The Physics of Tsunamis

1. The Physics of Tsunamis Wayne M. Lawton Department of Mathematics National University of Singapore 2 Science Drive 2 Singapore 117543 Email matwml@nus.edu.sg Tel (65) 874-2749

2. Tsunamis in the Media movie Impact – U.S. President claims tsunami speed = 2*sound is his claim real or exaggerated ? what about this tsunami photo from Phuket ?

3. Hollywood Hype Physical Facts: tsunami speed Pacific Ocean: 1-7 km http://www.es.flinders.edu.au/~mattom/regoc/text/8topo.html Atlantic Ocean: 1-7 km http://www.es.flinders.edu.au/~mattom/regoc/text/14topo.html Indian Ocean: 1-7 km http://www.es.flinders.edu.au/~mattom/regoc/text/11topo.html 356 < speed (4 km) = 713km/hour < 943 speed of sound in air (0 C) = 1192 km / hour ocean depth needs to be 7 km * 6.4 = 44.8 km

4. Internet Assertion Be sure and open the picture for a shock of your life to see what the tsunami looked like just before hitting Puket, Thailand. This picture is not a fake. It appears to have been taken from a hi-rise building window in downtown Phuket Thailand. The power of nature is hard to comprehend, especially the destructiveness of water. We have all seen the pictures on TV but I don't think any of us really understand how big or how bad this wave was. This may be the most impressive picture I've seen. It gives me a better understanding of how 150,000 people perished in this disaster. If you look at this picture that was taken right before the wave hit, it will send a chill down your spine. Just look at the top of the wave compared to the top of the building it is about to hit.

5. Urban Legends Origins:   This is another photograph being circulated as a picture of the tsunami that struck Indian Ocean shorelines in Asia on 26 December 2004, this one purportedly taken from atop a high-rise building in Phuket, Thailand. This looks to be another case of any image depicting large waves being grabbed and passed around as a "real photograph" of the December 2004 tsunami. The image clearly doesn't fit its accompanying description because: It looks like something other than a photograph, such as a still frame from a movie or a composite image. The waves that struck the coast of Thailand after the December 2004 Indian Ocean earthquake were about 4 meters in height, but the ones pictured here look several stories tall. The skyline depicted doesn't appear resemble the city of Phuket. The traffic flow shown isn't right for Thailand, where motorists drive on the left-hand side of the road. As the operator of the World City Photo Archive helpfully informed us, this image is actually a manipulated depiction of the skyline of Antofagasta, Chile:

6. Scientific Approach to Tsunamis while lacking the entertainment appeal, provides understanding that has proven both necessary and useful for the prediction and control of natural events Why are earthquakes the major source of tsunamis ? Why do many earthquakes not cause tsunamis ? What is the surface geometry of tsunamis ? What is the water movement in tsunamis ? How is energy transported in tsunamis ? How, after a powerful earthquake, can a tsunami be detected and how can its propagation be predicted ?

7. Tsunamis are physically generated by events that result in the rapid and coherent (in the same direction) motion of a massive amount of sea water which of the following energy sources can physically generate tsunamis ? sun heating, whales, impacts from extraterrestrial objects (meteorites, comets, asteroids), thermonuclear explosions, storms, landslides, earthquakes, tidal forces, evil spirits, volcanoes

