRODUCTION

The Miyagi-ken-oki earthquake of June 12, 1978 occurred in the outer zone of seismicity in

Japan, along the subduction zone that bounds the east side of northeast Honshu. This was

only one of the many damaging earthquakes that Japan experiences because of its active

tectonic setting, and the third in 1978. Most of the larger earthquakes are directly

associated with the subduction zone along which the margin of the westward drifting lithosphere under the Pacific Ocean is plunging beneath Japan at a long-term rate of about 10 cm per year. The area where damage occurred in the June 12 earthquake lies on the east

coast of northeast Honshu about 300 km north of Tokyo, in a region of low, flat alluvial

plains, local alluvial terraces, and steep bedrock terrain of largely moderate relief.

This chapter describes the Miyagi-ken-oki earthquake and its setting as background for the more detailed reports on the effects of the earthquake. The tectonic setting of the earthquake is described, together with the reason that a larger earthquake following the June 12

event was (and still is) a serious, although uncertain, possibility. The June earthquake

and its pattern of aftershocks are described, and this pattern is used to illustrate the

important distinction between epicentral and fault distance in attenuation studies. Finally, the geology of the affected region is summarized, because of its influence on the

distribution, character, and severity of earthquake damage.

This chapter is based on the literature (in English) available in Menlo Park, and on information gained from discussions with, and documents and maps provided by, Japanese officials

and scientists during the author's visit to Japan as a U.S. Geological Survey representative

on the U.S. team in June 1978. The information is necessarily incomplete because only two

weeks had been available for study of the earthquake by the Japanese at the time of the

visit to Japan by the U.S. team, and time for discussion and observation during the visit was brief. More thorough accounts will undoubtedly result from the Japanese studies.

3.2 TECTONIC SETTING

Japan is located along the leading overthrust margin of Asia against subducting sea floor

of the Pacific plate (inset, Figure 3.1). That plate is drifting northwestward toward

the nearly stationary Asian continent, as recorded over the past 40 million years by the

Hawiian chain of volcanoes strung out northwest of the eruptive source now beneath Hawaii.

The subduction zone beneath northeast Honshu is marked at the surface by the Japan deep-sea

trench and associated island arc, one of several extending around the perimeter of the

northwest Pacific (Aleutian, Kurile, Northeast Honshu, Izu-Bonin, and Mariana arcs).

The northeast Honshu arc system consists of a concentric sequence of tectonic elements

(Figures 3.1 and 3.2): from east to west, (a) the subducting oceanic plate and deep-sea

trench, (b) a submerged forearc terrane consisting largely of the inner-trench slope and

a broad deep-sea terrace underlain by more than 2 km of Tertiary sediments, (c) the emergent frontal arc, (d) a volcanic chain atop the front of (e) a deformed backarc geosyncline,

and (f) a backarc basin. Most of the arc system is underlain by ancient continental basement, which is bounded on the east and west by thinner oceanic crust, on the east by the

Pacific plate, and on the west by the crust of the backarc basin, formed during the early

Tertiary opening of the sea of Japan.

This pattern of tectonic features concentric with the Japan trench was established about 25

million years ago, when the Mizuho orogeny began in northeast Honshu with block faulting,

subsidence, and extensive volcanism west of the Morioka-Shirakawa tectonic line

(Figure 3.1). The Miocene faults broke obliquely across the older north-northwesterly

trending structure, such as the Tanakura tectonic line (Figure 3.2). The present tectonic

regime is a later phase of that orogeny, in which Quarternary compressional deformation

marked by northeast-trending reverse faults and overturned folds has supplanted the earlier

extensional regime.

Prepared by Carl Wentworth, U.S. Geological Survey, Menlo Park, California

.12
Explanation of Symbols for Figure 3.1

Quaternary sediments, consisting of alluvium, terrace deposits and lake beds

Neogene sediments and Cenozoic volcanics, including the extensive Early

Miocene green tuff, folded younger sediments, and Quaternary volcanics

Pre-Neogene rocks, including Paleogene and Mesozoic rocks, metamorphic

rocks, and Cretaceous or older plutonic rocks; exposed rocks as old

as Silurian are recognized. Abukuma block largely plutonic rocks;

Kitakami block largely late Paleozoic and early Mesozoic metasediments

and scattered plutonic masses

Active volcano

Morioka-Shirakawa tectonic line (MSTL, approximate location) and the

boundary in early Miocene rocks between thick, mainly marine, altered

tuff (the green tuff) on the west and thin, mainly terrestrial volcanic

rocks on the east

Contact, dashed offshore where location very approximate, dotted along

limits of information offshore

Major fault, including the Itoigawa-Shizuoka tectonic line (ISTL) along

the west margin of the Fossa Magna zone of deformation and low topography,

the Median tectonic line (MTL) of Southwest Japan, and the Tanakura

tectonic line (TTL) . Dashed where approximately located; dotted where

concealed

Quaternary fault, longer than 10 km, which offsets or deforms late

Pliocene or Quaternary deposits

Arc (inset): A - Aleutian; K Kurile; H - Northeast Honshu; I-B - Izu-Bonin; M - Mariana. Teeth on upper plate

13
Figure 3.1 Geologic map of northeast Honshu region and plate tectonic

setting, compiled from Dickinson (1979), Geological Survey

of Japan (1964), Ishiwada and Ogawa (1976), Isomi (1968),

Research Group for Quaternary Tectonic Map of Japan (1969)

,

and Yoshida (1975)

14
Explanation of Symbols for Figure 3.2

Qu Quaternary volcanic rocks

Qs Quaternary sediments

N Neogene sediments and volcanic rocks

Pe Paleogene sediments

Mz Mesozoic rocks

Pz Paleozoic rocks

b Basement rocks (pre-Silurian)

a Accretionary wedge - deformed sediment presumably scraped from oceanic

plate during subduction

Envelope of seismicity along and above top of subducting slab,

from Figure 3.4

0 Location of hypocenter and apparent dip of focal mechanism for

June 12, 1978 earthquake —— Approximate extent of June 12 fault rupture in section

6.1 Seismic velocity in km/s

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16
The known reverse faults in northeast Honshu are short, scattered, and few relative to the numerous Quaternary faults of varied style in central Honshu and the 800-km-long strikeslip fault along the Median tectonic line in southeast Honshu (Matsuda, 1977). Most of the

faults occur along and west of the Morioka-Shirakawa tectonic line and in the Sendai region

between the Abukuma and Kitakami structural blocks. Some of these faults have undergone

quite recent movement, but apparently none were involved in the June 12 event.

Most of the present relief in northeastern Honshu has formed during this Quaternary compressional phase of the Mizuho orogeny. Beginning 1 to 3 million years ago, the average rate of

the vertical movements that accomplished these changes increased tenfold to the order of 1 to 10 mm/yr (Matsuda, 1976). Concurrently, renewed volcanism built the modern volcanoes

alined just west of the frontal arc.

This third and current phase of the Mizuho orgeny, following the initial volcanism and

development of the backarc geosyncline and its subsequent breakup and gradual uplift,

suggests some change in the subduction regime that drives the system. One possibility is a change in subduction rate. Based on study of the ages and positions of volcanoes in the

Emperor-Hawaiian chain, Shaw, Jackson, and Bargar (1979) suggest that a threefold increase

in the rate of west-northwestward drift of the Pacific plate relative to the magma source

occurred about 1.3 million years ago.

Modern seismicity indicates that subductive underthrusting continues along the northwest

Pacific island arcs. The regularity of great thrust earthquakes in space and time that

characterizes the Aleutian and Kurile arcs decreases along the northeast Honshu arc, however, and such earthquakes appear to be lacking along the Izu-Bonin and Mariana arcs to the

south. The degree to which the convergence rate of the plates is expressed in major thrust

earthquakes also seems to decrease southwestward: in the Aleutian arc, probably all the

plate convergence is accounted for by faulting associated with major earthquakes, whereas

only about one fourth is accounted for at the southwestern end of the Kurile arc and almost

none at the southern end of the northeast Honshu arc (Kanamori, 1976, 1978).

Decoupling between the converging plates seems required to permit subduction along the

Northwest Honshu arc without the crustal strain that produces major earthquakes. This

decoupling may be associated with the anomalously small accretionary wedge found at the

trench off northeast Honshu by Von Huene, Nasu, and others (1978). They indicated that the

volume of sediment brought to the trench atop subducting oceanic lithosphere in the late

Cenozoic has far exceeded that now caught in the accretionary wedge. Most of it must have

been subducted, therefore, either to cause, or more likely, to result from, decoupling

between the plates. This lack of close coupling is attributed by Kanamori (1976) to active

sinking of the subducting slab away from the Asian continent. By this argument, the subducting plate is not only plunging westward beneath Honshu and the Sea of Japan but is

bodily sinking, so that the downward bend beneath the forearc terrane is migrating eastward.

The Miyagi-ken-oki earthquake occurred beneath the forearc terrane midway between the ends

of the Northeast Honshu arc. Its setting is thus largely independent of the structural

nodes at the junctions with adjoining arcs in the Tokyo-Fossa Magna region and south of

Hokkaido. As shown in the schematic cross section representing structure across the center

of the arc system (Figure 3.2), the subduction zone extends westward beneath the forearc

terrane at an initial shallow angle of about 3-1/2°. Beneath the forearc basin, where the

top of the subducting plate abuts the lower crust of northeast Honshu, the subduction zone gradually steepens until, free of the continental crust at about 30 km, it extends into the

mantle at a dip of about 25°.

The full extent of the subduction zone is best shown by the three-dimensional pattern of

earthquakes in the region (Figure 3.3). The earthquakes occur at greater and greater depth

to the west, defining a Benioff zone that extends westward for more than 1,000 km beneath

northeast Honshu and the Sea of Japan at an angle of about 25°, reaching depths greater than

500 km near the coast of Korea.

In greater detail (Figures 3.4 and envelope of seismicity in Figure 3.2), microearthquakes

more precisely define the upper part of the subducting plate. The upper boundary of the

subducting slab is clearly defined as dipping westward at about 25° beneath northeast

Honshu, with a second westward-dipping zone of earthquakes within the slab about 40 km

17
Figure 3.3 Earthquake hypocenters beneath Japan for the

period 1964-1974. Epicenter symbols show depth

of hypocenter, depth contours in kilometers.

From Coordinating Committee on Earthquake

Prediction (1978).

Figure 3.4 Distribution of microearthquakes (dots) beneath northeast Honshu in vertical, east-west

section in the vicinity of 39-40

degrees north latitude, and

subducting oceanic lithosphere.

Horizontal line above section

represents land, the upright

triangle the volcanic front, and

the overturned triangle the Japan

Trench. From figure 6 of Takagi

and others (1977)
beneath the first (Hasegawa and others, 1978, Takagi and others 1977). A zone of high activity is also shown above the subduction zone beneath the forearc terrane. The frontal arc

is nearly aseismic, and a shallow zone of earthquakes extends westward from the edge of the

frontal arc beneath the backarc geosyncline.

Analysis of the sense of first motions of microearthquakes recorded by the northeast Honshu

seismographic network has been made by Hasegawa and others (1978) to determine the style

of faulting associated with the earthquakes. These composite focal-mechanism solutions,

although varied in detail, indicate that thrust faulting with compression nearly perpendicular to the trench is underway at and above the upper boundary of the subducting slab, as would be expected from the plate motions. In contrast, the band of seismicity within the

slab involves extension along its dip direction.

Historic damaging earthquakes along the northeast Honshu arc form three groups evident in a compilation of damaging earthquakes that have occurred in and near Japan over the past one

and a third millenia (Japan Meterological Agency, no date, and Figure 3.5). A modest number

of great earthquakes have occurred with epicenters near the trench, largely involving

faulting along the gently dipping part of the subduction zone. Closer to shore, more numerous intermediate-size damaging earthquakes have occurred with epicenters in a band along the

forearc basin trend. These earthquakes appear to involve faulting along the top of the

steeper part of the subduction zone. A scattering of generally smaller damaging earthquakes

has occurred with epicenters onshore, along and west of the Morioka-Shirakawa tectonic line.

The frontal arc appears to be nearly free of damaging earthquakes, except in the gap between

the Abukuma and Kitakami highlands near Sendai.

3.3 SEISMIC GAP AND PRECURSORS

The Miyagi-ken-oki earthquake of June 12 occurred adjacent to an area for which there was

some evidence to suggest a forthcoming major earthquake. Gaps of uncertain significance

existed in the pattern of both major and smaller earthquakes. The following summary is

based on discussions held during the team visit in Japan and on Abe (1977), Coordinating

Committee on Earthquake Prediction (1978), Mogi (1968), Kanamori (1976, 1978), and Shimazaki

(1978).

The regularity with which great thrust earthquakes have occurred along subduction zones has

led to the use of gaps in the pattern of fault rupture areas as a basis for identifying

expectable earthquakes. The focal areas of the earthquakes tend to fill the length of the

subduction zone with little or no overlap between adjacent events, and gaps in the pattern

of the most recent earthquakes tend to be filled in. This regular pattern of repeated

earthquakes extends around the northwest Pacific as far as the junction between the Kurile

and Northeast Honshu arcs (Figure 3.6). At that junction, interpretation of tsunami data

suggests that major thrust faulting and associated earthquakes occurred in 1677, 1763, 1856,

and 1968, or about every hundred years.

The latest earthquake in that sequence, the Tokachi-oki earthquake of 1968 (Figures 3.5 and

3.6), is also the southwesternmost in the latest round of great earthquakes along the Kurile

arc. East of the Kitakami block (or Sanriku region), the repeat history of major earthquakes seems less regular. And farther south, between latitude 36° and 38° N east of the

Abukuma block, the 1938 Shioya-oki series of five large earthquakes (three thrust, two normal) seems to have been the only major earthquake event in at least the past 800 years.

The transition along the Northeast Honshu arc from regular behavior of great thrust earthquakes at the north to almost no major earthquakes at the south complicates the application

of seismic gap theory to the region east of Sendai. It is not clear whether or when the ongoing subduction involves sufficient straining of the lithosphere to produce major earthquakes.

The last major subduction-zone faulting east of the Kitakami block between latitude 38° and

40°N occurred in 1896-1897, when the focal areas of the 1896 Sanriku and associated large

earthquakes extended from within the focal area of the 1968 Tokachi-oki earthquake southward

to about 38°. Only three earlier major earthquakes are known from the area—in 869, 1611,

and 1677 —although the historic record is incomplete. Thus the regular, hundred-year repetition of major earthquakes that characterizes the southwest Kurile arc does not persist

south of about 40°. If strain has been accumulating since the Sanriku earthquakes of the

19
4

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A

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A V

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I—ii—i- i I i i i I

Figure 3.5 Historic damaging earthquakes in the northeast Honshu

region. Compiled from 1:2,000,000 map. Disastrous

Earthquakes in and near Japan, covering the period 599

to 1975. Older historic data are incomplete. Age classes

are based on null points in temporal frequency of earthquakes throughout map area.

20
Figure 3.6 Source areas of recent major earthquakes along

the subduction zone off Japan, with date and

magnitude, and potential great earthquake at latitude 38. From Coordinating Committee on Earthquake Prediction (1978).

21
late 1890's, it has yet to be relieved by major thrust earthquakes. The role of the 1933

Sanriku earthquake is not clear. Apparently it was not a subduction-zone thrust event, but

rather the product of normal faulting within the oceanic plate along a steeply west-dipping

plane that extended through the oceanic crust.

Many large earthquakes seem to be preceded, for a period of years, by a lack of smaller

earthquakes in the epicentral region. The absence of small earthquakes in the forearc

terrane between about 37° and 39° (Figure 3.3) for a period of at least ten years amounts to such a gap in seismicity. This reinforces the uncertain suggestion from the pattern of

major earthquakes that the region east of Miyagi may be about due for another major earthquake (Figure 3.6). Because the Miyagi-ken-oki earthquake of June 12 occurred adjacent to,

but not within, this gap, a major earthquake may yet occur in the gap.

Particularly because of the seismic gap, other indications of the imminence of a large

earthquake have been of interest. Spirit leveling had demonstrated an eastward tilt of the

land opposite the gap, but no short-term precursors were recognized prior to the June 12 earthquake. Abundant data from the seismic network of Tohoku University showed no clear

change in seismic velocities. Similarly, no indications of imminent earthquakes were evident from the extensometers and tiltmeters that are part of each station in that network.

Comparisons of measurements along two east-west level lines run by the Geographical Survey

Institute that end at Sendai and Kamaisi show relative downward tilt to the east of 2 to 5 cm between the center of the island and the east coast in a 7-to-8-year period beginning in

1966. The tilt is greater at Sendai than farther north, an additional 3 cm of decline at Sendai may be related to withdrawal of ground water. Detailed tidal records in the area

showed no evident changes with a resolution of a few centimeters within hours after the main

shock of June 12, so that little or no coastal uplift accompanied that earthquake.

3.4 MIYAGI-KEN-OKI EARTHQUAKE OF JUNE 12

The magnitude 7.4 Miyagi-ken-oki earthquake occurred on June 12, 1978 at 5:14 PM local time,

with its hypocenter at a depth of 30 km at latitude 38.2°N longitude 142. 2°E (National

Research Center for Disaster Prevention, 1978b). It followed by about 4 months a magnitude

6.7 earthquake that occurred 65 km to the north (latitude 38.7°N, longitude 142. 2°E) at a depth of 60 km (National Research Center for Disaster Prevention, 1978a). The February 20

earthquake had a pattern of aftershocks distinct from that of the June 12 earthquake

(Figure 3.7) and therefore was not simply a foreshock of the larger earthquake. The main

June 12 shock was preceded by one foreshock a few minutes earlier, and was followed by many

aftershocks, which were recorded by the seismographic network of Tohoku University

(Figure 3.8). Figure 3.9 shows the hypocenter of the main shock and aftershocks through

the first 7 hours (A) and aftershocks for the first 10 days following the main shock (B).

A focal-mechanism solution for the main shock, using worldwide data, indicates thrust movement along a preferred plane dipping to the west-northwest at 20° (Figure 3.10, Otsuka and

others, 1978). Figure 3.2 shows this solution at the appropriate depth and position relative to the trench and volcanic front. Within the crude accuracy limits of the schematic

cross section, the focal plane lies at the top of the subducting oceanic slab.

The aftershock pattern supports and extends this association. The two aftershock patterns

of Figure 3.9 are nearly identical, indicating relative stability through time, and suggest

mainshock rupture on a west-dipping plane that extends to a depth of about 50 km. The

aftershock pattern of Figure 3.9B_ lies entirely within the equivalent pattern of Figure 3.4, at and above the top of the subducting slab.

The extent of the fault rupture zone can be estimated from the early aftershock pattern

(Figure 3.9A). In the dip direction, it extends from at or somewhat above the mainshock

hypocenter to a depth of about 50 km (Figure 3.2). This represents a fault width (or downdip dimension of the focal area) of about 70 km, down which the rupture propagated from

the up-dip hypocenter location. The lower end of the fault rupture is here estimated from

the depth of the aftershocks, whereas the upper end is estimated from the relative positions

of the mainshock epicenter and the eastern end of the aftershock pattern. The strike length

of the aftershock pattern, although less well constrained than the east-west direction

because of its position offshore of the seismic network, suggests a rupture-zone length of

22
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Figure 3.7 Epicenters of the earthquakes of February 20 and

June 12, 1978 and principal aftershocks. From

Coordinating Committee on Earthquake Prediction (1978)

.

Figure 3.8 Numbers of aftershocks of the June 12 earthquake

through time. Arrow shows time of largest aftershock.

From Coordinating Committee on Earthquake Prediction (1978) .

23
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24
about 50 km. These dimensions are similar to the focal dimensions reported by Kobayashi and

others (1978), a fault width of 80 km and a length of 30 km.

The June 12 earthquake thus occurred along the subduction boundary where it steepens before

extending to depth in the mantle. Inasmuch as the focal area of the earthquake lies west of

the seismic gap (Figure 3.6), the faulting did not encroach upon the area of unrelieved

strain suggested by the gap. The locations of the June 12 earthquake and the earlier

earthquake in February raised the possibility that they were precursors of a larger earthquake that would fill the gap. On June 16 several earthquakes as large as magnitude 5.9

did occur in the gap area (Figure 3.7). The aftershock train of the June 12 earthquake

decayed rapidly, however, perturbed only by one aftershock somewhat larger than magnitude 6 and an associated increase in activity on June 14 (Figure 3.8).

3.5 LOCATION OF ENERGY SOURCE

The location of the source of seismic energy is an important parameter in studies of the

attenuation of seismic shaking. The earthquake epicenter is commonly used as an approximation of this location, largely because epicentral locations are available for most modern

earthquakes. Despite the convenience, however, measurement of attenuation distances from the

epicenter of an earthquake can be highly misleading, as implied by Page and others (1972) in

their discussion of peak acceleration and described by Youd and Perkins (1978) in their

discussion of liquefaction.

Strike-slip rupture, for example, can pass close to a site of interest, even where the epicenter of the associated earthquake is far distant. This difference can be accommodated by

using the shortest distance to the rupture trace rather than the longer epicentral distance.

In the reverse faulting at San Fernando, California in 1971, the epicenter lay far north of

the damage area in the San Fernando Valley. The inclined rupture surface extended to the

ground surface within the damage area, however, so that distances to the nearby fault could

be readily measured.

The fault rupture surface in the Miyagi-ken-oki earthquake of June 12 is less obvious,

because the epicenter is offshore and the damage area on land lies in the down-dip direction

of the inclined rupture surface. The epicenter of this earthquake is about 115 km east of

the city of Sendai. The down-dip extent of the early aftershock pattern, however, lies 60

km west of the mainshock epicenter at a depth of about 50 km beneath the Osika Peninsula

(Figure 3.9A). If these early aftershocks delineate the mainshock rupture surface, as is

probable, then the faulting reached within about 75 km of Sendai in three dimensions and

within 55 km in plan view.

3.6 GEOLOGY OF THE DAMAGE REGION

Most of the damage resulting from the June 12 earthquake occurred within the Miyagi region

(shown in Figure 3.11), which consists of a broad central lowland bounded east and west by

low mountains. To a considerable extent, the distribution and character of the damage were

related to the geology of the region (see, for example, chapters 5 through 9 of this

volume). The following discussion is compiled largely from the sources of Figures 3.11,

3.12, and 3.13 and Table 3.1, and discussions during the team visit in Japan, including

information provided by H. Nakagawa (written communication, 1978).

The broad central lowland, in which much of the damage occurred, consists of low bedrock

hills and extensive alluvial plains. It is bounded east and west by north-trending mountain

ranges and on the southeast by Sendai Bay. Bedrock in the region consists of granitic and

low-grade inetamorphic basement, exposed almost exclusively in the southern Kitakami block

and the northern tip of the Abukuma block, and a complex sequence of Miocene and Pliocene

volcanic rocks and nonmarine to marine clastic rocks that overlie basement in the gap

between the two highlands in the Sendai-Ishinoraaki area. West of the Morioka-Shirakawa

tectonic line, similar rocks are capped by Quaternary volcanoes. Uplift of the region during Quaternary time placed the Pliocene rocks well above sea level and raised the Abukuma

and Kitakami blocks even further. Concurrent oscillation of sea level, as the world's glaciers waxed and waned, produced a sequence of coastal and river terraces that is well represented in the vicinity of Sendai. The alluvial plains of the central lowland represent the

youngest deposits in the region, formed during recovery of sea level from the last glacial

maximum 18,000 years ago.

25
Explanation for Figure 3.11

Oa Quaternary alluvium

Qt Quaternary terrace deposits

Qv Quaternary volcanic rocks

Tp Pliocene sedimentary and volcanic rocks

Tm Miocene sedimentary and volcanic rocks

pN pre-Neogene basement rocks: slate, sandstone, and schist

Rifu-Nagamachi tectonic line; dotted where concealed

—-40— Contour on late Pleistocene erosion surface beneath alluvium

contour interval 20 m, sea-level datum —5 Limit of bedrock information

26
Figure 3.11 Geology of the Miyagi region. See Figure 1.1 for location.

Compiled from 1 : 200 , 000-scale topographic maps published by

the Geological Survey Institute of Japan, Geologic Map of

Miyagi Prefecture at 1:200,000, Geological Survey of Japan

(1968) and Hase (1967)

.

27
Explanation for Figure 3.12

Quaternary peat; in part overlaps alluvial fan deposits

Quaternary alluvium; much silt and clay, coarser along rivers

Quaternary alluvial fan deposits; sand and gravel

Quaternary terrace deposits; sand and gravel; numbered 1 to 4 with

increasing age

Pliocene sedimentary and volcanic rocks

Miocene sedimentary and volcanic rocks

Contour on late Pleistocene surface buried by Quaternary alluvium;

contour interval 10 m, sea-level datum

Selected topographic contours, in meters

Boundary of area of artificial cut and fill, superimposed on geology; hachures on inside

2?.
Figure 3.12 Geologic map of the Sendai area. Geology enlarged and

generalized from discordant sources: Geologic Map of

Miyagi Prefecture at 1:200,000, Geological Survey of

Japan (1968), Hase (1967), and Shibata (1962). Base from

1 : 25 , 000-scale topographic map. See Figure 3.11 for

location

.

