2011-Field Investigation Report Thohoku Earthquake

8/6/2019 2011-Field Investigation Report Thohoku Earthquake

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Field Investigation Report

2011 TOHOKU EARTHQUAKE AND TSUNAMI

EARTHQUAK

STRUCTURALENGINEERS


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0 | CONTENTS

1 Preface 2

2 Tohoku Earthquake and Tsunami 4

3 Arahama 8

4 Sendai 13

5 Tagajyo 17

6 Kesennuma 18

7 Minami Sanriku 208 Rikuzen-Takata 22

9 Ofunato 24

10 Kamaishi 27

11 Discussions 26


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THE TOHOKU EARTHQUAKE AND TSUNAMI CAUSED WIDE-SPREAD DAMAGE.


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1 | PREFACE

In my reconnaissance of the Tohoku Earthquake and tsunami, I visited the Sendai Airport,

which had been incapacitated by a 2-meter-high tsunami-induced ood. I also visited a

beach close by and found 6-meter-high seawalls that had been destroyed by a 10-meter-

high tsunami The seawalls were a massive, impressive concrete fortress that proved to be

insufcient. This failure also contributed to the Fukushima nuclear plant crisis.

The biggest issue that I saw was overcondence with our current level of engineering knowl-

edge We engineers should be humble enough to say, What if the design wave height is not

adequate? We should place the emergency generator on higher ground If someone had

challenged the norm during the design of the nuclear plant, the meltdown could have been

avoided This issue is is not exclusive to Tokyo Electric Power Company or Japan alone This

event could easily have happened in the United States

When we design buildings or sea walls, we use mandated codes and the standard of prac-

tice These guidelines have accepted risks that the public and legal system are unaware of

Most people think that meeting the code or standards means complete safety But the truth

is that the code ensures minimal life protection at best It does not guarantee sustainability of

a building or community after a large earthquake

I found many warning signs posted on streets that indicated the limits of tsunami water, and

they were accurate Japanese engineers knew about the possibility of a 10-meter wave andhow far it could reach The 6-meter-high sea walls failed Fortunately, the sophisticated warn-

ing system saved hundreds of thousands of lives Still, we lost more than 11,000 people,

many towns, and 400,000 people are homeless The 6-meter-high sea wall was built per

design

The implication for the rest of the world, including the United States, is signicant. We engi-

neers know what the worst-case scenarios may be But we rarely communicate the risk to

the public and stakeholders in such a way that they understand it, and we fail to inform then

that cost-effective, innovative engineering solutions exist to make structures safe and sus-

tainable for cities Buildings in tsunami areas should be multi-story concrete or steel struc-

tures; these are the only structural types that will survive large tsunamis These structures

can also be architecturally attractive and sustainable

Civilization is fragile In 90 seconds, we lost a big piece of eastern Japan There is no power,

no gas, no food, and no water Lives, and some communities, were lost forever Nature has a

way of proving us wrong in our assumptions and standards The additional cost for smarter

ways to protect civilization is insignicant compared with what is at stake. We know how to

do better


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22011 TOHOKU EARTHQUAKE AND TSUNAMI | FIELD REPORT

On my return home, as I walked out of the arrival hall at San Francisco International Airport,

my wife and kids ran up to meet me. My ve-year-old boy hugged me tight and did not want

to let me go. My mind briey ashed to an image of a little boy who was crying in a cold,

snowy Japanese town that had been destroyed

ACKNOWLEDGMENTS

I would like to acknowledge the people of the Tohoku disaster area Despite losing every-

thing, they are determined to have their lives back I did not see a single occasion of civil

unrest or looting, or the presence of armed forces or armed police I respect their courage

and endurance I know that they will overcome

I also acknowledge the dedicated staff of Miyamoto International and Global Risk Miyamoto

Their round-the- clock technical and logistical support for our team was critical for collecting

technical data I thank the media crew of ITN from England Their collaboration was very im-

portant during this very difcult initial phase. Finally, to my family in Davis, California, and To-

kyo, I always appreciate your support I know that I always make you worry during a disaster

response, and I especially want to say to my little kids Mimi, Julia, and Alexander, I love you

H Kit Miyamoto, SE, PhD

2 April, 2011 Davis, California


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2 | THE TOHOKU EARTHQUAKE AND TSUNAMI

The magnitude (MW) 90 event occurred at 2:46 pm local time on 11 March 2011, in the

western Pacic Ocean off the coast of Japan. Its epicenter was approximately 130 kilometers

from Sendai, Honshu, Japan This earthquake occurred in the subduction zone between the

