Earthquakes

Most Tsunamis are caused by earthquakes.

"To generate a tsunami, the fault where the earthquake occurs must be underneath or near the ocean, and cause vertical movement of the seafloor (up to several meters) over a large ara (up to a hundred thousand square kilometers). Shallow focus earthquakes (depth less 70km or 42 mi) slong subduction zones are responsible for most destructive tsunamis. The amount of vericla and horizontal motion of the sea floor, the area over which it occurs, the simultaneous occurrence of slumping of underwater sediments due to the shaking, and the efficiency with which energy is transferred from the earth's crust to the ocean water are all part of the tsunami generation mechanism." (unesco.org)

-LIFE OF A TSUNAMI (usgs.gov)

-Initiation: potential energy resulting from the displacement of land and water causes the propagation of tsunami wave (kinetic energy).

-split: wave splits into two tsunamis. One that travels out into deep ocean and one that travels towards shallower coast line.

-amplification: Amplitude and wavelenfth of waves increase as waves run up shallower coast.

-run-up: water run up--the height of the water onshore from sea level--occurs like a very strong and quick tide.

Measuring earthquakes

Richter scale: logarithmic scale of the amount of energy released

M=1 to 3: Recorded on local seismographs, but generally not felt

M=3 to 4: Often felt, no damage

M=5: Felt widely, slight damage near epicentre

M=6: Damage to poorly constructed buildings and other structures within 10's km

M=7: "Major" earthquake, causes serious damage up to ~100 km (recent Taiwan, Turkey, Kobe, Japan, and California earthquakes).

M=8:"Great" earthquake, great destruction, loss of life over several 100 km (1906 San Francisco, 1949 Queen Charlotte Islands) .

M=9: Rare great earthquake, major damage over a large region over 1000 km (Chile 1960, Alaska 1964, and west coast of British Columbia, Washington, Oregon, 1700). BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH BLAH
Sources:
UNESCO Intergoernmental Oceanographic Commission & International Tsunami Information centre & Laboratoire de geophysique, France & U.S. National Oceaninc & Atmospheric Administration. "Great Waves." June. 2005. [http://ioc3.unesco.org/itic/files/great_waves_en_2005_small.pdf]
Geist, Eric. "Life of a Tsunami." 15 September 2005. [http://walrus.wr.usgs.gov/tsunami/basics.html]
Earthquake Hazards Program. 21 Mar 2005. [earthquake.usgs.gov]

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