Tsunamis

1
Tsunamis

• An engineers perspective

Griffith University January 12, 2005
2
Talk outline

• What are tsunamis?
• What causes them?
• What do they look like?
• The Asian earthquake tsunami
• How can engineers help?
• Disaster prevention/minimisation
• Disaster relief and rebuilding

3
What are tsunamis?

• A tsunami is a series of ocean waves generated by
  a large disturbance of the water column
• Tsunami is a Japanese word meaning Harbour (tsu)
  Wave (nami)
• Sometimes called seismic sea waves
• Sometimes incorrectly called tidal waves

4
Earthquake Tsunamis
(4)
(1)
(5)
(2)
(6)
(3)

• The movement in the earths crust causes the
  water surface to lift

(Source School of Ocean and Earth Science and
Technology, University of Hawaii)
5
Earthquake Tsunamis

• Animation

(Source Prof. Miho Aoki, University of Alaska)
6
Landslide Tsunamis
(1)
(3)
(2)
(4)

• Sub-marine landslides can be caused by earth
  quakes, tides, storm waves
• The effect of landslide tsunamis tends to be
  localised

(Source School of Ocean and Earth Science and
Technology, University of Hawaii)
7
Some other causes of tsunamis

• Sub-marine volcanic activity (eruption or
  collapse)
• Impact of meteorites
• Pyroclastic flows

(Source US Office of Naval Research)
8
What do they look like?

• In deep water they move very fast but may only be
  0.5 to 1m high
• In shallow water they slow down and become higher

(Source National Oceanic and Atmospheric
Administration, NOAA)
9
A comparison with wind waves

• Energy loss in waves is inversely proportional to
  the wave length
• Therefore tsunamis experience very little energy
  loss and can travel long distances

10
A comparison with wind waves at the coast

• Tsunamis are often the same height as wind-waves
• It is the volume of water behind them that causes
  the damage

(Source Department of Earth and Space Sciences
at the University of Washington)
11
An example

• Video from Penang, Malaysia, Dec 26 2004

12
The Asian earthquake tsunami

• Main earthquake epicentre
• Aftershocks
• _ Plate boundaries

(Source US Geological Survey)
13
The Asian earthquake tsunami

• Red high water
• Blue low water
• Shows the processes of diffraction, reflection,
  refraction and shoaling

(Source National Institute of Advanced
Industrial Science and Technology, Japan)
14
The Asian earthquake tsunami

• Travel time in hours

(Source National Institute of Advanced
Industrial Science and Technology, Japan)
15
The Asian earthquake tsunami

• Maximum tsunami heights

(Source West Coast/Alaska Tsunami Warning Centre)