1. Hazards Planning and Risk Management
Lecture No. 23
Tsunami
Fall 2016
US – Pakistan Center for Advanced Studies in Water

2. Learning Objective Tsunamis
What are they?
Where do they occur?
Why do they occur?
Consequences of their occurrence? 2 2

3. Reading Material
Tsunami Hazard Mapping in Developing Countries – ICHARM Publication _tsunami_hazard_mapping.pdf
International Centre for Water Hazard and Risk Management

4. Tsunami
The Killer Sea Wave

5. Tsunami
Tsunamis are waves generated by earthquakes, volcanic eruptions, or underwater landslides
When large areas of the sea floor elevate or subside, a tsunami can be created
Can be 15 m or high and can enter inland several hundreds of meters
Velocities of normal ocean waves are about 90 km/hr while tsunamis have velocities up to 950 km/hr (about as fast as jet airplanes)
Tsu = harbor, nami = waves
Consist of series of waves.
Source: Together towards a safer India, CBSE
Subduction earthquakes are particularly effective in generating tsunamis

6. Tsunami
Unlike ordinary tides, tsunami are barely noticeable in their deep sea formation stage
When caused by nearby earthquakes reach the coast in minutes
Tsunami danger period can continue for many hours after a major earthquake

7. Causes Earthquakes Volcanic Eruptions Landslides Meteorite Impacts
Tsunami may be generated by
Earthquakes
Volcanic Eruptions
Landslides
Meteorite Impacts

8. Tsunami
When caused by far away earthquakes in ocean, waves travel at hundreds of kilometers per hour reaching coast after several hours of earthquake
Can occur anytime of the day or night
When waves enter shallow waters they may rise in height striking the coast with devastating force
Source: Together towards a safer India, CBSE

10. http://earthsci. org/education/teacher/basicgeol/tsumami/tsunami
d = depth of wave to ocean bed

11. 4 Stages of Tsunami Tsunami wave activity is unfelt in the open ocean
Source: Together towards a safer India, CBSE
4 Stages of Tsunami

12. Local and Regional Tsunami
Local or Near Field Tsunami
Source of the tsunami within 1,000 km of the area of interest.
Waves have a very short travel time (30 minutes or less)
Regional Tsunami or Mid Field
Source of the tsunami greater than 1,000 km of the area of interest
Waves have travel times on the order of 30 minutes to 2 hours
Also called teletsunami, distant-source or far field tsunami
Source:
Note: " Local" tsunami is sometimes used to refer to a tsunami of landslide origin.
teletsunami: Source of the tsunami more than 1,000 km away from area of interest.

13. Measurements In terms of Inundation Inundation Inundation Area
The depth, relative to a stated reference level, to which a particular location is covered by water
Inundation Area
An area that is flooded with water
Inundation line (limit)
Inland limit of wetting measured horizontally from the edge of the coast
Source:

14. Signs of Possible Inundation Level
Based on numerical estimation or past inundation record
Source:

15. Measurements In terms of Wave Amplitude Runup
Maximum height of the water onshore observed above a reference sea level
Marigram
Tide gauge recording showing wave height as a function of time
Marigraph
Instrument that records the wave height
Amplitude: Rise above or drop below the ambient water level as read on a tide gage
period: The length of time between two successive peaks or troughs. May vary due to complex interference of waves. Tsunami periods generally range from 5 to 60 minutes.
travel time: Time (usually measured in hours and tenths of hours) that it took the tsunami to travel from the source to a particular location.

16. Source: http://www. icharm. pwri. go

17. Prediction and Early Warning
Areas far from sources of tsunamis may have enough warning time
Seismographic stations
Tidal stations
National Oceanic and Atmospheric Administration (NOAA) has set up a Pacific warning system for areas in the Pacific Ocean, called the Pacific Tsunami Warning Center

18. Nature’s Tsunami Warning
Sometimes Tsunami causes the water near the shore to recede exposing the ocean floor
If the trough of the tsunami wave reaches the coast first, this causes a phenomenon called drawdown, where it appears that sea level has dropped considerably
Leading-depression wave: Initial tsunami wave is a trough, causing a draw down of water level
Source: Together towards a safer India, CBSE

19. Detecting Tsunami
Utilizing satellite technology nearly immediate warning of potentially tsuna-migenic earthquakes
Warning time depends on distance of epicenter from coast
Warning includes predicted times at selected coastal communities
Tsunami detectors ‘Tsunameters’ ……
Tide Gauges
Satellite altimeters
Deep-ocean Assessment and Reporting of Tsunamis (DART) system in Pacific Ocean (NOAA)
Source: Together towards a safer India, CBSE
Tide gauges measure the height of the sea-surface and are primarily used for measuring tide levels.
Satellite altimeters measure the height of the ocean surface directly by the use of electro-magnetic pulses.

20. Sea surface (in blue) measured by the Jason satellite
2 hours after the initial earthquake hit the region southeast of Sumatra (shown in red)

21. Reducing Vulnerability of Houses
Elevate coastal homes
Source: Together towards a safer India, CBSE

22. Risks Damages caused by Tsunami waves Secondary effects include the
debris acting as projectiles
Erosions
Fires

23. Mitigation Measure Proper awareness and preparedness is must
The giant loss of 2004 IOT was mainly due to the lack of proper awareness and preparedness
Tsunami Hazard Map (THM) − one of the most effective ways of raising awareness and reducing tsunami disaster risk
Any warning system will be useless if people are not aware about the disaster itself and perform incorrect responses
Tsunami events are very rare therefore it is not easy to sustain public awareness towards tsunami disaster mitigation
Both structural and non structural measures are to be sought

24. Structural Measures
Source:
To reduce tsunami flow, 50 to 200m thickness of coastal vegetation belt is suggested in combination with 1-2m height of embankment along the coastline.
BW: Breakwater
All post tsunami disaster investigation results have also shown that coastal vegetation belt posed none mitigation effects for tsunami inundation greater than 5m. For area with tsunami hazard potential of inundation depth greater than 5m, coastal vegetation belt would provide no protection at all. In such cases coastal vegetation belt may be used as a supplement to the main protection structure such as seawall etc. Even for tsunami inundation less than 5m coastal vegetation belt never provide a hundred percent protection.

25. Mitigation Measures

26. Public Awareness

27. Indian Ocean Tsunami disaster 2004
Source:
More than half of Asian people live in the coastal zone [Yu, 2007].

29. Tsunami Hazard Maps
See Figs 4.4 and 4.6 of reading material 1

31. Discussion/Comment/Question