G7-Earthquakes – Outward Expression of Earth’s Dynamic Interior-800-900L-03

The San Andreas Fault system is perhaps the most studied fault system in the world. The San Andreas Fault is the boundary between The Pacific and North American Plates. These tectonic plates, or pieces of Earth’s crust, are not stationary. As they move, some areas get stuck against each other, thereby stopping the motion. At some point, the rocks can no longer withstand the forces being placed upon them. Eventually, they will break free of each other. When this happens, the two plates move suddenly, causing an earthquake. We often think of earthquakes as a surface phenomenon. The truth is their cause lies deep within Earth.

The thermal energy, or heat, contained deep within Earth is what causes the plates to move. The origin of this heat comes from two sources. One source of heat comes from the ancient heat left over from Earth’s creation. The other source of heat comes from radioactive decay in Earth’s crust and mantle. It is this heat that drives the powerful convection currents within the mantle that causes the plates to move.

The mantle is the thickest layer of Earth. The material in the mantle is solid, but as a result of high temperatures, the material is ductile. Ductile simply means it can slowly flow over time. The heat being transferred from the hotter core toward the cooler surface in the form of convection currents causes plate motion. Plate motion, in turn, causes earthquakes.

The deeper you travel into Earth, the hotter the temperature. Below the mantle is the core. The core is composed of iron and nickel. The core is divided into two parts, the liquid outer core and the solid inner core. Even though the inner core is hotter than the outer core, its depth provides enough pressure for it to remain a solid. How do we really know there is a solid core? Better yet, how do we know where the boundary is?

As scientists studied earthquakes, they started to notice something interesting.