29
A

I25m r

a'

Rifu-Nagamachi

tectonic line

Bedrock Gravel Sand Silt Clay

Figure 3.13 Cross section of surficial geology across Sendai

terrace and coastal plain. Compiled from Hase

(1967), Geological Survey of Japan (1968), and

l:50,000-scale topographic map. See Figure 3.11

for location.

30
Table 3.1

Stratigraphic Section in the Sendai Region

An approximate, composite section compiled from H. Nakagawa

(written communication, 1978) and Shibata (1962)

Quaternary alluvium: sand, gravel, and clay —UNCONFORMITY

Alluvial terrace deposits: sand and gravel —UNCONFORMITY

Pliocene Sendai Group

Dainenji Formation - 280 m, shallow marine: sandstone, with siltstone, tuff, and

lignite

Mukaiyama Formation - 180 m, nonmarine sandstone, : tuff and conglomerate with a 4- to 15-m tuff (Hirosegawa) near the base

—UNCONFORMITY

Tatsunokuchi Formation - 300 m, marine: sandstone and conglomerate, siltstone,

and tuff

Kameoka Formation - 100 m, nonmarine to brackish: sandstone and siltstone,

conglomerate, tuff, and lignite

Mitaka Andesite - 200 m: lava and some agglomerate

—UNCONFORMITY

Miocene Shirasawa Formation - 200 m, lacustrine: tuff, sandstone, siltstone, and conglomerate, with a 120-m tuff near the middle

—UNCONFORMITY

Natori Group

Yumoto Tuff - 100 m: dacite tuff, pummice boulders

Hayama Tuff - 50 m: rhyolitic tuff

Tsunaki Formation - 475 m, marine: sandstone, tuff breccia, and siltstone and

tuff

Hatate Formation - 200 m, marine: sandstone, siltstone, and tuff

Moniwa Formation - 75 m, marine: sandstone and conglomerate, calcareous

Takadate Formation (or Andesite) - 125 m: andesite, agglomerate, some rhyolite

Tsukinoki Formation - 15 m, nonmarine —UNCONFORMITY

Cretaceous Basement rocks of the Paleozoic wariyami Formation (slate and schist), the Triand older assic Rifu Formation (slate and sandstone), and Cretaceous granitic rocks.

31
Uplands throughout the region are eroded into intricate, steep-sided ridges, but differences

in altitude and relief and in the extent of alluviated lowland distinguish three northtrending topographic belts. (1) On the east, facing the sea, the southern end of the Kitakami block stands 200 to 500 m above sea level, with most slopes inclined between 30 and

50 percent. (2) West of this bulwark, across the south-flowing Kitakarai River that marks

its western edge, extend the alluvial plains and intervening areas of low, steep-sided hills

that form the Kitakami lowland. The heads of the east-trending flood plains on the northwest and the inland edge of the coastal plain facing Sendai Bay on the southwest mark the

western limit of this central belt. (3) The lowland is bounded on the west by hills that are nearly everywhere higher than 200 m. Southwest of Sendai, however, a wedge of lower,

steep-sided hills extends northward off the end of the Abukuma block. At the northern end

of this wedge, the hills bordering the Sendai terrace have valley walls commonly no steeper

than 20 to 30 percent and a local relief generally less than 100 m.

The south end of the Kitakami block consists largely of hard, fractured slate and bedded

sandstone of Triassic and Jurassic age that very locally contain Cretaceous granitic

intrusions. Natural exposures seem nearly absent except along the coast, but the con- sistantly steep slopes of this topographic belt bear only a very thin soil mantle over bedrock where observed in quarries and road cuts.

Most of the bedrock exposed in the region (Table 3.1) accumulated during Neogene time in a structural low in the Sendai region that crosses the frontal arc between the persistently

emergent Abukuma and Kitakami blocks. The north-northwest trend of the boundaries of this

gap suggests that it was controlled by pre-Mizuho basement structure. Andesitic to rhyolitic volcanism associated with the Mizuho orogeny extended through the Neogene, producing

various flows, agglomerates, tuff breccias, and abundant tuffs. Superimposed on the sporadic eruption and erosion of these volcanic rocks was a sequence of three marine transgressions from the southeast and the accumulation of associated terrestrial to marine clastic

sequences, separated by intervals of erosion. The limited areal distribution of individual

volcanic units, erosion between times of accumulation, facies changes, and onlap relations

of the transgressive sequences all combine to produce a complicated arrangement of geologic

units

The Quaternary deposits in the region, on which much of the earthquake damage occurred,

consist of extensive young alluvial deposits in the lowlands and a sequence of late Pleistocene terrace deposits. The terrace deposits occur along the upper reaches of the eastflowing rivers near the margin of the western highland and in the Sendai area, where they

underlie parts of the city.

The old part of Sendai City was built on the complex Sendai terrace, which consists largely

of sand and gravel some 5 to 7 m thick overlying Neogene bedrock (Figure 3.12). These sediments are slightly consolidated, and yield N values of 20 to 60 (Kobayashi and others,

1978). Recent growth of. the city led to expansion into the adjacent hills, where higher

terrace deposits as well as Neogene bedrock were encountered, and eastward onto the Holocene

coastal plain.

The alluvial sediments of the Sendai coastal plain and the other plains of the central lowland bury a late Pleistocene topography that consists of river valleys, flanking terraces,

and divides (Figures 3.11 and 3.13). At the coastline, the bottoms of these valleys lie 60

to 90 m below sea level; they extend upstream approximately along the courses of the present

surface drainage. From Ishinomaki, a deep, buried gorge extends northwestward for more than

10 km. North of Matsushima Bay, bedrock is 20 to 40 m deep along the Yoshida River for

nearly 10 km above its junction with the Naruse River, and farther north, the paleo-Naruse

valley beneath the center of the Osaki plain 30 km from the coast is still 40 m below sea

level. In contrast, the valleys buried beneath the Sendai plain shallow rather abruptly

from 50 to 60 m to less than 10 m below sea level within 6 to 8 km of the coast, near the

Rif u-Nagamachi techtonic line

The late Pleistocene topography was buried by alluvium in the past 18,000 years as the con- tinental ice sheets of the last glaciation melted and sea level rose more than 100 m to its

present position. The rise in sea level proceeded about an order of magnitude faster than

the average rate of Quaternary uplift in the region, so that the rivers draining the uplands

to the west and north found their progress gradually blocked by the rising sea. This caused

32
their sediment load to be deposited along their lower reaches, resulting in an effective

drowning of the late Pleistocene topography that left upland islands and headlands flooded

in a sea of alluvium. Along the outer side of the Kitakami block, the intricate drowned

coastline misleadingly suggests major tectonic depression of the block.

As sea level rose, gravel and sand began to accumulate within the deep channels, and near

the coast, ultimately filled them. Then, toward the middle of the liolocene, a central clay

zone that ranges from 5 to 35 m thick was deposited across most of the alluvial terrane. Finally, a sand unit 10 to 20 m thick and an overlying sequence of clay and sand of similar

thickness were deposited. This generalized alluvial section varies in detail from place to place in the central lowland. It closely represents the section beneath the Sendai plain,

except that the central clay zone is limited to the shoreward part of the plain (Figure

3.13). The Osaki plain tends to lack the shallow sand unit, whereas in the Ishinomaki area

the surface section is dominantly sand, giving way to thick clay sections in the eastern

embayments

.

The uppermost part of the alluvial section consists of an intricate assemblage of sediment

types produced as the rivers migrated about on the aggrading plain. Under such circumstances, broad ribbons of channel sand and gravel are left as the rivers change their position

from time to time, finer sand and silt are deposited in flanking natural levees in time of

flood, and organic silt and clay accumulate in the intervening backmarsh areas. Low ridges

of beach sand form along the shore. The sediment is soft and water-saturated, because it

is young and the water table is very shallow.

The surface of the alluvial deposits is quite flat, and is still crossed by the several

rivers responsible for depositing the sediment. Where not used for housing, much of the

alluvial surface is covered with rice paddies. Surface geologic mapping distinguishes the

four facies described: active and abandoned river channels, levees, intervening backmarsh

peats and silts, and coastal beach sands (H. Nakagawa, oral communication, 1978). N values

range from 1 to 10 in the Ishinomaki region, and to 20 on the Sendai plain. Frequent flood

ing of the rivers has led to the construction of many dikes, some of which were damaged in

the June 12th earthquake.

3.7 REFERENCES

3.1 Abe, K. , 1977, Tectonic implications of the large Shioya-oki earthquakes of 1933:

Tectonophysics , v. 41, p. 269-289.

3.2 Coordinating Committee on Earthquake Prediction, 1978, Unpublished packet of information used by the Japan Coordinating Committee on Earthquake Prediction in its consider

ation on June 21, 1978 of the off-Miyagi earthquake of June 12, 1978, various payings.

3.3 Dickinson, W. R. , 1979, Plate tectonic evolution of north Pacific rim: Journal of

Phy sics of the Earth, in press.

3.4 Geological Survey of Japan, 1964, Geological map of Japan: Geological Survey of Japan

scale 1:2,000,000.

3.5 Hase, K. , 1957, Geology of the alluvial plains of Miyagi Prefecture: Contributions

from the Institute of Geology and Paleontology, Tohoku University, no. 64, p. 1-45

(in Japanese, with abstract and figure captions in English)-

3.6 Hasegawa, A., Umino, N. , and Takagi, A., 1978, Double-planed structure of the deep

seismic zone in the northeastern Japan arc: Tectonophysics, v. 47, p. 43-58.

3.7 Ishiwada, Y. , and Ogawa, K. , 1976, Petroleum geology of offshore areas around the

Japanese islands: United Nations Economic and Social Commission for Asia and Pacific,

Committee for Co-ordination of Joint Prospecting for Mineral Resources in Asian Offshore Areas, Technical Bulletin v. 10, p. 23-34.

3.8 Isomi, H., 1968, Tectonic map of Japan, II, Geologic provinces: Geological Survey of

Japan, 1:1,000,000 Map Series No. 12, sheet 2 of 2.

33
3.9. Japan Meteorological Agency, no date, Disastrous earthquakes in and near Japan: Japan

Meteorological Agency scale 1:2,000,000 (publication recent but no date given).

3.10. Kanamori, H. , 1976, Seismic and aseismic slip along subduction zones and their tectonic implications in Talwani, Manik, and Pitman, W. C. Ill (eds) Island arcs, deep

sea trenches and back-arc basins: American Geophysical Union, Maurice Ewing Series

1, p, 168-174.

3.11. , 1978, Nature of seismic gaps and foreshocks, in_ Evernden, J. F., Isacks, B. L.

,

and Plafker, George (convenor and coorganizers ) Methodology for identifying seismic

gaps and soon-to-break gaps: U.S. Geological Survey Open File Report 78-943, p. 319-

334 and 904-906.

3.12. Kitamura, N., and Onuki, Y., 1973, Geological and crustal sections of the A-zone,

northeast Japan rn Japanese National Committee for Upper Mantle Project 1973, The

crust and upper mantle of the Japanese area, part II, geology and geochemistry,

Geological Survey of Japan, p. 38-60.

3.13. Kitamura, Shin, no date, Geologic map of Miyagi Prefecture: Tohoku University,

scale 1:200,000. Publication recent but no date given.

3.14. Kobayashi, H. , and others, 1978, A report on the Miyagi-ken-oki, Japan earthquake

of June 12, 1978: National Science Foundation and others, Proceedings of the Second

International Conference on Microzonation, v. 1, p. 587-614.

3.15. Matsuda, T., 1976, Empirical rules on sense and rate of recent crustal movements:

Journal of the Geodetic Society of Japan, v. 22, no. 4., p. 252-263.

3.16. , 1977, Estimation of future destructive earthquakes from active faults on land

in Japan: Journal of Physics of the Earth, v. 25, suppl. p. s251-s260.

3.17. Mogi, K. , 1968, Some features of recent seismic activity in and near Japan (1):

Earthquake Research Institute Bulletin, v. 46, p. 1225-1236.

3.18. National Research Center for Disaster Prevention, 1978a, February 20, 1978 Miyagiken-oki earthquake: National Research Center for Disaster Prevention, Science and

Technology Agency Japan, Prompt Report on Strong-Motion Accelerograms No. 14.

3.19. National Research Center for Disaster Prevention, 1978b, June 12, 1978 Miyagi-kenoki earthquake: National Research Center for Disaster Prevention, Science and Technology Agency [Japan], Prompt Report on Strong-Motion Accelerograms No. 15.

3.20. Okutsu, Haruo, 1968, Hydrogeological map of the coastal region of Bay of Sendai:

Geological Survey of Japan, map scale 1:100,000.

3.21. Otsuka, Michio, Sudo, Ken, Seno, Tetsuo, and Eguchi, Takao, 1978, Study of focal

mechanism of the earthquake on the east coast of Miyagi Prefecture, Japan: International Institute of Seismology and Earthquake Engineering, Building Research Institute, and Faculty of Science, Tokyo University, unpublished report, 3 pages, 5 fig- ures .

3.22. Page, R. A., Boore, D. M., Joyner, W. B., and Coulter, H. W. , 1972, Ground motion

values for use in the seismic design of the Trans-Alaska pipeline system: U.S. Geological Survey Circular 672, 23 p.

3.23. Research Group for Quaternary Tectonic Map, 1969, Quaternary tectonic map of Japan:

Japanese National Research Center for Disaster Prevention, Science and Technology

Agency, scale 1:2,000,000, 6 sheets (1 - Vertical displacements estimated with

geomorphological method, 2 - Vertical displacements estimated with geological method,

3 - Vertical displacements compiled from the maps Nos. 1 and 2,4- Distribution of

faults, 5 - Distribution of folds, 6 - Gipfelflur).

34
3.24. , 1973, Explanatory text of the Quaternary tectonics map of Japan: Japanese

National Research Center for Disaster Prevention, Science and Technology Agency,

167 p.

3.25. Shaw, H. R., Jackson, E. D., and Bargar, 1979, Volcanic periodicity along the

Hawaiian-Emperor Chain: American Journal of Science, Jackson volume, in press.

3.26. Shibata, 1962, Geology of the Sendai and Nanakita-Sambongi areas Miyagi Prefecture,

Science Rep. Tohoku University, 2nd Series, v. 34, p. 239-301.

3.27. Shimazaki, K. , 1978, Correlation between intraplate seismicity and interplate earthquakes in Tohoku, northeast Japan: Seismological Society of America, v. 68,

no. 1, p. 181-192.

3.28. Takagi, Hasegawa, Akira, and Umino, Norihito, 1977, Seismic activity in the northeast

Japan arc: Journal of the Physics of the Earth, v. 25, Supplement p. S95-S104.

3.29. Von Huene, R., Nasu, N. , and others, 1978, Japan trench transected: Geotimes,

April 1978, p. 16-21.

3.30. Yoshida, T. (ed.), 1975, An outline of the geology of Japan: Geological Survey of

Japan, 61 p.

3.31. Youd, T. L. , and Perkins, D. M., 1978, Mapping liquefaction-induced ground failure

potential: Proceedings of the American Society of Civil Engineers, Journal of

the Geotechnical Engineering Division, v. 104, no. GT4 , p. 433-446.

35
4. STRONGMOTTON RECOPJ)S AND DATA*

4.1 INTRODUCTION

In Japan, several government agencies are responsible for independent networks of strongmotion instruments located throughout the country. Among the larger of these accelerograph

networks are those operated by the following agencies:

Railway Technical Research Institute (RTRI), Japanese National Railways

Strong Earthquake Motion Observation Center, Earthquake Research Institute (ERI),

University of Tokyo

Port and Harbor Research Institute (PHRI), Ministry of Transport

International Institute of Seismology and Earthquake Engineering, Building Research

Institute (BRI), Ministry of Construction

Public Works Research Insititute (PWRI), Ministry of Construction

Other organizations with interest in strong-motion recording include:

National Research Institute of Agricultural Engineering, Ministry of Agriculture and

Forestry

Nippon Telegraph and Telephone Public Corporation

Japan Building Center Foundation (JBC)

The Strong-Motion Earthquake Observation Council was established in 1967 within the National

Research Center for Disaster Prevention (NRCDP) of the Science and Technology Agency.

Records recovered from particular earthquakes by the various government agencies are made

available to the public in the council's "Prompt Report" publication, which describes the

records, gives peak accelerations and epicentral distances, and contains copies of some of

the more interesting records. These and other earthquake records are published in the

council's annual report. The agencies responsible for the accelerograph networks also

report on digitization and analysis of the records collected by them that they consider

significant.

4.2 THE SMAC ACCELEROGRAPH

The SMAC strong-motion accelerograph in its various versions has been the main Japanese

strong-motion recording instrument since its development between 1951 and 1953 by the

Japanese Committee for the Standard Strong Motion Accelerograph. In its earliest form (the

SMAC-A), it consisted of a set of three mechanical oscillators which, through a series of

linkages, scribed analog traces on a waxed-paper record that was driven past the recording

pens at lcm/sec by a hand-wound spring motor. The natural period of the transducer was 0.1 sec (frequency, 10 cps), and critical damning was provided with an air piston mechanism. A sensitivity of 25 gal/mm (i.e., 25 cm/sec per mm), corresponding to approximately 4cm/g, was arranged for in the mechanical linkage and allowed recording of accelerations of lg

amplitude without the pens moving off-scale. Some of the models developed after the SMAC-A

are listed with their important characteristics in the following table.

Prepared by A. Gerald Brady, U.S. Geological Survey, Menlo Park, California.

36
Damping

(fraction

of critical)

Natural

period

(sec)

Sensitivity

(cra/g)

Recording

speed

(cm/sec)

Approximate

Number

SMAC-A

SMAC-B

SMAC-B2

SMAC-C

SMAC-D

SMAC-E2

SMAC-Q

1.0

1.0

1.0

1.0

1.0

0.60

0.60

0.1

0.1

0.14

0.1

0.05

0.05

0.05

4.0

4.0

8.0

4.0

1.0

1.0

0.5

1.0

1.0

1 .0 1.0

0.5

0.25

0.5

33

90

240

1821

45

1 I

The last column indicates the distribution of the various models in 1975 obtained from the

response to a questionnaire from the author while at the International Seismological Centre

in Edinburgh. An additional 400 strong motion instruments were not included in this

response and the total in March of 1974 was actually about 850 (Kuribayashi and others,

1977). By March of 1978 the number of SMAC-type instruments installed throughout Japan in

structures or at ground level had reached 1200 (Iwaskai and others, 1978). Additional

instrumentation, for example electromagnetic recorders, and special downhole systems are

not included.

It is important to note from this table that the majority of the instruments of the SMAC

type that are operated in Japan at this time have frequency-response characteristics that

are different from the most common modern United States instruments that record on 70-mm

or 7-in. film. In particular, the SMAC response at frequencies higher than 7 cps (for

the SMAC-B2) or 10 cps (for the SMAC-A, -B, and -C) has been designed to be much less than

we are used to seeing with United States instruments such as the SMA-1 or RFT-250. A glance at recordings from these earlier SMAC instruments confirms this lack of highfrequency content.

Another feature of the records made by SMAC-type instruments is that the pens draw arcshaped curves that have constant radius which are obvious in the higher-amplitude motions.

Although peak accelerations can be scaled off without requiring significant correction, it

is evident that after digitizing a record with high amplitudes correction procedures must

be adopted to handle this instrumental behavior before arriving at true time histories.

Recent developments in Japanese instrumentation have included higher natural frequencies (in

the SMAC-D, -E2 , and -Q instruments), the use of moving-coil electromagnetic transducers

(in the ERS accelerograph developed by the Earthquake Resistant Structures Laboratory,

Port and Harbor Research Institute), and recording on analog magnetic tape (in the SMAC-M

Instrument). The two instruments in the Engineering Building at Tohoku University, which

recorded 240 gal (240 cm/sec 2

, or 0.24g) and 980 gal (lg) at ground level and at the

9th floor, respectively, are SMAC-M instruments operated by the Building Research Institute.

4.3 ACCELERATION RECORDS AT GROUND LEVEL

Figure 4.1 shows the northern part of Japan and the locations of the strong-motion accelerograph stations that provided ground level, basement, or free-field records of the June 12,

1978, earthquake. The codes for the stations are indicated (for example, TH020) and their

pertinent characteristics have been obtained from National Research Center for Disaster

Prevention (1976) and are reproduced in Table 4.1. In addition to the records shown on the

map, there exist 61 additional records taken at basement, first-floor, or ground level,

mostly in Tokyo or its vicinity. Of these 61 records, the highest peak acceleration is

0.045g at an epicentral distance of 305 km.

The epicenter was provided by the Japan Meteorological Agency (JMA) and published by the

National Research Center for Disaster Prevention, (1978). We have chosen to use these

epicenter coordinates, namely, 38°09'N, and 142°13'E, in the sections of this report that

discuss the epicenter and epicentral distances.

Figure 4.1 also shows the peak accelerations recorded at ground level, or at the basement

of first-floor level in structures. The cities of Sendai and Miyako each have more than

one recording. Each set of the three numbers shown gives the peak acceleration recorded

37
n

o

TH020 Aomori

21,21,9 (F)

TH006 Akita 1°

25,23,13 (F)

THOI5 Yuhei Br

25,34,13 (F)

O

TH033 Shiogama

266,288,166 (F)

TH030 Tohoku Univ

240, 190 , 150

TH038 Sumitomo

253 , 227, 120

TH0I8 Sendai Kokutetsu

438 , 238 , 100

100 KM

TH029 Hachinohe

65,60, 31 (F)

TH032 Mazaki Br~

104, 75, 30

TH009 Miyako

80,92,90

TH0I4 Miyako

150, 113,47 (F)

TH0I9 Ofunato

126,170,61 (F)

TH0I6 Kaihoku Br

200, 294, 113 (F)

Epicenter

June 12 . 1978

TH02I Taira Br

75, 88, 38 (F)

TH0I3 Onahama

48, 50, 21 (F)

KTOOI Tokai

88, 125, 30

Ibaraki

138' 140' 142'

Figure 4.1 Locations of stations providing ground level, basement, or free-field records of the June 12, 1978 earthquake. Peak

values in the two horizontal and the vertical directions are given in cm/sec/sec. An (F) following these values indicates

an approximate free-field station.

38
39
in two perpendicular horizontal directions and in the vertical direction. For most groundlevel stations the two horizontal directions referred to are north-south and east-west, in

that order, whereas the instruments at the lowest level of a structure are generally aligned

in the longitudinal and transverse directions of the structure and acceleration values are reported in that order. The acceleration units used are cm/sec^, commonly called a gal.

Conversion to g units is simply, if slightly inaccurately, accomplished by dividing by

1,000. An (F) following the acceleration levels indicates that the recording could be con- sidered a free-field recording, although it must be realized that any instrumental housing

disturbs the true free-field motion.

The section on seismicity indicates that, although the epicentral distance to Sendai is

about 110 km to 115 km, it might be inferred from the aftershock pattern that the main shock

rupture plane actually reached a point within about 75 km of Sendai, measured in three dimensions, or within a distance of 55 km, measured in plan. Such a conclusion would play a significant part in studies of the attenuation of peak accelerations for this earthquake, particularly for those stations within latitude 37.5° and 38.5° north that lie approximately due

west of both the epicenter and the closest point on the rupture plane. Other stations on the east coast would not be affected because, for each of these, the epicentral distance is

approximately equal to the distance to the closest point of the inferred rupture surface.

To illustrate this point in rather elementary fashion, Figure 4.2 shows the peak horizontal

accelerations for three groups of ground-level records plotted against epicentral distance.

A distinction is made between stations on the coast in a generally northern direction from

the epicenter, those generally to the west, and those on the coast to the southwest. A curve labelled "Attenuation to the north" passes through the first group to the north and

is a satisfactory approximation for the points of the third group, those to the southwest.

Accelerations for the records lying to the west are higher than this curve would indicate,

but on moving the points so that their plotted distance is the distance in plan, to the

nearest point of the rupture, 60 km to the west of the indicated epicenter, a better fit

is possible to an extrapolated attenuation curve. This curve only shows the trend of peak

accelerations attenuating with distance - the scatter is evident and its explanation in

individual cases will have to wait for detailed study.

4.4 INTENSITIES

Intensities for earthquakes in Japan are prepared by the JMA from information received at their headquarters from observational stations throughout the country. Like their Modified

Mercalli equivalents used in the United States, JMA intensities are generally expressed in

Roman numerals, but in the tables and figures of this report we have used Arabic numerals

for clarity in their presentation.

