One of the most frightening and destructive phenomena of nature that man experiences is a severe earthquake and its terrible aftereffects. Since long before man existed, probably for more than 4 billion years, the forces within the Earth that produce earthquakes have played an active role in shaping the Earth's surface. These unpredictable catastrophic movements of the Earth have caused a great number of human casualties and extensive property damage. Today man is challenging the assumption that earthquakes must present an uncontrollable and unpredictable hazard to life and property. Scientists have begun to explore the means of predicting earthquakes. Sites of greatest hazard are being identified, and definite progress is being made in designing structures that will withstand the effects of earthquakes.