The planet earth is comprised of several layers. Located at the very top, is what we call the earth's crust. Since the earth has oceans and land, there are two types of the earth's crust. Oceanic crust is located in the oceans, and is very dense. It is about 4-6 miles deep. Continental crust is located where we have land. It is thicker, but is less dense than oceanic crust. Continental crust is about 15-43 miles deep. When you walk on land, you are walking on the earth's continental crust. If you stand on the bottom of the ocean, you are standing on the oceanic crust.

Below the earth's crust is a layer called the mantle. It is about 1,700 miles deep. As strange as it seems, the mantle is made up of several sections. (why they don't give each section a different layer name is another topic for discussion)

The top section of the mantle is called the upper mantle. It is about 450 miles deep, but is still part of the 1,700 mile total mantle depth.

The overlapping areas where the bottom section of the earth's crust sits on top of the top section of the upper mantle is called the lithosphere. It is still a bit rigid (more solid like). But the further down you go, the more plastic it becomes. Even further down, it becomes melted.

The lithosphere has been broken into several tectonic plates. These plates float on the molten section of the upper mantle. These plates are always moving, although very slowly. In addition, they are pushing against each other.

An earthquake is the result of tectonic plates suddenly slipping while being pushed together. The surface where they slide against each other is called a fault or a fault plane. Below the earth's surface where the earthquake begins is called the hypocenter. The location directly above on the surface of the earth is called the epicenter.