A brief description of the JMA intensity levels is given in Table 4.2. A comparison of these

descriptions with those of the Modified Mercalli Intensity Scale (Wood and Newman, 1931), the

standard intensity scale in use in the United States, allows an approximate translation from

JMA to MMI values. Considerable engineering judgment regarding the dynamic behavior of the

various buildings and other structures in both cultures would be required for such a comparison to be accurate and useful. One possible comparison is shown in the following (Trifunac

& Brady, 1975).

JMA 0 1 2 3 4 5 6 7

MMI 1 2 3 4 5 6 7 8 9 10 11 12

Figure 4.3 is a highly idealized isoseismal map constructed from the plotted JMA intensities

at specific locations. The indicated elongation of the isoseismals in the north-south diretion is controlled by the locations of the lines as they pass over the land area, where

observations are possible. Dashed lines across the Sea of Japan serve only to connect the

two portions of the several isoseismals. No attempt is made to estimate the locations in

the Pacific Ocean to the east.

The boundary between JMA 4 and 5 is reasonably well constrained to the north and west but

less so to the south. The other isoseismals are more arbitrarily chosen. If a circular

area were approximated to the JMA 5 region, its center would lie close, in plan, to the

40
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42
Table 4.2 JMA Intensity Scale

0: Not felt. Shocks too weak to be felt by humans and registered only by seismographs.

1: Slight. Extremely feeble shocks felt only by persons at rest, or by those who are observant of earthquakes.

2: Weak. Shocks felt by most persons; slight shaking of doors and Japanese latticed

sliding doors (shoji).

3: Rather strong. Slight shaking of houses and buildings, rattling of doors and shoji,

swinging of hanging objects like electric lamps, and moving of liquids in vessels.

4: Strong. Strong shaking of houses and buildings, overturning of unstable objects, and

spilling of liquids out of vessels.

5: Very strong. Cracks in sidewalks, overturning of gravestones and stone lanterns, etc.; damage to chimneys and mud and plaster warehouses.

6: Disastrous. Demolition of houses, but of less that 30% of the total, landslides,

fissures in the ground.

7: Very disastrous. Demolition of more than 30% of the total number of houses, intense

landslides, large fissures in the ground and faults.

westernmost down-dip end of the inferred rupture surface mentioned above. This lends credence to the conclusion that for this earthquake the distance from points on the ground surface to the nearest point of the rupture surface is the distance of importance in attenuation

and related studies.

4.5 RECORDS FROM STRUCTURES

The Prompt Report (NRCDP, 1978) lists 191 strong motion records of the earthquake at epicentral distances ranging from 80 km (TH016 - Kaihoku Bridge) to almost 600 km, and includes

records from 46 multi-instrumented structures such as buildings, bridges, and dams. About

100 of these records are from multi-instrumented buildings in the Tokyo area, at epicentral

distances between 355 and 370 km. Although ground level accelerations here are low, some structural records have peaks of 10 percent g.

A selection of 22 instrumented structures are listed in Tables 4.3 to 4.6 with their instrument locations and peak accelerations at the various levels. Table 4.3 lists two low-rise

buildings with less than six stories, Table 4.4 lists five medium height buildings between

six and fifteen stories, Table 4.5 lists nin high-rise buildings with more than 15 stories,

and Table 4.6 lists five bridges and a dam. All structures included in the tables have an associated ground level or basement record, and some of these have been included in Table 4.1

in the earlier section on ground level records.

The lists include the names, addresses and coordinates of the stations. Buildings are described by the number of stories above and below ground, while bridges, and the dam, have

their length and width listed. The instrument locations in the buildings are indicated by

story, including basement and penthouse or roof. For the bridges and dam the ground level

recording station is usually off to one side of the structure on firm ground, while the

structural recording station is usually on a pier cap, effectively at deck height. The peak

accelerations at the listed instrument locations are given in cm/sec/sec (or gals) in groups

of three - two horizontal and vertical component. Although the horizontal components are often listed as N-S and E-W in Japanese literature, these component names may actually be

translated to mean the longitudinal and transverse axes of the recorder, and therefore also

the longitudinal and transverse directions of the structure.

43
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The investigating team inspected three of the structures on these lists: the Faculty of

Engineering Building at Tohoku University, Aramaki, Sendai, described in a later section of

this chapter; the Sumitomo Sendai Building, Chuodori, Sendai, described in the chapter on earthquake performance of buildings; and the Kaihoku Bridge, Inai, Ishinomaki, described in

damage to transportation structures.

4.6 A Comparison with the Recorded Results of the San Fernando Earthquake, 1971 .

An overall comparison, from an engineering viewpoint, of the recorded strong-motion data from

the San Fernando, 1971, and Miyagi-ken-oki, 1978, earthquakes can be based on the following

information.

1. The San Fernando magnitude was 6.4 with a focus at a depth of 13 km, the rupture propagating to the surface at the northern edge of the large metropolitan area of the city of Los Angeles and its surrounding cities and communities. The tall buildings of the city

lie between 21 and 50 km from the epicenter.

The Miyagi-ken-oki magnitude was 7.4 with a focus at a depth of 30 km, the rupture

probably travelling deeper but at a shallow angle towards the metropolitan area of Sendai. The aftershock pattern indicates that the rupture on the fault possibly approached

as close as 75 km to Sendai. The high rise buildings of Tokyo are 350 km and more from

the epicenter and from the nearest part of the fault rupture.

2. The closest recording to the San Fernando epicenter was at Pacoima Dam, at 8 km, or 4 km

from the surface faulting, where the topography is extremely complicated.

The closest recording to the Miyagi-ken-oki epicenter was the ground level instrument at Kaihoku Bridge at 80 km. The closest distance to the rupture, at depth, however, is

closer to 60 km and this distance in plan is 20 km. The peak acceleration recorded here

was 0.29g.

3. At San Fernando, the next closest record was a 7-story building, the Holiday Inn at 8244

Orion, Los Angeles, with ground level accelerations of 0.27g.

At Miyagi-ken-oki the two buildings with complete instrumentation, that is at least two recorders including the lowest level of the structure, are at epicentral distances of 115

km, which reduce to 75 km to the nearest fault rupture, or 55 km in plan. Peak accelerations at ground level range up to 0.25g. None of these buildings, in either earthquake,

suffered any severe structural damage; minor cracks in columns was the extent of the

observed damage to structural members.

4. A total of 35 buildings higher than six stories produced complete sets of records from

the San Fernando event at epicentral distances from 24 to 50 km, and ground accelerations

ranging from 0.26g down to 0.04g. Minor cracking of structural members and extensive

damage to nonstructural components were common.

The Miyaki-ken-oki event produced no further sets of records from tall buildings until

the Tokyo area was reached, at epicentral distances of 340 to 370 km where acceleration

amplitudes were .03g and less.

5. Recordings sufficient to give a useful engineering indication of ground accelerations and

associated structural performance exist for San Fernando at epicentral distances from 20

km out to 75 km.

The same type of information for Miyagi-ken-oki ranges in distance from 80 km (reduced to 60 km, see above) out to about 200 km. Structures involved here are bridges, with ground

level and pier cap accelerations, and various harbor installations.

6. The San Fernando records have been the basis for a large number of engineering and seismological studies, particularly, of course, the digitized versions of the records. Even

now, there are still complete sets of building records that could be analyzed to study

particular building behavior.

47
4 . 7 Tohoku University, Engineering Building

Tohoku University is situated in the northwest part of Sendai, in the district of Aramaki, an area of hills and steep terrain. The Engineering Building is a reinforced concrete framed

structure and is built on a reasonably flat area, but a steep cliff falls off close to the rear of the building. Figure 4.4 is a photograph of the central 9-story tower and also shows

the two lower levels which cover a larger plan area. A floor plan and two elevations are shown in Figure 4.5. Two SMAC-M instruments are installed in the building, at ground level

(there is no basement), and at the 9th floor level. They are on the same vertical line,

against an exterior wall of the central tower, as shown in Figure 4.5. These instruments

record on FM analog tape, and functioned correctly during the earthquake.

The analog tape recordings were recovered and analyzed by the Building Research Institute,

which was responsible for the instruments. After analog-to-digital conversion, a computer

analysis was possible, and was completed within seven days (Watabe, 1978). The following

figures are reproduced from the preliminary work.

Figure 4.6 shows a 25-sec portion of the record from the ground level instrument, after A/D

conversion. The peak horizontal accelerations are 240 and 190 cm/sec/sec, and the peak vertical acceleration is 150 cm/sec/sec, as indicated in Table 4.1. Figure 4.7 shows a similar

plot of the 9th floor record peak values of 980, 480, and 300 cm/sec/sec (Table 4.4). A preliminary analysis of the high-amplitude oscillations in the horizontal directions at this

level indicate that the corresponding displacements are approximately 10 in (25.4 cm). This

is consistent with the damage in the interior of the building, (discussed in Chapter 5), and

indicates the building was approaching the structural damage state.

Figures 4.8, 4.9 and 4.10 show the correction procedures applied to the three ground level

components. Acceleration velocity and displacement are plotted. Figures 4.11, 4.12, and

4.13 show spectral analyses performed on these records. The analyses include absolute acceleration response, relative velocity response, relative displacement response, and pseudo

velocity response, the last being plotted in the tripartite 3-way response spectrum style.

4.8 Tracings of Records

Tracings of sections of the records from some of the closer stations are included. Figure

4.14 is the ground level record on the premises of Shiogama Harbor Office, site No. TH033

,

with peak values scaling off at 266, 288 and 166 cm/sec/sec. The arc-shaped curves drawn by

the hinged arms are clearly evident on the high-amplitude excursions. Figure 4.15 shows the

ground level record for site No. T11019, the breakwater of Ofunato Harbor, with peak values

of 126, 170 and 61 cm/sec/sec. The amplitudes here are sufficiently high in a few instances

to show their arc-shaped character. Figure 4.16 shows the first basement record at the J Nit building at Sendai. The peak NS reading of 438 cm/sec/sec is the highest ground level amplitude in the city. The building has six stories, but no record was recovered from the station

at the sixth floor. Consequently it is difficult to analyze this basement record and to ascertain the extent of the interaction between building and ground.

4 . 9 References

4.1. National Research Center for Disaster Prevention; Science and Technology Agency

(Japan), March 1976, Strong-motion earthquake records in Japan, 1974, vol. 19.

4.2. National Research Center for Disaster Prevention, July 1978, June 12, 197b, Miyagi-kenoki Earthquake: National Research Center for Disaster Prevention; Science and Technology Agency (Japan), Proupt Report on Strong-Motion Accelerograms No. 15.

4.3. Wood, ii. 0., an.l Newman, K. (1931). Modified Mercalli Intensity Scale of 1931, bull.

Seism. Soc. Am., 21, 27 7-283.

4.4. Trifunac, M. 0. , ami Brady, A.G. (1975). on the correlation of seismic intensity

scales with the peaks of recorded strong ground motion, Bull. Seism. Soc. Am., o5, 1, 139-162.

48
Figure 4.4

Engineering Building,

Tohoku University,

Aramaki, Sendai.

.EXPANSION JOINT

Wtt" v? firip fn? Yin?

ni

6 @ 3.3 m

I

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Figure 4.5

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the Engineering Building

SECTION AA

49
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Building

1000-

-1000-

Time 0.

1000-

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Time 0.

1000-

--1000-

Figure 4.7 Three components at 9th floor level,

Engineering Building.

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4.5. Kuribayashi, E., Tsuchida, H. , and Watabe s M. (1975). Maintenance of the Strong Motion

Accelerograph and Data Processing of Records Obtained, Proc. 7th Conference UJNR Wind

and Seismic Effects, May 1975, Tokyo, Japan.

4.6. Iwasaki, T. , Katayama, T. , Kawashima, K. , and Saeki, (1978), Statistical Analysis of

Strong Motion Acceleration Records Obtained in Japan. Proc. 2nd Int. Conf. on Microzonation, November 1978, San Francisco, Calif., USA.

4.7. Watabe, M. , 1978. Personal communication, and tentative report by Building Research

Institute.

60
5. EARTHQUAKE PERFORMANCE OF BUILDINGS*

5 . 1 Introduction

As shown in the aerial photograph in Figure 5.1 and in Figure 5.2, Sendai is a large modern

city. It is the center for commerce and industry for Miyagi Prefecture. Many buildings in

the city can be considered to be modern highrises, in excess of five to six stories. In particular, the downtown center of the city has a multitude of modern buildings in the 10- to 20-story range. The map in Figure 5.3 shows the metropolitan Sendai area; Table 5.1 identifies the points of interests on the map.

The U.S. team arrived in Sendai June 23rd, 11 days after the earthquake. The first impression upon entering the city was that a significant earthquake had not even occurred. This

was due in part to the speed with which the Japanese authorities had responded to the disaster. Evidences of damage that would have otherwise impeded the normal operations of the city

had already been cleared away. Upon closer inspection, minor facade damage became obvious

(Figures 5.4, 5.5, 5.6, and 5.7. This sort of damage was not widespread by any means and numerous modern buildings did not show any damage to their architectural veneers or glazing.

It was reported that many chimneys and stacks had collapsed or were severely damaged (e.g.,

Figures 5.8 through 5.10).

As the investigation proceeded, it became obvious that numerous pockets of damage existed

throughout the city. These apparently are correlated to the local geological and soil conditions, discussed in Chapter 3. Soil conditions in the downtown Sendai area (Figure 5.3,

within 2 km N and W of the railway station) generally are quite good. Many highrises in this

area have raft foundations and are situated on a gravel-type soil. The area to the west and

south of the Hirose river are stable terrace deposits. However, the area to the east of the

railroad and to the south of Japan National Highway 45 is a former agricultural area. The

underlying soil is a young alluvial deposit, and from an engineering point of view, the soil

conditions are quite poor.

This chapter begins with an overview of seismic engineering and construction practices in

Japan. This will be followed by a discussion of investigations of commercial and retail

establishments, schools, apartment buildings, and single family residences. Industrial

facilities are covered in Chapter 6.

5.2 Seismic Engineering and Construction Practice

The general seismic design philosophy in Japan is that it is not economically feasible to provide complete protection against all earthquakes. Prevention of loss of life is the overriding concern. Thus, the design criteria are aimed at preventing structural damage aud

minimizing damage due to moderate earthquakes, and avoiding collapse or serious structural

damage due to severe, infrequent earthquakes.

The Japan Building Code governs the design of buildings and related structures such as chimneys and elevated water towers. The method of seismic coefficients is similar in concept to the U.S. equivalent lateral force method recommended by the Uniform Building Code (1976) and

other standards. It is still commonly used in Japan, particularly for buildings five stories

and less in height, but it is recognized as being unsuitable for many flexible structures.

Dynamic analyses are required for buildings over five stories in height.

There are a number of general guidelines and requirements, which are discussed in further

detail in Refs. 5.1 - 5.4. For example seismic calculations are required in buildings of more than 100 m^ floor area used for schools, hospitals, and places of public assembly, and

in structures having more than two stories or 200 m floor area. No buildings with total

floor areas exceeding 3000 m^ can be wood, nor can buildings in excess of 13 m in height

be wood or unreinforced stone, brick or concrete block masonry, or concrete. There are

additional detailing requirements that depend on the construction material.

* Prepared by Bruce Ellingwood, Center for Building Technology, National Bureau of Standards,

Washington, D.C.

61
Figure 5.1 View of the downtown area of Sendai (Tohoku Electric

Power Company photograph)

62
Figure 5.2 Typical buildings of the downtown Sendai area.

63
Figure 5.3 Map of Sendai City, showing major landmarks

and sites of damaged structures. See Table 5.1

for identification

64
Table 5.1 - Numbered sites in Figures 5.3 and 6.1

1

.

Sendai railway station

2

.

Second government building

3. 77 Bank building

4

.

Sumitomo Insurance Building

5

.

Japan National Railway bui lding

6

.

Maruyoshi building

7

.

Obisan building

8

.

Kinoshita building

9

.

Maruhon building

10

.

Yazaki Industries

11

.

Taiyo Fisheries Plant

12. Paloma Sendai building

13. Tonan High School

14. Haronamachi Gas Plant

15. Cement plant

16

.

Hirose Bashi Bridge

17. Tohoku Institute of Technology

18

.

Aoba Castle

19

.

Tohoku University

20. Sendai Substation, Tohoku Electric Power Company

21

.

Izumi City High School

22. Yuriage Bridge

23. Abukuma Bridge

24. New Sendai Power Plant, Tohoku Electric Power Company

25. Tohoku Oil Company, Ltd . refinery

26

.

Ono Bridge

27

.

Kimazuka Bridge

28. Eaigawa Railway bridge

29. Kaihoku Bridge

30. Tenno Bridge

31

.

Iinogawa Bridge

32. Yanaizu Bridge

33. Toyoma Ohashi Bridge

34. Maiya Ohashi Bridge

35. Kin-no Bridge

36. Kitakami Ohashi Bridge

37. Sendai Ohashi Bridge

38. Sunny Heights Apartment building

b5
Figure 5.4 Minami Machidori Building,

Sendai. The cracking to the

brick veneer is typical for

many similar buildings in

the city.

Figure 5.5 Minami Machidori Building. Closeup o the lower floors of the building.
Figure 5.6 Second Eastern Building Company Building, Sendai. A

typical modern building in Sendai; the only apparant

damage to the glazed tile veneer on the exterior was cracking on spandrels and shear walls

.

Figure 5.7 Second Eastern Building Company Building. Closeup of exterior

wall

.
13

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The seismic base shear V is calculated by multiplying the sum of dead and a portion of the

live load by a seismic coefficient k that is calculated as the product of a standard seismic

coefficient k a site seismicity coefficient k-^ and a soil and building type coefficient,

k2 . Coefficient ki is determined from a map, and takes into account the intensity and frequency of earthquakes anticipated for the location. For Sendai and environs, k-^ = 0.9.

Coefficient k

2 accounts for the characteristics of the ground at the site and the probable

mode of behavior of the building. The product of k^k

2 is in no case taken as less than 0.5.

This procedure is summarized as follows:

V = kW

W = Dead plus a portion of live load

k = k

Q

k

1 k2

k = standard seismic coefficient

o =0.2 for heights less than 16m

= 0.2 + ^~ (h-16) for heights greater than 16m

4 = 0.3 for wood structures on soft ground (alluvium greater

than 30m thick, reclaimed marshes, etc.)

k-^ = Site seismicity coefficient (map provided)

1<2 = Soil and building coefficient

Values of k->

Rock Wood Steel R/C Masonry

Sand-Gravel 0.6 0.6 0.8 1.0

Sandy Clay 0.8 0.8 0.9 1.0

Note that k

Q varies with the height of the building; however, building period does not enter

the seismic force equation explicitly.

The Japan Building Code permits the allowable stresses to be increased by a factor of 100

percent for earthquake, while most standards in the U.S. permit only 33 percent increase.

However, U.S. standards (e.g., Uniform Building Code, 1976 Edition) do not include live load

in determining W, except for warehouse and storage occupancies. The basic force coefficient

k

Q is larger than the factor C in the Uniform Building Code, to which it is analogous.

Unreinforced masonry buildings are generally two stories or less in height. A reinforced

concrete collar beam must be provided at the top of each story wall, and the height-thickness

ratio of walls must be less than 15.

Earthquake resistance of wooden buildings is generally provided by specifying minimum lengths

of walls and diagonal bracing. The Japanese Building Code requires a minimum length of wall

or a framework with diagonal bracing for wooden buildings over 50 m^ in floor area and two or more stories in height. The required bracing or length of wall depends on the floor area. Bracing must be provided for horizontal floor diaphragms also. These requirements result in

a structural frame that is stiffer than those found in single family dwellings in the U.S.

Earthquake resistance in steel buildings is provided either through the use of momentresisting frames or through diagonal bracing. When braces are used as earthquake resisting

elements, it is normal practice to design them so as to carry all of the horizontal force.

An example of such a structure is a steel framed furniture warehouse on the outskirts of

Sendai shown in Figure 5.11. There were many examples where the bracing members buckled

under stress reversal or the connections failed. A number of the transverse diagonal braces

used in this warehouse sheared at their bolted cross connections (Figure 5.12).

69

Many modern high-rise buildings in Sendai have steel frames, and these generally performed

very well during the earthquake. One example is the Sendai Second Government Building in

the downtown area (No. 2 in Figure 5.3), a 17-story structure built in 1973 (Figures 5.13

and 5.14.) The building is situated on a raft foundation, where the underlying soil conditions are good. The frame was designed by dynamic analysis for a maximum base acceleration

of 0.2 g. The building is instrumented with strong motion accelerometers at the 15th floor

and second basement levels, and a downhole at 40 m below grade. The building suffered virtually no damage, although there was some minor diagonal cracking in the concrete stairwells

leading to the basement.

A number of changes were made to the Japan Building Code in 1971, many of which relate to the

design of reinforced concrete buildings. While the standard seismic coefficient remained

0.2, requirements for minimum spacing of column ties became more stringent in the 1971 edition. In the pre-1971 code, the maximum tie spacing in normal weight concrete columns was

300 mm or 15 times the diameter of the main reinforcement; in the new code, the maximum spacing permitted is 100 mm. The minimum allowable bar cover is 30 mm. Section A. 6. 5. 3 of ACI

Standard 318-77 (Ref. 5.7) and Chapter 11 of Ref. 5.6 have similar requirements that limit

vertical spacing of ties in columns to 4 in (100 mm) at locations above and below beam-column

connections. Undeformed reinforcing bars were commonly used in Japan until about 10 years

ago. The 1971 Japan Building Code requires the use of deformed bars, however.

Numerous modern buildings in Japan, particularly those between six and fifteen stories, use

the SRC (Steel and Reinforced Concrete) system, in which the reinforcement is provided by

embedded steel shapes in conjunction with conventional reinforcing bars. The fire resistance

and safety against buckling are high, while the the cross sectional dimensions of the structural members can be made smaller than in conventional reinforced concrete structures. The

systems is quite ductile. The Sumitomo Insurance Building in downtown Sendai (No. 4 in

Figure 5.3) is an example of such a structure (Figures 5.15 - 5.17). This is a modern 18-

story SRC building with continuous reinforced concrete shear walls around the elevator core

and on the outside transverse walls. The interior shear walls around the elevator core and

some of the construction joints in the stairwells and nonstructural partitions showed minor

diagonal cracking. However, the main structural elements are believed to be undamaged. It was reported that after the February 1978 earthquake, the Sumitomo Insurance building had

diagonal cracking in secondary walls and that after the June earthquake, these had become

more extensive. Vibration tests conducted before and after the February earthquake showed

that the fundamental frequency decreased from 1.2 Hz to 1.0 Hz due to cracking. The structural damping also increased. The Sumitomo Insurance Building had strong motion instrumentation in the 2nd basement, the 9th and 18th floors (see Chapter 4). Peak accelerations of

0.26 g (2nd basement) and 0.56 g (18th floor) were recorded during the June 12 earthquake.

The 77 Bank Building is located in downtown Sendai not far from the train station (No. 3 in

Figure 5.3). An exterior elevation and a floor plan are shown in Figures 5.18 and 5.19.

The basements and first three stories are SRC, while the remainder has a steel frame. Like

many of the high-rises in the main area of the city, it has a raft foundation. As shown in

the plan, the building has an eccentrically located elevator core, surrounded with reinforced concrete shear walls. A quick walk-through inspection revealed no signs of damage

to interior columns, their stucco panel facing, or the marble veneer in lower story corridors. The building was completed in 1977 (hence its name), and was designed according to the 1971 seismic code.

5 . 3 Commercial and Retail Establishments

The map of Sendai in Figure 5.3 shows a shaded area east of the railroad tracks and south of

Japan National Highway 45. Until about 10 years ago, this was an agricultural area that was

mainly rice paddies. The water table is known to be quite high and, from an engineering

point of view, the soil conditions are poor. There are numerous buildings in the two- to four-story range which are used for small business, retail, and other commercial establishments. These buildings typically have a ground-story used to display merchandise with large

open areas and few walls. The upper floors are used for offices and for storage. This type

of building layout creates a structure in which walls are not placed symmetrically with

respect to the center of the structure and in which the first-story lateral force-resisting

elements are relatively flexible when compared with the upper portions of the structure.
72
Figure 5.15 Sumitomo Insurance Building, Sendai, plan view.

The building has continuous shear walls around

the elevator core and on the transverse

outside walls.

7 3
Figure 5.16 Sumitomo Insurance Building.