Pacic Plate and Northern Honshu Plate. The rupture length is expected to exceed several

hundred kilometers and the event had an approximate depth of 25 kilometers

As shown in Table 1, United States Geological Survey (USGS), 2011, a large population of

more than 21 million people was exposed to high earthquake intensity during the event The

main earthquake was preceded by a number of large foreshocks. The rst major foreshock

was a MW

72 event on 9 March The main event was followed by hundreds of aftershocks of

magnitude 5 or greater Figure 1 (USGS 2011) presents the intensity and aftershock maps

for this event

TABLE 1. POPULATION EXPOSURE

CITY POPULATION (THOUSANDS) MODIFIED MERCALLI INTENSITY (MMI)

Furukawa 76 IX

Sendai 1,038 VIII

Iwaki 357 VIII

Koriyama 341 VIII

Hitachi 186 VIII

Ishinomaki 117 VIII

Japan has an extensive array of strong-motion sensors One minute before the earthquake

was felt in Tokyo, the Earthquake Early Warning system, which includes more than 1,000

seismometers in Japan, sent out warnings of impending strong shaking This warning likely

prevented further loss of life

The unprocessed strong-motion data, for example, see Figure 2, California Geological

Survey (CGS) 2011 indicates large accelerations In the Miyagi Prefecture, approximately 75

kilometers from the epicenter, peak ground acceleration (PGA) values as high as 27g were

recorded in the horizontal direction By contrast, in Tokyo, which was approximately 370

kilometers from the epicenter, the maximum PGA was 016g The strong motion lasted ap-

proximately 90 seconds

Japan is one of the worlds most earthquake-prone countries, with tremors occurring daily

Major earthquakes and tsunamis also affected this region in 1896 and 1933


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Intensity map Aftershocks

FIGURE 1. EARTHQUAKE DATA (USGS 2011)

FIGURE 2. RECORDED GROUNDACCELERATION (RAW DATA) FROM STATIONMYG013 IN SENDAI (CGS 2011)


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The earthquake was followed by a large tsunami Waves averaging 10 metersand some

as high as 296 metersstruck, traveling as far as 6 miles inland Smaller waves reached

other countries, including the United States, and caused damage in excess of several mil-

lions of dollars (US) in costal California The tsunami inundated a total area of approximately

470 square kilometers An hour after the earthquake, the Sendai Airport was inundated with

waves that wept away cars and planes and ooded buildings. A 4-meter-high tsunami hit

Iwate Prefecture Wakabayashi Ward in Sendai was hit particularly hard The water column

height on 11 March, 2011, at the Deep-Ocean Assessment and Reporting of Tsunamis

(DART) Station there shows the effect of the tsunami

The Japan Meteorological Agency issued a major tsunami warning The initial estimates

indicated that the tsunami would take 10 to 30 minutes to reach the areas rst affected, and

then areas farther north and south, based on the geography of the coastline This warning

allowed hundreds of thousands of people to escape to higher ground inland

The damage from the tsunami was far greater than that from the earthquake One factor

contributing to the damage and high death toll was the sheer size of the water surge topping

the tsunami walls, which were designed to withstand smaller tsunami heights The height

and inland reach of the tsunami surprised many people who thought that they were located

either on high enough ground or in locations far enough away inland

Considering the data available at the time of this report, the extent of casualties and damage

from his event is astonishing (see Table 2 from various news organizations)

TABLE 2. CONSEQUENCES OF THE 2011 EVENT (FROM VARIOUS NEWS ORGANIZATIONS)

DESCRIPTION COMMENT

Deaths 11,000+

Missing 16,000+

Injured 3,000+

Building collapsed or severely damaged 120,000+

Transportation (roads, bridges) All major ports were damaged; the rail system and

Road 45, the major road along the coastline, wereinaccessible; Tohoku Way, the main freeway, was openonly to authorized rescue vehicles; Sendai Airport wasdamaged by a 2-meter-high tsunami

Lifelines (electricity, water, gas, etc) The entire coastal area lost all services; Sendai lostextensive power and fuel

Critical facility affected Fukushima nuclear reactors; oil tanks in Kesennuma

Direct damage $300 billion


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Just one day after the earthquake, an engineering team from Miyamoto International and

Global Risk Miyamoto was on the ground in the affected area, investigating and analyzing

the damage for response, recovery, and reconstruction data, and documenting failures and

successes to reduce the risk of catastrophic losses in future earthquakes. The teams nd-

ings on the earthquake effects on people, structures, and local industry are presented here

for various important locations, identied in Figure 3.

