In Science class we are learning about earthquakes right know. Do you know what an earthquake is? An earthquake is the shaking of the Earth's surface caused by the fast movement of the Earth's crust. Earthquakes occur when strain underneath the Earth's crust is released. Strain is what causes deformation of rocks and Earth's crust. Strain causes the build up of stress.The three types of stress are compressional, tensional, and shear. They act to change the shape or volume of a material.

Compressional Stress: causes blocks of rocks to squeeze
- causes a rock to shorten
- rock is pushed higher up and deeper down
- makes rocks denser by making volume smaller

Tensional Stress: causes blocks of rocks to pull apart or elongate
- rock becomes thinner in the middle than at the ends
- makes rocks less dense by making volume larger

Shear Stress: causes blocks of rock to slip past each other
- causes rock to twist or tear apart


Earthquakes ruin people's life all over the world. People are homeless because of earthquakes. I just hope there wont be anymore.

Check out the sources!!!!

http://encarta.msn.com/encyclopedia_761571674/Earthquake.html
http://scign.jpl.nasa.gov/learn/plate5.htm