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Mechanism of tsunamigeneration,propagation and runup

-sharing experiences with Japanese

■Mechanism of tsunami generation

■Predicting the propagation, runup and inundation oftsunamis

■Near and far-field tsunamis

■Countermeasure; hard and soft type

■Tsunami warining system

■Community based workshop to make Hazard map

Fumihiko Imamura, DCRC, Tohoku Univ.

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What is a tsunami ?　津波とは？• harbor+wave　津＋波• International word in 1946 academically• Tsunami committee in IUGG started in 1960

Historical Tsunamis• BC.14th Santorini, the oldest in the world records• The tsunami documented in Japan Well documented and more than 195 tsunamis over

1,313 years. 684年南海道、白鴎地震、Tonanaki　

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Several reasons to generate tsunami;seismic and non-seismic

• Fault• Landslide• Volcano• Comet compact

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Seismicity in the Pacific & world

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Estimation of a seabed movement(deformation)

A fault movement is described by its location including its depth,•Mechanical characteristics; (strike, dip- and slip-angles of the fault plane),•Geometrical characteristics (length, width and dislocation of the fault plane), and•Dynamic characteristics(rupture direction, rupture velocity and rise time of the faultmovement). •Earthquake magnitude

•Depth of the fault•Length and width of the fault plane•Strike and dip angle of the fault plane•Dislocation and slip angle

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Earthquake induced tsunamis

Tsunamis can be generated when the sea floor abruptly deforms andvertically displaces the overlying water.

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Landslide/volcano induced Tsunamis

Caldera formation; surrounding water rushing into a cavity

Landslide flowing into water

10% of tsunamis over 100 years

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Tsunami Wave System• Generation

– A seafloor disturbance, such as motion along a fault, pushes upthe overlying water.

• Propagation– The wave propagates across the deep ocean at jetliner speeds– Shoaling and refraction to amplify the wave

• Inundation– As the wave moves into shallower water, increased energy

density increases both the wave height and the currents.– Runup on a land and run-down

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Propagation : Shoaling effect

The deeper the water and the longer the wave, the faster the tsunami propagate.

The back of wave overtakeanother,decreasing thedistance between them

larger disatance

 larger larger disatancedisatanceshorter disatance

shorter shorter disatancedisatancedicreasing of wave leng,amlificaton of wave height

dicreasingdicreasing of wave of wave leng,leng,amlificatonamlificaton of wave height of wave heightFaster wave propagatingspeed in a deep sea

Faster wave propagatingFaster wave propagatingspeed in a deep seaspeed in a deep seaslower wave propagatingspeed in a shallow sea

slower wave propagatingslower wave propagatingspeed in a shallow seaspeed in a shallow seawave tail

wave tailwave tailwave front wave frontwave front

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Headland

Crest line of wave

Propagation : Refraction effect

Energy concentration

Wave fronts tend to align parallel to the shoreline so that they wrap arounda headland

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Generation and Propagation of the1896 Sanriku tsunami

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遺体の処置

釜石では筵さえ不足。

広田では、１度では多すぎ２度に分けて回収

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岩手県内踏査行程

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Functions of disaster prevention --- Function to stop drifts

Coastal forest

Tsunami direction

Cultivate rafts

Fishing boat

1960 Chileian tsunami at Kesen-numa Japan, (Izumi,1961)

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Prevention Works & Researchon Tsunamis

Before :■education/memorial■Resettlement to higher location

Recent after 1960■Structural mitigation (hard)

■sea wall, breakwater

■Integrated prevention with soft

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Local Propagation• Locally generated tsunami waves may propagate from their generating source to

the near shore area of a nuclear power plant site;• hence, the wave propagation phenomena become important.• Numerical techniques,FDM, are applied to determine modification during

propagation.• The accuracy of bottom topography has a vital effect on the computed results

TIME -project; Tsunami inundation modeling exchangeBy UNESCO/IOC and IUGG ,manual 34

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Distant Tsunamis

Wave system

The fact that the wavelength of atsunami is much longer than thewater depth leads to the system oflong waves.The wave amplitude of a tsunami inthe deep ocean is infinitesimallysmall compared to the water depth ;Linearity of the water wave .

A distant tsunami can be solved withthe aid of liner equations for longwaves with the Coriolis force ,frequency dispersion included,described in the longitude-latitudecoordinate system. 1996 Irian Jaya tsunami, made by DCRC Tohoku Univ.

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チリ地震津波1960 Chile

国際太平洋津波警報センターの設立津波防波堤の建設（大船渡）津波高潮防潮堤の建設（全国の沿岸）津波水門が初めて建設される

142名犠牲者津波警報発令されず北海道から沖縄にかけての広い地域

チリ地震津波

1960.5.24

対　策主な被害・課題津波イベント名

年月日

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チリ津波による被害Damage caused by the tsunami

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北上川で成長する波状段波

第一波

第二波

第三波

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新潟・十勝沖地震津波1964 Niigata &1968 Tokachi

52名犠牲者（ほとんどが地震による）防潮堤の機能発揮

十勝沖地震津波

1968.5.16

26名犠牲者津波・石油タンク被害・火事が連動した液状化による被害大

新潟地震津波

1964.6.16

対　策主な被害・課題津波イベント名

年月日

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津波による火災の発生Fire caused by a tsunami

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１９６４年新潟地震の場合

津波と地下水とが溜まった地域焼失区域

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Tsunami Warning System

1. Estimating the occurrence of a tsunami by seismicinformation(magnitude, location and depth)

2. Data base of the simulation with assumptions3. Real time analysis with the tentative fault model4. Revision of the tentative fault model by the observation data

JMA Tsunami warning

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The “Three Helps” of disaster measures

To reduce damage and casualties

Public help

Self help

Mutual help

The people could not see theimpact/terror of tsunami only bywarning with the tsunamiinformation; arrival time andheights.They should understand its impacthave the imagination before thetsunami attack through makinghazards map and having workshop.

workshop

Tsunami warning Risk communication

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Community-based Programs forawareness of tsunami disaster

■Location of the program leadership■Program goals and training approaches■Use of volunteers■Targeted organisational unit■Knowing what to do in the face of hazard■Curriculum intervention for disaster mitigation from the

hazard management community■Curricula for responsible citizenship

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Making the original hazard maps

■ In the past, the map was provided by the localgovernment but no use for the people

■Original information should be included■Selecting the base map■Collecting the information of risk■Discussion what information be included■Checking them by town-walking

inundation

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Hazards map and WorkShopmaking HM with the residents

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Powerful & future tool to support the awareness;Example of Hazards map and Data base Using the image fromSattelite on GIS

Safety area

Damage in past

Damage in past

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Criteria to estimate damage by tsunamis

runupheightinundation

height

inundationdepth

ground elevation

trace

distance from shoreline

tide levelat theevent

M.S.L.

Inundation depthHuman: killed >> 50cmHouse: partially damaged >> 1.0m totally damaged >> 2-3.0mBuilding: damaged >> 5.0m

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安全な避難のために

１次避難場所

For Safe Evacuation

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Integrated Tsunami Countermeasure

No system Structure & Facility;sea wall andbreakwater

Combination with ;green belt andtsunami information

PAST PRESNT FUTURE

Public education for awareness andevacuation system

with consideration of life and culture at reachregion

Memorial day, International Tsunami Mitigation day; 26 December