Exterior Elevation
75
In this general area, referred to as Oroshicho, numerous buildings suffered extensive damage

and there were several reinforced concrete structures which collapsed. The latter were all

in the two to four-story range. Most of the buildings in this area were reported to be

built on pile foundations, although no particulars for specific buildings were obtained. The

collapsed reinforced concrete structures were all designed and built in the middle 1960's

prior to the adoption of the 1971 seismic building code.

There were no acceleration records obtained in this area. However, shaking in the N-S direction apparently was stronger than in the E-W direction, at least in the area visited, since

most of the damage observed to buildings resulted from strong motion in the N-S direction.

There was extensive evidence of ground settlement in the Oroshicho area, including settlement

of asphaltic concrete sidewalks and slumping around building foundation walls, as in Figures

5.20, and 5.21.

Maruyoshi Building (No. 6, Figure 5.3). This was a three-story reinforced concrete frame

building, one span by three, with the long axis of the building running in the E-W direction.

There was a 2 m overhang on the north side of the structure (Figure 5.22). The wall shown

at the west end was continuous from the second-story on up. The building had a flexible

first-story. The building suffered extensive damage to the first-story (Figure 5.23) and,

as shown in Figure 5.24 was tilting toward the north. The first story columns on the south

side of the building failed in shear due to the strong N-S motion. A detail of the beamcolumn joint where the second-story floor beam frames into the first-story column is shown

in Figure 5.25. Column ties appeared to be spaced at about 300 mm. The shear wall on the

west end of the structure appeared to be undamaged. Unfortunately, this caused the structure to behave as an inverted pendulum and caused the first-story columns to accept even more

shear. Note the use of the undeformed bars in the beam-column joint (Figure 5.25).

The building was being demolished at the time it was visited.

Obisan Building (No. 7, Figure 5.3) . This was a three-story reinforced concrete frame building with one span in each direction (Figure 5.26). The portion of the building which overhung

the column line by about 2 m contained a heavy stairwell. There were no openings in the over- hanging part of the building, which added to the eccentric mass. Coupled with the strong N-S

motion, this caused a failure in torsion as the columns at the west end of the building were unable to withstand the forces resulting from the large eccentric mass. Figures 5.27 and

5.28 show the Obisan Building after the earthquake viewed from the north and south, respectively. It may be observed that the upper stories rotated almost as a rigid body when the

first floor columns failed. The first-story of the building had been used as a display area, and was completely open. A detail of the SE column is shown in Figure 5.29 and in the plan.

As shown in Figure 5.30, the first floor support beams were practically resting on the ground

at the west end of the building. The walls above the first-story suffered extensive cracking

during the earthquake, but remained intact (Figure 5.31). The reinforcing bars that can be seen are undeformed.

Kinoshita Building (No. 8, Figure 5.3) . This three-story reinforced concrete frame building,

two spans by six, had its main axis in the N-S direction. As shown in Figure 5.32, there was extensive diagonal cracking on the east face. The first floor on the west side of the building, Figure 5.33, was used as a showroom. Unlike the backside of the building, where the

columns were stiffened by spandrels, the columns on the west side were relatively flexible,

and there appeared to be very little damage on that side of the building. The brick facing

on the west side remained intact. The interior columns on the east side of the building

showed large shear cracks and buckling of exposed undeformed bars. A reinforced masonry partition wall also failed here. It is apparent that most of the seismic force was attracted to the relatively stiff east side of the building. In addition, there appeared to be significant

settlement of about 100 - 150 mm in the interior of the building on the east side. This,

along with the relative stiffness of the east face, would explain the diagonal cracking pattern observed on the east face as well as cracking patterns observed in columns and panels.

Failures of this sort were also observed following the Niigata earthquake (Okamoto, 1973).

Maruhon Building (No. 9, Figure 5.3) . This six-story reinforced concrete frame building is

located one block of west of the Kinoshita Building. There was a construction gap of approximately 30 mm between the two parts of the building and no evidence of pounding. There is

7 6
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Figure 5.26 Plan and column details of Obisan Building, Oroshicho area

80
Figure 5.27 Obisan Building, viewed from the North. This three story

reinforced concrete frame building had a heavy eccentric stairwell

cantilevered over the column line at the right end of the building.

Figure 5.28 Obisan Building, viewed from the south. The upper stories rotated

as a rigid body when the first floor column support was lost.
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83
Figure 5.32 Kinoshita Building, Oroshicho area, of Sendai. Extensive

diagonal cracking was observed on the east face (rear) of the

building

Figure 5.33 Kinoshita Building. The brick facing on the west side of the

structure showed little sign of damage.

1

84
extensive diagonal cracking in the panels between window openings on both east (Figure 5.34)

and west faces (Figure 5.35); this damage is especially severe on the west face, as shown in

the detail in Figure 5.36. The decorative ceramic brick facing on the north side of the

building did not appear to be damaged.

Despite the level of damage in the Oroshicho area, many buildings performed quite well. As

an example, Figure 5.37 illustrates a 9-story building which was only slightly damaged. No

details about its construction are known.

Yazaki Industries (No. 10, Figure 5.3) . Figure 5.38 shows portions of the three Yazaki

buildings. The building on the left has a steel frame with diagonal bracing used as a warehouse. The middle building (tilted) has a four story reinforced concrete frame, 3 spans by

5, which was used as an office building. It was built around 1970. The design acceleration

was 0.2 g. The two-story building on the right, a steel frame completed in 1973, was used

as a showroom. The buildings are aligned in the N-S direction.

I The strong N-S component of the earthquake caused shear failures in the first story concrete

columns in the middle building and a collapse at the ground story, causing the entire buildI ing to tilt north. This racked the two-story steel frame building forward, causing extensive

damage to the steel frame and popping glass panes from showroom windows. The area of impact

between the two buildings is shown in Figures 5.39 and 5.40 and 5.41. Figure 5.42 shows a detail of the beam-column joint at the top of the first-story column on the east side of the

1 middle building. The column shear failure extended up into the beam. A detail of the column

on the northeast corner of the middle building in Figure 5.43 shows the gross vertical displacement and badly distorted bars in the columns. Unlike the other collapsed buildings in the Oroshicho area, deformed reinforcing bars were used in the Yazaki building. The building service systems between the two impacted buildings were damaged.

The steel frame warehouse behind the collapsed building (Figure 5.38) did not appear to be

' damaged. The warehouse contained numerous heavy tubular steel frame storage racks with

diagonal braces, as shown in Figure 5.44. The storage racks stand approximately 7 m in

height and are anchored to the concrete floor by being bolted or welded to steel plates in

j the floor. Although none of the racks had collapsed, the bottom diagonal braces appeared to

1 have buckled on several racks, as shown in Figure 5.45.

On an adjacent site to the south of the warehouse, there are two five-story reinforced con-

' crete frame apartment buildings with shear walls oriented in the N-S direction. There was no apparent damage to either of these buildings, one of which is shown in Figure 5.46.

Paloma Building (No. 12, Figure 5.3) . This reinforced concrete frame structure faced north

and was located on Japan National Highway 45. It was a three-story rectangular building, two

spans by three, with a shear wall on the west end of the building. The first floor was used

for display, and had a large open area on the north and east side of the first floor. The

main axis of the building ran in the E-W direction. Figures 5.4 and 5.48 show the Paloma

Building viewed from the east following the earthquake. Failure occurred in the columns at

this end of the building, causing the building to tilt toward the east. However, the shear

wall at the west end of the building was also badly damaged (Figures 5.49 and 5.50). It is

likely that the eccentricity caused by the presence of the shear wall on only one end of the

building caused a torsional mode of failure for the structure.

I The exposed reinforcing bars in the columns were undeformed. The columns at the east end

j measured 500 mm by 500 mm. The column ties were 9 mm in diameter and were spaced at 300 mm,

I at least where the reinforcing was exposed. There was less than 25 mm concrete cover for the

reinforcing bars in may instances. We were informed that this building was completed in

1963, making it one of the oldest buildings investigated.

Taiyo Fisheries Plant (No. 11, Figure 5.3) . This was a three-story building with a reinforced concrete frame, one span by five, the main axis of which was in the N-S direction.

There were shear walls on the north and south ends of the structure. As shown in Figures

5.51 and 5.52, the first-story columns in the middle of the building failed, causing the

central portion of the building to collapse but leaving the ends standing. The shear walls

at the north end of the structure (running in the E-W direction) were badly cracked. At the

time the site was visited, the building was being demolished.

85
Figure 5.34 Maruhon Building, Oroshicho area, showing shear cracking in the

panels on the east face between window openings.

Figure 5.35 Maruhon Building, west face, showing cracking of curtain

wall panels.

86

Figure 5.38 Yazaki Industries Buildings, viewed from the northeast, Oroshicho

area. Portions of three Yazaki buildings are shown. Failure of

the reinforced concrete middle building caused it to rack forward

against the front steel structure.

Figure 5.39 Yazaki Industries Building, viewed from the east.

88
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Figure 5.46 Apartment building adjacent to Yazaki Industries warehouse

building to the south. The building was undamaged.

Figure 5.47 Paloma Building - Viewed from the east. Collapse occurred at the east end of the building.

9 2
Figure Paloma Building. Detail of first story, east

end, showing inferior quality concrete.

Figure 5.49 Paloma Building,

west face.

93
Figure 5.50 Paloma Building, detail of shear wall on west

end of building.

Figure 5.51 Taiyo Fisheries Plant, viewed from the west. The

first story columns in the center portion of the

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standing. (Japan National Land Agency photograph)

94
Taiyo Fisheries Plant, viewed from the northeast. The

reinforced concrete shear wall on the north end was badly

damaged

.

95
5.4 Schools

Four schools and university campuses were visited: (1) Tonan High School (two buildings),

(2) Izumi Prefectural High School (four buildings), (3) Tohoku University, and (4) Tohoku

Institute of Technology (two buildings). As may be seen from the map in Figure 5.3, these

facilities are spread out over the Sendai metropolitan area, and they represent only a small

precentage of the total number of school buildings.

Tonan High School (No. 13, Figure 5.3) . This was a three-story reinforced concrete frame

building oriented in the N-S direction with shear walls in the E-W direction. The school was built about 12 years ago using the pre-1971 code.

The school is located on the east side of the city where the soil conditions are relatively

poor. The east side of the building sits on a small bluff approximately 6 m in height. This

may have amplified the ground motion at the site. The school was badly damaged by the earthquake and has been closed.

The west face elevation and the school yard are shown in Figures 5.53 and 5.54. The exterior

first-story columns were all severely damaged, the shear cracks occurring just above the infill panels, (Figures 5.55 and 5.56). In many cases the width of the cracks was over 20 mm. The upper story columns showed less shear cracking. The interior columns did not appear to

be damaged. They lacked the stiffening provided by the infill panels. A corridor ran along

the length of the building in the middle, and the shear walls were not continuous across the

width of the building. Undeformed reinforcing bars were used in the columns. The ties in

the exterior columns were spaced at roughly one-half the maximum dimension of the column.

Much of the damage at Tonan High School may be attributed to the unfavorable orientation of

the shear walls with respect to the direction of strongest shaking (N-S). A building adjacent to the school but oriented perpendicular to it, which was constructed about the same

time and in which the shear walls run in the N-S direction, was undamaged, aside from a few

broken windows.

Izumi High School (No. 21, Figure 5.3). The school campus is located in the suburb north of

Sendai, approximately 2 km from the Tohoku Electric Power Company Substation, which is discussed in Chapter 7. The buildings were completed in 1973, and their design was based on the

1971 building code. The school was occupied at the time of our visit. Several other schools

in the same general area, also designed according to the new standard, suffered less damage

than Izumi High School. We were informed that relative to Tonan High School, the soil conditions at the Izumi site were better.

The building plan in Figure 5.57 shows three interconnected classroom buildings, and a steel

frame assembly hall (auditorium or gymnasium). The steel frame building appeared to be only

lightly damaged from the outside. The classroom buildings are three-story reinforced con- crete frame structures with transverse shear walls (not shown, but coinciding with the end

classroom walls and stairwells). Classroom corridors extend along the north side of each

building.

Figure 5.58 shows the east elevation of the three classroom buildings, and Figure 5.59 shows

the front entrance on the north side of building 1. The badly cracked panel above the

entrance is not connected to the ground floor. The interior corridor walls in the building

had extensive diagonal cracks, as shown in Figure 5.60. Figure 5.61 shows the northeast

corner of building 2 along the foundation. The diagonal crack at the corner of the exterior

wall indicates that either uplifting or settlement of the foundation took place. Figures

5.62 and 5.63 show typical damage on the north and south sides of one of the classroom

buildings. Damage was relatively greater on the north side of the building where the columns were stiffened by the infill panels. Although there were numerous diagonal cracks

emanating from window openings on the north side, the main columns did not appear to be badly cracked.

Note from Figure 5.57 that the interior shear walls do not run the width of the building, as they are interrupted by the corridor on the north side of the building. The cracking was

less severe on the open side of the building, where the shear walls connect to the columns.
Figure 5.53 Tonan High School, west face. A small bluff on the

opposite side of the building may have amplified

ground motion. The adjacent structures were undamaged.

Figure 5.54 Tonan High School - Detail of damage to west face.

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hall and three reinforced concrete classroom buildings.

99
Figure 5.59 Izumi High School. Detail of panel over north entrance

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Tohoku Institute of Technology (No. 17, Figure 5.3) . The campus consists of several buildings

located southwest of the downtown area of Sendai. The building layout is illustrated in

Figure 5.64. The underlying soil conditions are reasonably good, being older terrace deposits. All building are situated on sand and have pile foundations. As may be observed from

the contour map in Figure 3.12, this area of the city is quite hilly. Buildings No. 3 and 5 (labeled on Figure 5.64), constructed in 1965, were inspected in some detail. There were no strong motion instruments at the campus; however, ground accelerations at the site were estimated as 0.25g.

Figure 5.65 shows a partial view of the northeast facade on Building 5. Building 5 is situated on a steep hill running to the southwest and the northeast side entrance is actually

located on the fourth-story of the eight-story reinforced concrete frame building. The upper

five floors contain large classrooms and open spaces. Damage to building 5 was substantial,

particularly on the northeast side. Light fixtures were shaken down and bookcases, wooden

lecterns, and statues were overturned. Surprisingly, the elevator remained functional. Wall

panels and floor diaphragms were cracked, (Figure 5.66). Such cracking was particularly

noticeable near shear walls of the stairwell on the northeast side of Building 5.

The columns on the northeast side of building 5 were seriously damaged. Figure 5.67 and 5.68

show typical damage to exterior columns on the upper stories (stories 6-8). The infill

panels stiffened the exterior columns on the northeast side of building 5. In contrast,

the exterior columns on the southwest side and the interior columns had no such stiffening,

were relatively flexible (Figure 5.69) and suffered no apparent damage. The lower story

columns on the northeast side showed significant shear cracking and spalling, as illustrated

in figure 5.70 for one exterior column on story four. Crack widths exceeded 10 mm in several

instances. Visible column ties were spaced 250 mm apart and were wrapped around the corner longitudinal bars without hooks. Interior transverse shear walls also showed diagonal

cracks. In at least one case where the transverse wall was connected to a column, the

diagonal crack in the wall continued on into the column. The transverse walls were connected

to the columns on the north side with the tie beams. Figure 5.71 shows one of these tie

beams following the earthquake.

Adjacent to building 5 on the northwest is a three-story reinforced concrete frame building

completed in 1972. Figures 5.72 and 5.73 show this building and its walkway connection to building 5. It was constructed according to the post-1971 building code. Although the

building was not entered, an inspection of its exterior revealed no signs of damage.

The northeast facade of building 3 is shown in Figure 5.74. This is a four-story reinforced

concrete frame building, ten spans by two. While the relatively flexible interior columns

were undamaged, all of the exterior columns on the first-story cracked in shear just above

the infill panels, as shown in Figure 5.75. Figure 5.76 illustrates this more clearly at

one of the first-story columns on the northeast side of building 3. As can be seen, the

reinforcement is undeformed. We were informed that core samples taken out of the spandrels

showed no apparent damage to the concrete.

Around the entrance on the east side of building 3 and the southeast corner of its firststory, large areas of the tile facing and concrete underneath had spalled off, exposing the

reinforcement (Figure 5.77). At this location, the vertical reinforcing bars were bent

manually during construction in order to force them to conform to the building working drawings. The reinforcement appeared to have less than 10 mm concrete cover. The interior

walls of building 3 showed extensive diagonal cracking (Figure 5.78). However the interior

columns were apparently not damaged.

Figure 5.79 shows the area between walkway along the northeast side of building 5 (see also

Figure 5.65). The backfill along the northeast side of building 5 has settled, causing damage to the stairs to the entrance of building 5 and adjacent retaining walls. Ground settlement also has caused the paving of the walkway to crack.

It was reported that building 3 will be demolished and building 5 will be repaired. Estimates of the costs of repair for these structures were unavailable.

Tohoku University Engineering and Architecture Building (No. 19, Figure 5.3) . Tohoku University is located west of the downtown area. As may be observed from the contour map in Figure

103
Figure 5.64 Tohoku Institute of Technology, Sendai, plan of campus.

Hatching along walls of buildings 3 and 5 shows location

of severely damaged columns.

104
Tohoku Institute of Technology. Partial view of the

entrance and north facade of building 5. Most serious

damage to columns occurred on this side of the building.

Figure 5.66 Tohoku Institute of

Technology. Typical

cracking of floor diaphragms at the sixth floor

level, building 5.

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Figure 5.71 Tohoku Institute of Technology, Building 5. The tie beam

over a sixth floor corridor connecting two shear walls

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Figure 5.73 Tohoku Institute of Technology. Passage between Building 5 and the building to its west.

Figure 5.74 Tohoku Institute of Technology, Building 3. General view

of the north elevation.

109
Figure 5.75 Tohoku Institute of Technology, Building 3. Damage to the ground floor columns on the south

side of the building. Similar damage is present

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Figure 5.76 Tohoku Institute of Technology, Building 3. Typica

damage to ground story ex- terior column on north side

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Figure 5.79 Tohoku Institute of Technology, walkway and north entrance

of building 5 shows settlement of backfill along length of

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112
3.12 this area of Sendai is quite hilly. The underlying stable terrace deposits provide a good foundation for buildings. The Engineering and Architecture Building on the Campus is a nine-story reinforced concrete frame structure with pile foundation approximately 10 years

old. The structure was designed for a peak ground acceleration of 0.2g. A general view is

shown in Figure 4.4 and plans and elevations are shown in Figure 4.5. The building is

instrumented with two strong motion accelerometer instruments on the ground floor and the

ninth floor. The records are discussed in detail in Chapter 4. The maximum accelerations

j recorded were 0.24 g at the ground floor and l.Og on the ninth floor, both in the N-S direction.

i The building performed very well in the earthquake. The February 1978 earthquake caused

some cracking in shear walls and window breakage. The maximum ground floor acceleration

measured then was 170 gal. After the June earthquake, the diagonal cracks had widened, but

'they still can be easily repaired. Figure 5.80 shows an interior transverse wall at the

ground floor. The decorative glazed tile veneer has cracked and spalled along a diagonal

crack in this wall. A number of windows on the upper stories were broken out and bookcases

! and filing cabinets were overturned. The main structural elements of the building appeared

to be intact; however, minor cracks in the structural frame were reported at the lowest

levels. Assuming that the first mode dominated the dynamic response, the maximum displacement

amplitude at the ninth-story, computed from A/(2nf)^ in which A = 980 cm/sec^ and f = 1 Hz, was about 25 cm (10 in).

5.5 Residences

Sunny Heights Apartment Building (No. 38, Figure 5.3) . This 190-unit private apartment

building (Figure 5.81) is located on the east side of Sendai city on soft ground. It is a 14-story steel and reinforced concrete structure with a pile foundation, L-shaped in plan,

which was built in two sections about two years ago. The L-shaped plan is not conducive

j to earthquake resistance because torsional effects may be amplified. The earthquake caused

numerous diagonal cracks throughout the height of the building, particularly around doorways

and window openings, as shown on the east face of the building in Figure 5.82. The extensive

cracking in the nonstructural panels adjacent to doorways created major problems for occupants attempting to open doors and windows in the first ten stories. The most severely damaged panels were oriented in the N-S direction. Despite the extensive damage to nonstructural elements, the main loadbearing structural members appeared to be undamaged by the

earthquake.

There was extensive evidence of ground cracking and settlement adjacent to the foundation and

j the walkway surrounding the building, as can be seen in Figure 5.83, where the support post

below the bottom rail of the fence is exposed. The ground adjacent to the foundation subsided several inches in some cases. Portions of the parking area around the building

appeared to have settled about 18 in (460 mm). There was a large water shortage tank located

I on top of the roof. It was shaken loose from its anchorage when the anchor bolts failed and

| the horizontal movement also caused the supply pipe to be damaged.

Single Family Dwellings . Major causes of the destruction to dwellings were landslides and

rockfalls, inadequate foundations, and construction which lacked lateral bracing. Many

homes in the Sendai vicinity have heavy tile roofs, and literally thousands of buildings

' had damaged roofs of varying degrees. Falling tile resulted in some injuries.

A major cause of deaths and injuries was collapsing or falling walls made of stone or con-

, crete cinderblock. These walls serve as fences, for privacy, and as noise barriers. The

f Japan Building Code requires that walls over 1.5 m in height be reinforced in both directions. Although some of the walls that failed contained reinforcing, in most cases they

contained less reinforcing than called for by the modern code. More fatalities resulted from

falling walls containing inadequate reinforcing than from walls with none. Those with no reinforcing tended to crumble while those with reinforcing toppled as units on people who

were nearby or who held onto them for stability when the earthquake occurred. In some cases,

the masonry block cores were grouted but the reinforcing steel had been omitted.

Figure 5.84 shows an example of the ground cracking resulting from subsidence in one of the

hilly areas in Sendai. The loss of foundation support has caused extensive cracking in the

building walls. In Figure 5.85, the front steps and breezeway have separated some 30 cm

113
i iiiiwiignwii

Figure 5.80 Tohoku University Engineering Building. Damage to glazed

tile veneer of shear wall at ground level.

Figure 5.81 Sunny Heights Apartment Building, Sendai. General view from

the southwest.
Figure 5.82 Sunny Heights Apartment

Building. Detail of cracking of panels adjacent to doorways . Such cracking was typical at all levels on the

east facade of the structure.

Sunny Heights Apartment Building. Ground cracking and

settlement adjacent to walkway surrounding the building,

115

from the remainder of the structure due to ground settlement. There were many instances

where tile roofs were badly damaged even when the structure remained standing (Figure 5.86).

Two examples of collapsed masonry-unit walls are shown in Figures 5.87 and 5.88. The wall

shown in Figure 5.87 was not reinforced, and crumbled during the earthquake. The wall in

Figure 5.88 contained reinforcement but was not anchored adequately to its foundation and

toppled over practically as a unit.

Many single family dwellings were undamaged by the earthquake and, perhaps surprisingly,

undamaged homes were found adjacent to larger engineered buildings that had been damaged.

In a residential neighborhood at the bottom of the slope south of building 5 at Tohoku

Institute of Technology, there was no visible damage to walls or tile roofs in any of the

houses. Similarly, only minor damage could be observed to homes at the bottom of the bluff

next to Tonan High School.

5.6 Summary

Considered collectively, severe damaged or collapsed reinforced concrete buildings shared a number of common features. Probably most significant, they were all designed prior to the

1971 revisions to the building code, at which time detailing requirements became more stringent. These older structures probably had little ductility and energy-absorbing capacity

due to the use of undeformed bars and widely spaced column ties, insufficient ties and

anchorage of reinforcement at beam-column joints, failure to provide hooks on ties, etc. None of the columns in failed buildings appeared to be spirally reinforced, which would be more ductile in their behavior. Damaged buildings frequently had flexible first stories and

rigid upper stories. Building layouts were irregular and caused structural discontinuities.

Partial infilled spandrel walls between columns contributed to many column failures. In

some cases, the fate of an entire building rested on the integrity of a single column or

wall. Mechanisms for load transfer following local failure through good floor plans, logitudinal spline walls and returns on shear walls would reduce the occurrence of complete

collapse following failure of a single element. Stiffer structures with shear walls tended

to have less damage than more flexible buildings.

It should be borne in mind that many of the buildings investigated have been through two recent major earthquakes (February 20 and June 12, 1978) without suffering damage. The

total damage due to the June 12th earthquake constitutes a small percentage of the total

capital investment in buildings and structures, despite recorded ground accelerations of as high as 0.25g to 0.30g.

5.7 References

j 5.1 Okamoto, S., Introduction to Earthquake Engineering , John Wiley, 1973 (Chapter 8, esp)

5.2 Standards for Aseismic Civil Engineering Construction in Japan , Ministry of Construction Standard No. 1074.

,5.3 Watabe, M., "Summary of Present Codes and Standards in the World," 1978.

j5.4 "Design Essentials in Earthquake Resistant Buildings," published by the Architectural

Institute of Japan, Elsevier Publishing Co., London, 1970.

