An earthquake is a sudden shaking or disturbance of the earth's surface caused by movements in the earth's outer layer. A fault is a layer in the earth's outer surface where rocks have moved due to high levels of energy. Once a fault slips, vibrations occur, and an earthquake results.
Aftershocks are as small earthquakes which come immediately after an earthquake.
Aftershocks are felt as a series of shaking movements and most often accompany larger earthquakes. The study of earthquakes is defined as seismology. By carefully analyzing the earth's surface before, during, and after a quake, seismologists are able to see how the earth's energy moves. In recent years, extensive study by seismologists has been able to pinpoint the devastating effects of quakes and educate the public on how to prepare for the violent ground shaking. Such work has assisted in reducing property and structural damage, injury, and death around the world.