This sudden rupture results in a huge amount of energy which in turn causes seismic waves that shake the ground. Friction is the result of two large rocks or tectonic plates rubbing against each other and often becoming trapped along each other's edges. When these plates stick together, there will be a buildup of energy and pressure that will eventually lead to the rocks breaking apart. This breaking causes an earthquake, but during and after this rapture, the broken pieces of rock will continue to move until they meet again. The point where the two plates meet in the Earth's crust is called the earthquake focus, while the point directly above it on the Earth's surface is called the earthquake epicenter. Seismic waves are energy waves caused by the sudden rupture of rock in the earth's crust, or due to a man-made explosion; these waves travel through the earth and can be recorded by seismographs. There are many different types of seismic waves, but the two main types are surface waves, which can only move across the Earth's surface like a sort of ocean wave, and body waves, which travel through the earth's innermost layers. Earthquakes constitute both surface and body waves. Both surface and body waves can be divided into two main ones