:5.5 Uniform Building Code , 1976 Edition, International Conference of Building Officials,

Whittier, CA. 1976.

5.6 "Tentative Provisions for the Development of Seismic Regulations for Buildings,"

Nat. Bur. of Stand. Special Publication SP510 (ATC 3-06), Washington, D.C., June 1978.

5.7 "Building Code Requirements for Reinforced Concrete," (ACI 318-77), American Concrete

Institute, Detroit, MI, 1977.

117
Figure 5.86 Typical damage to tile roofs in Sendai (Japan National Land

Agency photograph)

Figure 5.87 Failure of unreinforced concrete masonry wall in Sendai (Japan

National Land Agency photograph)
119
6. EFFECTS ON INDUSTRIAL FACILITIES AND LIFELINES

6.1 Introduction

As discussed in Chapter 2, the preliminary Japanese estimates of damage at the end of June,

1978 amounted to approximately $830 million. Of this total $455 million was to factories,

stores and other business establishments. This represents about 55 percent of the total

damage. Damage to transportation, electrical, gas, and other lifeline facilities also represents a substantial proportion of the remaining damage. Of course, these figures do not

include secondary types of damage, such as lost production for factories, lost revenue for

power and gas utilities, etc. Thus, losses to industry and other business establishments

dominate the damage statistics from the Miyagi-ken-oki earthquake of June 12, 1978. In

this respect, the earthquake is very different from the majority of damaging earthquakes

that have been reported in the literature.

Most of the significant structures in the Sendai area are modern structures, designed under

advanced earthquake engineering concepts. The construction and inspection practices also

appear to be of generally excellent quality. However, most of the capital investment in

industrial facilities is concentrated in equipment systems, which typically are not protected against earthquakes to the same degree as the buildings which house them. This lower

level of seismic resistance may explain why a high proportion of the total damage was caused

to factories, stores and other business establishments.

A small number of industrial facilities and lifeline structures were briefly inspected.

Damage varied from negligible, at the Fukushima Nuclear Power Plant, to severe, at the Sendai

Gas Facility. Sendai is a large industrial city, with more than 6,500 business/manufacturing

firms. The investigated sample of facilities represents a small fraction of the damage

caused by the earthquake and of the facilities that were affected.

At the time of the reconnaissance, Japanese engineers were already conducting investigations

of some of the facilities mentioned herein, and detailed reports will be available in the

future. This is particularly true of the power facilities in and near Sendai. Let us hope

that much of this important information will be translated into English.

This section of the report contains observations that were collected and recorded in a very

brief time, and undoubtedly contains some data errors. In addition, no attempt is made here

to analyze the structures and equipment or their performance. The primary objective of this

report, and of the reconnaissance investigation, is to observe the performance of earthquakeresistant and other buildings, structures, and equipment.

The maps of Figures 1.1, 5.3 and 6.1 show the sites and facilities treated in this section

of the report.

6 .2 Fukushima Nuclear Power Plant Complex

The Fukushima Nuclear Power Plant Complex is owned and operated by the Tokyo Electric Power

Company. It is located on the Pacific coast of Fukushima Prefecture, about 7 km south of

the town of Namie, and is southeast of the town of Fukushima. The site is approximately 140

km from the epicenter of the earthquake. According to Chapter 3, faulting may have extended

as much as 60 km west of the epicenter. In that case, the plant site may be located about

80 km (50 mi) from the nearest location of the source of energy, as shown in Figure 1.1

The complex has six nuclear units, as shown in Figure 6.2, for a total of approximately 4,700#

MW, and is the largest nuclear power complex in the world. The site is heavily instrumented

with strong motion accelerometers. Numerous records were made; the peak ground acceleration was 0.125 g and the duration of strong motion was in excess of 30 seconds. Because most U.S. nuclear power plants are designed to criteria that is similar to the seismic motion to which

the Fukushima site was exposed, this earthquake represents a unique event. This is the first J

* Prepared by Peter I. Yanev, URS/John A. Blume and Associates, San Francisco, California.

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time that a modern nuclear power plant was exposed to strong ground motion with long duration. In addition, the presence of six units at one site represents a good statistical

sample.

Table 6.1 summarizes some of the pertinent data for this six-unit complex:

At the time of the UJNR team visit, June 23, 1978, 11 days after the earthquake, Units 1, 2,

3 and 5 were operating; Unit 6 was still under construction, but was essentially completed,

and it is believed that Unit 4 was scheduled to go into commercial operation soon. The above

table indicates that the expected date of commercial operation for the unit was sometime in

October of 1978.

Units 1 through 5 have a Mark 1 (light-bulb-torus) type of containment structure; Unit 6 has

a Mark 2 (over /under) type of containment (see Figures 6.3 and 6.4). USR/Blume Engineers

• formulated the seismic design criteria for the plant and performed the original seismic

analyses for the General Electric Company and the Tokyo Electric Power Company.

The plants are founded on a competent soft mudstone formation with a thickness in excess of

i 300 m. Extensive cuts were necessary to level the site and to reach the mudstone, which has

a shear wave velocity of about 600 m/sec.

j Unit 1 was designed for a peak ground acceleration of 0.18g and a response spectrum based on

' the Taft record from the Southern California (Kern County) earthquake of 1952.

The reconnassiance team inspected the exterior of Unit 1 and the exterior and interior of

Unit 6, including the containment structure, the reactor vessel pedestal, some of the equipment on the refueling floor, some of the equipment in the reactor building, the underside

L of the control rod drive in the containment, miscellaneous critical and non-critical piping,

I various critical and non-critical cable trays, the reactor building, the turbine building,

the turbine overhead crane, and various auxiliary structures, equipment and tanks (see Figures 6.5 through 6.9)- There was no damage or evidence of working of connections in any

2 of the inspected areas. The only reported damage to the complex was to some non-critical

a I electrical insulators, shown in Figure 6.10, some distance to the west of Units 1 and 2 (see the following discussion on the effects to electrical insulators at the Sendai Substaj i tion in Izumi, near the city of Sendai).

Units 1 and 6 are instrumented with between 20 and 30 strong motion accelerometers and much

j : valuable information was obtained from the earthquake. The peak ground acceleration, which

could be considered to be a "free-field" acceleration (see Figure 6.11) is 0.125g. (EW

direction). The corresponding accelerations in the NS direction and Up/Down directions are O.lOOg and 0.050g. The strong motion exceeds 30 sec in duration. The reported maximum

i response acceleration in the buildings is reported to be about 0.5g. Higher accelerations

~i would be expected in instrumented equipment or piping systems. It is interesting that

0 records were obtained from instruments located on the base slabs of the two units and at

1 downhole instruments, about 30 to 40 m below two of the containments. Thus, it may be pos-

: sible to conduct a detailed soil-structure interaction study for the plant.

[ Tokyo Electric Power Company is also conducting model studies of the plant at the site. A

l/15th scale model of the containment has been constructed a few hundred yards away from the

nuclear units. The model, shown in Figure 6.12, was also instrumented, including another

downhole instrument, and additional records are available from the study. At the time of the

investigation the company was beginning to evaluate the recorded data.

6.3 New Sendai Power Plant, Tohoku Electric Power Company

The New Sendai Power Plant, owned and operated by the Tohoku Electric Power Company, is

located on the Pacific shore, 15 km east of the center of Sendai. The site is adjacent to the Sendai refinery of the Tohoku Oil Company which suffered extensive damage from the

earthquake (as discussed elsewhere in this chapter). The plant shown in Figure 6.13, has

two Mitsubishi oil-fired boilers. Unit 1 was completed in 1971 and has a capacity of 350

MW; the 600-MW Unit 2 was completed in 1973 and is the largest unit of the company. The

total capacity of the Tohoku Electric Power Company is 5,715 MW, this plant representing

about 17 percent of that capacity.

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Figure 6.4 Fukushima Nuclear Power Plant: Typical elevation view through

the reactor/containment building and the turbine building and

a plan view across the refueling floor of the reactor building

and the operating floor of the turbine building.

126
Figure 6.5 Fukushima Nuclear Power Plant:

large, undamaged safety related

water storage tanks that are located between units 1 and 5.

Figure 6.6 Fukushima Nuclear Power Plant: a view of the braced

steel frame roof and the overhead crane of the turbine

building of Unit 6.

127
Figure 6.7 Fukushima Nuclear Power Plant: a partial view of the Unit 6 control

rod drive and its supports. The unit is still under construction and was more than 95% completed at the time of the reconnaissance. There was no apparent damage or any evidence of working connections at this

system or at the other systems of Unit 6 that were examined.

Figure 6.8 Fukushima Nuclear Power Plant: a typical view of massive seismic

and/or pipe whip bracing of critical piping inside the reactor building

of Unit 6. The equipment showed no evidence of damage. This unit is

still under construction.

128
Figure 6.9 Fukushima Nuclear Power Plant: a partial view of the control room of Unit 5. At the time of the visit on June 23, 1978,

11 days after the earthquake, this unit was operating.

Figure 6.10 Fukushima Nuclear Power Plant. Broken ceramic insulators were the only damage reported for the site. The damaged

insulators had been replaced, as illustrated above, within

hours after the earthquake and before the reconnaissance visit.

129
Figure 6.11 Fukushima Nuclear Power Plant: a view of some of the

auxiliary structures to the north of Unit 1. Free-field

acceleration was recorded in the water treatment building

(the white, 1-story building in the middle of the photograph),

which is located approximately 100 m from the Unit 1 containment structure. The SMAC instrument recorded a peak ground

acceleration of approximately 0.125g.

Figure 6.12 Fukushima Nuclear Power Plant:

view of the l/15th scale model

of the containment of one of

the nuclear units. The free

field and downhole instrumentation is located away from the

test structure (note the cables

to the right)

130
Figure 6.13 New Sendai Power Plant, Tohoku Electric Power Company: a general

view of the two-unit, oil-fired power plant. The turbine building

is in the foreground, and the two boiler structures are in the background. Unit 2, the large unit, has a 600-MW capacity. Unit 1 has a capacity of 350 MW. Note the massive seismic bracing to the

combined stacks and to the boiler support frames. (Tohoku Electric

Power Co. photograph)

131
Because the SMAC accelerograph at the station was being inspected at the time of the earthquake, no records were obtained. However, the plant's seismic alarm, located at the level

of the turbine operating floor, was triggered at approximately 0.15g. Because the plant

is closer to the epicenter of the earthquake and the assumed area of faulting (as discussed

in Chapter 3), it may be assumed that the ground motion at the plant was somewhat stronger

than in the city of Sendai where the recorded peak ground accelerations varied between 0.20

and 0.40g.

The plant is located in an area of recent alluvium and on filled land; the depth of uncon- solidated sand is approximately 15 m (45 ft).

Both of the units were damaged during the earthquake, and the plant was shut down for 6 days

for repairs. Total damage to the facilities of the Tohoku Electric Power Company is approximately $15 million; estimated damage to the plant accounts for about 10 percent of the

loss. The total assets of the company in property, plant and equipment for Fiscal Year 1976 were $3,840 million. Damage from this earthquake caused a loss of about 0.4 percent of

those assets. The plant was operating at the time of the investigation of June 24th, 12 days after the earthquake.

Three types of damage occurred at the plant: (1) damage due to local, minor settlement, (2)

damage to the structural and architectural elements of buildings, which was minor, and (3)

damage to the equipment, which constituted the bulk of the loss.

Minor settlement occurred throughout the site. Much of this settlement occurred in the

vicinity of buried piping (Figure 6.14 ). About 1 cm of settlement occurred at the intake

structure and the paving around the structures was cracked; however the structure was operational and did not seem to require repairs (Figure 6.15).

Building damage was limited to some of the interior walls of the administration building and

to the facing precast panels of the turbine buildings (Figure 6.16). Some of these panels were loosened; presumably the attachments to the steel framing were damaged.

Both Unit 1 and Unit 2 suffered damage to tubing inside the boilers (Figure 6.17). A small

furnace platen cooler tube inside the slag screen was sheared in the Unit 1 boiler (Figure

6.18). A similar failure occurred in the boiler of Unit 2 to one of the reheater spacer

tubes. The suspended boilers and their structural supports also pounded against one another

and also sustained some damage (Figure 6.19).

There was no other reported damage. The turbine pedestals and the operating floor of the

turbine buildings in Japan are usually separated by a 3 to 4 inch gap and, in this case, there was no pounding between the two structures.

6.4 Sendai Substation, Tohoku Electric Power Company

The Sendai Substation of the Tohoku Electric Power Company is located on a low hill in the

city of Izumi, about 7 km north-northeast of the center of Sendai. The substation is a large, multilevel complex. It was constructed during the last few years to the current

Japanese seismic code, which specifies a minimum design acceleration of 0.20g for low-rise

structures

Figure 6.20 shows a general layout of the complex. The upper portion of the substation is

the high-side 274 KV bus, and the lower portion of the substation is the low-side bus which

is 154 KV. Locations of damage to equipment are circled in the figure.

Extensive cuts and fill were necessary because of the topography of the hill on which the

station was located. The filled areas are indicated in Figure 6.20. Some of the fills, all

of which were engineered, were as deep as 15 m (45 ft). The underlying bedrock is a competent, soft mudstone which was left exposed with slopes exceeding 60°. Due to seismic considerations, the most important electric components of the station were placed on the cut portions of the site, over a mudstone foundation. For example, all of the main transformers were placed on the cut sites, as shown in Figure 6.20. According to utility engineers,

there seemed to be no difference in the amount of damage sustained by equipment whether on fills or on cuts. There was extensive damage to equipment in all parts of the facility. It

132
igure 6.14 New Sendai Power Plant; Tohoku Electric Power Company: A

view of the entrance area to the power plant showing settlement of fill and subsequent repair work to the pavement.

The pavement settled approximately 15 cm (6 in) and was primarily in the vicinity of a backfilled underground

pipeline

.

gure 6.15 New Sendai Power Plant, Tohoku Electric Power Company: damage

around the water intake structure from minor settlement. Other

examples of minor settlement were observed throughout the site.

133
Figure 6.16 New Sendai Power Plant, Tohoku Electric Power Company: a loosened

exterior facing panel in the turbine building. This was the only

obvious damage to the exterior of the structure. The shear walls

of the adjacent administration building showed extensive cracking.

Figure 6.17 New Sendai Power Plant, Tohoku Electric Power Company. The arrow

points to the location of the damaged horizontal spacer tubes in the

600-MW boiler of Unit No. 2. (See Figure 6.18).

134
Figure 6.18 New Sendai Power Plant, Tohoku Electric Power Company: damage to the two boilers consisted of shearing of spacer tubes for the

furnace platen cooler tubes inside the boiler. (Tohoku Electric

Power Company photograph)

Figure 6.19 New Sendai Power Plant, Tohoku Electric Power Company: a view of

the exterior of the boiler walls showing evidence that the suspended

boiler had pounded against the surrounding support structure.

(Tohoku Electric Power Company photograph)

135
Sendai Substation, Izumi: plan of the facility showing the

location of damaged equipment (circled) . The solid contour

lines indicate areas that were filled.

136
was immediately apparent during the investigation (June 24, 12 days after the earthquake),

that all of the equipment was adqequately anchored to its foundations, or braced. No overturning or other structural bracing failures were noted. Apparently, the damage was limited

to various ceramic insulators in lightening arresters, potential devices, circuit breakers,

transformers, bushings, reactors or line traps, switches, etc. Thus, there was a striking

difference between the damage to this substation, as compared to the damage at the Sylmar

Convertor Station from the San Fernando, California earthquake of February 9, 1971. In the

latter case much of the damage was caused by the overturning of equipment with inadequate

anchorages or supports.

By June 24th much of the damage to the substation had been repaired (Figures 6.21 and 6.22),

and the damaged equipment (Figures 6.23 through 6.27) had been dumped in piles on the periphery of the substation (Figure 6.28). Repairs were still going on to the bushings and

lightening arresters of some of the main transformers (Figure 6.29), and various pieces of

equipment had not yet been replaced. The total damage at the substation is estimated to be on the order of $15 million.

A Japanese team has been assembled to conduct a special investigation of the performance of

the substation during the earthquake.

6 .5 Haranomachi Plant of Sendai City Gas Bureau

The Sendai City Gas Bureau's Haranomachi Plant, located approximately 3.7 km northwest of the

center of Sendai, suffered major damage. The total collapse of a large propane gas holder

(Figure 6.30) was partially responsible for the stoppage of gas for the city. It was estimated that gas services for the city would not be restored until the end of June, some three

weeks after the earthquake. At the time of the investigation (June 25, 13 days after the

earthquake) many restaurants in Sendai were closed because of lack of gas. According to Chapter 2 about 60 percent of the 200,000 households in Sendai are dependent on gas for

heating and cooling, and as of June 28, 1978, 22,000 of these households were still without

| gas. An additional 10,400 households elsewhere in the prefecture were also without gas.

The holder diameter was 38 m; its height was 27 m. At the time of the earthquake, the holder

contained 14,000 m of propane gas, at the relatively low pressure of 1 kg/m , and held water

in a 9-m section at the bottom of the structure. The tank had at least two, but more probably three, telescoping sections constructed of riveted plate, 1 cm (3/8 in.) thick, stiffened with ring stiffeners at approximately 2 to 3 m. The tank was surrounded by an outside

containment dike also constructed of riveted steel plate.

The collapsed holder caught on fire shortly after failure, and all of the stored gas was

consumed. The fire burned out, or was extinguished, about 25 minutes later, and did not spread to the nearby high pressure propane tanks. The most serious damage to the gas facility was caused by the collapsing holder. It struck the nearby pipeway for many of the

tanks at the plant, causing much damage to the piping systems and other associated equipment.

Figure 6.31 shows the collapsed holder and the damaged pipeway just after the earthquake.

At the time of the investigation a new pipeway had been erected on the concrete pedestals of

the old pipeway, and repairs of the pipelines were proceeding, Figure 6.32. These pipes

| service the remaining undamaged gas tanks.

There was evidence of damage throughout the facility (Figures 6.33 through 6.38); however,

j none of the other tanks at the facility are believed to have suffered major damage. Some

j damage was due to pounding between buildings and pipes that penetrated the building walls

J (Figure 6.39). Unanchored pipe supports often moved on their pedestals, and reinforced

concrete block structures suffered damage to their structural elements.

6.6 Sendai Refinery, Tohoku Oil Company Ltd.

Figures 6.40 through 6.49 give an overview of damage to the Sendai Refinery of the Tohoku Oil

Company, Ltd., which is located on shore about 15 km east of the center of Sendai and adjacent to the New Sendai Power Plant. A plan of the refinery, which is a major installation

and was completed in 1971, is shown in Figure 6.40. The refinery covers an area of 1,600,000

j . Its capacity is approximately 100,000 barrels/day.

137
Figure 6.21 Sendai Substation, Izumi: a general view of a portion of one of

the buses. Damage was not reported to these steel structures.

Figure 6.22 Sendai Substation, Izumi: three replaced 3-phase circuit

breakers. This type of T-shaped circuit breaker suffered a high percentage of damage. Often the three symmetrical guides

broke before the main stem. In all cases the structural steel

supports appeared to be undamaged.

138
Figure 6.23 Sendai Substation, Izumi: typical damage to 3-phase T-shaped

circuit breakers (as shown in previous figure) . Note the complete

failure of one and the damage to the three guides of the second

circuit breaker. All steel supports appear to be undamaged. The

photograph was taken immediately after the earthquake before repairs were initiated. (Tohoku Electric Power Co. photograph)

Figure 6.24 Sendai Substation, Izumi: another three failed 3-phase, T-shaped

circuit breakers. Note the failed main stems, the loose guide wires

and the undamaged steel supports which are attached to their foundations. (Tohoku Electric Power Co. photograph)

139
Figure 6.25 Sendai Substation, Izumi:

damage to a circuit breaker

(right), and two lightening

arresters (center) . The

bushings of the transformer

in the background appear to be undamaged; however, the

lightening arrester is leaning. (Tohoku Electric Power

Co. photograph)

Figure 6.26 Sendai Substation, Izumi: Severe damage to circuit

breakers (center of photograph - note the failed columns

of live tank design, probably with gas reservoirs), current

transformers (with the tapered bushings - some of the stems are also damaged) , and reactors (to the left) with presumably

broken connections. (Tohoku Electric Power Co. photograph)

140
igure 6.27 Sendai Substation, Izumi. Severe damage to several

circuit breakers of live tank design. Note the lack

of damage to the structural steel supports and the

steel components of the equipment. (Tohoku Electric

Power Co. photograph)

igure 6.28 Sendai Substation, Izumi; one of several piles of broken

equipment, including several line traps or reactors in

the back (note the damaged base of the left stem) and

the horizontal tanks of several circuit breakers of the

live tank type (in the foreground are the failed columns

of the circuit breakers and of other equipment)

.
Figure 6.29 Sendai Substation, Izumi; a repaired but still disconnected

transformer. All of the transformers at the substation

lost some bushings or lightening arrestors. Some damaged

parts were being replaced at the time of the investigation.

Figure 6.30 Haranomachi Plant, Sendai City Gas Bureau: an overall

view of a collapsed propane gas holder and some of the

surrounding propane storage tanks and affected pipeway

and equipment. (Kahoku Newspaper Co. photograph)

142
K~

Figure 6.31 Haranomachi Plant, Sendai Gas Bureau; collapsed gas

holder and the damaged adjacent pipeway structure just

after the earthquake, (Sendai Gas Bureau Photograph)

Figure 6.32 Haranomachi Plant, Sendai City Gas Bureau: The newly

erected pipeway, with the collapsed holder in the background. Note the undamaged pressurized propane gas

sphere in the back.
Haranomachi Plant , Sendai City Gas Bureau

damage to piping and other equipment and supports

caused by impact from the collapsed gas holder

and the adjacent pipeway. The newly erected

pipeway is to the right.

Figure 6.34 Haranomachi Plant, Sendai

City Gas Bureau: damage to the telescoping gas holder

and to some of the nearby

pipeways and equipment . The

trusses are portions of the

original support structure

that had surrounded the tank.

144
Figure 6.35 Haranomachi Plant , Sendai City

Gas Bureau: buckling damage

to the lower portion of one segment of the gas holder.

Figure 6.36 Haranomachi Plant, Sendai City Gas Bureau:

a fracture of the 3/8-in. plate wall of the

collapsed gas holder. The length of the

fracture is approximately 1.5 m (5 ft).

145

Figure 6.39 Haranomachi Plant, Sendai City Gas Bureau: a damaged

reinforced concrete block structure. Some of the damage

was due to pounding between the large diameter pipe and

the structure at the pipe penetration.

Figure 6.40 Plan of the Sendai Refinery, Tohoku Oil Company, Ltd.

Tanks are shown as circles in the plan. The circles

that represent the three failed TC tanks have been

blackened; ones that represent the three other damaged

tanks are marked with an X. The refinery structures

are located to the right of the tank farms.

147
Figure 6.41 Sendai Refinery, Tohoku Oil Company, Ltd.: an overall

view of the refinery's tank farm. The spilled oil

appears as the dark area of the photograph. (Tohoku

Oil Company photograph)

Figure 6.42 Sendai Refinery, Tohoku Oil Company, Ltd.: one of the

three failed storage tanks. The damage illustrated is

due to suction caused by rapid evacuation of the oil

through the ruptured connection of the base and wall

of the tank. The several tanks, of similar size, in

the foreground are thought to be undamaged.

I \
Figure 6.43 Sendai Refinery, Tohoku Oil Company, Ltd. Two other

failed TC oil storage tanks.

149
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150
Figure 6.46 Sendai Refinery, Tohoku Oil

Company, Ltd. : an undamaged

LPG storage tank. Note the

heavy diagonal bracing in

the supporting structure.

Figure 6.47 Sendai Refinery, Tohoku Oil Company, Ltd.:

a partial view of the refinery.

151
Figure 6.48 Sendai Refinery, Tohoku Oil Company, Ltd.: ground

settlement at the refinery.
As illustrated in Figure 6.40, the complex is divided in two parts by a river and some port

facilities. The new Sendai Power Plant is to the east (right). The tank farms and the

refinery complex itself are located on the eastern portion, adjacent to the port facilities,

which can handle super tankers. The gas producing and pumping facilities are located on the

western half of the complex. The land transportation facilities are also located on the

west side.

The damage of the refinery and the lost oil represent one of the major losses from the

Miyagi-ken-oki earthquake. At the time of the investigation (June 24, 12 days after the

earthquake) the total amount of damage was unknown, as investigations were still continuing.

