This outline of basic information on earthquakes starts with an explanation of an earthquake, including the forces acting on rock, (tension, compression, and shear) and plastic and elastic deformation of rock. Next, the principle of the seismograph, seismometer, and seismogram along with the three types of seismic waves are discussed. Information is then presented to help the student distinguish between the focus and epicenter of an earthquake, describe the world-wide distribution pattern of earthquake activity, and explain the earthquake magnitude (Richter) scale and the Modified Mercalli scale of earthquake intensity. This site also includes an explanation of how the epicenter of an earthquake can be located. There is a discussion of some past earthquakes along with a description of the effects of earthquake activity.