地震概论第11单元1.pptVIP

地震概论 第11章海 啸Tsunami The killer Wave 2010.12.13/4/5 Indian Ocean Tsunami, 26 December 2004 Cause death and destruction in 13 countries 245,000 death (Indonesia 198,000; Sri Lanka, 30,000; India, 11,000; Thailand 6000) Last major tsunami in Indian Ocean occurred in 1883 when the volcano Krakatau collapsed into the sea, killed 36,000. Population growth In Sri Lanka, 40% death were children The first tsunami arrived in Sri Lanka two hours after the earthquake. Couldn’t warning have been spread to stop trains and alert people in time to save lives? Think about following questions What is a tsunami What is the difference between tsunami and wind-generated waves How is a tsunami generated Tsunami Japanese Word. (Tsu=Harbor; nami= waves) “津波” Harbor waves emphasizes the greater heights that waves reach in inlets and harbors because the narrowed topography focuses the waves into smaller spaces. A tsunami is a very long-wavelength wave of water that is generated by sudden vertical displacement of the seafloor or disruption of any body of standing water. In USA, tsunami is often called “tidal waves”, which is silly. Tsunami have nothing to do with tides or winds or storms. Tsunami are sometimes called seismic sea waves, although, as we will see, they can be generated by mechanisms other than earthquakes. Physical characteristic of wave All types of waves, including tsunami, have Wavelength Normal ocean waves have wavelengths of about 100 meters. Tsunami have much longer wavelengths, usually measured in kilometers and up to 500 kilometers. Wave height Wave amplitude Wave period 200-2000s Wave velocity Tsunami are excited by large-scale displacements of water due to submarine landslides, volcanic eruptions, or most commonly, sea-bottom displacements caused by submarine fault motions. Gravitational energy making up more than 95% of the energy in tsunami waves. Wave equation for tsunami wave height h Equation behaves distinctively depending upon the wavelength of the