http://video.google.com/videosearch?q=tsunami+2004&emb=0&aq=0&oq=tsunami

underwater earthquakes

Earthquakes can occur underwater as well as on soil. These underwater earthquakes are very dangerous, as they produce large waves called tsunami's. These's big waves can be very destructive. We saw this on the 26th of december 2004. An tsunami caused by a 9.0 magnitude hit the malaysian coast and surrounding countries. These tsunami's travelled as far as 91000 miles. The death toll of the asian tsunami was over 200000. It was the worst natural disaster ever to hit the asian counties.

The Richter scale

The Richter magnitude scale was developed in 1935 by a man called Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes. The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs. Adjustments are included for the variation in the distance between the various seismographs and the epicenter of the earthquakes. On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions. For example, a magnitude 5.3 might be computed for a medium siezed earthquake, and a strong earthquake might be rated as magnitude 6.3 or higher. Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; as an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.

science.howstuffworks.com/earthquake8.htm

Here is a picture of the Earths continental plates.

The Earth's rocky outer crust solidified billions of years ago, soon after the Earth formed. This crust is not a solid shell; it is broken up into huge, thick plates that drift atop the soft, underlying mantle.

The plates are made of rock and drift all over the globe; they move both sideways and up and down. Over long periods of time, the plates also change in size as their margins are added to, crushed together, or pushed back into the Earth's mantle. These plates are from 50 to 250 miles thick.

The San Francisco earthquake of 1906

The San Francisco earthquake of 1906 was a huge earthquake that struck San Francisco, California and the coast of Northern California at 5:12 A.M. on Wednesday, April 18, 1906. The most widely accepted estimate for the magnitude of the earthquakeof have been proposed from 7.7 to as high as 8.3 on the richter scale. The main shock epicenter occurred offshore about 2 miles from the city, near Mussel Rock. It ruptured along the San Andreas Fault both northward and southward for a total length of 296 miles. Shaking was felt from Oregon to Los Angeles, and inland as far as central Nevada.
The earthquake and resulting fire is remembered as one of the worst natural disasters in the history of the United States. The death toll from the earthquake and resulting fire, estimated to be above 3,000, represents the greatest loss of life from a natural disaster in California's history. The economic impact has been compared with the more recent Hurricane Katrina disaster.

pubs.usgs.gov/gip/dynamic/San_Andreas.html