FIGURE 3. MAP OF VISITED SITES


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3 | ARAHAMA

This area experienced tsunami waves approximately 7 meters high causing extensive and

widespread damage Even 5 kilometers from the shore, many houses and structures were

destroyed (see Figure 4) Typical Japanese residential housing uses wood framing and

concrete foundation This type of construction does not perform well in a tsunami surge type

of loading Many cars were washed away over great distances by the tsunami As part of the

search and rescue effort, the Japanese recovery teams checked cars, looking for survivors

or bodies and then tagged the vehicles (see Figure 5)

FIGURE 4. COLLAPSED HOUSES 5 KILOMETERS FROM SHORE

Many industrial buildings survived the tsunami For example, the industrial building in Figure

6 did not suffer severe damage This performance stems in part from the fact that these

types of buildings are constructed with steel and concrete, and they have better foundation

anchorage from the super structure In addition, the buildings have seismic detailing, which

provides toughness, system integrity, and strength for seismic and tsunami surge and im-

pact loading Steel and concrete buildings performed well For example, the four-story con-

crete school building in Figure 7, less than 1 kilometer from the ocean, experienced 7-meter-

high waves and was essentially undamaged The gymnasium structure was damaged by

water surging in from one side at the bottom oor and bursting through the other side but

there was no evidence of structural damage In Arahama the only buildings left standing had

either steel or concrete construction


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FIGURE 5. INSPECTED CAR FIGURE 6. SURVIVING INDUSTRIAL BUILDING

FIGURE 7. UNDAMAGED CONCRETE SCHOOL BUILDING


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In general, steel and concrete buildings have much better anchorage to the foundation than

does the comparable wood construction that uses sill plates and anchors, which is similar

to California construction (see Figure 8) Note in Figure 8 that the superstructure has been

washed away

Many inlet bridges also suffered damage The bridges parallel to the shore sustained most

of the damage, being subjected to perpendicular wave forces (see Figure 9) In contrast,

bridges perpendicular to the beach performed better (see Figure 10)

FIGURE 8. TYPICAL WOOD-FRAME FOUNDATION


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FIGURE 9. BRIDGE PARALLEL TO THE SHORE

The tsunami seawall in this area was approximately 2 meters tall The protection for the city

was provided by the seawall and a row of pine trees planted near the beach (see Figure 11)

FIGURE 10. SEA WALL


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FIGURE 11. PINE TREES PLANTED FOR TSUNAMI WAVE PROTECTION


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4 | SENDAI

Sendai is the capital city of Miyagi Prefecture, Japan, and the largest city in the Tohoku

region It has a population of more than 1 million and is a modern city with extensive new

high-rise construction

Although preliminary reports have indicated large PGAs in this area, there was no evidence

of wide spread major earthquake damage; however, some older nonductile concrete build-

ings were damaged There was also no evidence of major liquefaction All commercial build-

ings were closed (see Figure 12), however, and residents had to line up to shop (see Figure

13) There was a wide-spread shortage of basic food and gas in the surrounding unaffected

area, caused by the following factors: (a) all eastern ports were damaged; (b) the rail system

was damaged; (c) Tohoku Waythe only freeway between Tokyo and Tohokuwas open

for emergency vehicles only; and (d) residents in unaffected areas such as Tokyo over-pur-

chased essentials such as food and gas

FIGURE 12. CLOSED RETAIL STORES


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FIGURE 13. LINE FOR PURCHASING ESSENTIAL ITEMS

The Sendai Airport was closed This facility is located approximately 5 to 10 kilometers from

the ocean and experienced 2-meter-high tsunami-induced ood. The main structure itself did

not sustain much damage (see Figure 14) Many industrial facilities close to the port were

undamaged (see Figure 15), but nancial losses for this sector will be large because of busi-

ness interruptions

FIGURE 14. SENDAI AIRPORT MAIN BUILDING FIGURE 15. INDUSTRIAL FACILITY NEAR PORT


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The seawall in this area was about 6 meters tall (see Figure 16) The wall had extensive dam-

age likely resulting from the erosion and land-slide caused by suction as the water went over

the top The ocean side of the wall was not damaged (see Figure 17) Note that damage to

the seawall becomes more pronounced at the place where the dolosconcrete blocks used

to protect the harbor wallsstopped

FIGURE 16. AIRPORT SEAWALL

FIGURE 17. ERODED SEAWALL


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FIGURE 18. FLOODED MAJOR ROADWAY


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5 | TAGAJYO

There was major ooding of the main roadway in Tagajyo (see Figure 18) and a shortage of

foodstuffs and goods, similar to the shortage in Sendai Transmission towers were damaged

(see Figure 19) because the tsunami picked up cars and slammed them onto the tower legs

FIGURE 19. DAMAGED TRANSMISSION TOWER


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FIGURE 23. LARGE TUNA FISHING BOAT THAT WAS SWEPT INTO TOWN


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7 | MINAMI SANRIKU

Many residential (see Figure 24) and industrial buildings (see Figure 25) were destroyed in

Minami Sanriku As in Kesennuma, almost the entire stock of wood buildings was destroyed

in the tsunami-affected area but modern concrete structures designed per Japanese seismic

code performed well (see Figure 20 for an example in Kesennuma)