It was expected that the damage investigations and evaluations by the company and the local

fire authorities would continue well into July. The reported intensity at the site was 5 on

the JMA scale, and the epicentral distance is approximately 100 km. The adjacent power

plant had an accelerometer , which did not operate, and a 'seismic alarm, located at the turbine building operating floor, which was triggered by the earthquake. As the alarm was set

at approximately 0.15 g, the motion was probably in excess of 0.15 g. In all probability,

the motion exceeded 0.25 g.

The investigation revealed that the complex had been designed to reasonable seismic criteria. All of the observed tanks, equipment and piping systems were anchored and no overI turning failures were observed. As discussed further, some of the tanks were designed for a 0.30 g peak ground acceleration. Major portions of the facility were located on engineered

| fill. There was some evidence of settlement, however it could not be determined if the

settlement had occurred in filled areas.

There are at least 87 storage tanks in the facility. The tanks have different designs, and

different functions; some stored oil, others stored liquid propane gas (LPG); some had fixed

roofs, others had movable roofs. Three large tanks containing refined fuel called Top Crude

(TC) failed, spilling approximately 68,100 kl of oil. The capacity of the tanks was 85,000

kl. The surrounding reinforced concrete dike could accomodate only 35,000 kl. The oil

overtopped the dike, inundated much of the refinery area, and spilled over into the port

(Figure 6.41). Because the surface soils are sandy, it is believed that much of the oil

that was contained in the dike subsequently leaked under the walls and contributed to the

spill.

At the time of the investigation a thick film of oil still covered much of the refinery

grounds. Thus, the fire hazard was great, and the investigating team was unable to observe

the details of the damage to the tanks. It is believed that the tanks shown in Figures 6.42

through 6.44 failed at their bases. The oil drained rapidly, causing a vacuum inside,

which imploded the tanks. Three other tanks suffered damage and will need repair.

Another large water storage tank experienced interesting damage (Figure 6.45). The welded

steel plate tank was anchored with bolts, spaced at approximately 6 ft (2 m), and embedded

in a continuous concrete pad. The bolts around the entire circumference were stretched,

or more likely, pulled out from their embedment from 1 to 6 in (2.5 to 15 cm). However,

there was no apparent buckling or other damage to the steel base of the tank.

Visual inspection of several of the LPG tanks at the refinery, revealed no damage. There

were minor cracks in the concrete supports and some spalling of paint in the steel connections due to working. The tanks were designed for 0.30g peak ground acceleration. As illustrated in Figure 6.46, the tanks were heavily braced with diagonal braces with circular

cross-sections.

Figure 6.47 shows a partial view of the refinery, including several towers, heaters, boilers

and a heavily braced steel stack. These structures are reportedly undamaged. The team was

able to view some of the lower structures; no structural damage was observed. At the time

of the reconnaissance, most of the equipment within the refinery complex had not yet been

checked for operability. There was concern that some of the control equipment, and other

minor operating equipment might have been damaged. Local settlements may have damaged some

equipment, as illustrated in Figure 6.48. The pipeway support structures that were examined

showed no significant damage.

153
Most of the refinery was shut down during the earthquake for its annual inspection. Thus a serious fire hazard from the spilled oil fortuitously was averted. During the investigation, the company was checking much of the equipment throughout the complex for damage, and

a large scale clean-up effort was under way. The seriously damaged tanks were still not approachable because of the spilled oil.

6 . 7 Concrete Batch Plant, Sendai

This concrete batch plant is probably a representative small facility for the many thousands

of similar (in size) industrial or manufacturing establishments in the metropolitan area of

Sendai. It was operating at the time of the investigation. The facility sustained various

types of structural damage to equipment and tank supports, buckling of storage tank walls,

damage to structural steel framing, etc. It is very possible that this damage (and damage

to similar small facilities), was not reported and is not included in the preliminary damage

statistics that were available to the UJNR team members. The plant was inoperable for two

days after the earthquake while repairs were being carried out. Because most of the damage

was to structural steel braces, it apparently was easily repairable. In many cases the

bolted connections of the braces to the vertical load carrying supports were sheared.

Repairs were usually of two types: (1) the undamaged braces were realigned and the braces were welded to the gusset plates (in lieu of the previous bolting) and (2) damaged (presumably buckled) braces were replaced with new members, which were also welded in place (Fig- ures 6.50 and 6.51). The most remarkable feature of the repairs was how quickly the work

was completed, particularly at a time when skilled labor was presumably in short supply.

Some serious structural damage had not yet been corrected at the time of the investigation;

however, that damage was not to operating equipment and did not affect the day-to-day production. Except for some of the foundations and lower supporting structures, which were

not damaged, all of the structures, tanks, and equipment at the site are made of steel.

A large welded steel plate storage tank, containing sand and gravel, and reportedly full

during the earthquake, which was supported on a massive concrete pedestal, suffered buckling

along several locations at the base of the steel plate (Figures 6.52 and 6.53). It seems apparent that the buckling was caused by overturning forces, rather then by sloshing of the

contents. The tank and its superstructure and support structure did not experience any

other damage.

One of the light steel-framed structures at the plant was damaged, as shown in Figure 6.54,

apparently because of inadequate lateral bracing. The differential displacement caused by

the failure of the structure was responsible for damage to a connecting vertical steel stack

and associated piping. The stiffer first floor reinforced concrete structure was undamaged.

A similar structure, Figure 6.55, located in the immediate vicinity of the plant and properly braced with light steel cable or rod braces, did not suffer damage. The latter type

of construction is quite common in Sendai, and generally appeared to experience no significant damage.

154
Figure 6.50 Concrete Batch Plant, Sendai: view of the

repaired supporting substructure of a cement

bin and related equipment . The sheared bolts

at the brace connections have been removed and

the braces have been welded to the gusset plates.

Some of the buckled braces have been replaced

entirely.

155
Figure 6.52 Concrete Batch Plant, Sendai

a large gravel-and-sandstorage tank experienced

buckling of the welded steel

plate at its base.

Figure 6.53 Concrete Batch Plant, Sendai: a detailed view of the

damaged base of the sand and gravel storage tank.

Note the closely spaced anchor bolts. Similar damage

occurred at several locations along the circumference

A

156
Figure 6.54 Concrete Batch Plant, Sendai:

displacement due to damage to the light, unbraced steel

superstructure damaged the

vertical stack and the con- veyor belt structure.

Figure 6.55 Concrete Batch Plant, Sendai: a typical undamaged

light steel-framed structure braced with cable or rod braces.

157
7. EARTHQUAKE PERFORMANCE OF TRANSPORTATION LIFELINES*

7.1 INTRODUCTION

The Japanese Ministry of Construction (JMOC) reported that 78 highway bridges had been damaged as a result of the June 12, 1978, Miyagi-ken-oki earthquake. There were, however, no reports of damage to a multitude of pedestrian bridges in Miyagi prefecture. Only those

bridges having an estimated repair cost of 1 million yen ($5,000) or more were included in an inventory of damaged highway structures. Although damage to bridges was principally con- fined to those structures within Miyagi prefecture, some bridges sustained moderate damage

in Iwate and Fukushima Prefectures also. Of approximately 100 bridges in Sendai, only four were reported as having been damaged. Two of those bridges were inspected by UJNR team

members. The majority of damaged bridges were located in an area extending about 90 kilometers northeast of Sendai (see Table 5.1 and Figures 5.3 and 6.1).

The UJNR inspection team visited 13 highway bridge and four rail bridge sites, viewing

representative damage. Typical types of damage included flexural and torsional cracking of

concrete piers, displaced of dislodged girder bearing devices, settlements of abutments or

piers, and vibratory induced settlements of fills at bridge approaches.

Significant strong motion records were obtained from the Kaihoku Bridge, 65 km northeast of

Sendai and the Date Bridge about 75 km southwest of Sendai (just north of Fukushima City).

Only the Kaihoku Bridge site was visited by UJNR team members. Maximum ground acceleration

at Kaihoku was 294 gal, while maximum pier acceleration was greater than 500 gal. No ground record was obtained from the Date Bridge site. Maximum pier acceleration was 475

gal.

The Japanese National Railways stopped all trains following the earthquake until safety

inspections could be made. Most damage was caused by blockage of track, by landsliding, and

most train service was restored within 3 days following the earthquake. Heavy pier damage

occurred at a rail bridge site which required 10 days to reopen.

There was no reported damage to highway tunnels in Miyagi prefecture. Only one railway

tunnel on the New Sendai Shinkansen Line (fast train) northeast of Sendai was reported to have suffered minor, hairline cracks in its concrete lining.

The public bus system in Sendai was not adversely affected by the earthquake.

It is reported that airline traffic to and from Sendai was interrupted only briefly while a quick inspection of the airport was made by airport officials. Minor damage of the terminal

was reported.

No major damage was reported at Shiogama Port 18 km northeast of Sendai. Some pavement

settlement was noted. One free field strong motion record obtained from a SMAC B2 instrument at Shiogama Port recorded maximum accelerations of 266 gal in the N-S direction, 288

gal in the E-W direction, and 166 gal vertical component. For further discussion of strong

motion records, see Chapter 4 of this report.

7.2 BRIDGE DESIGN CRITERIA

A comparison of current (1978) seismic bridge design criteria used in the United States and

in Japan is presented prior to the documentation of bridge damage.

The bridges which were damaged in the June 12 earthquake in Japan were designed and con- structed using pre-1971 design criteria. Most of the damaged bridges are two-lane structures, situated in rural areas northeast of Sendai. The most noticeable difference in the

construction of bridges is the use of massive substructure elements. Most Japanese bridge

piers are very large, massive appearing structures which are designed to resist seismic

forces. Subtructures in the United States are designed for lower seismic force levels

and rely on ductile behavior of columns.

* Prepared by James D. Cooper, Federal Highway Administration Washington, D.C.

158
For purposes of comparing current U.S. and Japanese seismic design criteria the 1977 American Association of State Highway and Transportation Officials (AASHTO) and the 1971 Japan

Road Association (JRA), "Specifications for the Earthquake-Resistant Design of Highway

Bridges" are considered (see Refs. 7.1 and 7.2). The 1977 AASHTO criteria is an adaptation

of the criteria developed by the California Department of Transportation in 1973. The 1971

JRA criteria superseded provisions found in several different Japanese bridge codes, and were established in order to give a common basis for the seismic design of bridges. They

emphasize the method of evaluating seismic forces, the basic principles to be exercised

for testing site soil conditions, and general provisions to be observed in structural

detailing

.

Both criteria allow for the use of three alternate approaches for determining design earthquake force levels. The most commonly used is the equivalent static force method. For more complex bridges, either a response spectrum analysis or full dynamic analysis can be performed. The more common, equivalent static force method used by both countries is compared.

Table 7.1 summarizes the 1977 AASHTO and 1971 JRA criteria.

The approach is similar in that the lateral force design coefficient is comprised of factors relating to location (A and v^'kg), soil conditions (S and V2), and structure response

(R/Z, F, and 6). In addition, the JRA criteria incorporates an importance factor, v^. The

vertical seismic force is generally not considered in either criteria, except in the JRA

criteria for the design of bearings at the connection of the super and substructures. The

vertical design seismic coefficient of k

v

= 0.1 is used.

Use of either criteria requires the computation of the fundamental period of the bridge.

The AASHTO criteria specifies the following formula to approximate the period (T) of the

structure

T = 0.32/ W/P

which W is the dead load and P is the total uniform force required to cause a 1-inch maximum

horizontal deflection of the total bridge. The JRA presents several alternate equations for use in estimating the period of the bridge which are dependent on the type of structural

system, type of foundation, material of the pier, and direction of motion. The methods used

to calculate period give slightly varying values which, when used in conjunction with a design spectra, give greatly varying values for design force levels.

For purposes of comparing the AASHTO and JRA criteria, the lateral force design coefficients

are plotted in Figure 7.1. The comparison is made for a site having a depth of alluvium

between 24 and 46 meters (80 and 150 feet), in a highly seismic area. For this condition,

AASHTO requires A = 0.5g and JRA requires v^ = 1.0. Additionally, the JP^A importance

factor, v^ , which is 1.0 for bridges on expressways, general national highways, and principal prefectural highways, etc., and 0.8 for all others, is assumed to be 1.0.

For the conditions assumed, the value of the JRA lateral force design coefficient (k^) varies between 1.6 and 2.6 times the value given by the AASHTO criteria. The AASHTO criteria

are applicable to structures having a period less than or equal to 3 seconds while the JRA

criteria are applicable to structures having a natural period less than 5 seconds. The

discontinuity of k^ at T = 0.5 is due to the increase of the modification factor (6) to reflect structural dynamic response and ground conditions. The larger JRA lateral force

design coefficients would thus require the use of large substructure designs to resist

earthquake forces when compared to designs using AASHTO criteria.

Seismic design criteria for highway bridges are currently (1979) under review by both the

Japanese Ministry of Construction and the Federal Highway Administration. Both countries

are in the process of revising requirements for determining seismic design force levels

and structural details to provide improved resistance to earthquake induced ground motion.

7.3 BRIDGE DAMAGE

Significant bridge damage occurred during the June 12 earthquake. Given, however, the magnitude of the earthquake and the fact that most bridges damaged were pre-1960 vintage,

159
Criteria

TABLE 7.1

Equivalent Static Force Method Code Comparison

1975 AASHTO 1971 JRA

Lateral Force

(EQ) CFW k

h

W

Lateral Force

Design Coefficient

C = ARS

Z

Graphs of C as a function of bridge

period and depth of alluvium are given where:

A = max. expected to bedrock.

acceleration and related to 3 U.B.C. seismic zones.

R = normalized rock response as a function of bridge period.

S = soil amplification spectral

ratio as a function of bridge

period.

Z = reduction factor for ductility

and risk.

k

h

= (v lV2v

3 k0

)3

k = 0.2

3 is a modification

factor used when the

bridge period is > 0.5

sec. and is a function

of period and ground

condition, where:

v^ = seismic zone factor.

v

2 = soil factor based on depth of alluvium.

v.j = importance factor

based on qualitative

definition.

kg = standard horizontal

design seismic

coefficient = 0.2.

6 = modification factor

as a function of

bridge period when

period > 0.5 sec.

Framing Factor F = 1.0 for single columns.

F = 0.8 for continuous frames.

None

Vertical Force

Design Coeff.

None ky

= 0.1 for design of

bearing between sub

and superstructure.

Design Force for

Seismic Earth

Pressure

No Yes

Hydrodynamic

Pressure During

Earthquake

Mo Yes

160
BRIDGE PERIOD-SECONDS (Tj

Figure 7.1 Comparison of AASHTO and JRA Lateral

Force Design Coefficients

161
some dating back to 1930, bridges performed relatively well. The area of bridges affected

extended from 20 km south of Sendai to 90 km northeast of Sendai. Refer to Figure 6.1 for

location of bridges discussed. Table 7.2 summarizes the performance of those bridges

inspected following the earthquake.

The UJNR inspection team arrived in Japan 10 days following the earthquake. The response

plan to repair damage and open bridges incorporated by the Japanese Government was most

impressive. Three bridges in or near Sendai which suffered major pier damage were in the

process of being repaired and open to traffic. Other bridges in outlying areas were either

in various stages of repair or plans were being made to build replacement structures.

Following is a description of damage to those visited by the UJNR inspection team.

Kin-noh Bridge

The Kin-noh Bridge, (Figures 7.2 - 7.10) located about 65 km northeast of Sendai on National

Highway, Route 346, is a two-lane, 15 span multi-configuration structure that is 575 meters

long. The structure was constructed in 1956 and is comprised of nine simply supported plate

girder spans, each 28 m in length; four of the spans are totally suspended; five are simply

supported through-truss spans, each 60 m in length; and one is a simply supported plate girder span, 23 m in length. Three major earthquakes have occured in the region since con- struction of the Kin-noh Bridge: (1) in 1962 (2) on February 20, 1978, in which significant

damage occurred at one of the abutments and to the bearing devices; and (3) the current

earthquake in which one of the suspended spans dropped. Repair work from the February 20

earthquake was underway at the time of the June 12 earthquake and had included the replacement of bearings on the five truss spans and tying the truss spans together with restrainers

The abutment at the end of the nine plate girder spans had been shored, but not repaired.

Miyagi Prefecture has proposed replacing the bridge at an estimated cost of 16 million dollars (3.2 billion yen).

Yuriage Bridge

The 10-span Yuriage Bridge (Figures 7.11 - 7.18), constructed in 1962, is located 1.2 km

from the mouth of the Natori River on the outskirts of Sendai and is 107 km from the epicenter. It has seven prestressed concrete T-girders each 45 m in length and three main

spans which are twin cell, segmentally constructed, post-tensioned concrete box girders, 60,

90, 60 meters in length. The bridge was open to one lane of traffic because of heavy column

damage. No damage was reported to the three-span box structure. Excavation at the first

pier at the opposite side of the bridge was being done to determine the extent, if any, of

foundation damage.

Sendai Ohashi Bridge

The Sendai Ohashi Bridge over the Hirose River on Japan National Highway, Route 4, con- structed in 1965, suffered heavy pier damage (Figures 7.19 - 7.27). The structure is a nine-span, simply supported composite concrete and steel plate girder bridge with 34 m span

lengths. The bridge had been retrofitted at points across the joints at the piers with

steel restraining plates bolted to the girder webs. The bridge was closed to traffic the

night of June 12 while temporary pier supports were constructed at two of the more severely

damaged piers.

Although the UJNR team inspected the bridge site only 11 days after the earthquake, repair

efforts were well underway, making it impossible to view much of the original damage.

Abukuma Bridge

The Abukuma Bridge (Figure 7.28), located about 20 km south of Sendai on National Highway,

Route 6, near the junction of Route 4, is a two-lane, 17-span structure 571 meters long.

The structure is comprised of eight plate girder approach spans, each 18 m in length, seven

through truss-spans, each 55 m in length, which cross the Abukuma River, and two 18 m plate

girder spans. Significant damage occurred to the portal frame piers which were being

repaired at the time of the inspection (Figures 7.29 and 7.30).

162
TABLE 7.2

Summary of Highway Bridges Inspected

Name Map Location No. Type Main Damage

from Fig. 6 .

1

Kin-noh 35

Yuriage 22

Sendai 37

Abukuma 23

Kaihoku 29

Tenno 30

Kitakami 36

Kimazuka 27

Maiya 34

Toyoma 33

Ono 26

Iinogawa 31

Yanaizu 32

Steel Plate Girder,

Through Truss

Prestressed Concrete

I-Girders and Concrete

Box Girder

Steel Plate Girder

Steel Plate Girder

Steel Box Girder

Steel Plate Girder

and Tied Arch

Steel Deck Truss

Steel Plate Girder

Steel Gerber Truss

Concrete T-Beam

Steel Plate Girder

Steel Box Girder

Steel Deck Truss

Down-in span dropped out,

bearings dislodged.

Massive pier cracking,

bearing dislodgment;

pier settlement,

abutment cracking.

Massive pier cracking

footing damage, bearings

dislodged, abutment

damage.

Pier cracking.

None. Settlement of

roadway at abutment.

Pier cracking.

None. Apron settlement

at abutment.

Bearing dislodgement

;

possible pier tilting.

Brittle fracture of top

chord member and buckling

of top lateral truss bracing.

Flexural cracking of

T-beams and shear cracking of hinge seats; abutment cracking.

Abutment damage, bearing

damage, and possible pier

tilting.

Bearing dislodged.

Abutment settlement and

bearing damage.

163

Kin-noh Bridge. View of the collapsed

suspended plate girder span. Similar

damage occurred to bridges in the 1971

San Fernando and 1976 Guatemala earthquakes

because of lack of superstructure restraint

and small bearing seats. Suspended spans

are no longer used in seismically active

areas. (Courtesy J.M.O.C.)

Kin-noh Bridge. The only

visible pier damage occurred

at Pier 8, which is adjacent

to the collapsed suspended

span. Shear cracking extended

125 cm through the 152 cm deep

pier, approximately one-fourth

the way up the column from

grade

.

j

165

Figure 7.4
Figure 7.5 Kin-noh Bridge. The girders at Pier 8 displaced

longitudinally toward the abutment 55 cm allowing

the unrestrained suspended span to drop off the 45 cm hinge seat. The movable girder bearing plate came to rest at the edge of the pier cap. The fixed bearing

on Pier 7, the opposite side of the suspended span,

displaced longitudinally 0.5 cm. Figure 7.6 Kin-noh Bridge. Evidence of minor transverse displacement of the main girder with broken keeper. This

reportedly occurred at the time of the February 20

earthquake

166
Figure 7.7 Kin-noh Bridge. Damaged abutment from the February 20,

1978, 6.7 magnitude earthquake. New web stiff ener at point of temporary shoring.

Figure 7.8 Kin-noh Bridge. Detail of bearing damage and abutment

ledge failure, from February earthquake. Note extension

of anchor bolt caused by 20 cm displacement of span

towards abutment.

167
Figure 7.9 Kin-noh Bridge. Extension of anchor bolts at Pier 6. The foreground shows a portion of repaired lower

chord t russ member

Figure 7.10 Kin-noh Bridge. Bearing restraining device used on

the repaired bearing supports of the truss spans. The

restrainers were placed before the June 12 event.

168
Figure 7.11 General view of the Yuriage Bridge showing the first

two columns which were heavily damaged.

Figure 7.12 Yuriage Bridge. Liquefaction in the flood plan below

the bridge.

169
Yuriage Bridge. Evidence of light girder

impacting with the abutment and pronounced

shear cracking of exterior girder at the

bearing

Figure 7.14 Yuriage Bridge. Pier 1,

founded on a caisson 19 m

deep and 2 m by 4 m in plan,

suffered heavy shear cracking,

The pier cap was reported to have settled uniformly 5 cm.

170
.15 Yuriage Bridge. The face of Pier 1 showing

severe distress. The plaster of paris patchwork

is used to determine if additional pier cracking

has occurred.

Figure 7.16 Yuriage Bridge. Detail

showing 1 cm offset of

cracking, indicating torsion

in pier

.

171
Figure 7.17 Yuriage Bridge. Temporary girder supports at Pier 1. Bearings showed evidence of girder displacement - broken

keeper and containment plates.

Figure 7.18 Yuriage Bridge. Evidence of 8 cm of longitudinal movement as shown at the handrail expansion joint, Pier 2. However, there was no evidence of damage to the girders

or the second pier.

172
Figure 7.19 General view of the Sendai Ohashi Bridge . The deck arch

bridge in the background, which is comprised of two steel plate girders with cross bracing and supported on slender circular columns, carries an industrial water

pipeline and was reportedly undamaged.

Figure 7.20 Sendai Ohashi Bridge. Temporary cribbing used to support

the steel plate girders.

173
Figure 7.21 Sendai Ohashi Bridge, cross pier dimensions

the massive pier caps

Typical pier configuration,

are approximately 5 m x 2 m. (Courtesy J.M.O.C.

)

The

Note

Figure 7.22 Sendai Ohashi Bridge. Typical pier damage at the con- struction joint between pier and cap. The vertical rebars

are buckled across the joint. Significant concrete spalling is evident. Horizontal cracking around the pier was discovered upon excavation of soil around the piers.

(Courtesy J.M.O.C.)
Figure 7.23 Sendai Ohashi Bridge. Detail showing buckled vertical

rebar at the construction joint. Strong motion records

in Sendai indicated approximately 100 gal. vertical

accelerations. (Courtesy J.M.O.C.)

Figure 7.24 Sendai Ohashi Bridge. Typical damage to the base of a pier before repair.

175
Figure 7.25 Sendai Ohashi Bridge. Typical damage being

repaired at the base of the pier. Note the

outward buckling of the underformed vertical

rebar. The concrete cover had been roughened,

the footing strengthened, and additional rebar

placed to strengthen the pier.

Figure 7.26 Sendai Ohashi Bridge. Details

showing the added reinforcing

concrete form work. The pier

thickness will be increased on each side by 50 cm at the top,

tapering to 70 cm at the base.

176
Figure 7.27 Sendai Ohashi Bridge. Abutment damage. Bearing plate

broken and evidence of girder impact at abutment.

Figure 7.28 General view of the Abukuma Bridge. Note the trace of

pier cracking on the pier in the foreground and scaffolding at and surface preparation of the pier in the background.

177
r.r'

tioi h

m

Figure 7.29 Abukuma Bridge. Outward buckling of vertical

rebar at one of the damaged piers.

Figure 7.30 Abukuma Bridge. Typical

repair of a damaged pier includes epoxy injection of

cracks, epoxy covering of

buckled rebar, preparation of

existing concrete surface to accept fresh concrete, em- placement of vertical rebar

into the footing and horizon- , tal rebar into the pier, and

an increase of the gross cross sectional area of the pier

with new concrete. The technique is similar to that used on the Yuriage and Sendai

Ohashi bridges.

178
Caihoku Bridge

The Kaihoku Bridge, located on Principal Route 51, approximately 45 km northeast of Sendai,

Ls a two-lane, five-span continuous single cell steel box girder, 285 m in total length

(Figure 7.31).

