Mechanism of tsunami generation,propagation and runup -sharing experiences with Japanese

Transcription

1 Mechanism of tsunami generation,propagation and runup -sharing experiences with Japanese Mechanism of tsunami generation Predicting the propagation, runup and inundation of tsunamis Near and far-field tsunamis Countermeasure; hard and soft type Tsunami warining system Fumihiko Imamura, DCRC, Tohoku Univ. Community based workshop to make Hazard map F.Imamura, DRCR 1

2 What is a tsunami? harbor+wave 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 Tonanaki F.Imamura, DRCR 2

3 Several reasons to generate tsunami; seismic and non-seismic Fault Landslide Volcano Comet compact F.Imamura, DRCR 3

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5 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 fault movement). 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 F.Imamura, DRCR 5

6 Earthquake induced tsunamis Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. F.Imamura, DRCR 6

7 Landslide/volcano induced Tsunamis 10% of tsunamis over 100 years Landslide flowing into water Caldera formation; surrounding water rushing into a cavity F.Imamura, DRCR 7

8 Tsunami Wave System Generation A seafloor disturbance, such as motion along a fault, pushes up the 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 F.Imamura, DRCR 8

9 Propagation : Shoaling effect The deeper the water and the longer the wave, the faster the tsunami propagate. The back of wave overtake another,decreasing the distance between them F.Imamura, DRCR 9

10 Propagation : Refraction effect Wave fronts tend to align parallel to the shoreline so that they wrap around a headland Headland Energy concentration Crest line of wave F.Imamura, DRCR 10

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12 Generation and Propagation of the 1896 Sanriku tsunami

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15 Functions of disaster prevention --- Function to stop drifts Tsunami direction Coastal forest Fishing boat Cultivate rafts F.Imamura, DRCR Chileian tsunami at Kesen-numa Japan, (Izumi,1961)

16 Prevention Works & Research on Tsunamis Before : education/memorial Resettlement to higher location Recent after 1960 Structural mitigation (hard) sea wall, breakwater Integrated prevention with soft F.Imamura, DRCR 16

17 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 exchange By UNESCO/IOC and IUGG,manual 34 F.Imamura, DRCR 17

18 Distant Tsunamis Wave system The fact that the wavelength of a tsunami is much longer than the water depth leads to the system of long waves. The wave amplitude of a tsunami in the deep ocean is infinitesimally small compared to the water depth ; Linearity of the water wave. A distant tsunami can be solved with the aid of liner equations for long waves with the Coriolis force, frequency dispersion included, described in the longitude-latitude coordinate system Irian Jaya tsunami, made by DCRC Tohoku Univ. F.Imamura, DRCR 18

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26 Tsunami Warning System 1. Estimating the occurrence of a tsunami by seismic information(magnitude, location and depth) 2. Data base of the simulation with assumptions 3. Real time analysis with the tentative fault model 4. Revision of the tentative fault model by the observation data JMA Tsunami warning F.Imamura, DRCR 26

27 To reduce damage and casualties The Three Helps of disaster measures The people could not see the impact/terror of tsunami only by warning with the tsunami information; arrival time and heights. They should understand its impact have the imagination before the tsunami attack through making hazards map and having workshop. Public help Tsunami warning Self help workshop Mutual help Risk communication F.Imamura, DRCR 27

28 Community-based Programs for awareness 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 F.Imamura, DRCR 28

29 Making the original hazard maps In the past, the map was provided by the local government 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 F.Imamura, DRCR 29

30 Hazards map and WorkShop making HM with the residents F.Imamura, DRCR 30

31 Powerful & future tool to support the awareness; Example of Hazards map and Data base Using the image from Sattelite on GIS Safety area Damage in past F.Imamura, DRCR 31 Damage in past

32 Criteria to estimate damage by tsunamis Inundation depth Human: killed >> 50cm House: partially damaged >> 1.0m totally damaged >> 2-3.0m Building: damaged >> 5.0m trace inundation height tide level at the event inundation depth M.S.L. ground elevation distance from shoreline runup height F.Imamura, DRCR 32

33 For Safe Evacuation F.Imamura, DRCR 33

34 Integrated Tsunami Countermeasure PAST PRESNT FUTURE No system Structure & Facility; sea wall and breakwater Combination with ; green belt and tsunami information Public education for awareness and evacuation system with consideration of life and culture at reach region F.Imamura, DRCR 34 Memorial day, International Tsunami Mitigation day; 26 December