PartⅠ: Report on the GEJET 10:00 - 12:00

Summary on the great East Japan earthquake and tsunami
Prof Shoichi Yoshioka, Research Center for Urban Safety and Security, Kobe University

The Behavior of 3.11 Tsunamis in the Sendai Plain and the Damage to the Disaster
Prevention System
Prof Akira Mano, Disaster Control Research Center, Tohoku University

Present Status of Japanese Nuclear Power Plants and Radiation Disaster
Prof Keiji Oda, Graduate School of Maritime Sciences, Kobe University

Damage situations of ground, infrastructures and others
Prof Yasuo Tanaka, Research Center for Urban Safety and Security, Kobe University

about 24 km. The earthquake fractured the plate boundary
there, approximately 450 km in the north-south direction andSummary on the great East Japan

200 km in the east-west direction on the inclined plate

earthquake and tsunami

boundary.

Prof Shoichi Yoshioka, Research Center for Urban

In Japan, large trench-type earthquakes tend to occur, for theSafety and Security, Kobe University

Japanese islands are located where four diﬀerent plates meet
together. The oceanic Paciﬁc plate is gradually subducting
beneath the continental North American platewith a velocityof several centimeter per year. Last March, the continental
plate released accumulated strain abruptly, causing theearthquake and tsunami in northeast Japan. The magnitude
7.3 Sanriku-oki earthquake, which occurred just two days
before the Great East Japan earthquake, is considered to be
its foreshock. Numerous aftershocks were also observed,
including three major earthquakes with magnitude greaterthan 7.0 occurred in this region within one hour after the mainshock.
The earthquake caused the crustal deformation in the Tohoku
region. According to the data obtained at GPS stations,
Tohoku region moved eastward about 5.3 m and subsided
about 1.2 m. The crustal deformation can still be continued.

On March 11th 2011, the large earthquake and tsunami hit

One of the characteristics of the Great East Japan

Tohoku region, northeast Japan. The Magnitude of theearthquake is the damage caused by tsunami. A wave of more

earthquake was 9.0, which is the fourth largest trench-type

than 15 m high was recorded in various places along the east

earthquake ever recorded in the world. The hypocentre wascoast of Tohoku region.

just oﬀ the coast of the Tohoku region and the depth was

Last April I visited some areas in the Tohoku region to survey

8the tsunami height and to investigate its behaviour in theshallow water in the sea, tsunami propagation was very slow,

V-shaped bays. One area in Miyako City, where a large

resulting in some energy dissipation crossing the bay. Verytsunami levee had been constructed, was entirely damaged

low frequency in large tsunami is the greatest characteristic

and other area in Rikuzen-takata City, one of the mostof this area. Joban Coast has similar characteristic. In aseriously damaged cities, everything was washed away. At

recent research a geologist found very old tsunami traces in

Ryori Bay, which is a bay with small aspect ratio, the height of1869, Joban Tsunami, whose magnitude was about the sametsunami wave was ampliﬁed 1.3 to 1.9 times the size at theas that of 2011.

bottom of the bays. On the other hand at Hirota Bay, which is

The Tsunami last march destroyed over 100,000 houses anda bay with large aspect ratio, the ampliﬁcation of tsunami was

killed around 20,000 people, although tsunami reached thesenot found between the mouse and bottom of the bay. As aareas about one hour after the main shock. Why couldn t

result of the survey, the damage caused by tsunami lastpeople escape from tsunami before it reached them? OneMarch is considered to be depending on the shape of the bay.

reason for the delay of evacuation is explained by the tsunami
warning underestimate. The Japan Meteorological Agency(JMA) issued its ﬁrst large tsunami warning just threeminutes after the main shock, the estimated wave height ishowever, three metres in Iwate Prefecture, six metres inMiyagi Prefecture, and three metres in Fukushima Prefecture.

The Behavior of 3.11 Tsunamis in theSendai Plain and the Damage to theDisaster Prevention System
Prof Akira Mano, Disaster Control Research Center,Tohoku University

They are too low compared with the actual tsunami height,and even lower than the levee height, so that the ﬁrst warning
gave some kind of relief to people. After 30 minutes, the JMA
revised the warning that tsunami is much higher thanestimated.
People however couldn t get the revised information, becauseof the blackout. So many aftershocks caused serious
damages to the electricity facilities, for example televisions,and hazard information transfer systems, so that people wereshut down from the information. In addition, traﬃc signals
were widely stopped, it caused traﬃc jam and many cars on
the road were washed away by the tsunami. And the blackout
also caused the meltdown in the nuclear power plant inFukushima.
There was historically a very good mitigation system along
the Sendai Bay Coast composed of sandy beach, and coastal
channels, forests, and levees, even though urban growth may
have added vulnerability by clearing away some of the coastal
forests. Reconstruction of robust levees requires restorationof broad beaches, and control of the return ﬂow concentration

The coast aﬀected by the tsunami is categorized into three

through the development of coastal channels and forests.