The bearings are movable at all piers except Pier 2, Figures 7.32, where a SMAC-B type

strong motion accelerograph is located. Hydraulic dampers acting in the longitudinal direction have been incorporated into the bearing system. All piers and the abutments are

skewed. A free field SMAC-B instrument was located on rock between Pier 1 and Pier 2,

approximately 30 meters from the structure. The axes of the pier and free field instruments

rfere aligned with principal axes of the bridge. The peak recorded accelerations are:

Longitudinal Vertical Transverse

Free Field 200 gal 113 gal 294 gal

Pier 500 gal or more (off scale) 138 gal 338 gal

The only damage noted was minor settlement of an abutment wing wall. Closer inspection by

the Japanese revealed detachment of mortar near anchor bolts of the dampers. There was not visible damage to the piers or bearings, and no evidence of girder impacting with the east

abutment.

Tenno Bridge

flhe Tenno Bridge, Figure 7.33, located approximately 50 km northeast of Sendai on National

jRoute 45, is comprised of several steel plate girder approach spans with a tied arch main

span. The total bridge length is 367 meters. The only damage occurred at the southwest

wall pier where a 45° crack extended from the pier cap to a point one-third the way down the

pier. Traffic was limited to one lane at the damaged pier.

Kitamami Ohashi Bridge and Dike

The seven-span, 400 m Kitakami Ohashi Deck Truss Bridge, completed in 1976, crosses the

Kitakami River, 60 km northeast of Sendai on Principal Route 23 (Figure 7.34). The structure suffered no visible structure damage although there was minor settlement of the abutment apron. The structure was designed with the latest Japanese criteria and incorporated

new abutment bearing details (Figure 7.35). Significant damage occurred to the dike and

roadway along the Kitakami River south of the bridge site, (Figure 7.36). The most severe

damage occurred along the approximately one-half kilometer length in which the roadway

on top of the dike settled about 1.5 m. The roadway was closed to traffic, the dike sandbagged, and continuous steel sheet piling was being driven to stabilize the dike.

Kimazuka Bridge

The Kimazuka Bridge, constructed in 1931, is located on Principal Route 32, approximately 35

km northeast of Sendai (Figure 7.37). It is a 19-span, simple supported, steel plate girder

structure 236 m in length. Damage occurred to the top of the piers where bearing shoes

pulled out of the top of the portal frame (Figures 7.38, 7.39). Longitudinal movement of

the girders almost exceeded the bearing area of the bent cap. Sand boils and ground cracking were noted at the bridge site.

Maiya Ohashi Bridge

The Maiya Ohashi Bridge, Figure 7.40, is a three-span Gerber-truss bridge located on National Highway Route 342 approximately 62 km northeast of Sendai. The 181 meter long

truss bridge, constructed in 1928, was closed to traffic because of a brittle fracture

through the rivet holes of the top chord channel members at the first pier, Figure 7.41. Four steel plates had been welded around the top chord members. Some of the small steel

angle top lateral bracing members were buckled in the vicinity of the pier, Figure 7.42.

No damage was reported to either of the piers or abutments. The Maiya Bridge is scheduled

to be replaced.

179
Figure 7.31 General view of the Kaihoku Bridge. (Courtesy J.M.O.C.)

Figure 7.32 Kaihoku Bridge. Pier 2 showing the SMAC-B2 instrument (which recorded a peak acceleration greater

than 500 gal. in the longitudinal direction) and

the fixed bearing and hydraulic damper system.

180
Figure 7.33 The main tied arch span of the Tenno Bridge with the

cracked wall pier in the foreground. Note the smaller,

pedestrian bridge in the background.

Figure 7.34 Kitakami Ohashi Bridge. No structural damage was

reported

.

Figure 7.37 Spalled concrete at bent cap of Kimazuka Bridge.

183
Figure 7.39 Vertical displacement of dislodged span.

Figure 7.40 The Maiya Ohashi Bridge.
Figure 7.41 Maiya Ohashi Bridge. Steel plates welded to the top

chord channel members. Note the clean fracture at a line passing through the centerline of the rivet holes

of the lattice bracing and the permanent 2.5 cm separation.

Figure 7.42 Maiya Ohashi Bridge. Buckled lateral bracing of the

overhead truss.

185
Toyoma Bridge

The Toyoma Bridge is a 13-span concrete T-beam bridge constructed in 1945, (Figure 7.43).

Prior to the earthquake, the bridge, located about 60 km northeast of Sendai, was restricted

to automobile traffic because of damage suffered during the February 20, 1978, earthquake.

The bridge was closed following the June earthquake. Flexural induced cracking of the girders occurred at the center of the spans and at the haunched ends over the piers. Shear

cracking was also noted at the corners of the concrete hinge seats of several suspended

spans. The ground motion, between 0.1 and 0.2g, was sufficient enough to induce pavement

cracking of the roadway.

7.4 HIGHWAY DAMAGE

Widespread highway damage (e.g., Figure 7.44) occurred in the region north and east of Sendai. Typical damage included settlement of bridge approaches, cracking of pavements, failure of roadway embankments, and blockage of roads from rockslides. This type of damage has

been documented in reports on previous large earthquakes in Alaska, Japan, California, and

Guatemala and is virtually impossible to design against.

A major toll road expressway, owned and operated by the Japan Highway Public Corporation,

experienced pavement cracking in numerous spots where fill material was used. Additional

settlement occurred at the approach to bridges along the expressway which was closed from

the time of the earthquake until 7:00 a.m., June 15, while temporary repairs were made.

Reinforced concrete approach settlement slabs were used at many of the bridge abutments.

Use of the slabs forced settlement to occur at the end of the slab instead of at the abutment, as illustrated in Figure 7.45.

In areas of rugged terrain, particularly along the

tected against earthquake induced landslides by st way with a covering of shotcrete. Rockslides are mesh screening which is anchored and hung from the

the roadway or by the construction of rock bins at 7.46 and 7.47). These techniques worked quite wel

but were not utilized in the area affected by the

West Coast of Japan, roadways are proabilizing the steep slopes above the roadcontained or controlled by emplacing wire

crest of the slope and extends down to the base of the roadway cut (see Figures

1 in the January 1978 Off-Izu earthquake,

June earthquake.

7.5 RAILROAD DAMAGE

The Japanese electric railroad serves a vital role in Japan. The train is relied upon by

most Japanese in major cities such as Sendai as the means of commuting between home and

work. The train is also the most popular form of intercity travel within Japan. Major damage was reported at one rail station when the retaining wall supporting the boarding platform collapsed, resulting in track blockage. The main Sendai train station, including the

structural portion of the electrification system, was reportedly undamaged. However, the

trains were inoperative because of massive power failures. Several rail bridges were

severely damaged and are discussed below.

Eai River Rail Bridge

The Eai River Bridge (Figure 7.48), owned by the Japanese National Railways (JNR), is a dual

eight-span steel plate girder structure 160 m in length, which is located 40 km northeast

of Sendai. The superstructure is supported by massive unreinforced concrete gravity piers

on caisson foundations. Ground acceleration in the area was estimated by the Ministry of

Construction to be 200-250 gal. Two piers were severely damaged when large wedged shaped

sections of concrete dropped out below a construction joint.

The JNR New Sendai Shinkansen Trunkline

JNR is constructing the New Sendai Shinkansen Trunkline, a series of elevated structures for

the fast train, extending through Miyagi Prefecture to the northern tip of Honshu. The

line is scheduled for completion in 1981. The majority of the elevated structures, a series

of prestressed concrete T, I, and box girders with varying configurations of single and

multiple column bents, are completed and experienced varying degrees of damage, namely to thf

186
Figure 7.43 General view of the Toyoma Bridge which was closed to traffic. The columns in the background support an independent steel box girder

pedestrian structure which was undamaged.

Figure 7.44 Typical Road Fill Failure.

187
~ 10 cm SETTLEMENT

R/C SETTLEMENT SLAB

I

7 m

GIRDER

ABUTMENT

Figure 7.45 Detail of Reinforced Concrete Approach Settlement Slabs,

Figure 7.46 Wire mesh screening used to contain land and rockslides along

highways

188
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189
bearing shoes and columns (see Figures 7.49 - 7.54). Damage was concentrated to those new structures located approximately 30 to 40 kilometers northeast of Sendai. All structures were designed using the 1971 Japanese seismic code.

7.6 TUNNEL PERFORMANCE

Five short, unreinforced concrete-lined highway tunnels through rock, located about 20 km

northeast of Sendai on National Highway Route 45, suffered no apparent damage (e.g., Figure

7.55). The Japanese National Railways reported that one concrete-lined tunnel on the Sendai

New Shinkansen Line about 40 km northeast of Sendai had hairline cracking.

7.7 CONCLUSION

The June 12 Miyagi-ken-oki earthquake demonstrated the ability of the Japanese Government,

both local and national, to respond to the adverse conditions created by a major natural disaster. Specifically, the prompt enactment of their disaster response plan alleviated major

problems which could have resulted from the prolonged loss of major transportation routes. The plan allowed for the immediate identification of damaged structures, emergency temporary

repairs, and initiation of permanent repair within a matter of days after the earthquake*

Major routes, although severely damaged, were opened to traffic within three days after the

earthquake.

Bridge substructures which were severely damaged were massive reinforced concrete piers,

which responded essentially as non-ductile, rigid bodies to the earthquake motion. In spite

of the major damage of these elements, the designs proved satisfactory in that collapse was avoided and the bridges remained operational for emergency use. Although this type of con- struction proved successful, it would be prohibitively expensive for use in the United

States where the philosophy is to utilize more ductile, energy absorbing designs.

Evidence of pier tilting and abutment movement existed which probably caused rather extensive damage to bridge bearing devices. This type of movement is exceptionally difficult to control. This damage indicates the need to perform in-depth site investigations in areas where high water tables exist and to make special considerations in foundation design.

The Kin-noh Bridge was being repaired as a result of damage induced by the February 20

earthquake. Bearings were being strengthened and spans were being restrained at their

expansion joints. The failure of the suspended span which had not been retrofitted could

be expected and demonstrates once again the need to provide for continuity of the superstructure across all joints.

Damage to bridges inflicted by this and past earthquakes reinforces the need to consider an agressive retrofit program for those structures built under older seismic design criteria.

The most vulnerable components requiring retrofit are bearings and columns, including con- nections into the foundation. Modest investments can significantly reduce future damage and

help to avoid collapse of older, important structures.

As in previous earthquakes, significant damage occurred to roads in the area of strong

ground shaking. Embankments fail, fill material settles, and land- and rockslides block

roads and trackage. These types of damage are difficult to control, although stabilization

and control techniques utilized by the Japanese do help. Special consideration, including

the use of control and stabilization techniques described earlier in this chapter and/or

the development of specific emergency response plans in susceptible areas, should be given

to those important routes which must remain open following a major earthquake.

Given the magnitude of the Miyagi-ken-oki earthquake, transportation structures in general

performed very adequately. Air, train, bus, and highway travel, although temporarily interrupted, did not adversely hinder emergency operations or affect the general movement of commerce or people.

7 .8 REFERENCES

7.1 "Earthquake Resistant Design for Civil Engineering Structures, Earth Structures, and

Foundations in Japan," compiled by the Japan Society of Civil Engineers, Tokyo, Japan,

1977.

7.2 "Standard Specifications for Highway Bridges," Twelfth Edition, American Association

of State Highway and Transportation Officials, Washington, D.C., 1977.

190
The Natori River Bridge is a three-span continuous single

cell reinforced cast-in-place concrete box girder structure

on 3 m x 6 m piers approximately 8 meters above grade.

Typical damage included cracking in the central part of

the pier where the gross cross-sectional area of vertical

steel was reduced.

Natori River Bridge. Detail of spalled concrete at the

Natori River Bridge site showing the buckled vertical rebar.

191
Figure 7.51 Typical structures which experienced pier cracking

near the Rifu Construction Office of the Sendai

Shinkansen Construction Bureau, JNR.

Figure 7.52 Shear cracking in the relatively lightly reinforced

upper portion of the pier.
193
Typical undamaged highway tunnel on Route 45 along

the coast between Sendai and Ishinomaki to the

north.

194
8. LIQUEFACTION AND DAMAGE TO DIKES

8.1 INTRODUCTION

The June 12, 1978, Miyagi-ken-oki earthquake caused soils to liquefy at several sites on the

coastal flood plain bordering the Bay of Sendai. The engineering structures most extensively damaged by liquefaction were flood-control dikes composed of earth fill. The damage

iconsisted primarily of cracking, settlement, and minor lateral spreading and slumping. Durling a trip to Miyagi Prefecture on June 26, 1978, six sites were visited where dike damage

had occurred (Figure 8.1). Additional information on earthquake-induced dike damage was

! provided by officials of the Public Works Research Institute (PWRI), the Japanese government

I agency charged with building and maintaining river works. Liquefaction-induced damage also

occurred in an uncompacted sand fill in the port of Ishinomaki.

18.2 SUMMARY OF DIKE DAMAGE

Reported damage sites are scattered in an arc extending from the Abukuma River on the southwest to the mouth of the New Kitakami River on the northeast (Figure 8.1). Within this

II region, damage occurred along parts of the Abukuma, Natori, Hirose, Yoshida, Eai, Naruse,

'old Kitakami, and New Kitakami rivers (Figure 8.1, Table 8.1). Most or all sites are underJ lain by unconsolidated Holocene coastal flood plain deposits; a few may be underlain by

Holocene alluvial fan deposits (Geological Survey of Japan, 1968; Geologic Map of Miyagi

Prefecture). Many of the damaged dikes are founded on river channel deposits less than 500

l years old. Because of the proximity of all dikes to rivers, the water tables under them are

I close to the ground surface at all times. A total of 28 linear kilometers of dikes was damaged in this earthquake, and total repair costs of dikes and other river works amounted to about 10 billion yen (approximately $50 million) (Ministry of Construction of Japan, unpublished data). Most of this damage was caused by liquefaction.

The dikes are composed chiefly of compacted sand. They are built directly on alluvial fan

1 or flood plain sediments with little or no ground improvement. Most dikes are several

meters high, several meters wide at the crest, and have side slopes of 2 Horizontal: 1 VerS tical or less. At the time of the visit, repairs to the dikes were already well advanced.

' The repairs consisted of regrading and filling cracks, placing sand bags, and driving steel

sheet piles to reduce seepage under the dikes.

8.3 GEOLOGIC SETTING

Most sites of damage are on the coastal plain bordering the Bay of Sendai; a few are on the

margin of Natori River alluvial fan and may be underlain by alluvial fan deposits (Geologij cal Survey of Japan, 1968; Geologic Map of Miyagi Prefecture). The coastal plain sediments

are unconsolidated Holocene gravels, sands, silts, and clays primarily deposited by rivers;

beneath most dikes these deposits are several tens of meters thick (Hase, 1967). The river

deposits are of three main types: channel, natural levees, and back marsh deposits (Tohoku

Regional Construction Bureau, MoC , unpublished data; H. Nakagawa, Tohoku University, unpublished data). Engineering structures including dikes founded on channel or back marsh

deposits performed relatively poorly during the earthquake. Liquefaction occurred most com- monly in channel deposits.

Performance of engineered structures founded on natural levee deposits varied from place to place. These deposits are generally thin, and the performance of structures was therefore

strongly influenced by the materials underlying the natural levees (H. Nakagawa, Tohoku

University, oral communication). Structures near the coast, founded on beach ridge and

dune sand deposits sustained little damage in the earthquake. Natori River alluvial fan

materials consist primarily of gravel but also contain a few thin layers of sand and silt

(Hase, 1967).

Prepared by David K. Keefer, U.S. Geological Survey, Menlo Park, California.

195
Figure 8.1 Dike Damage in Miyagi Prefecture

196
TABLE 8.1

DIKE DAMAGE IN MIYAGI PREFECTURE

Total length of dike

affected by cracking,

settlement, lateral

Number of spreading, or slumping

River Bank 1 damage sites (kilometers)

Abukuma left 2 0.38

r i eh t 5 0.68

Natori left 11 1.87

right 6 2.17

ni lUbL left o o right 5 0.38

Yoshida left 9 0.51

right 12 5.50

Eai left 5 2.90

right 6 0.21

Naruse left 13 0.79

right 10 1.08

Old Kitakami left 3 0.15

right 9 0.29

New Kitakami left 16 7.13

right 17 4.13

TOTAL 129 28.17

Information furnished by the Tohoku Regional Construction Bureau.

Right or left relative to an observer facing downstream.

197
8.4 FIELD OBSERVATIONS OF DIKE DAMAGE

8.4.1 Natori River (Sites 1 and 2)

Lateral spreads, fissures, and sand boils were apparently widespread along the Natori River

for 3 km upstream from its mouth (T. Tazaki, PWRI, oral communication). In this area the

flood plain is underlain by fluvial sand that extends to a depth of 15 m or greater (Hase,

1967). Two damaged dikes in this area (Figure 8.1) were visited.

At Site I, liquefaction caused slumping, lateral spreading, and settlement of up to 1.5 m

along a 160-m-long section of the dike (Figures 8.2, 8.3, and 8.4). Longitudinal cracks

several tens of meters long opened in the dike crest. Between the dike and the river,

fissures striking obliquely to the dike formed, and sand was ejected from them (Figure 8.5).

Other fissures trending parallel to the dike and the river formed near the river bank, more than 100 m from the base of the dike. The occurrence of fissures and sand boils in ground

away from the dike indicates that liquefaction took place primarily in material beneath the

dike and not in the dike material itself.

The configuration (Figure 8.4) and composition of this dike are typical of those seen throughout Miyagi Prefecture. The dike is composed primarily of compacted, fine to medium

sand. It rises 2 m above the high water level of the river and is 4 m wide at its crest.

Its riverward flank has a slope of 2H: IV. The opposite flank descends as a series of

slopes (2H: IV) and benches to the agriculture land beyond.

The damaged section is built on a former channel abandoned by the river less than 500 years

ago. Beneath the dike, fluvial sand extends to a depth of at least 60 m (Hase, 1967), and

much of the top 15 m of sand is fine grained, loose, and well sorted (poorly graded) (Tohoku

Regional Construction Bureau, MoC, unpublished data).

Liquefaction previously took place at this site during a M 6.7 earthquake in February 1978

(T. Tazaki, PWRI, oral communication). The same section of dike was affected and the same materials liquefied in both the February and June earthquakes.

At Site 2 (Figure 8.1), the dike is contained by a concrete retaining wall (Figures 8.6,

8.7, 8.8, and 8.9). A section of the retaining wall several hundred meters long moved about

30 cm toward the river. Longitudinal fissures opened in the dike behind the retaining wall

and in a concrete pavement along part of the dike. The dike also settled by as much as 30 cm. This site, at the mouth of the river, is underlain by at least 20 m of sand (Hase,

8.4.2 Yoshida River (Site 3)

This was one of the most severely damaged sections of dike in Miyagi Prefecture. Settlements of up to 1 m occurred over a distance of 5 km, longitudinal cracks and scraps formed

in the dike crest, bulges appeared in the lower slopes, and sand boils occurred along some cracks (Figures 8.10, 8.11, 8.12, and 8.13). The cracks and bulges indicate that lateral

spreading and slumping took place. The damaged section rests on the fan-delta of a small

stream, and a boring near this site penetrated 15 m of silt, 2 m of fine sand, and 5 m

of coarse sand (Tohoku Regional Construction Bureau, MoC, unpublished data; Hase, 1967).

Bedrock lies at an average depth of 35 m.

8.4.3 Eai River (Site 4)

Sand boils were common in an old river channel at Site 4, on the right bank of the Eai River

(Figure 8.14). A concrete block fence near this channel was cracked by lateral spreading

toward the old channel bank (Figure 8.15). Damage to the dike on this side of the river was

minor. Across the river from Site 4, cracks up to 80 cm deep and 10 cm wide occurred in the

dike. On both sides of the river, the foundation material contains much soft clay. Some

layers of silt and sand may also be present. It was reported that the dikes were built

relatively slowly, and significant settlement took place during construction (K. Kawashima,

PWRI, oral communication).

1967).

198
Figure 8.2 Site 1, Natori River, view downstream (southeast) along

repaired portion of dike. Dike is made of compacted

sand. It rises 2 m above the high water level of the

river and has side slopes of 2H:1V. Natori River in

center-left background.

Figure 8.3 Site 1, Natori River. Slumping of dike on flank away

from river. View north. (Photo courtesy Tohoku Regional

Construction Bureau)

199
Figure 8.4 Site 1, Natori River—cracking, settlement, slumping, and lateral

spreading induced by liquefaction. (From Tohoku Regional Construction Bureau, MOC, unpublished data)

v H.W.L

Pre-earthquake outline of dike

Post-earthquake outline of dike

I i l 0 12 34m

Figure 8.5 Site 1, Natori River. Liquefaction-induced cracks and sand

boils in ground between river and dike indicate that liquefaction took place in materials beneath the dike. Sand in

center-ground to left of crack is from sand boil. Sand bags on dike were placed after the earthquake as a repair measure, View is south.

,

200
Figure 8.6 Site 2, Natori River. View

is west along repaired portion

of dike. Note patch across

offset in retaining wall offset

caused by lateral spreading

during earthquake. Retaining

wall rises approximately 1 m

above roadway

.
Figure 8.8 Site 2, Natori River. View is west

across tributary of Natori River,

Dike section shown in Figs. 8.6 and

8.7 is to right of houses in background of this figure. Note crack

in concrete pavement in foreground

is aligned with crack in retaining

wall in background.

Figure 8.9 Site 2, Natori River —Retaining wall

moved laterally and dike crest settled

(From Tohoku Regional Construction

Bureau, MOC, unpublished data)

area of cracking and settlement

3m

crack

202
Figure 8.10 Site 3, Yoshida River. View east (downstream)

along section of dike where repairs are underway

Dike crest settled as much as 1 m over a length

of 5 km. Sand bags have been placed as part of

repair process.

Site 3, Yoshida River.

Cracks in dike caused by

slumping and lateral spreading. Cracks are 10-30 cm wide. View is west. (Photo

courtesy K. Kawashima, PWRI)

203

Figure 8.11
Figure 8.12 Site 3, Yoshida River. Scarps in dike caused by slumping.

Note man in background for scale. (Photo courtesy

K. Kawashima, PWRI)

Figure 8.13 Site 3, Yoshida River. Steel sheet piles being placed by

vibratory driver as part of repair process. Purpose of

sheet piles is to reduce seepage under part of dike weakened

by earthquake.

204
s

.<5 *?

W RIVER

100 —*- 200 —h- 300 meters

1 LEGEND

Q Sand boil

ZT.'Z Dike

Old river channel

Figure 8.14

nrrrn 1

Ground crack caused by lateral spreading

Concrete block fence

Site 4, Eai River —Most

sand boils occurred in old

river channel. Minor

cracking of dike apparently

occurred where dike crosses

old channel, but cracks were repaired prior to visit. (After Tohoku

Regional Construction

Bureau, MOC, unpublished

data)

n igure 8.15 Site 4, Eai River - View southwest from crest of

dike. Crack (indicated by heavy line) in fence

and rice field caused by lateral spreading toward

bank of old channel in background.

205
8.4.4 Old Kitakami River (Site 5)

Sand boils occurred in the rice field adjacent to the dike (Figure 8.16), but damage to the

dike itself was apparently minor. Subsurface material at Site 5 consists of alternating

layers of silty sand and clay to a depth of 15 m. (T. Tazaki, PWRI, oral communication).

8.4.5 New Kitakami River (Site 6)

The dike and paved roadway at Site 6 settled up to 1.5 m and cracked over a distance of 4 km

(Figures 8.17 and 8.18), and sand boils formed on both flanks of the dike, which is built over an old river channel. According to data from borings completed by the Tohoku Regional

Construction Bureau, MoC , the soil under the damaged part of the dike is similar to the soil

under an adjacent, undamaged section. To a depth of 8 in, the soils consist of gravels,

sands, and silts with a few thin layers of clay. N-values (blows/foot from a standard penetration test) for most soil layers under both sections are less than 10. Reasons for the

differences in behavior between damaged and undamaged sections are currently under study

by Japanese engineers.

8.5 LIQUEFACTION IN THE PORT OF ISHINOMAKI 1

In the port of Ishinomaki, a fine-sand fill liquefied, causing severe damage to anchored

steel-sheet-pile bulkheads. The fill material had been dredged from the seafloor and

placed hydraulically with no compaction. It was placed next to old beach deposits, and

the boundary of the liquefaction damage followed the contact very closely; the beach deposits were not involved in the liquefaction.