FIGURE 24. RESIDENTIAL BUILDINGS FIGURE 25. INDUSTRIAL BUILDINGS

The bridge perpendicular to the inlet bay was washed away, and only the bridge railing and

some portions of the pier were left behind (see Figure 26) This particular bridge did notseem to have adequate anchorage Bridges such as the one in this photo near the inlet of

the narrow bay were subjected to large impact and perpendicular tsunami wave forces

Steel buildings fared well, as shown in Figure 27 In this building, the moment frame itself is

intact, and the non structural walls were damaged from the force of the tsunami

FIGURE 26. DESTROYED BRIDGE FIGURE 27. STEEL MOMENT-FRAME BUILDING


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The three-story concrete building shown in Figure 28 did not sustain any damage, even

though it is located right at the bay This modern structure was designed and constructed

according the to current seismic code in Japan. This design provided sufcient strength and

ductility for the building to withstand the tsunami forces This particular building was opera-

tional and back in business only one week after the tsunami

FIGURE 28. UNDAMAGED AND OPERATIONAL BUILDING


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8 | RIKUZEN-TAKATA

The school building in Rikuzen-Takata suffered erosion damage at the foundation (see Fig-

ure 29) Most of the town was washed away (see Figure 30) Many residential and industrial

buildings were destroyed in the town of 50,000 people Figures 24 and 25 show examples of

such damage in the region

FIGURE 29. SCHOOL BUILDING FOUNDATION EROSION

FIGURE 30. DESTROYED WOOD BUILDINGS


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The steel truss bridge superstructure over Highway 45 was washed inland about 05 kilo-

meters from its original site (see Figure 31) Note that the concrete pier walls were severely

cracked in shear, as shown in Figure 32 The river became a focal point of the tsunami wave

It increased the tsunami velocity and height substantially

Modern concrete structures performed well as shown in Figure 33, but older concrete build-

ings did not. The older building shown in Figure 34 did not have connement steel and used

smooth bars, and it collapsed

FIGURE 33. UNDAMAGED NEWER CONCRETEBUILDING

FIGURE 31. PIERS AND WASHED AWAY STEELTRUSS SUPERSTRUCTURE FIGURE 32. CRACKED PIERS

FIGURE 34. DAMAGED OLDER CONCRETEBUILDING


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9 | OFUNATO

Damage in the residential district of Ofunato was limited Only the wharf district (see Figure

35), sustained major damage However, the industrial steel buildings in this area collapsed,

as seen in Figure 36 The column-to-foundation anchorage was inadequate and it failed,

causing these collapses

FIGURE 35. DAMAGED WHARF DISTRICT

FIGURE 36. COLLAPSED STEEL BUILDINGS


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Figure 37 presents a street sign that was placed by the Japanese government predicting theextent of a tsunami Remarkably, the tsunami reached to within 1 meter of this sign, indicat-

ing both the planning and the accuracy of the modeling used by the engineers

FIGURE 37. SIGN PREDICTING THE EXTENT OF A TSUNAMI


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10 | KAMAISHI

The damage in this town was limited to the wharf area This town was powered by a genera-

tor from a steel mill, pointing out the effectiveness of self-sustainable disaster management

and an intact electrical power grid

11 | DISCUSSION

The 2011 Tohoku Taiheiyo Oki Earthquake caused wide-spread signicant damage and

resulted in more than 11,000 deaths After an initial reconnaissance, the Miyamoto team has

made the following observations:

Japan has an extensive and elaborate tsunami warning system. The warning was com-

municated by radio, public address (PA) system, cell phone, etc, and saved hundreds

of thousands of lives Preparedness and disaster management for self-sustainability are

critical for post-disaster response It is important for government agencies and profes-

sional organizations to educate citizens on such events

This event differed from the more localized Kobe Earthquake of 1995 and affected an

area of more than 400 kilometers A coordinated damage response is required for sucha widespread and non-localized event Limiting the Tohoku Way freeway only to govern-

ment-authorized emergency vehicles led to a lack of basic necessities in surrounding

unaffected areas

The tall seawalls seem to have slowed down the tsunami velocity in certain areas.

However, after water had breached them, they were not effective Emergency and lifeline

facilities such as the nuclear power plant and gas tanks, need to be relocated to higher

ground or else seawalls designed for extreme events need to be constructed to protect

them

Seismic detailing such as connement, system integrity, toughness, and adequate an-

chorage work well for tsunami loading It is possible to cost-effectively construct tsuna-

mi-resistant structures Multistory steel and concrete-frame buildings with a mechanism

for water travel are good candidates


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THE 2011 TOHOKU TAIHEIYO OKI EARTHQUAKE CAUSED WIDE-SPREAD SIGNIFICANT DAMAGE


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2011-Field Investigation Report Thohoku Earthquake