2) Wave Types

In this blog, unlike the last one, we will touch on the hazards of earthquakes.

One of the most important features about earthquakes are the ‘waves’ they produce. Similar to dropping a pebble into a pool of water, an earthquake is a series of waves that move the ground like the pebble moves the water into an up and down motion. There are two types of waves that earthquakes make; body waves and surface waves. 

If we continue with the pebble into water analogy, the body wave would be the relatively small ripple underwater caused by the pebble. As the names suggest, body-waves travel through the ‘body’ of the earth (they can travel all the way through the earth to the other side of the globe). There are two types of body waves, S-waves and P-waves. The S waves are more familiar as they move in the same way as a normal wave does, in an up and down motion. P-waves work differently as they pull the rock together and then apart again. This diagram should explain: 

  

(Source http://www.earth.northwestern.edu/individ/seth/202/lectures/Seismology/p&swaves.htm)

These waves, although they can be powerful and they are faster than surface waves, are generally not as hazardous. It is surface waves that cause the majority of the damage from an earthquake. 

Using our pebble into water analogy, the surface waves would be the relatively large ripple on the surface of the water. These waves, as the name also might show, travel along the surface of the earth. Although they cannot travel very fast, these waves have far greater strength than body waves and cause far more damage.

There are two types of these surface waves; Love Waves and Rayleigh Waves. Love waves move the ground from side to side, just think of the pictures of farmer’s fences that don’t match up after an earthquake. For Rayleigh waves, the motion is very similar to that of a wave at sea, it moves up and down in a rolling motion.

It is important to understand that the body waves arrive before the surface waves as they travel faster. In it’s simplest form, the thunder comes before the lightning. If you feel the ground starting to shake moderately you now understand the most dangerous waves are yet to come. 

#Quaketips1

There is always an important notion with earthquake hazards; earthquakes don’t kill people, buildings do.