8.6 CONCLUSION

The Miyagi-ken-oki earthquake caused cracking, settlement, lateral spreading, and slumping

of man-made dikes along several rivers in the prefecture. Most of the damage was due to liquefaction. A total of 28 linear km of dikes were damaged, and total damage to dikes and

other river works was approximately $50 million. Liquefaction also occurred in hydraulic

fill composed of fine sand in the port of Ishinomaki. These effects are currently being

investigated by several Japanese scientists and engineers; some reports have already been

published (Yoshimi and others, 1978; Okubo and Ohashi, 1979; Tatsuoka and others, 1979; Yamamura and others, 1979), and other reports should be forthcoming in the near furture.

8.7 REFERENCES

1. Geological Survey of Japan, 1968, Hydrogeological Map of the Coastal Region of Bay of Sendai. Hydrogeological Maps of Japan 16, 1 map, scale 1: 100,000.

2. Geologic Map of Miyagi Prefecture, scale 1: 200,000 (legend in Japanese).

3. Hase, Kotaro, 1967, Geology of the Alluvial Plains of Miyagi Prefecture (in Japanese

with English figure captions), Contributions from the Institute of Geology and Paleontology, Tohoku University, No. 64, 45 p.

4. Okubo, T., and Ohashi, M. , 1979, Miyagi-ken-oki, Japan earthquake of June 12, 1978, general aspects and damage, Report distributed at 2nd U.S. National Conference on Earthquake Engineering, Stanford, California, 15 p. (In English)

5. Tatsuoka, F., Ohkochi, Y., Fukushima, S., Igarashi, H., and Yamada, S., 1979, Soil

liquefaction and damage to soil structure during the earthquake off Miyagi Prefecture

on June 12, 1978, Institute of Industrial Science, University of Tokyo, Bulletin of

Earthquake Resistant Structure Research Center, No. 12, p. 3-13. (In English)

6. Yamamura, K. , Iwasaki, T., Sasaki, Y. , Koga, Y., Taniguchi, E., and Tokida, K. , 1979,

Ground failures and damage to soil structures from the Miyagi-ken-oki, Japan earthquake

of June 12, 1978, Report distributed at 2nd U.S. National Conference on Earthquake

Engineering, Stanford, California, 16 p. (In English)

7. Yoshimi, Y., Tohno, I., and Tokimatsu, K. , 1978, A report on the Miyagi-ken-oki, Japan,

earthquake of June 12, 1978: Part II: Geotechnical aspects of damage, International

Conference on Microzonation, 2nd, San Francisco, Proc, v. 1, p. 600-605. (In English)

1 Data kindly provided by Mr. Hajime Tsuchida, Chief, Earthquake Resistant Structures Lab, Port and Harbor Research Institute, Ministry of Construction.

206
Figure 8.16 Site 5, Old Kitakami River - Sand boils in rice field.

Plants are several centimeters tall. Damage to the

dike at this site was minor. (Photo courtesy

K. Kawashima, PWRI)

Figure 8.17 Site 6, New Kitakami River. View east along crest of

dike and highway that are being repaired. Uneven

nature of highway surface is due to liquefaction-induced

differential settlement. Settlements of up to 1.5 m

occurred along a distance of 4 km.

207
Figure 8.18 Site 6, New Kitakami River. Cracking

of dike crest and roadway due to liquefaction-induced slumping.

(Photo courtesy K. Kawashima, PWRI)

208
9. SEISMIC- INDUCED LANDSLIDES

9.1 INTRODUCTION

Several thousand landslides were triggered by the June 12, 1978, Miyagi-ken-oki earthquake.

Landslides were concentrated within Miyagi and northern Fukushima Prefectures. The landslide distribution was densest along the coast nearest the epicenter from Sendai northeast

to the area around Matsushima. Landslides were responsible for 1 death, 1 injury, 2 houses

destroyed and 13 houses damaged (Y. Tsuruya, 1978, unpublished data; Tohoku University

i report, 1979).

Small rock falls and rock slides issuing from steep slopes /ere the most abundant landslides.

Along the mountainous roads of the Ojika Peninsula, these landslides were generally less than

J 10 m

J in volume and occurred in closely fractured Triassic and Jurassic slate and interbedded

j quartzite. The largest contained several thousand cubic meters of debris and occurred on natural slopes in tuffaceous deposits near Matsushima and eastward on slopes near the mouth

of the Naruse River (Figure 9.1).

Although fewer in number, rotational slumps in artificial fill were larger than most rock

falls and slides and caused significant damage to highways and buildings. Such slumps within the city limits of Sendai were responsible for damage and destruction to houses. The

poor seismic performance of fills indicates that they could be hazards in future earthquakes.

j The author spent approximately three days surveying seismic-induced landslides and their

effects from south of Sendai along the Natori River to the mouth of the New Kitakami River.

Data included within this report comprises observations from the author's reconnaissance,

information provided by Mr. Y. Tsuruya of the Japanese Ministry of Construction, and data

from a report published by Tohoku University (1979).

The following descriptions of seismic-induced landslides are presented at site observations

, (referring to Figure 9.1 for locations of individual landslide sites and local geography).

The landslide sites depict noteworthy and representative examples of the different kinds of

landslides that occurred in this earthquake. Sites 1 and 4 through 8 are described with the

aid of supplemental data and photographs provided by Mr. Y. Tsuruya of the Slope Protection

J Division, Ministry of Construction, Tokyo.

9.2 ROCK FALLS AND ROCK SLIDES ON NATURAL SLOPES

9.2.1 Site No. 1

Two of the largest rock falls from the earthquake occurred near Takayamashita in Matsushima

town west of the Takagi River on steep (greater than 45°) natural slopes. The larger of

these rock falls (Figure 9.2) occurred in a deeply weather and closely jointed Miocene tuff

breccia (Geologic Map of Miyagi Prefecture) exposed in a 45-m scarp. The slope affected is

approximately 110 m wide, and the volume of debris is about 6,000 m^. The rock fall damaged

four houses built next to the slope. A close view of some of the damage to the house second

from the left in Figure 9.2 is shown in Figure 9.3.

About 0.5 km to the north, a smaller rock fall occurred on a steep slope in dark brown volcanic rocks (Miocene tuffs (?)). The scarp is about 20 m high and about 50 m wide (Figure

9.4). The debris is blocky and includes boulders up to 2 m in diameter. The scarp reveals

extensively fractured bedrock. The fractured surfaces probably provided planes of weakness

j along which the rock failed.

' 9.2.2 Site No. 2

Three rock falls occurred on steep east-facing bluffs flanking a broad flood plain near the

mouth of the Naruse River. All three were narrow failures, about 15 m wide, that occurred

in dark brown volcanic rock similar to the smaller rock fall at Site No. 1. The slides

extended from near the crest of the bluffs to the base, a height of approximately 30 m. Two

j of the slides are shown in Figure 9.5.

Prepared by Edwin L. Harp, U.S. Geological Survey, Menlo Park, California.

209
Figure 9.1 Sendai area showing sites of landslides described in text (dots).

210
Figure 9.2 Rock fall on steep slopes of Miocene pumiceous tuff breccia

near Takayamasuita . This rock fall damaged four houses

close to the base of the slope. (Photograph courtesy of

Y. Tsuruya, Slope Protection Division, Ministry of

Construction)

.

Figure 9.3 Closeup of rock fall damage to houses shown in left portion

of figure 9.2. (Photograph courtesy of Y. Tsuruya)

211
Figure 9.4 Rock fall on steep slopes in volcaniclastic sediments.

Figure 9.5 Rock falls (arrows) in steep bluffs bordering flood plain

near mouth of Naruse River

212
(9.2. 3 Site No. 3

'A small rock fall south of the New Kitakami River occurred on the end of a narrow ridge of

Triassic slate and quartzite. Slopes adjacent to this end of the ridge showed no failure,

suggesting that this point, which was the narrowest part of the ridge, experienced stronger

shaking than adjacent slopes. This phenomenon has been documented in other earthquakes

(Bonilla, 1959; Nason, 1971; Harp and others, 1978) and has been attributed to the topographic focusing of seismic energy.

9.3 ROCK FALLS AND ROCK SLIDES IN CUT SLOPES

9.3.1 Site No. 4

Near Atago in Matsushima, approximately 1.0 km east of the Site No. 1, rock falls from tuff,

similar to the tuff forming the larger rock fall at Site No. 1, damaged outbuildings near

three houses. About 500 m of debris was shaken from cut slopes 15 m in high beneath which

houses and storage buildings were closely juxtaposed (Figure 9.6). Most of the damage was

not to the houses proper but to attached storage sheds and outbuildings as shown in Figure

9.7.

9.3.2 Site No. 5

Approximately 3 km east of Atago in Mototetaru, Matsushima, small rock falls occurred in

tuff-breccia deposits, damaging several storage buildings adjacent to houses. Failures

occurred along a section of cut slope about 100 m in long and produced about 200 m^ of

debris. The slope is 10-13 m high and is inclined at about 60°. One rock fall and a scarp

exposing tuff breccia is shown in Figure 9.8.

9.3.3 Site No. 6

3 At Kakinoura in Matsushima, about 100 m of blocky debris was produced by a seismic-induced

rock fall in tuff that damaged a concrete wall adjacent to a house. This rock fall occurred

on the nose of a narrow ridge of about 35 m local relief. The slope failed along preexisting fractures or joints and produced blocks of debris as long as 1.0 m. The size of

the blocks reflects the fracture spacing of the rock. The rock fall and the house adjacent

to the damaged concrete wall are shown in Figure 9.9. Two other small rock falls nearby did

minor damage to walls of three other houses.

l| 9.3.4 Site No. 7

j At Kitashionai, Murata, 25 km southwest of Sendai, another steep slope in tuff failed, geni erating a small rock fall damaging one house. Figure 9.10 shows several houses near the

nearly vertical cut slope about 15 m high. One of these houses suffered damage to a retainjl ing fence and part of the roof. A closeup of the rock fall and roof damage is shown in

[I, Figure 9.11.

1 9.3.5 Site No. 8

3

l A rock fall of approximately 1000 m occurred at Hebinumayama, Sanbongi, on a 20 m high, 110

; m long, nearly vertical cut-slope no more than 10 m from five houses at the base of the

;j slope (Figure 9.12). The falling rock did minor damage to two houses and attached storage

sheds (Figure 9.13). Rock fall occurred along the entire length of the slope which is

composed of a bedded tuff containing numerous fractures. Here, as at Kakinoura, failure

j, took place along the pre-existing fracture surfaces. Block size of the debris ranged from

several centimeters to several meters.

9.3.6 Site No. 9

A typical roadcut failure (Figure 9.14) was derived from weakly cemented sandstone along a valley west of the Naruse River. The rock fall is less than 1 m thick, and slope height

is about 10 m.

213
Figure 9.6 Panoramic view of houses damaged by rock fall from adjacent cut slope

in tuff*. Rightmost arrow points to area shown in figure 9.7.

(Photograph courtesy of Y. Tsuruya)

* Arrows point to failure scarps.

Figure 9.7 Closeup of rock fall and damage to buildings shown in right-hand

portion of figure 9.6. (Photograph courtesy of Y. Tsuruya)

214
Figure 9.8 Rock fall from steep slope in

pumiceous tuff breccia near Motot^taru. Failure was about

200 m in volume. (Photograph

courtesy of Y. Tsuruya)

Figure 9.9 Rock fall in Miocene tuff causing damage to concrete

wall adjacent to house. (Photograph courtesy of

Y. Tsuruya)

215
Figure 9.10 Panorama of cut slope near Kitashiona in Miocene tuff which produced

rock falls during earthquake damaging nearby houses. Arrow points to damaged house shown in closer view in figure 9.11. (Photograph

courtesy of Y. Tsuruya)

216
Figure 9.12 Steep slope near Hebinumayama in heavily fractured tuff which

underwent failure as rock falls damaging portions of houses

in front of the slope.

Figure 9.13 Rock fall from slope shown in figure 9.12 impinging on

storage shed next to slope.

217
Figure 9.14 Rock fall from roadcut in weakly cemented sandstone.

218
3.3.6 Site No. 10

k rock fall in Triassic slate and fine-grained quartzite occurred on a steep roadcut slope

on the north side of the New Kitakami River. The scarp of the rock fall is inclined at about 60° and is formed by prominent slaty cleavage planes (Figure 9.15). The blocky debris

broke into pieces of up to 30 cm in longest dimension. Almost all of the debris consisted

pf blocks that had separated along pre-existing fractures.

|9.3.7 Ojika Peninsula

(Reconnaissance of the Ojika Peninsula and area immediately to the north was along winding

mountain roads that traversed heavily vegetated slopes. The slopes had a thin soil mantle,

[generally less than 0.5 m thick. Numerous small rock falls were derived from the near

vertical roadcuts in these slopes. None contained more than a few cubic meters of debris.

9.4 LANDSLIDES IN ARTIFICIAL FILL

9.4.1 Site No. 11

| Several artificial fill failures occurred on roads on the Ojika Peninsula; one such failure

is shown in Figure 9.16. The fill material slumped away from beneath the road surface and

(formed a scarp cutting about 2 m into the highway. The fill appeared to be either uncomi pacted or poorly compacted sandy clay derived from adjacent bedrock and soil. This failure

J occurred at a site where rainfall-induced slumping had occurred repeatedly before the earthquake (T. Tazaki, 1978, oral communication). At the time of the visit, plastic sheets had

been spread over the extensively cracked pavement to prevent or minimize rainfall infiltration into the scarp area. During observation, heavy rainfall was mobilizing the debris into

! small mudf lows.

: 9.4.2 Site No. 12

Many slope failures in artificial fill took place within the city limits of Sendai. These

failures were mainly slumps. In the neighborhood of Midorigaoka, a large rotational slump

occurred in a fill slope of about 15°, composed of gravelly clay. From the headwall scarp

to toe, the slump extends approximately 70 m horizontally and 20 m vertically (Y. Matsuzaki,

1978, unpublished data); it is approximately 30 m wide and about 14 m in maximum thickness,

thus the approximate volume is 30,000 m"^. Most of the slump was above and to the right of one of the 1400 concrete slope-protection dams (sabo works) in Sendai (Figure 9.17). The

slump-mass had been covered with nylon tarps before the photograph was taken to prevent

|j infiltration of rainfall.

Many houses had been removed from this slope in previous years due to rainfall-induced slumpi ing; as a result, only one house near the headwall scarp was severely damaged by the seismicj induced sliding. Figure 9.18 shows this house, which was being undercut by the multiple

| scarps at the head of the slump. The fence in the figure shows the rotational component of

|. slump movement.

About 5 m of horizontal displacement (Y. Matsuzaki, 1978, unpublished data) occurred, placing the toe of the landslide mass only a few meters from houses below. One such house,

which had been evacuated because of the threat of recurrent movement is shown in Figure

! 9 * 19 '

At the time of observation,' engineers from the Sabo Section of the Miyagi Prefectural

I government were engaged in a geotechnical investigation of the slump mass and surrounding

area. Boreholes had been drilled in the slide material to establish the depth of the failure surface, to provide samples for strength testing, and to emplace slope inclinometers

to monitor any continuing movement. Adjoining areas were also being drilled and monitored

to detect any movement that might be precipitated by the slide, such as deformation downslope from the toe in response to the weight of the encroaching slide mass or retrogressive

slumping upslope from the headwall scarp.

Many other artificial fill slopes in Sendai underwent similar failure. At a site about 0.5

km east of Midorigaoka, six houses were condemned by the mayor of Sendai because of cracking

219
Figure 9.15 Rock fall in roadcut . Note

slaty cleavage planes that

form the rock fall scarp.

Figure 9.16 Slump in artificial fill along a highway on the

Aj ika Peninsula
Figure 9.17 Rotational slump in artificial fill in Sendai (area covered

by tarps) which destroyed one house and is threatening

others. To left of slump is concrete slope protection dam

(sabo works)

.

Figure 9.18 House near head of slump. House was removed due to undercutting by headwall scarp (Photograph courtesy of Y. Tsuruya)

.

221
Figure 9.19 Toe of slump and house below in danger of

being overridden by slide mass. House has

been evacuated.

222
beneath and around the houses within the fill area. The decision to destroy the houses was

made to protect the houses downslope because the failure of the slope was judged to be

imminent unless the weight of the damaged houses was removed (T. Tazaki, 1978, oral communication) .

A large, spectacular slump in artificial fill, derived from Miocene ash-flow tuff, occurred

in Shiroishi City, about 35 km southwest of Sendai. One fatality occurred from this failure.

This slump took place in a planned residential area under conditions of a high water table.

The slump movement was accompanied by mudflow (Tohoku Univ. report, 1979). This landslide

was not seen by the author, but is described by the Tohoku University report (1979).

Judging from the extensive failure of artificial fill slopes, as compared to the few noticeable landslides on the many steep natural slopes in the same areas, the artificial fill is

particularly susceptible to seismic-induced failure. These artificial-fill slopes are

j likely to be hazards in future earthquakes.

9.5 SUMMARY OF FINDINGS

The June 12, 1978, Miyagi-ken-oki earthquake triggered several thousand landslides in Miyagi

and Fukushima Prefectures. A field reconnaissance of the coastal region nearest the epicenter two weeks after the earthquake led to the following general findings:

(1) Most landslides were rock falls and rock slides and occurred on natural and cut slopes

i steeper than 45°. Damage to houses and other structures was a result of the close proximity

of houses to the base of steep slopes.

(2) Many slopes and roadways constructed on artificial fill failed during the earthquake.

The slumping of artificial slopes also caused extensive damage to houses. The heaviest

damage from these failures occurred in areas occupied by housing developments in Sendai and

in Shiroishi.

(3) Many slopes composed of artificial fill were more susceptible to seismic-induced fail-

| ure than steep natural slopes. This susceptibility is probably a result of insufficient

compaction of the fill material. Artificial fill slopes could constitute a significant hazard in future earthquakes.

9.6 REFERENCES

9.1. Bonilla, M. C, 1959, Geologic observations in the epicentral area of the San Francisco earthquake of March 22, 1957, in Oakeshott, G. B., ed. , The San Francisco earthquake

of March 1957: California Division of Mines Special Report No. 57, p. 25-37.

9.2. Geologic Map of Miyagi Prefecture, legend in Japanese.

9.3. Harp, E. F., Wieczorek, G. F., and Wilson, R. C, 1978, Earthquake-induced landslides

from the February 4, 1976 Guatemala earthquake and their implications for landslide

hazard reduction: International Symposium on the February 4, 1976 Guatemalan Earthquake and the Reconstruction Process, Guatemala City, Proceedings.

9.4. Nason, R. D. , 1971, Shattered earth at Wallaby Street, Sylmar, in the San Fernando,

California earthquake of February 9, 1971: U.S. Geological Survey Prof. Paper 773,

p. 97-98.

9.5. Tohoku University Report, 1979, Phenomena and disasters associated with the Miyagiken-oki earthquake of 1978 in the East-central part of Northeast Honshu, Japan:

Institute of Geology and Paleontology, Tohoku University, no. 80, 97p., 34 figs.,

2 tables, 7 pis., (summary and captions in english).

223
10. GENERAL CONCLUSIONS

The effect of the Miyagi-ken-oki earthquake of June 12, 1978 on the Sendai area was quite

moderate, considering its magnitude and the potential for disaster. This was in large measure due to good engineering practice and the extremely quick and comprehensive response of

the Japanese authorities to the earthquake. At the time of the team investigation beginning

11 days following the earthquake, much of the debris had been cleared away and repair and

recovery operations were well underway. The approaching rainy season gave a sense of urgency

to these tasks. With the exception of a few establishments still without city gas service,

the situation in Sendai was essentially normal. It was obvious that the response to the

earthquake was well planned and that the disaster mitigation and relief activities are well

coordinated among the different levels of government. The fact that the main energy release

occurred some distance from any inhabited areas lessened the impact that an earthquake of

this magnitude otherwise would have had.

Subsequent investigation showed that modern structures and facilities suffered little damage. In particular, structures designed subsequent to the promulgation of the new seismic

design provisions of 1971 performed exceedingly well. The successful performance of most

modern multistory buildings shows that modern seismic engineering practices can provide

resistance to strong earthquake motions at reasonable cost. The total damage due to Miyagiken-oki earthquake constituted a small percentage of the total capital investment in buildings and structures, despite recorded ground accelerations in the range 0.25g - 0.40g in

the Sendai area, and accelerations as high as l.Og in upper stories of high rise buildings.

Numerous pockets of damage existed throughout the city that apparently were correlated to the local geology and soil conditions. Acceleration magnitudes across Sendai varied considerably with location. The eastern part of the city, where many of the damaged structures were located, is built on alluvial deposits which, from a foundation standpoint, are poorer

than the remaining portion of the city. Soil conditions in the central portion of Sendai

are considerably better, and the damage was limited.

Analyses of the earthquake and the performance of structures are currently being conducted

or recently have been completed by Japanese engineers and seismologists. One of the first

of these is the report on strong motion records and data issued by the Strong Motion Earthquake Observation Council, National Research Center for Disaster Prevention of Japan.

Digitization of some of the traces has been performed by the Building Research Insitute

and Public Works Research Institute. Tokyo Electric Power Company engineers are conducting

a comprehensive analysis of the strong motion data gathered at the Fukushima nuclear power

plant. When this information is released, probably within the next year or so, it will be

of considerable value to engineers and licensing officials in the U.S. as well as Japan.

These reactors and containments are similar to those operating in the U.S. and they suffered

no damage in the earthquake.

Although similar observations have been made in the aftermath of previous earthquakes, it seems worthwhile to reemphasize the following points about achieving earthquake resistant

design:

(1) Structure should be laid out so that they are as symmetrical as is consistent with their

function. Practically all severely damaged or collapsed engineered structures exhibited

a significant asymmetry of some kind in the form of an eccentric mass or placement of

shear walls.

(2) When infill panels or spandrels are used, particular attention should be paid to detailing and to the design of structural members connected to them. When used on only

one side of a building, their stiffening effect causes most of the damage to occur to that side.

(3) The apparent correlation of structure damage to local soil and geologic conditions suggests that this factor should receive additional attention in the design of structures

of even moderate size and cost. Seismic regulations in codes should include a soils

parameter in their load criteria.

(4) Performance of buildings clearly is related to quality control and design detailing.

There were cases of failures where column ties appeared to be minimal and improperly

224
anchored. In other instances, they appeared to be adequate. The question arises

whether discrepancies exist between the structure as built and the code recommendations.

Post earthquake investigation of damaged bridges has taught many lessons. The 1964

Niigata and 1971 San Fernando earthquakes pointed to the importance of providing 1)

restraining devices across hinges and joints and 2) proper column reinforcement details

including the foundation connections. The 1976 Guatemala earthquake demonstrated that

the longitudinal restraining devices across hinges can provide the continuity required

to keep spans from falling. The Miyagi-ken-oki earthquake has provided incentive to further investigate the need for and performance of transverse restraining devices and

to examine the philosophy behind ductile and non-ductile column/pier design. Another

topic of interest is correlation of soil type to foundation/substructure damage.

The collapse of the Kin-noh bridge, which was previously damaged in a February 1978

earthquake, indicates that structural damage may occur due to either strong aftershocks

or multiple event excitation.

In regions of high seismicity, critical and important structures should be identified

and additional care should be taken in detail design and in field inspection (quality

assurance) during construction.

225
U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS SP 592

2. Gov't Accession No, 3. Recipient's Accession No.

1

4. TITLE AND SUBTITLE

An Investigation of the Miyagi-ken-oki , Japan

Earthquake of June 12, 1978

5. Publication Date uctoDer lytsu

6. Performing Organization Code

7. AUTHOR(S)

Bruce R. Ellingwood

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

Same as item 9.

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 80-600116

|

| Document describes a computer program; SF-185, FiPS Software Summary, is attached.

IS. ABSTRACT (A 200-word or less tactual summary of most significant information. If document includes a significant bibliography or

literature 3urvey. mention it here.)

On June 12, 1978, a destructive earthquake with Richter magnitude of 7.4 occurred

off the east coast of Miyagi Perfecture, Japan. Preliminary estimates by the

National Land Agency of Japan indicated that the earthquake caused an equivalent

of $800 million in total damage. There is a cooperative agreement between the Governments of the United States and Japan termed the U.S. -Japan Program in Natural

Resources (UJNR) . Following the earthquake, it was arranged through UJNR that teams

of U.S. structural engineers and geologists would visit Miyagi Prefecture and inspect

the damage caused by the earthquake. This report assembles the information and

collective experiences of the investigation team 10 as to describe the earthquake

and document its effects. Field investigations conducted by geologists and structura

engineers are described in detail and some of the implications for seismic resistant

design and construction of structures in the United States are also discussed.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons) Bridges; buildings; dikes; earthquakes; foreign engineering; geology; highways;

housing; landslides; liquefaction; power plants; railroads; rock slides; seismicity

structural engineering.

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