8. Energy of an Earthquake http://www.seismo.unr.edu/ftp/pub/louie/class/100/magnitude.html log E(joules) = 4.8 + 1.5*Richter-Scale-Magnitude 1 J (joule) = kg * meter^2 / second^2 = watt * second One Ton (2000 lbs) TNT = 4.148x10^9 J Richter TNT for Seismic Example Magnitude Energy Yield (approximate) -1.5 6 ounces Breaking a rock on a lab table 1.0 30 pounds Large Blast at a Construction Site 2.0 1 ton Large Quarry or Mine Blast 4.0 1,000 tons Small Nuclear Weapon 4.5 5,100 tons Average Tornado (total energy) 5.0 32,000 tons 6.0 1 million tons Double Spring Flat, NV Quake, 1994 7.0 32 million tons Hyogo-Ken Nanbu, Japan Quake, 1995; Largest Therm. Weapon 7.5 160 million tons Landers, CA Quake, 1992 8.0 1 billion tons San Francisco, CA Quake, 1906 8.5 5 billion tons Anchorage, AK Quake, 1964 (THIS IS 2 X 10^19 j) 9.0 32 billion tons Chilean Quake, 1960 12.0 160 trillion tons (Fault Earth in half through center, OR Earth's daily solar energy)

9. Physical Properties of Water Water is incompressible, viscous, massive which of these properties explains the following ? • when the container is turned the water • does not immediately turn with it, but eventually will start to turn as long as the container is turning 2. the water will fall when the bottom is not held 3. when the container is raised the water is raised raises the same distance

10. Energy Transmission Earthquakes generate tsunamis when they cause large water displacements, this requires that they cause large movements of earth in direction normal (perpendicular) to the earth-ocean interface which of the motions can generate tsunamis? ocean ocean ocean earth earth earth earth

11. Slow Rising of Ocean Floor We consider a large area of ocean floor that raises up air ocean earth if it moves very slowly it transmits energy from the earthquake (seismic energy) into potential energy of the water, equivalent to lifting a certain volume of, water up to the sea level. the potential energy remains as potential energy

12. Fast Rising of Ocean Floor air ocean earth if it moves fast it transmits more energy from the earthquake (seismic energy) into more potential energy of the water, equivalent to lifting a certain volume of water up to a height above sea level why does the earth do more work when it rises fast ? does the lifted water stay above the sea level ?

13. Falling of Lifted Water As gravity works to restore equilibrium to the incompressible water the falling water lifts water n its sides and that water falls in a cascade

14. Real Picture wavelength of course water near the edge is rounded, after several fall-rise cycles the picture (from far right side looks more like) at the bottom direction of propagation

15. Surface Geometry wave height graph of direction of propagation

16. Wave Velocity depends on both wavelength and water depth http://hyperphysics.phy-astr.gsu.edu/hbase/waves/watwav2.html deep water - surface (wind generated) waves shallow water - tsunami waves

17. Surface Wave Parameters on the Deep Ocean Amplitude = maximum H(x), y = 0 sea level Period = time one cycle of wave to go by = http://observe.arc.nasa.gov/nasa/exhibits/tsunami/tsun_physics.html Wind Waves A = 10ft = 300 ft = 10-20mph = 316800 ft = 450-650mph Tsunamis A = 1.6ft convert these parameter values into civilised units ! what is ratio of periods of tsunamis to wind waves ? why are tsunamis hard to detect ON the deep ocean ?

18. Water Movement in Tsunamis Wind Waves: water particles move in near circles, whose diameters decrease rapidly with depth Tsunamis: water particles move in elongated ellipses whose lengths decrease linearly to zero at the bottom http://electron4.phys.utk.edu/141/dec8/December%208.htm http://www.coastal.udel.edu/faculty/rad/linearplot.html http://mmu.jcu.edu.au/coastal/wavemaker.html would tsunamis be easy to detect by scuba divers ?

19. Energy Transport in Tsunamis is through kinetic energy of horizontal water motion in deep ocean, and in contrast to wind waves little viscosity loss since velocity changes slowly no dispersion since v does not depend on wavelength as wave approaches land amplitude increases to A > 100 ft, lambda = 5000-10000ft, v = 30-200mph

20. Tsunami Detection and Prediction how can tsunamis be detected in deep oceans ? once detected how can their future propagation be predicted rapidly to issue effective warnings ? http://serc.carleton.edu/NAGTWorkshops/visualization/collections/tsunami.html http://wcatwc.arh.noaa.gov/