Earthquakes are caused by the sudden release of built-up energy along fault lines in the earth's crust. They begin at a focal point below the surface and radiate seismic waves outward. The location directly above the focus on the earth's surface is called the epicenter, which is important for understanding where damage and shaking will be strongest. Earthquakes are measured on the Richter scale, which quantifies the amount of energy released. Areas near fault lines are more susceptible to earthquakes, and the severity of shaking and damage depends on the quake's magnitude, distance from the epicenter, and local geology.