Principle objective of this lecture is to present on What are Earthquakes. The shaking or trembling caused by the sudden release of energy. Usually associated with faulting or breaking of rocks. Continuing adjustment of position results in aftershocks. This lecture also describe on where do Earthquakes occur and how often. 80% of all earthquakes occur in the circum-Pacific belt; most of these result from convergent margin activity. 15% occur in the Mediterranean-Asiatic belt and remaining 5% occur in the interiors of plates and on spreading ridge centers.