parts, Sanriku Coast, Sendai Bay Coast, and Joban Coast.
Sanriku Coast, a cliﬀ coast in the north, is uplifting sotsunamis are ampliﬁed by collision. In the submerging southpart of the coast, tsunamis are ampliﬁed by energy concentration and bay water resonance. In this area people had
frequently tsunami attacks, especially in 1896 there werearound ten to 25 metres high tsunamis.
In the Sendai Bay Coast, where a long, sandy beach and9action, the Japanese government decided to take action
according to the guideline of IAEA, and restricted people fromPresent Status of Japanese Nuclear

entering the area within 20 kilometres from the nuclear power

Power Plants and Radiation Disasterstation. The evacuation area was also established afterProf Keiji Oda, Graduate School of Maritime Sciences,
Kobe University

referring to the estimated radiation map. Decontamination
work will continue in this area for several years or tens ofyears. By this nuclear accident, Japan received much
radioactive exposure. However, to avoid meaningless panicand rumor, I want the people of Japan and the world tounderstand several scientiﬁc facts. The ﬁrst is the existing of
natural radiation as essential element in all living bodies, withan activity of 7,000 becquerel. The second is that living cells
have the inherent ability of repairing DNA damages. Every day
almost all damages to the cell are repaired. And third, themost reliable data, delivered from long-term investigation
against atomic bomb survivors, more than 100,000 people in
Hiroshima and Nagasaki, shows that there is no eﬀect onembryo and fetus under 100 millisievert. Over 300
millisievert, cancer risk increases signiﬁcantly, but about 30
percents of cancer death are caused naturally by otherreasons. So, we don t need to be anxious, even for children.

There are 17 nuclear power stations and 54 plants in Japan.
Five stations are facing the Paciﬁc Ocean and there are sixunits in Fukushima. In a steady operation, eﬃcient products ofradioactive materials are normally contained by pellet in therod, which is the fundamental unit of nuclear fuel, and thepressure vessel of about 16 centimetres thick steel, and thecontainment vessel of about one metre concrete in thereactor building. In addition, all the plant stations facing thePaciﬁc Ocean were constructed on the higher ground thanthe expected height of tsunami. Actually, the three units wereoperating at the moment of the huge earthquake, and all ofthem were successfully stopped. No additional ﬁssion energy
was produced after scram. About 40 minutes later, however,the 15 metre high tsunami, much higher than expected,
destroyed everything needed for cooling system, leading to
the heartbreaking accident of meltdown.
In the reactors number 1, 2, 3, the temperature of the fuelrose and increased up to 1,000 degrees as a result of loss ofcooling system. At such a high temperature, the metal reacts
chemically with the pressurized water, producing hydrogengas. This very light gas permeated through the small gap ofmetal and accumulated in the upper area of the reactor
building. It was a matter of time before the hydrogen explosion
releasing some of the light radioactive materials, such as
iodine and cesium into the air. As a radiation protective

10

shaking. These diﬀerent patterns of strong motion combinedwith ground condition of each area caused various types ofDamage situations of ground,infrastructures and others
Prof Yasuo Tanaka, Research Center for Urban Safetyand Security, Kobe University

ground failure, for instance, extensive liquefactions andsubsequent diﬀerential settlements in Urayasu, roadembankment failure in Hitachi-Naka Port, natural slope inShirakawa, earth ﬁll dam in Fujiwara and so on.
The GEJET is a super wide area disaster and its eﬀect iscompound or cascading. As a result, the recovery is muchcomplicated and takes longer. However, we are now going into
the reconstruction stage. Our task is to how to derive asolution and implement DRR for such compound disaster. Arecommendation report Towards Reconstruction - Hopebeyond the Disaster presented by the Reconstruction Design
Council on June 25th, says that towards reconstruction, key
solution is how to bridge and link the people, communities,regions, and countries.

Last March the earthquake and tsunami hit super widespreadareas in East Japan. The Great East Japan Earthquake andTsunami (GEJET) caused large human casualties as well as
wide physical damages to houses, public buildings, andinfrastructure such as roads, railways, water, electricity andgases, compared with even the Kobe Earthquake in 1995,
which is the largest one until 2011. The amount of theeconomic loss in Kobe is 10 trillion yen, two percent of GDP
at that time, but this time it is estimated around 17 trillion
yen, 3.5 percent of GDP. The number of collapsed houses issimilar, 104,906 against 112,528, but the victims are quite
diﬀerent. The Kobe Earthquake killed 6,434 people and 83.3
percent of them died due to collapsed houses. This time, asof September 6th, on the other hand, 15,769 people are killed
and 4,227 are missing and 92.4 percent of them are drowned
because of tsunami. Infrastructural damages are also more
serious, for instance, electricity, gas and water are notprovided to the 2-3 times more houses than in case of Kobe.
The highest intensity 7 of ground motion is observed in theboth disasters, but the predominant frequency of shaking isvery diﬀerent. In Iwate Prefecture, the northern part of Tohoku
region, the ﬁrst phase of shaking is really strong, in Miyagi
Prefecture, south to the Iwate, there are two strong phases,
and in Fukushima, where nuclear plants are, the second phaseis larger. And further south, there is only one phase of11