An earthquake is the shaking and trembling of Earth's topmost layer, the crust. The crust shakes because of tectonic
plates moving underneath the surface. The plates moving add energy to the rock. After the energy adds up, it will eventually
release itself and cause an earthquake. Earthquakes occur most often along active faults. A fault is where two tectonic plates
have slid past each other or slid apart. The more movement along a fault, the higher the probability of an earthquake.
We who live in California are at great earthquake risk. The reason for this is because we live along an active fault. This
fault is one of the longest in the world. It is called the San Andreas Fault. That is why we have great earthquake risk.
Here is an interesting chart of past earthquakes
Click here to go to a page where you can see the damage caused by past earthquakes