Feel the Waves

10 05 2008

What causes an earthquake? What makes the ground move? I have always wondered this and there are several geographical factors that contribute to a shaking ground. The shaking and damage that earthquakes cause are the result of three basic types of elastic waves [Bolt, Earthquakes, 5th ed.]. These waves that are created within Earth or on Earths crust. 

Lets begin with the body waves, the faster of the two is the Primary or P wave. P waves, like sound waves, travel through solid rock and liquid material.

The second body wave is the Secondary or S wave. It is also slower than the P wave (s wave, slow wave, I made that simpler). S waves cannot go through liquid in Earth, like the ocean.

The third general wave are surface waves and their motion is restricted to the ground surface.  We divide the surface waves into two parts Love waves and Rayleigh waves. They both travel much more slowly than Body waves. Love waves do not have vertical motion like P, S and Rayleigh waves and Love waves do not go through liquid. The horizontal shaking of Love waves tend to be the worst on foundations. 

Why are waves so important? The wave can determine how big of an earthquake will occur and how much damage will occur. We need to consider waves because evidence shows that soil conditions and topography affect waves and need to be understood when discussing earthquake safety. 

Watch Seismic Waves propagate (go through) Earth. 

Learn more about Seismic Waves, from this article that simplifies the description. I found it informative and easy to read. Have fun!

Why do we have waves? What causes them? Lets talk about that next! Let me know what you know!