Seismology is the study of waves of energy, especially earthquakes, that move through and around the Earth. These waves of energy are called seismic waves, and the scientists who study them are called seismologists.
Seismic waves are caused by the sudden breaking or cracking of rocks beneath the Earth's surface. Tectonic plates are constantly moving, though slowly, and cause earthquakes when they collide or rub against each other. The subsequent waves of energy move through the Earth and are recorded on seismographs. Earthquakes occur every day but are often too small to be felt by humans. Earthquakes produce two main types of waves, known as body waves and surface waves, which move differently through the Earth.